null  null
42
CHAPTER 2
LITERATURE REVIEW
2.1
INTRODUCTION OF LITERATURE SURVEY
In the first phase of this research work, available literature relevant to
this work was reviewed.
2.2
HISTORICAL BACKGROUND
In the beginning, all engine experiments were designed for burning a
variety of gases, including natural gas, hydrogen, and propane. There had been
many investigations on hydrogen enriched combustion in internal combustion
engines. Rivaz (1807) of Switzerland invented an internal combustion engine with
electric ignition which used the mixture of hydrogen and oxygen as fuel. He
designed a car for his engine. This was the first internal combustion powered
automobile (Bruno 1996, Eckermann 2001, Dutton 2006). Later, he obtained
French patent for his invention in 1807. The sketch of his engine taken from his
patent is shown in Figure 2.1. Cecil (1820) described a hydrogen engine in his
paper entitled "On the application of hydrogen gas to produce a moving power in
machinery; with a description of an engine which is moved by pressure of the
atmosphere upon a vacuum caused by explosions of hydrogen gas and
atmospheric air." In this document, he explained how to use the energy of
hydrogen to power an engine and how the hydrogen engine could be built. This is
probably one of the most primitive inventions made in hydrogen-fueled engines.
43
In 1863, Lenoir made a test drive from Paris to Joinville-le-Pont with his
hydrogen gas fueled one cylinder internal combustion engine Hippomobile with a
top speed of 9 km in 3 hours (Energylibrary 2014).
primitive elements by electricity, which will then have become a powerful and
manageable force. Water will one day be employed as a fuel, that hydrogen and
oxygen which constitute it, used singly or together, will furnish an inexhaustible
source of light and heat of an intensity of which coal is not capable. Some day the
coal rooms of steamers and the tenders of locomotives will, instead of coal, be
stored with these two condensed gases, which will burn in the furnaces with
In 1920
Erren converted over 1000 S.I engines into hydrogen fueled engines (Erren &
Campbell 1933). His convertion included trucks and buses. For his inventions he
got patent in Great Britain in 1932 (Erren, 1932) and later in the United States in
1939 (Erren, 1939).
Figure 2.1 Patent drawing of Rivaz
44
2.3
HYDROGEN ASSISTED COMBUSTION
Hydrogen can compensate some of the demand for hydrocarbon fuel by
being combusted along with gasoline, diesel, or natural gas in an internal
combustion engine. This type of combustion is called dual-fuel combustion. It
either uses very small amounts of hydrogen to modify combustion or uses a large
amount of hydrogen as the principal source of energy in the combustion chamber.
This type of operation has been investigated by numerous researchers for several
types of hydrogen assisted combustions.
2.4
COMBUSTION OF HYDROGEN WITH GASOLINE
Stebar & Parks (1974) investigated about the hydrogen supplemention
by means of extending lean operating limits of gasoline engines to control the
NOX emissions. They carried out their test in a single cylinder engine. Their
results showed that small additions of hydrogen to the fuel resulted in very low
NOX and CO emissions for hydrogen-isooctane mixtures leaner than 0.55
equivalence ratio. They also obtained significant improvement in thermal
efficiency beyond isooctane lean limit operation. However, HC emissions
increased markedly at these lean conditions. They concluded that the success of
hydrogen supplemented fuel approach would ultimately hinge on the development
of both a means of controlling hydrocarbon emissions and a suitable hydrogen
source on board the vehicle.
Houseman & Hoehn (1974) presented the first engine dynamometer
test results for a modified fuel system based on hydrogen enrichment for a V-8 IC
engine. The engine burnt mixtures of gasoline and hydrogen under ultra lean
conditions and yielded extremely low NOX emissions with increased engine
efficiency. They produced hydrogen in a compact on-board generator from
45
gasoline and air. They cooled hydrogen-rich product gas and mixed with the
normal combustion air in a modified carburettor. The engine was then operated in
the conventional manner on atomized gasoline with spark ignition, but with
hydrogen-enriched air and with a high spark advance of 40°-50° BTDC. Thus the
engine received two charges of fuel: a charge of gaseous fuel from the hydrogen
generator, and the normal gasoline charge. The results on hydrogen enrichment
were compared with the 1973 V-8 baseline stock engine with emission controls
and the same engine without controls and operated at maximum efficiency under
lean conditions. Relative to the stock 1973 350 CID engine, an approximate 10%
reduction in brake specific fuel consumption was measured over the entire level
road load speed range. For the same condition, NOX emissions were reduced to
below the equivalent 1977 EPA Standards.
Rose (1995) made researches on the method and apparatus for
enhancing combustion in an ICE through electrolysis and produced hydrogen
along with oxygen yielded enhanced combustion at low engine loads for all types
of engines.
2.5
COMBUSTION OF HYDROGEN WITH DIESEL
Varde & Frame (1983) carried out an experimental study to investigate
the possibility of reducing diesel particulates in the exhaust of the diesel engine by
aspirating small quantities of gaseous hydrogen in the intake of the engine. For
this study, they used a single cylinder, naturally aspirated, four stroke, DI diesel
engine with compression ratio of 17.4:1. They found that hydrogen flow rate
equivalent to about 10% of the total energy, substantially reduced smoke
emissions at part loads. At the full rated load, reduction in smoke levels was
limited. They related this to the lower amounts of excess air available in the
cylinder. They found that the engine thermal efficiency was dependent on the
46
portion of hydrogen energy, out of the total input energy supplied to the engine. In
this investigation, they conducted two different types of tests. In the first set of
tests, hydrogen flow rate was maintained constant while the diesel fuel flow rate
was increased to increase the engine output at constant engine speed. In the
second set of tests, again the engine was made to run at a constant speed of 40 rps
but the hydrogen flow rate was varied. The maximum hydrogen flow rates used in
this set of tests comprised about 14% of the total energy at full rated load and
about 17% at 82% of full rated load. In general, the efficiency steadily increased
as the portion of hydrogen energy increased at both the power levels. At the
lowest hydrogen fuelling rate, the engine efficiency either decreased or remained
almost constant relative to the baseline operation, i.e., when no hydrogen was
supplied to engine. The premixed hydrogen fuel to air equivalence ratios at these
fuelling rates were extremely low, typically 0 to 0.03, which might make the fuel
to burn in a very erratic manner. They stated that the combustion of hydrogen air
mixtures at such low hydrogen fuel concentrations was dependent on the local
temperature around parcels of fuel mixtures. At 82% of full load, the overall
temperature in the combustion chamber was lower than full rated load operation.
As a result, the mixtures containing very low hydrogen content would burn better
as full rated load than at part load operation. When the flow rate of hydrogen was
0.65 KJ/s, the resulting thermal efficiency was consistently lower than the baseline
value. On the other hand, increasing the rate to 1.65 KJ/s resulted in higher
thermal efficiency over all the load range. Peak pressure increased sharply beyond
about 11% of hydrogen in the mixture at full rated load. At the same time, the
time for the occurance of peak pressure got decreased from the baseline value.
They also noticed that the peak cylinder pressures for mixtures containing less
than 6% hydrogen energy was higher than the baseline value but it occured late.
The late occurence of peak cylinder pressure at low rates of hydrogen energy
supply was believed to be due to delayed burning of hydrogen in the combustion
chamber. Increasing the portion of hydrogen increased the exhaust temperature
due to rapid combustion and higher flame temperature. They witnessed smoke
47
levels starting to decrease as hydrogen content was increased. They related this to
increased H/C ratio of the fuel. At part loads, smoke levels got decreased by over
50%. Oxides of nitrogen increased faster than hydrocarbons as hydrogen content
was increased. They attributed this to higher local temperature due to rapid
combustion of hydrogen.
Roy et al (2010) investigated the engine performance and emissions of
a super charged four-stroke, single cylinder, water cooled diesel engine fueled
with hydrogen and ignited by a pilot amount of diesel fuel in dual-fuel mode. The
engine was tested for use as a cogeneration engine. The experiments were carried
out at a constant pilot injection pressure of 80 MPa and pilot quantity of 3
mg/cycle for different fuel-air equivalence ratios and at various injection timings
without and with charge dilution. The intake pressure of air was kept constant at
200 kPa and the temperature was maitained at 30 oC throughout the study. Their
experimental strategy was to optimize the injection timing to maximize the engine
power at different fuel-air equivalence ratios without knocking and within the
limit of the maximum cylinder pressure. They first tested the engine with
hydrogen-operation condition up to the maximum possible fuel-air equivalence
ratio of 0.3. A maximum IMEP of 908 kPa and a thermal efficiency of about 42%
were obtained. They observed that the equivalence ratio could not be further
increased due to knocking of the engine. The emission of CO was only about 5
ppm, and that of HC was about 15 ppm. However, the NOX emissions were high,
100 to 200 ppm. Then they performed charge dilution by N2 to obtain lower NOX
emissions. They achieved 100% reduction in NO X. According to them, this was
due to the dilution by N2 gas which paved the way for injection of higher amount
of hydrogen without knocking. Because of this charge dilution, they got 13%
higher IMEP than IMEP produced without charge dilution. At an equivalence
ratio of 0.20, the maximum cylinder pressure increased gradually with advancing
injection timings. The maximum cylinder pressure was 9.27 MPa at an injection
timing of 10o BTDC, and reached its highest level of about 12 MPa at 18 o BTDC.
48
The maximum cylinder pressure at an injection timing of 5o BTDC and an
equivalence ratio of 0.25 was 8.6 MPa, and reached its highest level of 12.6 MPa
at 13o BTDC. The maximum cylinder pressure at an injection timing of 4 o BTDC
and an equivalence ratio of 0.30 was 8.75 MPa, and reached its highest level of
about 10 MPa at 6.5o BTDC. The maximum cylinder pressure was very low at an
equivalence ratio of 0.30 because in that case the injection timing needed to be
retarded to avoid knocking. At a constant equivalence ratio, the NO X emission
increased with advanced injection timings. Advancing the injection timing
increased the peak cylinder pressure, and higher peak cylinder pressures resulted
in higher peak burned gas temperatures, and hence more NOX emission. More
NOX was produced as the equivalence ratio got increased, although the injection
timings were retarded. The highest NOX emission level was about 200 ppm at an
equivalence ratio of 0.25 to 0.30. HC emitted by the dual-fuel engine fueled by
hydrogen varied from only 14 to 18 ppm. The CO emitted by the dual-fuel engine
fueled by hydrogen varied from only 5 to 7 ppm. The level of NOX of 200 ppm
with hydrogen-operation was reduced to 0 ppm level with 60% N2 dilution. There
was about 98% and 99% reduction in NOX for 40% and 50% N2 dilution,
respectively. However, HC increased to the level of about 80 ppm with 60% N2
dilution. CO increased to the levels of about 80 ppm and 500 ppm with 50% and
60% N2 dilution, respectively. They concluded that by diluting the charge with N2,
the hydrogen engine could be operated without engine knock.
Lilik et al (2010) reported about the hydrogen assisted diesel
combustion on a DDC/VM Motor 2.5L, 4-cylinder, turbo-charged, common rail,
direct injection light-duty diesel engine. Their main focus was on the study of
exhaust emissions of the engine. They substituted hydrogen for diesel fuel on an
energy basis of 0%, 2.5%, 5%, 7.5%, 10% and 15% by aspirating hydrogen into
conditions of the engine. They observed a significant retardation in injection
49
aspirated. This resulted in significant reduction in NOX emission. They also
observed that the same emission reductions were possible without aspirating
hydrogen by manually retarding the injection timing. To study the hydrogen
assisted diesel combustion, they locked the injection timings of the pilot and the
main fuel. They also used computational fluid dynamics analysis (CFD) for
hydrogen assisted diesel combustion. CFD of the hydrogen assisted diesel
combustion process captured the trend and reproduced the experimentally
hydrogen addition caused the maximum in-cylinder pressure to increase in all
modes. The effect was greater in the high load modes, where more complete
combustion of the fuel occurred. At 1800 rpm and 75% maximum output with
15% hydrogen substitution, the maximum pressure got increased by 2% over base
line condition and at 3600 rpm and 75% maximum output, the maximum pressure
increased by 7%. Also, they observed that the maximum pressure peak occurred
earlier in the high load modes. The substitution of hydrogen for diesel fuel
decreased the amount of diesel fuel injected in both the pilot and main injections.
When hydrogen assisted the diesel combustion, there was a slight ignition delay in
the premixed combustion phase. They further stated that this was due to the fact
that the diesel fuel acted as a pilot to ignite the hydrogen, since hydrogen has a
lower cetane number than diesel fuel. They further stated that increasing levels of
hydrogen slightly increased the apparent heat release rate of the premixed
combustion phase. With the increase in hydrogen, less diesel fuel was injected.
Thus, less heat was absorbed during the fuel vaporization phase between the
premixed combustion phase and the mixing-controlled combustion phase of the
main injection. The heat release during the mixing-controlled combustion phase
was decreased with the increase of hydrogen substitution.
Welch & Wallace (1990) converted a single-cylinder Lister ST-1 direct
injection diesel engine to operate on hydrogen to evaluate its performance and
combustion characteristics. They admitted hydrogen gas at 10.3 MPa pressure to
50
the engine combustion chamber through a hydraulically-actuated injection valve
which controlled the timing and duration of the hydrogen injection. They provided
ignition of hydrogen by a continuously operating sheathed glow plug that was
used in passenger car diesel engines to assist cold starting. Their results indicated
that the hydrogen-fueled diesel engine could produce higher power than an
ordinary diesel engine due to the absence of smoke emissions. Another positive
feature was NOX emissions got reduced compared to the ordinary diesel engine.
Indicated efficiency of the hydrogen-fueled diesel engine was about 90% of that
of the original diesel at moderate loads. At very light loads, however, the
efficiency of the hydrogen-fueled engine got decreased compared to that at
moderate loads. They concluded that the hydrogen-fueled diesel engine with glow
plug could be used to develop greater power with lower emissions than the same
engine operated on diesel fuel.
Shahad & Hadi (2011) found a way to reduce the concentration of
pollutants coming out from a diesel engine. They blended hydrogen gas with
hydrocarbon fuels used in internal combustion engines. They carried out their
experimental research in a four stroke air cooled diesel engine. Their hydrogen
fueling system consisted of a hydrogen bottle, two pressure reduction valves to
reduce the hydrogen pressure to 2 bars, a hydrogen flow meter and an injector.
The injector was mounted on the inlet pipe at 10 cm from the engine with an angle
of 45o with the direction of injection. The hydrogen injection timing was
controlled by an electronic control unit designed for this purpose. They chose
three different speeds of 1000 rpm, 1250 rpm, and 1500 rpm. They also varied the
load from no load to 80% of full load and the hydrogen blending ratio was varied
from zero (pure diesel) to 10% (by mass) of the injected diesel fuel. Their results
showed that 10% hydrogen blending reduced smoke opacity by about 65%. It
increased the nitrogen oxides concentration by about 21.8% and reduced CO2 and
CO concentrations by about 27% and 32% respectively. This trend was found at
all tested speeds and loads. They observed that the concentration of NOX generally
51
increased with hydrogen blending ratio for all loads. They related this to the
improvement of combustion process caused by the presence of hydrogen in the
fuel mixture which led to higher cylinder temperature. They also stated that the
NOX formation reactions were highly temperature dependent.
2.6
COMBUSTION OF HYDROGEN WITH CNG
Bysveen (2007) reported about the working characteristics of S.I
engine when CNG and HCNG were used as a fuel. The engine used for his
experiments was a three-cylinder, single spark plug, 2.7 litre Zetor Z4901
originally used for stationary applications. He rebuilt the engine for natural gas
use by reducing the compression ratio from 17:1 to 11:1. He equipped the test
engine with K-type thermo couples in the intake manifold, in the cooling water
system and in the exhaust. He employed hydraulic dynamometer for loading the
engine. He studied the sensitivity in spark timings for the fuels and the engine in
the range of 51o to 251o BTDC. The CNG fuel used for this work consisted of
about 99.5% vol. of CH4, and the HCNG consisted of a mixture of 29% vol. of
hydrogen. His results showed that the brake thermal efficiency was considerably
higher using HCNG than using pure CNG. This effect was most pronounced for
the high engine speeds. In general, he observed less production of unburned
hydrocarbons when adding hydrogen to the CNG for a given excess air ratio. He
reported that this was due to the fact that the lean limit for pure methane air
mixtures was much richer than the lean limit for hydrogen-enriched methane air
mixtures. With H2 addition, a smaller quenching zone resulted; this enabled the
flame to propagate closer to the walls. He further observed that the addition of
hydrogen to methane air mixtures increased the combustion speed and the
combustion temperatures; it led to increased NOX emissions compared to pure
natural gas.
52
Mohammed et al (2011) investigated on the performance and emission
of a CNG-DI and spark-ignition engine when a small amount of hydrogen was
added to the CNG using in-situ mixing. They set the injection timing to 30o
BTDC, kept the air fuel ratio at stoichiometric, and the ignition timing to
maximum brake torque. They performed experiments at 2000, 3000, and 4000
rpm of engine speeds with WOT conditions. From their results, it was interpreted
that the introduction of a small amount of hydrogen improved the engine
performance, brake specific energy consumption, and cylinder pressures. The CO
emission of the engine got decreased until the engine speed reached 3000 rpm and
then started to increase with the increase in engine speed. They stated that this was
mainly due to increase in completeness of combustion process and sufficiency of
oxygen. At high speeds, the CO emissions tended to increase due to retardation in
timing which also resulted in poor combustion. For all rates of hydrogen THC
tended to decrease. They attributed this to decrease in the carbon fraction in the
fuel blends and the increase in combustion temperature due to increase in H2
fractions.
Cowan et al (2010) reported about the effects of gaseous fuel additives
on a pilot-ignited, directly injected natural gas engine. The additives used in their
investigation were propane, ethane, hydrogen and nitrogen. They used a single
cylinder test engine equipped with a prototype fuelling system for their study.
They controlled the diesel and natural gas injection processes by electronic control
operated multi-fuel injector. They equipped the engine with a custom air-exchange
system to ensure that the charge conditions were independent of variations in fuel
composition and injection timing. They prepared the nitrogen, ethane, and propane
fuel blends using bottled gas combined with commercially distributed natural gas
in large volume storage tanks. They left the blends in the storage tanks for at least
48 hours to ensure that they were fully mixed before being supplied to the highpressure gas compression system for supply to the engine. To avoid condensation
of the heavy hydrocarbons, the kept all concentrations below the saturation partial
53
pressure at all times. They selected mid-load condition for their investigation to
compare the effects of the various fuels. For their study, they controlled the
combustion timing by varying the timing of the start of the pilot fuel injection
process. The timing of the gas start-of-injection (GSOI) was fixed at 1.0 ms after
the end of the diesel injection. The 50% IHR was used as the control variable
representing the combustion timing. They adjusted the start-of-injection timing for
the different fuel blends to maintain the 50% IHR at the specified value. For all
rate of the gaseous fuel. They fixed pilot quantity at 5% of the total fuel on an
energy basis; this amounted to approximately 6 mg diesel/cycle for all the
conditions tested. The pilot diesel and gaseous fuel rail pressures were constant at
21 MPa for all the tests. Their results showed that the hydrogen addition to the
fuel resulted in an increase in ignitability for the gaseous fuel, and a corresponding
reduction in ignition delay. The effects of ethane and propane were similar to
those of hydrogen. They observed higher NOX emissions when ethane, propane, or
hydrogen was added to the combustion process. They related this to increase in
adiabatic flame temperatures as they were generated pre-dominantly through the
strongly temperature-dependent thermal NO mechanism. All the fuel additives
reduced hydrocarbon emissions. When compared with other additives, the
hydrogen reduced more HC emissions. They related this to higher radical
concentrations and a wider flammability range which resulted in more complete
combustion of the fuel.
2.7
COMBUSTION OF HYDROGEN WITH LPG
Lata et al (2012) made an experimental investigation on performance
and emission of a dual fuel operation of a 4 cylinder, turbocharged, inter-cooled,
62.5 kW genset diesel engine with hydrogen, liquefied petroleum gas (LPG) and
mixture of LPG and hydrogen as secondary fuels. They carried out the
experiments at a wide range of load conditions of the engine with different
54
gaseous fuel substitutions. When only hydrogen was used as secondary fuel, the
maximum enhancement in the brake thermal efficiency was 17% which was
obtained with 30% of secondary fuel. When only LPG was used as secondary fuel,
maximum enhancement in the brake thermal efficiency was 6% with 40% of
secondary fuel. They observed that compared to the pure diesel operation,
proportion of unburnt HC and CO got increased while emission of NOX and
smoke got reduced in both cases. On the other hand, when 40% of the mixture of
LPG and hydrgen was used in the ratio of 70:30 as secondary fuel, brake thermal
efficiency got enhanced by 27% and HC emission got reduced by 68%. Further,
they observed that the dual fuel diesel engine showed lower thermal efficiency at
lower load conditions as compared to diesel. They attributed this to the fact that at
low concentration of hydrogen or LPG in the intake air, the combustion spread
throughout the gas-air mixture. This caused high heat transfer losses to the
adjacent walls. While, in the case of diesel engines under light load condition, the
penetration of the diesel spray was such that it did not reach the cylinder walls and
the combustion was confined to piston bowl and also, the surrounding coatings of
air acted as insulation in between burnt gases and the walls, which reduced heat
losses thereby giving better thermal efficiencies with diesel. They found that this
short coming of low efficiency at lower load condition in a dual fuel operation
could be removed when a mixture of hydrogen and LPG was used as the
secondary fuel at higher than 10% load condition.
Rao et al (2008) performed experiments on a conventional diesel
engine operating on dual-fuel mode using diesel and LPG. The experiments were
done at a constant speed of 1500 rpm and under varying load conditions. They
indicated that with the dual-fuel mode of operation, precious diesel could be
conserved up to 80%. However, in their work, it was done only up to 45% due to
severe engine vibrations. The brake power of the engine was found to be about
15% more on the dual-fuel operation, while the brake specific fuel consumption
55
was found to be about 30% lower than diesel fuel mode of operation. They related
this to better mixing of air and LPG and improved combustion efficiency.
Qi et al (2007) conducted an experimental investigation on a single
cylinder direct injection diesel engine modified to operate in dual fuel mode with
diesel-LPG as fuels. They used various rates of LPG diesel blends for their
experiments. They compressed LPG of 0, 10, 20, 30, and 40% by pressured
nitrogen gas to mix with the diesel fuel in a liquid form. They concluded that
LPG-diesel blended fuel combustion was a promising technique for controlling
both NOX and smoke emissions even on existing DI diesel engines.
2.8
COMBUSTION OF HYDROGEN WITH METHANE
Wallner et al (2007) analyzed
the
combustion
properties
of
hydrogen/methane blends (5% and 20% methane by volume in hydrogen
equal to 30% and 65% methane by mass in hydrogen) and compared them
to those of pure hydrogen as a reference. They confirmed that only minor
adjustments in spark timing and injection duration were necessary for an
engine to operate on pure hydrogen and hydrogen/methane blends. They used
automotive size, spark-ignited, single-cylinder, supercharged 6.0-L V-8 research
engine having a compression ratio of 11.4:1 and maximum torque of 30 Nm for
their investigations. They ran the engine at two different speeds of 2000 rpm and
4000 rpm. They selected three load conditions for their engine analysis as IMEP
of 2 bar, 4 bar, and 6 bar. They performed
a
detailed
analysis
of
the
combustion behavior in order to evaluate the influence of blending of
different concentrations of methane and hydrogen. They chose the spark timing
as constant at 10 deg CA before top dead center (BTDC). They observed that in
pure hydrogen operation, combustion took only about 25 deg CA whereas in
5% methane blend, it was 35 deg CA and in 20% methane blend, it was
56
significantly
longer to about 55 deg CA.
They found extremely
short
combustion duration for close-to-stoichiometric pure hydrogen operation that
resulted in high combustion temperatures and, thus, it increased the wall heat
losses. They also noticed that the maximum rate of heat release was significantly
higher for pure hydrogen operation, which also resulted in a higher
combustion peak pressure of 45 bar for pure hydrogen compared to 30 bar for
the 20% methane blend. These results showed that to achieve the maximum
efficiency, the spark timing had to be advanced in blended operation compared to
pure hydrogen operation. The NOX emission was more at IMEP of 6 bar compared
to IMEP of 2 bar and IMEP of 4 bar. They stated that at a higher engine load like
6 bar IMEP, due to higher combustion temperatures and the NOX emission
depended upon the logarithmic scale of temperatures, it got increased
exponentially.
Zhou et al (2013) conducted an experimental investigation on
combustion and emission characteristics of a compression ignition engine using
diesel as pilot fuel and methane, hydrogen and methane/hydrogen mixture as
gaseous fuels at 1800 rpm. The test engine was mounted on an eddy-current
dynamometer. They measured the in-cylinder pressure by a piezo electric sensor
of Kistler make and the pressure signals were amplified with a charge amplifier. A
crank-angle encoder was employed for crank-angle signal acquisition at a
revolution of 0.5° CA. The intake and exhaust gas temperatures were measured by
K-type thermocouples. For gaseous emissions, total HC was measured with a
heated flame ionization detector. NO/NOX was measured with a heated
chemiluminescent analyzer. CO and CO2 were measured with non-dispersive
infrared analyzers. O2 was measured with a portable gas analyzer. During the
investigation they observed that the ULSD-hydrogen combustion became unstable
and hard to control at high loads. When hydrogen was enriched in methane, the
BTE got increased at all loads. With the addition of hydrogen into methane, the
peak cylinder pressure got increased relative to ULSD-Methane operation and this
57
effect was more apparent at 90% load. At BMEP of 0.71 MPa, for ULSDMethane dual-fuel engine, the peak heat release rate increased apparently
compared with the baseline operation. The heat release rate profile for ULSDHydrogen revealed that the main combustion phase occurred at premixed
combustion phase and the heat released during diffusion combustion phase was
reduced a lot relative to other cases. They found that the CO emission increased
sharply when the combustion of metane and ULSD had taken place. This was due
to the incomplete combustion of methane. When ULSD-Hydrogen was combusted
in dual-fuel mode, the CO emission decreased at all load sowing to the direct
replacement of the carbon content from hydrogen to diesel fuel. The addition of
hydrogen into the methane extended the flammability limit of methane and the
incomplete combustion of methane was alleviated. When the engine was operated
at 90% of the full load with hydrogen induction, CO emission got reduced by
nearly 25% compared to base line operation.
It was further observed that the total HC emission was high when
ULSD-methane was combusted. On the otherhand, when ULSD-Hydrogen was
combusted, the total HC emission got decreased. For the BMEP 0f 0.08 MPa, 0.24
MPa and 0.41 MPa, the total HC emission was 12.01, 10.26, 9.03, 7.69, and 0.78
times than baseline for Methane, H30-M70, H50, M50, H70-M30 and Hydrogen,
respectively. For ULSD-Methane and ULSD-Hydrogen dual-fuel combustion,
NOX emission got decreased slightly at lower load and increased at medium to
high loads. This was due to the higher combustion temperature and faster burning
rate of hydrogen than methane, ULSD-Hydrogen combustion enhanced the NOX
formation. When small quantity of hydrogen was mixed with methane, it reduced
NOX emission. But, when the quantity of hydrogen was increased, the NO X
emission got increased. At H50-M50 case, the NOX was basically the same with
ULSD-Methane operation.
58
2.9
COMBUSTION OF HYDROGEN WITH MISCELLANEOUS
GASES
Park et al (2011) experimentally investigated the effect of addition of
hydrogen on the performance and emission characteristics of a naturally aspirated
S.I engine which was fueled with biogas. They ran the engine at constant engine
rotational speed of 1800 rpm under a 60 kW power output condition. They
blended H2 fractions ranging from 5 to 30% to the biogas. Their engine test results
indicated that the addition of hydrogen improved in-cylinder combustion
characteristics, extending lean operating limit as well as reducing THC emissions
while elevating NOX generation. In terms of efficiency, however, they observed a
competition between enhanced combustion stability and increased cooling energy
loss with a rise in H2 concentration. They got maximum engine efficiency at 5% to
10% of H2 concentration. They reported that an increase of H2 improved flame
propagation speed and extended lean flammability limit while NOX increased. As
H2% was increased, the burn duration got decreased due to the improvement in the
propagation speed of the blended fuel combustion. In addition, they observed no
knocking or back-fire phenomena during engine operations for all the fuel
conditions. This meant that stable and efficient combustion could be achieved
even in the lowest quality gas by H2 addition while abnormal combustion was still
suppressed.
Sahoo et al (2012) carried out the experiments in a Kirloskar TV1
diesel engine to evaluate its characteristics when syngas mixture of hydrogen and
carbon monoxide was inducted into the combustion of diesel. The engine used for
their study was a single cylinder, water cooled, direct injection, four stroke,
having a bore of 87.5 mm, stroke of 110 mm, compression ratio of 17.5:1, rated
power of 5.2 kW at 1500 rpm. They analyzed the flue gas compositions using a
multi-component analyzer based on infrared and chemical cell technique. Their
results showed that the 100% H2 syngas mode resulted in a maximum in-cylinder
59
pressure and combustion temperature which in-turn increased the NOX emissions
and the exhaust gas temperature compared to that of 75% and 50% H 2 syngas
modes. They observed the NOX emissions of 127 ppm, 175 ppm, and 220 ppm at
peak power output for 50%, 75%, and 100% H2 syngas modes respectively. They
related this to the higher flame speed and higher energy content of the syngas at
100% H2 syngas mode.
Mohammadi et al (2005) carried out an investigation on diesel engine
used for power generation to see the effects of addition of LCG (Low Calorific
Gases) and LCG with small portion of hydrogen and nitrogen on performance and
emissions characteristics of the engine. These gases were originally produced in
various chemical processes such as gasification of solid wastes or biomass. The
test engine used by them was a four-stroke single cylinder naturally aspirated
direct-injection diesel engine (Yanmar NFD-170) with a bore of 102 mm and a
stroke of 105 mm, injection nozzle spray angle of 150° with four holes and with
0.29 mm hole diameter. They carried out the combustion analysis by measuring
in-cylinder pressure at every 1o CA using piezoelectric pressure transducer
(Kistler 6052A). They used diesel having a density of 828 kg/m3, lower heating
value of 44200 kJ/kg, and cetane number of 55 for this tests. They conducted all
experiments at thermally steady state of the engine with injection timing of 12°
BTDC and engine speed of 1800 rpm. They introduced nitrogen from a high
pressure vessel into the intake of the engine using a gas mixer installed at
downstream of surge tank. And, they introduced hydrogen gas using an orifice
nozzle with diameter of 6 mm. They measured the flow rate of both gases
preciously using thermal mass flow meters. In their experiment, they first adjusted
the flow rate and composition of LCG and then the amount of diesel fuel injected
to achieve considered output. They fixed the engine load as constant at brake
mean effective pressure of 0.6 MPa. Their results showed that at rH = 0 and
rLCG=25% when 25% of intake air was replaced with nitrogen, the efficiency of
the engine was slightly lower than diesel fuel operation. However, when they
60
introduced hydrogen with LCG, it lowered the consumption of diesel fuel. At
rLCG=25% and rH=30%, the corresponding saving in consumption of diesel fuel
was about 40%. At rH=0 when only nitrogen was added to the engine intake, it
increased ignition delay with little effects on combustion process. However, at
given rLCG, increasing the hydrogen concentration, promoted the premixed and
diffusion combustions and it resulted in higher peak combustion pressure and
temperature. Increasing rH increased the peak level and advancement in its timing.
Fang et al (2008) investigated the driving performance and emission
characteristics of a 125 cc motor cycle equipped with an onboard plasma reformer
for producing Hydrogen Rich Gas (HRG). To produce HRG, they inducted butane
with suitable air flow rate into the plasma reformer. They ran the motorcycle
under steady and transient conditions on a chassis dynamometer to assess the
driving performance and exhaust emissions. Prior to run, they optimized the
operation parameters of the plasma reformer in a series of tests and they
concluded that the O2/C ratio of 0.55 and a butane supply rate of 1.16 lpm was the
optimum condition to produce HRG. They used gas chromatograph of Agilent
6850 GC for analyzing the gas emission and a scanning electron microscope for
observing carbon deposit arising from the reforming process. For analyzing the
driving tests, they used Japanese made Horiba 554JA emission analyzer; US made
CAI 600 NOX analyzer, a fuel flow meter, an oscilloscope and a temperature data
recorder. From their results, it was interpreted that at O2/C ratio of 0.55, the NOX
emission at a vehicle speed of 40 km/h got reduced from 600 ppm to 220 ppm.
They attributed this to the diluting effect of HRG, as it contained CO2 and N2 also.
They observed that when 2.95% HRG was added, the highest peak pressure was
obtained. Further, in the addition of 4.11%, the pressure rise rate became slower
and the peak pressure also became lower than other conditions. They concluded
that the acceleration characteristics of the vehicle were similar under both fuelling
systems.
61
Cecrle et al (2012) injected a hydrogen/carbon monoxide mixture into
the inlet manifold of a biodiesel fuled dual-fuel diesel engine to evaluate its
characteristics. The engine used for their testing was a Yanmar L100V singlecylinder DI diesel engine with a compression ratio of 21.2. The other operating
parameters of the engine were speed of the engine mainted at 3600 rotations per
minute, injection time as 15.5 before piston top-dead-center with a pressure of
19.6 MPa. To provide load on the engine, they employed a North-Star electric
generator coupled to the crankshaft. They outfitted various sensors to measure the
ambient air temperature, pressure, and relative humidity, engine air mass flow,
engine intake air emperature and pressure, fuel mass flow, fuel density, engine
torque, exhaust port temperature, downstream exhaust gas temperature and
pressure, and generator load on the engine and test stand. For their experiments
they used Reformate Assisted Gas consisting of 57% H2 and 43% CO. They had
chosen this mixture because it represented the best-case scenario for a noncatalyzed system in regard to assisted mixture energy as it was the partial
oxidation of glycerin without any formation of complete products of combustion.
When they added reformatted gas to the intake of the engine, the biodiesel fuel
flow rate got dropped significantly. This illustrated that the reformate mixture
increased the fuel economy of biodiesel under all loading conditions. CO 2
emissions also got increased for the 50% load point. The addition of reformate
also reduced total HC emissions. They reasoned this to a hotter burn that would
also have acted to diminish the incomplete combustion.
Plaksin et al (2008) conducted a study on reduction of NOX in diesel
engine emissions by using a hydrogen-rich synthesis gas produced by plasmatron
fuel reformer. They activated 10% to 20% of the diesel fuel in an arc discharge
and turned them into plasma chemical reformation fuel by using a DC arc
plasmatron that was fabricated to increase the ability of gas activation. They got
the yielding of diesel fuel reformation upto 80% to 100% when small quantity of
diesel fuel in range of 6 ml/min was used. They supplied this synthesis gas
62
mixture which contained hydrogen, carbon dioxide, carbon monoxide, nitrogen,
and hydrocarbons into the engine together with the rest of the fuel-air mixture.
They reported decrease in the NOX content in the emissions of the engine upto
23% and simultaneously the fuel combustion efficiency got increased.
2.10
INFLUENCE OF ADDITION OF HYDROGEN AND OXYGEN
MIXTURE IN COMBUSTION
Wang et al (2011) compared the effects of hydrogen and hydrogenoxygen blends (hydroxygen) additions on the performance of a gasoline engine at
1400 rpm and with a manifold absolute pressure of 61.5 kPa. The tests were
carried out on a 1.6 L, SI engine manufactured by Beijing Hyundai Motors. The
rated power of the engine was 82.32 kW at 6000 rpm and a rated torque of 143.28
Nm at 4500 rpm. They applied a hybrid electronic control unit to adjust the
hydrogen and hydroxygen volume fractions in the intake increasing from 0% to
about 3% and keep the hydrogen-to-oxygen mole ratio at 2:1 in hydroxygen tests.
For each testing condition, the gasoline flow rate was adjusted to maintain the
mixture global excess air ratio of 1. First, they ran the engine with pure gasoline
then with hydrogen and hydroxygen with varying volume fractions in the intake as
0% to 3% to simulate the case of hydrogen and oxygen produced by a water
electrolysis process. Their test results confirmed that engine fuel energy flow rate
was decreased after hydrogen addition but increased with hydroxygen blending.
They found that when hydrogen or hydroxygen volume fraction in the intake was
lower than 2%, the hydroxygen-blended gasoline engine produced a higher
thermal efficiency than the hydrogen-blended gasoline engine. They stated that
this increase in brake thermal efficiency was due to the addition of hydrogen
which helped to enhance the fast and complete combustion of the fuel-air mixture.
They achieved the peak value of 35.7% at the standard hydroxygen volume
fraction in the intake of 0.75%. They explained that the possible reason was that
the addition of hydroxygen increased the oxygen fraction in the intake; this
63
slightly reduced the fuel-rich area in the cylinder and this in turn increased the
complete combustion of the fuel-air mixtures. They observed that both engines
indicated thermal efficiency and fuel energy flow rates were raised after the
standard hydroxygen blending. They attributed this to the ignition energy of
hydrogen which was only 1/10 of that of gasoline and the addition of hydrogen
stimulated the formation of O and OH radicals. Since hydrogen has a short
quenching distance, they witnessed a decrease in HC emissions caused by the
crevice effect. They also related this to chemical equilibrium process. As the
raised cylinder temperature after hydrogen or hydroxygen addition helped to ease
the formation of HC emissions during the combustion process. They observed that
the CO emission got increased with the increase of hydrogen volume fraction in
the intake whereas it got decreased with the increase of the standard hydroxygen
addition fraction. When they raised hydroxygen volume fraction in the intake as
0% to 2.8%, CO got reduced by 21.86% for the standard hydroxygen-blended
gasoline engine. NOX emissions were raised after hydrogen and hydroxygen
additions. They attributed this to a high adiabatic flame temperature caused by the
additions of hydrogen and hydroxygen.
Karagoz et al (2012) studied the effect of hydrogen-oxygen mixture on
S.I engine performance and emission characteristics. They introduced the gas
mixture into the inlet manifold of the engine. They selected three different
supplementary fuels which contained 0% H2, 3% H2 + 1.5% O2, and 6% H2 + 3%
O2 by volume fractions of intake air. They used a mass-flow meter with a
measurement uncertainty of 1%. They reduced the flow fluctuations of H 2/O2
mixture by using a buffer tank. Their test results showed that a 6% H2 + 3% O2
addition increased engine brake power from 19.09 kW to 20.52 kW at 3500 rpm
engine speed. The brake torque got increased from 51.28 Nm to 63.24 Nm at 2000
rpm engine speed. An increase of BMEP from 575.3 kPa to 710.4 kPa at 2000
rpm was achieved with 6% H2 and 3% O2 addition. Best thermal efficiencies were
achieved partly by 3% and 6% hydrogen addition. An increase in brake thermal
64
efficiency from 21.77% to 24.50% at 2000 rpm engine speed was achieved using
6% gasoline-hydrogen mixture. A BSFC got decreased from 372.4 g/kWh to
330.9 g/kWh at 2000 rpm engine speed. HC emission got reduced from 274 ppm
to 84 ppm at 2000 rpm engine speed when 6% H2 and 3% O2 mixture was used as
a supplementary fuel. NOX emission got increased from 848 ppm to 1297 ppm at
2000 rpm due to higher in-cylinder temperature levels. They observed lower CO
emissions and higher CO2 emissions as a consequence of improved combustion.
2.11
COMBUSTION UNDER THE INFLUENCE OF HYDROGEN
AND OXYGEN MIXTURE PRODUCED ESPECIALLY BY
ELECTRO-CHEMICAL DISSOCIATION OF WATER
Shrestha et al (2000) conducted experiments on a Chevrolet Silverado
6.5 L turbocharged V8 diesel engine. They used three units of hydrogen
generation system (HGS) each having a capacity to produce hydrogen-oxygen
mixture of 690 cm3/min by the process of water electrolysis. They tested the
vehicle in three test driving cycles i.e., U.S. Federal Testing Protocol (FTP),
Japanese 11 Mode Test Schedule (JAPANESE 11), and Economic Commission
for Europe Schedule (ECE 1504A). They equipped the vehicle with an on-board
diagnostics system, which continuously monitored the engine parameters during
the test. In this test they used MD-GAS-5C gas analyser to measure CO, HC and
NOX. This analyser was interfaced with NID-7000 software for exhaust gas
analysis. The real time exhaust information was collected in conjuction with
vehicle load, power and torque outputs, with a sampling frequency of 10 Hz. Their
result showed that the addition of hydrogen to the main fuel could be beneficial
for the combustion process in internal combustion engines. Similarly, oxygen
enrichment in the intake was shown to provide substantial control in particulate
emissions, improved thermal efficiency, and reduced engine-out emissions in
diesel engines. According to their results, Particulate matter (PM) got reduced up
65
to 60%, CO up to 30% and NOX up to 19% when compared with diesel
combustion.
Shrestha & Karim (1999) reported that the addition of small quantity of
hydrogen and oxygen produced by the electrical dissociation of water to the
petrochemical fuel might contribute towards the speeding of the combustion
process of internal combustion engine and bring about significant improvements
in performance and emissions. For this investigation they tested an SI engine
operated with methane over a range of operating conditions. One of the main
features of methane fueled spark ignition engines is their relatively slow flame
propagation rates in comparison to liquid fuel applications which may lead to
relatively lower power output and efficiency with increased emissions and cyclic
variations. This is especially pronounced at operational equivalence ratios that are
much leaner than the stoichiometric value. They suggested that the addition to the
methane with the products of water electrolysis generated on-board of a vehicle
might produce some improvement in engine performance and also suggested that
the above procedure could be effectively implemented for relatively lean mixtures
and low compression ratios.
Uykur et al (2001) studied the effects of the addition of small amounts
of water electrolysis products on laminar premixed methane/air flames using
chemical kinetic simulation methods. They used CHEMKIN kinetic simulation
package with the GRI kinetic mechanism. Pollutant concentrations, flame speeds,
temperature
profiles
and
lean
flammability
limits
of
methane/air,
methane/hydrogen/air, and methane/hydrogen/oxygen/air systems were compared
at different addition percentages and equivalence ratios from 1.4 to the lean
flammability limit. The addition of 10% to 20% hydrogen in the fuel was found to
have a small effect in improving flame speed and lean flammability limit
properties. However, the addition of oxygen and hydrogen in the same ratio as
found in water was shown to be beneficial. Improvements in the flame speeds of
66
methane/air mixtures by the addition of 10% hydrogen and its associated oxygen
were equivalent to the improvements obtained by the addition of 20% of
hydrogen. They claimed that in near stoichiometric mixtures, the addition of
oxygen substantially increased the NOX concentrations, but for lean mixtures no
increase in NOX was predicted. CO emissions got reduced when hydrogen
displaced carbon containing fuels.
Sobiesiak et al (2002) explored the impact of the addition of small
amounts of molecular and atomic hydrogen/oxygen on laminar burning velocity,
pollutant concentrations and adiabatic flame temperatures of premixed, laminar,
freely propagating iso-octane flames using CHEMKIN kinetic simulation package
and a chemical kinetic mechanism at different equivalence ratios. They concluded
that hydrogen/oxygen additives increased the laminar burning velocities. Also,
carbon monoxide emissions got reduced due to increase in OH concentrations in
every stoichiometric ratio examined. In addition, the mixture of hydrogen and
oxygen increased the adiabatic flame temperature of iso-octane/air combustion
which resulted in increase in NOX emission.
Yilmaz et al (2010) investigated the effect of hydroxy gas addition on
compression ignition engine exhaust emissions and engine performance
characteristics. They used a four cylinder, four stroke, compression ignition (CI)
engine for their study. They fed the hydroxy gas to the intake manifold of a directinjection CI engine by a hydroxy system and a hydroxy electronic control unit
(HECU) under various loads. They produced hydroxy gas (HHO) by the
electrolysis process of different electrolytes of KOH(aq), NaOH(aq), NaCl(aq)
with various electrode designs in a leak proof plexi glass reactor (hydrogen
generator). The experiment results showed that constant HHO flow rate at low
engine speeds turned advantages of HHO system into disadvantages for engine
torque, carbon monoxide (CO), hydrocarbon (HC) emissions and specific fuel
consumption (SFC). Investigations demonstrated that HHO flow rate had to be
67
diminished in relation to engine speed. In order to overcome this disadvantage
they designed and manufactured a hydroxy electronic control unit (HECU). The
result of their investigation showed that HHO gas addition to the engine without
any modification resulted in increasing engine torque output by an average of
19.1%, reducing CO emissions by an average of 13.5%, HC emissions by an
average of 5% and SFC by an average of 14%. The reason for this happening was,
the increase in power was due to oxygen concentration of hydroxy gas and better
mixing of hydroxy with air and fuel that yielded enhanced combustion. High
laminar flame velocity of hydroxy yielded decreased ignition delay and shorter
combustion period that led to ideal constant-volume combustion.
Al-Rousan (2010) conducted experiments about the effect of HHO gas
supplementation on performance characteristics of a 197cc (Honda G 200) singlecylinder S.I engine with a compression ratio of 6:5:1. The result showed that the
optimal surface area of an electrode was needed to generate sufficient amount of
HHO. It was nearly twenty times that of the piston surface area. Also, the volume
of water needed in the cell was about one and half times that of the engine
capacity. The engine was subjected to a test of constant load with variable speed
(from 1000 to 2500 rpm). The auxiliary equipments used for this test were
tachometer for engine speed, voltmeter for cell voltage, thermometers for ambient
temperature, and thermocouples for exhaust gas temperature, clamp meter for
current measurements and flow meter for fuel consumption. He supplied a power
of 30 amps with 0-20V of DC to the fuel cell. He concluded that by
supplementing HHO gas into the combustion process of S.I engine, the brake
thermal efficiency got increased on an average of 3% to 8% and fuel consumption
got reduced by 20% to 30%.
Milen & Kiril (2004) carried out experiments to evaluate the influence
of the addition of hydrogen-oxygen mixture obtained from electro chemically
decomposed water to the inlet air of a single cylinder direct injection diesel engine
68
having cylinder bore of 98 mm and piston stroke of 130 mm. They loaded the
engine with DC dynamometer of Mezvetin MS 2218 4 make. The fuel
consumption was measured by mass method. The air consumption was measured
by laminar flowmeter of Cussons M79RH make. The smoke was measured by
Hartridge MK3 smokemeter. The NO emissions were measured by gas analyzer
Radas 1. The indicated pressure data were collected by piezo electric pressure
transducer of Kistler 6509 make and crank shaft position encoder Heidenhain rod
428D 163 make. The engine speed was measured by frequency meter FM1100.
This test run was conducted at constant load with variable speed of 1300 rpm to
1800 rpm. They maintained hydrogen-oxygen flowrate at 240 l/h and the injection
timing at 18o BTDC. The results showed that the engine power got increased with
hydrogen-oxygen mixture addition. The average power improvement obtained
was 15%. The peak pressure improvement at 1500 rpm was 14.8%. They
concluded that when a diesel engine was running with a small amount of hydrogen
addition, smaller than the present investigation, the NOX emissions were very
lower in comparison with the case without hydrogen addition. They attributed this
reduction in NOX with hydrogen addition to superior combustion characteristics of
hydrogen that burns more rapidly and cleanly than hydrocarbon fuels because its
amount was smaller and entered combustion reactions at higher velocity. Also,
due to its lower activation energy, it incurred more molecular collisions than
heavier hydrocarbon molecules. These characteristics might, not only have
improved the combustion process but also enhanced the transport processes by
reducing the hot spots in the combustion chamber that were one of the major
contributors to NOX emissions in IC engines.
The Canadian Hydrogen Energy Company Ltd (Canada 2005) tested
the effects of injection of hydrogen in a 1992 Detroit diesel heavy-duty engine.
The test was carried out on a go-power (Model DT-2000) heavy-duty
dynamometer rated at 800 HP. This test was based on the widely used AVL 8Mode heavy duty cycle for engine performance and emissions testing. In their test
69
of direct injection diesel engines, the Hydrogen Fuel Injection (HFI) kit injected
the gases during intake so that it got thoroughly mixed with intake air prior to
diesel injection. The electrolysis cell of the HFI kit was constructed of seamless
nickel tubing and the water chamber was made of seamless stainless steel. The
hydrogen was only produced, on demand, when the vehicle engine was operating.
Their experimental data showed that hydrogen burned nearly one order of
magnitude faster than petroleum fuels, thus approaching ideal thermodynamic
cycle. Hydrogen has a shorter flame quench distance, allowing flames to travel
closer to the cold zones, thus improving combustion. These facts resulted in the
reduction of fuel consumption by 4.44%, reduction of THC emissions by 6.17%,
reduction of CO emissions by 0.39%, reduction of NOX emissions by 4.34%, and
reduction of PM emissions by 7%.
Birtas et al (2011) conducted an investigation on a diesel engine
running with small amounts of the Hydrogen Rich Gas (HRG) provided by a
water electrolyzer aspirated in the air stream inducted in the cylinder. The test
engine was a naturally aspirated direct injection tractor diesel engine with 4
cylinders in line having the total capacity of 3759 cm3, nominal power of 50 kW
at 2400 rpm, maximum torque of 228 Nm at 1400 rpm, and the compression ratio
of 17.5. The engine was operated at light and medium loads and at various speeds.
They measured the engine operating parameters like instant torque, speed, engine
air consumption, fuel consumption, fuel temperature, exhaust emissions (CO2,
CO, NOX and THC) and the smoke opacity. Their results showed that at 2400 rpm
and 40% load, the brake thermal efficiency (BTE) got decreased by 1% with 4%
HRG (fuel energy) enrichment. This became 1.9% with 8% enrichment with
HRG. The same trend was found at 60% load. At HRG addition of 4%, the BTE
got reduced by 0.4% at 2400 rpm and by 0.8% at 1400 rpm. With 8% HRG, the
relative decrease was 1.14% at 1400 rpm and 0.7% at 1000 rpm. They averaged
300 consecutives cycles for main cylinder pressure characteristics. With 4% HRG,
70
the peak pressure got increased by 1.4% at 2400 rpm at 40% load. The rate of
pressure rise got increased by 12% at 2400 rpm at 40% load. The maximum rate
of heat release got increased due to the intensity of the first phase of combustion
when HRG was added. This increase was 1.8% and 3% at 2400 rpm and at 40%
load with HRG addition of 4% and 7.5% respectively. Oxides of nitrogen
emission got decreased by 13.3% at 2400 rpm when the load on the engine was
40% with 4% of HRG addition. At 2000 rpm, the decrease was 12%. At higher
HRG fractions, the decreasing trend of NOX emission was reversed. With 15%
HRG, the emission of NOX had a relative increase of about 8%. They concluded
that the higher NOX emission with HRG enrichment was due to the extended
Zeldovich kinetic mechanism. This also increased the peak pressure and the
temperature when HRG was added. The emission of CO got lowered by 6.7% at
2400 rpm and at 40% load with HRG enrichment of 4%. This reduction was 8.3%
at 1000 rpm and 11.5% at 1400 rpm. CO2 emissions were continuously reduced
when HRG was added. With 4% addition, the CO2 values were less compared to
the diesel operated engine by 3% at 2400 rpm and by 2.4% at 1000 rpm.
Increasing the enrichment to 8%, the reductions rose to 5.3% at 1400 rpm and to
5.2% at 1000 rpm. At 40% of load, the total hydrocarbon emission (THC) got
reduced by 1.7% and 7.6% at 1000 rpm by the enrichment of 4% and 8% of HRG
respectively. They attributed this reduction to the lower presence of carbon and a
possible more complete combustion. At 40% of load, the Filter Smoke Number
(FSN) got decreased by 30% at 2400 rpm and by 8.9% at 1000 rpm when the
HRG enrichment was 4%. The FSN change by HRG addition could also be
attributed to a change in nature of the particulate matter produced. Without HRG
induction, the particulates were black. With HRG induction, the particulates were
colorless.
Niculae & Chiriac (2013) made a solution to recover the decrease of
the gasoline spark ignition engines output which occurs in the case of transition to
an alternative fuel like liquefied petroleum gas. For this study, they had chosen the
71
numerical simulation by using the AVL BOOST code v. 2009. This solution
(HRG). This gas was resulting from water electrolysis. In their study, the spark
ignition engine was fuelled successively with gasoline and with liquefied
petroleum gas combined with different HRG flow rates of 5, 10, and 20 lpm
corresponding to mass fractions of 3.7%, 7.9%, and 15.3% respectively. The
engine was run at 2500 rpm. They also studied the effect of a possible increase of
the compression ratio associated with the using of the minimum HRG flow rate on
with changing the compression ratio of the engine to present the 9.5 to 11, the
effective output of the gasoline engine was not recovered when pure LPG fuel was
used with optimized start of combustion and the combustion duration. But, when
HRG of 5 lpm was added with LPG at the compression ratio of 11, they
successfully recovered the effective power output of the gasoline engine with
optimized start of combustion and the combustion duration.
Bari & Esmaeil (2010) evaluated the performance of a conventional
diesel engine when the diesel fuel was enhanced with hydrogen-oxygen mixture.
They generated hydrogen-oxygen mixture on-board through electrolysis of water.
They carried out experiment on a Hino, four-cylinder, direct injection, and water
cooled diesel engine having a compression ratio of 17.9:1 and maximum output
power of 38 kW at 1500 rpm. The engine was mounted to an electrical generator
and the generator was then connected to an adjustable load cell to put load on the
engine. In order to simplify the setup, they used 24V DC external power supply to
generate H2/O2 mixture. But in reality it can be produced from the vehicle
battery/alternator. They carried out experimental works under constant speed of
1500 rpm with three different power levels of 19 kW, 22 kW, and 28 kW and with
varying amount of H2/O2 mixture. The experimental results showed that by using
4.84%, 6.06%, and 6.12% of total diesel equivalent of H2/O2 mixture, the brake
thermal efficiency increased from 32.0% to 34.6%, 32.9% to 35.8%, and 34.7% to
72
36.3% at 19 kW, 22 kW, and 28 kW, respectively. These resulted in 15.07%,
15.16%, and 14.96% fuel savings. The emissions of HC, CO 2, and CO got
decreased, whereas the NOX emission got increased. At 19 kW the HC emission
dropped from 187 ppm to 85 ppm with 31.75 lpm induction of H2/O2. At 22 kW
and 28 kW the HC emission decreased from 189 ppm to 93 ppm by adding 29.84
lpm and from 192 ppm to 97 ppm by adding 30.6 lpm of H 2/O2, respectively. NOX
emission was found to have increased from 220 ppm to 280 ppm, 232 ppm to 307
ppm, and 270 ppm to 339 ppm at19 kW, 22 kW, and 28 kW of load, respectively.
The minimum amount of CO2 was achieved at 19 kW as 2.06 ppm with 31.75 lpm
of H2/O2 induction. The lowest CO2 level was found as 3.17 ppm and 3.54 ppm at
22 kW and 28 kW, respectively. CO was reduced from 0.26% to 0.005% at 19
kW, from 0.24% to 0.012% at 22 kW and from 0.26% to 0.021% at 28 kW. They
concluded that the flame speed of hydrogen was nine times faster than the flame
speed of diesel. Therefore, the burning of diesel in the presence of hydrogen
resulted in overall faster and more complete combustion. The peak pressure was
also obtained closer to TDC which produced more work.
Musmar & Al-Rousan (2011) introduced HHO gas along with air into
the intake manifold of a single cylinder unmodified Honda G 200, 197 cc, S.I.
engine to find its impact on the combustion and emissions characterstics of the
engine. The tests were conducted by varying the engine speed from 1000 rpm to
2300 rpm with constant load. A compact fuel cell had been designed for
generating HHO gas for this test. The fuel cell used in this research was basically
an electrolyte cell which decomposed distilled water (H2O) into HHO. The caloric
value of HHO gas was three times that of gasoline. The fuel cell was made of
plates of stainless steel grade 316 L. The cell plates had an anode and cathode.
Both of them were made of the same materials. According to their experience,
stainless steel grade 302 and 304 could be used for the cathode. But, the anode
must be made of stainless steel grade 316 L. Their results showed that a mixture
of HHO, air, and gasoline caused a reduction in the concentration of emissions
73
and an enhancement in engine efficiency. The NOX emission got reduced to about
50%, the carbon monoxide concentration got reduced to about 20%. And, there
was a reduction in fuel consumption in the range of 20% to 30%.
Dulger & Ozcelik (2000) reported that by using on-board hydrogen, the
fuel consumption and the engine-out emissions could be reduced. To prove this,
they carried out tests in four cars. These cars were a 1993 model Volvo 940, a
1996 model Mercedes 280, a 1992 model Fiat Kartal and a 1992 model Fiat
Dogan. In their study, the hydrogen was generated by the process of electrolysis of
water. In their test, the tap water was electrolysed by closed cell electrode
technology. For long lasting nature, the cathode electrode of the cell was made up
of compacted coal particles bonded together by a novel material. The anode
electrode was made of platinum. Because of the use of carbon electrode,
electrolysis efficiency got increased and heating of the electrodes got reduced.
Due to the simultaneous production and consumption of hydrogen, no storage was
used. The results showed that a small amount of hydrogen added to the incoming
fuel-air mixture would enhance the flame velocity and permit the engine to
operate with leaner mixtures. Consequently, because of the high catalytic
tendency of hydrogen, the fuel burnt more completely and yielded significant
reduction in exhaust emissions.
The driving tests under city traffic conditions showed that the fuel
consumption for the Volvo 940 dropped to 6 l/100 km from 10.5 l/100 km, a
reduction of 43%. The result for the Mercedes 280 was a drop from 11 l/100 km to
7 l/100 km, a reduction of 36%. The Fiat Kartal engine consumed 9.5 l/100 km
without the system. With the system installed, the fuel consumption was 7 l/100
km which corresponded to a 26% reduction. The Fiat Dogan engine yielded 9
l/100 km without the system and 6 l/100 km with the system, a reduction of 33%.
These results clearly demonstrated the fuel savings potential of the hydro gas
system. Emission tests showed that exhaust emissions such as CO, CO 2, and
74
hydrocarbons were not affected negatively by the system. Moreover, these
emissions reduced up to a margin of 40 ± 50% depending on the type of the
engine. Also, no performance penalty was observed. Acceleration, torque, and
maximum power remained unchanged. Therefore, without altering any
performance criteria, the system yielded 35 ± 40% fuel savings and reduced
exhaust emissions.
Niculae et al (2013) contributed the results of an experimental research
where LPG-air mixture was enriched with a Hydrogen Rich Gas (HRG) produced
by the electrical dissociation of water. They carried out experiments on a four
stroke SI engine. Main specifications of the engine were: 4 cylinders, 76 mm x 77
mm bore x stroke, 1397 cm3 displaced volume, 9.5:1 compression ratio. LPG and
HRG gas were individually supplied to the engine. The LPG was introduced in the
original carburettor adequately modified, the HRG was introduced upstream of the
carburettor. The addition of HRG was quantified by the gas flow rate of the
electrolyser (5, 10 or 20 lpm). They carried out the experiments at engine light and
mid load condition to measure engine torque and efficiency, exhaust emissions
like NOX, CO, CO2, HC and cyclic variability related to combustion
characteristics. They first inducted pure LPG to a certain relative airHRG was then gradually introduced and LPG was adequately reduced, to reach
-fuel ratio was progressively
-load. They also conducted
showed
that when HRG of 10 lpm was added, the BTE got increased by 15% more than
X
HRG. At 1600 rpm
emission got increased when LPG was enriched with
X
was higher by 30% with 5 lpm addition of
HRG, by 50% with 10 lpm of HRG and by 116% with 20 lpm of HRG. The NOX
extended Zeldovich kinetic mechanism. The CO emission was 20% less compared
lpm of HRG
75
addition, HC emission was same as pure LPG, but became lower for leaner fuel-
Chiriac et al (2006) investigated the outcome of the addition of
Hydrogen Rich Gas (HRG) to the gasoline-air mixture of a four cylinder gasoline
engine having a compression ratio of 9.5:1. The HRG was produced by the
electrical dissociation of water. Experiments were carried out at engine light load
(about 3 bar NIMEP) and partial load (about 6 bar NIMEP). The first load was
thus representative by its highest sensitivity to the fuel-air ratio, while the second
load was representative of typical engine operation. Experiments were carried out
close to stoichiometric conditions and at lambda of 1.2. They did detailed
measurements, namely, engine torque and efficiency, exhaust emissions, cyclic
variability, heat release rates, and combustion duration. They concluded that all
experiments with hydrogen addition had confirmed an extended range of the
engine stable operation towards the lean limits. The faster combustion which
approached the ideal Otto cycle and reduced engine knock tendency. The
experimental results showed that the break thermal efficiency got increased by
7.4% and net indicated mean effective pressure (NIMEP) got increased by 5.6%
more than gasoline combustion when 300 l/h of HRG was inducted. The overall
burning duration also appeared to lower by HRG addition. CO emission
concentrations were also substantially decreased by enriching the fuel with HRG.
In lean mixtures, the presence of hydrogen acted as a catalyst in the CO oxidation
kinetics. Also, the HC emissions got reduced due to improved combustion
variability by decreasing the incomplete combustion of fuel-air mixture.
Asad & Wattoo (2003) reported about the usage of hydrogen in a CNG
fueled engine. The engine used for their analysis was Suzuki Swift Sedan 1.3 L
G13BA having a bore of 77 mm and stroke of 78 mm, displacement volume of
1293 cm3, compression ratio of 7:1 and producing maximum power of 50 kW at
6000 rpm. The hydrogen used for this analysis was generated on-board by water
76
electrolysis process. They carried out the electrolysis process by using tap water.
For this, they stepped the alternator voltage to 96V and converted the same to DC
power of 96V using rectifier and supplied it to on-board generator to generate
hydrogen-oxygen mixture. They used stainless steel 316 material for anode
electrode and carbon-graphite for cathode electrode. This system produced 17
liters per hour of gas mixture. In this study, they did not store the hydrogenoxygen mixture; instead they generated and used the same when the engine was
running. This also resulted in safe operation. To study the performance of the onboard hydrogen system, they conducted various tests to find the effects of
hydrogen addition on fuel economy, engine power, efficiency, and exhaust
emissions. They did not carry out any adjustments in engine ignition time and it
was 6o CA BTDC. They carried out all the experiments under urban and high-way
driving conditions. From their results, it was interpreted that there was an increase
in fuel economy by 5% to 7%. Also, under urban driving conditions the power got
increased by about 4% to 7% when the hydrogen gas mixture was used with CNG.
They attributed this to clean burning characteristics of hydrogen. They observed
that at idle speed of 750 rpm, the CO emission for CNG was 0.07% by volume
whereas when hydrogen mixture was added to CNG the CO emission was nearly
zero. They also observed that the HC emission got reduced when hydrogenoxygen gas mixture was added to CNG. It was 37 ppm for CNG operation and
only 8 ppm for CNG with hydrogen mixture operation. They concluded that by
inducting a small amount of hydrogen gas mixture, the flammability limit of fuel
could be enhanced which in-turn reduced the exhaust emissions of the engine with
increase in power.
Wang et al (2012a) examined the effects of H2/O2 addition on regulated
harmful pollutants coming out from a heavy-duty diesel engine. They used a six
cylinder heavy-duty diesel engine of Cummins make. The rated power of the
engine was 118 kW at 2500 rpm and the maximum torque was 534 Nm at 1600
rpm. In their study, they used an oxy-hydrogen generator to generate the mixture
77
of oxygen and hydrogen (H2/O2) by the process of water electrolysis. The
generated gas mixture was aspirated into the diesel combustion process at various
flow rates. Their results showed that brake thermal efficiency got increased from
31.1% of neat diesel combustion to 31.4% for 10 lpm and to 39.9% for 70 lpm of
H2/O2 addition. They stated that this increase in brake thermal efficiency was due
to better mixing of hydrogen with air which resulted in better combustion. The
BSFC of neat diesel was 254.74 g/kWh, and was 262.06 g/kWh, 262.75 g/kWh,
260.42 g/kWh, 263.80 g/kWh, 246.51 g/kWh, 229.56 g/kWh, and 228.01 g/kWh
for 10 lpm to 70 lpm of H2/O2 mixture addition in steps of 10 lpm, respectively.
The THC concentration for neat diesel was 3.6 ppm and it got decreased to 3.51
ppm for 10 lpm of H2/O2 mixture, and to 3.25 ppm for 70 lpm of H2/O2 addition.
They attributed this reduction of THC to high flame velocity of hydrogen and also
to the absence of carbon atom in hydrogen fuel. The CO concentration was 26
ppm for neat diesel, and was decreased to 24 ppm for 70 lpm of H 2/O2 addition.
They related this decrease in CO emission to the operation of the hydrogen dual
fuel engine at leaner equivalence ratios. They noticed the CO2 concentration for
neat diesel as 7906 ppm, and it got decreased to 7893 ppm for 10 lpm of H 2/O2
addition and to 7523 ppm for 70 lpm of H2/O2 addition. They stated that the
reduction of CO2 emission was due to less carbon element in the formed mixture
of fuels than that in the neat diesel. In their study, they obtained the NO X
concentration of 60.05 ppm for neat diesel, and it got increased to 60.49 ppm for
10 lpm of H2/O2 mixture, and to 67.22 ppm for 70 lpm of H 2/O2 addition. They
attributed this higher concentration of NOX to both higher temperature and more
available oxygen in the formed mixture. From their results, it was concluded that
by using H2/O2 mixture in a diesel combustion process, the pollutants coming out
from the diesel engine could be effectively reduced except NOX emission.
78
2.12
COMBUSTION OF HYDROGEN UNDER VARIOUS
INJECTION TIMINGS
Saravanan et al (2007) made an experimental investigation in a diesel
engine using hydrogen as fuel with diesel as an ignition source for hydrogen.
Hydrogen was injected into the intake port, while diesel was injected directly
inside the cylinder. They varied the injection parameters such as injection timing
and injection duration of hydrogen for a wider range at a constant injection timing
of diesel as 23o BTDC. They kept hydrogen flow rate as 10 lpm for varied load
conditions. Their results showed that the brake thermal efficiency got increased
from 23.6% to 29.4% for the injection timing of 5o ATDC with injection duration
of 90o CA compared to diesel. But the maximum brake thermal efficiency
obtained was 31.67% at 15o ATDC with 60o CA duration but at this condition they
observed a knocking of the engine. The increase in brake thermal efficiency was
attributed to better mixing of hydrogen with air that resulting in enhanced
combustion. They found, the NOX emission was minimum of 783 ppm for the
injection timing of 5o ATDC with the injection duration of 60 o CA compared to
diesel of 1981 ppm at 75% load. The NOX emission for diesel fuel operation at
full load was 1806 ppm, whereas it got reduced to 888 ppm with injection duration
of 90o CA with injection timing of 5 o ATDC. The lowest NOX of 705 ppm was
obtained at full load with 60o CA while the injection was made at TDC. The
reduction was due to the operation of hydrogen engine at leaner equivalence
ratios. At no load the HC was 3 ppm for the start of injection at 5o AGTDC with
90o injection duration for hydrogen operation compared to 19 ppm for diesel. At
full load the hydrogen operated dual fuel engine resulting in increase in HC
compared to diesel. For hydrogen operation it was 7 ppm at the injection timing of
5o AGTDC with 90o injection duration compared to diesel which was 42 ppm. The
reduction in HC was due to the higher burning velocity of hydrogen; the absence
of carbon in hydrogen fuel also reduced the HC emissions to a great extent. At
75% load condition the hydrogen operated engine at the injection timing of 5 o
79
ATDC and with 90 o injection duration, the smoke value was 0.4 BSN whereas for
diesel it was 2 BSN. The lowest smoke value of 0.3 BSN was observed at the
injection timing of TDC with 60o injection duration. At full load for the start of
injection at 5o ATDC with 90o injection duration, the smoke of 0.3 BSN was
obtained compared to diesel of 3.8 BSN. They observed that at no load the CO
levels of hydrogen operated engine at all operating conditions was less than diesel.
The CO of 0.01% vol. for hydrogen operation at injection timing of 5 o ATDC and
90o injection duration compared to that of diesel of 0.17% vol. At 75% load the
peak pressure was 64.3 bar for the start of injection at 5o ATDC with 90o injection
duration for hydrogen compared to diesel operation of 68.9 bar. At full load the
hydrogen operated dual fuel engine resulted in an increase in peak pressure
compared to diesel. The peak pressure for hydrogen operation was 71.7 bar at an
injection timing of 5 o ATDC and 90o injection duration compared to diesel of 73.7
bar. This was due to higher burning velocity of hydrogen, which made combustion
as instantaneous. The peak heat release rate of hydrogen operated engine was 87.6
J/oCA compared to diesel of 81.5 J/oCA. The maximum heat addition also occured
nearer to ITDC for hydrogen operation, which made the cycle efficiency to
increase. They concluded that by operating the diesel engine in dual mode with
hydrogen, one had to optimize the injection timing and injection duration.
Roy et al (2011) investigated the engine performance and emissions of
a supercharged engine fueled by hydrogen, and three other hydrogen-containing
gaseous fuels such as primary fuels, and diesel as pilot fuel in dual-fuel mode.
They used energy share of primary fuels to about 90% or more, and the rest of the
energy by diesel fuel. The hydrogen-containing fuels tested in this study were
13.7% H2 content producer gas, 20% H2 content producer gas and 56.8% H2
content coke oven gas (COG). These fuels were simulated by mixing individual
gas components in the appropriate proportions and inducted into the intake pipe
with mass flow controllers. They kept intake pressure of air as constant at 200 kPa
(supercharged) and the temperature as 30 oC throughout the study. For
80
supercharging, they used a rotary type stationary compressor to compress the
intake air to the desired pressure level, and controlled by a solenoid valve
controlled regulator. This homogenous air-fuel mixture was ignited by a small
quantity of diesel fuel, known as the pilot fuel that was injected towards the end of
the compression stroke. Experiments were carried out at a constant pilot injection
pressure and pilot quantity for different fuel-air equivalence ratios and at various
injection timings. Their experimental strategy was to optimize the pilot injection
timing to maximize engine power at different fuel-air equivalence ratios without
knocking and within the limit of the maximum cylinder pressure. They observed
better thermal efficiency with the increase in H2 content in the fuels, and neat H2
as a primary fuel produced the highest thermal efficiency. They decreased fuel-air
equivalence ratio with the increase in H2 content in the fuels to avoid knocking.
Thus, neat H2 operation produced less maximum power than other fuels, because
of much leaner operations. In their tests they obtained two stages of combustion.
This was an indicator of maximum power output conditions and a precursor of
knocking combustion. The IMEP increased with advanced injection timings. The
maximum IMEP of 1444 kPa occurred at an injection timing of 7o BTDC. The
maximum cylinder pressure was 12.81 MPa at an injection timing of 20o BTDC,
and reached its highest value of 14.47 MPa at 23o BTDC. The cylinder pressure
and temperature got increased when the injection timing was advanced. They also
noticed that with advancement in injection time, the HC emission got decreased.
They found that CO and HC emissions got reduced by 98% to 99.9% and NOx
emissions by about 85% to 90% in neat H2 operation compared to other fuels
operation.
Fathi et al (2011) made a numerical analysis on a direct injection sparkignition (DISI) hydrogen-fueled engine using 3-dimensional CFD methods and the
results were compared with experimental data. For the analysis, they selected a
single cylinder, 4-stroke, natural aspirated SI engine, which was converted from a
direct injection diesel engine (Yanmar NFD-170), was used to evaluate engine
81
operating characteristics such as injection timing, initial charge temperature, and
initial charge pressure. In their study, they used AVL FIRE CFD code for
analyzing the parameters. This code uses a 3D moving mesh for combustion
chamber simulation. For their analysis of effect of initial charge temperature on
the emissions and combustion characteristics, they selected three injection timings
130o BTDC, 100o BTDC, and 80o BTDC. By comparison of the profiles, it was
understood that by early injection of hydrogen into the cylinder, the air and fuel
could mix homogeneously and combustion could occur completely. Therefore, the
work done per cycle also got increased. Retarding the hydrogen injection into the
combustion chamber resulted in a decrease in the work done per cycle. This was
due to the time needed for air-fuel mixing, which decreased with the retarding of
the hydrogen injection such that the air-fuel mixture would be inhomogeneous.
Additionally, a high concentration of hydrogen around the spark plug combustion
started fast and ceased rapidly. In other words, the combustion duration decreased
and therefore pressure was less in the expansion stroke, which resulted in
decreased work. By increasing the initial charge temperature, the maximum incylinder pressure was decreased. By increasing the initial charge temperature, the
density of inlet mass and the amount of oxygen got decreased, which led to
deficient combustion and a reduction of maximum in-cylinder pressure. By
increasing the initial charge temperature, the oxygen concentration got decreased
and the amount of energy needed for decomposition of N2 and O2 molecules got
increased. Because of the increased mean and maximum in-cylinder temperature
more NOX emissions were produced. Inhomogeneous mixture formation as a
result of retarding the injection timing (late injection) caused incomplete
combustion and, therefore, the maximum in-cylinder temperature also got
decreased. Because of decreased inlet air mass as a result of increasing the initial
charge temperature, the IMEP decreased and ISFC increased. In early injection,
due to complete combustion, IMEP increased and ISFC decreased. By increasing
the initial pressure, the mean and maximum in-cylinder pressure got increased.
This might be due to the fact that with the increasing of the initial pressure, the
82
inlet air mass got increased. They concluded that by advancing the hydrogen
injection time had a significant effect on engine performance characteristics such
as work, IMEP, ISFC, and the production of NOX emissions. By changing initial
conditions such as pressure and temperature, optimum engine operating conditions
could be found for DISI engines with alternative fuels.
Shioji & Mohammadi (2006) carried out an investigation on diesel
engine performance and emission characteristics when LCG (Low Calorific
Gases) and LCG with small portion of hydrogen was inducted into the inlet
manifold of engine with varied injection time of diesel fuel. The test engine used
by them was a four-stroke single cylinder naturally aspirated direct-injection
diesel engine (Yanmar NFD-170) with a bore of 102 mm and a stroke of 105 mm.
In their experiment, the original injection pump was replaced with a jerk type
pump (Zexel Type A) and nozzle (DLL-P) with four holes and hole size of 0.24
mm to match the plunger size. They varied the injection timing of diesel fuel in
the range of 7.5o BTDC to 15o BTDC at the engine load of 0.6 MPa. In their
experiment, they fixed the amount and composition of LCG as 15% and H2 as
30%. Their results indicated that advancing injection timing improved thermal
efficiency. This trend was similar for both fuels. This advancement in injection
timing also improved smoke, TC and CO emissions but the NOX emission got
worsened. They observed that at LCG addition, even at advanced injection
condition the NOX emission level was much lower than that in diesel fuel
operation. From their results, it was obvious that even in advancd injection
condition the LCG addition gave low NOX emission, along with almost same
thermal efficiency as diesel fuel operation.
Tomita et al (2000) investigated the effect of hydrogen injection in a
diesel engine running on dual fuel mode. The engine used for their study was a
single cylinder, four-stroke diesel engine with bore and stroke of 92 mm and 96
mm, respectively. The compression ratio was 17.7, and the type of combustion
83
chamber was deep dish. They varied the the injection timing of light oil over a
very wide range from 60 o BTDC to 5o ATDC. They equipped a pressure
transducer in the cylinder head to determine the cylinder pressure. They inducted
gaseous hydrogen into the engine cylinder from an intake port and injected light
oil in a conventional way into the cylinder. For reference, they took ordinary
diesel condition that only used air in the cylinder. Their results showed that when
the injection timing of the light oil was earlier, the value of the second peak of the
heat release became smaller because of the increase in the rate of premixed
combustion. When the injection timing was 11.7o BTDC, the value of the first
peak was the largest. When the injection timing was earlier than 30.4 o BTDC, the
value of the first peak became smaller without second peak and the heat release
rate showed the characteristics of premixed combustion. They reasoned this to
longer ignition delay. The ignition delay got increased with advancing of injection
timing. When they advanced the injection timing to near 25o BTDC, the NOX got
increased and had the maximum value. When the value of NO X was large, the heat
release rate was also large. When the injection timing was advanced more, the
value of NOX decreased gradually. They attributed this to well-mixing of light oil
with air. They witnessed a trade-off relation between hydrocarbon and the
nitrogen oxide when hydrogen was inducted. They stated that this was due to
more complete combustion. They further observed that when hydrogen was mixed
with inlet air, emissions of HC, CO and CO2 got decreased without smoke.
However, the brake thermal efficiency got decreased slightly less than the
ordinary diesel combustion. In particular, both smoke and NO X were almost zero
and HC was low when the injection timing was significantly advanced.
In another experiment, Tomita et al (2001) investigated a dual fuel
engine of hydrogen and diesel oil. Hydrogen was inducted into the intake port
with air and diesel oil was injected into the cylinder. They varied the SOI timing
of the diesel fuel across a wide range, holding the overall equivalence ratio equal
with and without the addition of hydrogen. Their test results showed a very low
84
NOX emission when SOI was advanced to or beyond 40° BTDC, with NOX
emissions rising with later injection timing. This was reasoned to have occurred
because of the thorough mixing of the hydrogen/air mixture and the diesel fuel
before ignition. They also observed that CO2 got decreased proportionally to the
amount of hydrogen substituted for diesel fuel, due to less carbon available in the
reactants. They stated that the addition of hydrogen caused an increased ignition
delay and they reasoned this to the large mole fraction of hydrogen in the air
which displaced oxygen. They witnessed both smoke and NOX becoming almost
zero and HC was low when the injection timing was significantly advanced
although the engine operation became unstable. In overall they obtained slight
decrease in efficiency of the engine with the addition of hydrogen.
2.13
COOLING LOSS IN HYDROGEN COMBUSTION ENGINES
Shudo et al (2001) analyzed the factors influencing the thermal
efficiency of a homogeneous charge spark ignition (SI) engine fuelled with
hydrogen, focusing on the degree of constant volume and the cooling loss. They
used a four-stroke four-cylinder spark ignition gas engine which was modified
from a gasoline engine for passenger cars (bore 85 mm, stroke 88 mm,
compression ratio 8.5) for their tests. They supplied hydrogen or methane
continuously into the intake manifold of the test engine. The fuel gas flow rate
was measured with a mass flow meter (Oval, F203S). In all the experiments, they
kept the engine speed as constant at 1500 rpm and the volumetric efficiency as 50
percent including fuel gas in order to avoid the flash-back phenomenon. They
measured the in-cylinder pressure with a piezoelectric type pressure transducer
(AVL, GM12D). They averaged the pressure data over 200 cycles and used it to
calculate the indicated thermal efficiency, the rate of heat release, the degree of
constant volume, etc. They measured the instantaneous temperature using a thinfilm-type thermocouple (Medtherm, TCS-103E, chromel constantan type). They
analysed the exhaust gas using an exhaust gas analyser (Horiba, MEXA 9100) for
85
calculation of the combustion efficiency. They evaluated the cooling loss from the
burning gas to the cylinder walls in a homogeneous charge SI engine
quantitatively by analysing the cylinder pressure diagram and the exhaust gas
composition. They also obtained degree of constant volume burning and the
degree of constant volume cooling by fitting the Wiebe function to the rate of heat
release calculated using the cylinder pressure diagram. To evaluate the cooling
loss, they compared the hydrogen combustion with methane. They revealed that
the cooling loss in hydrogen combustion was higher than that of methane
combustion due to a thinner quenching distance and faster burning velocity for
hydrogen combustion. They also measured the cylinder pressure and
instantaneous wall temperature by varying the ignition timing for both hydrogen
and methane combustion. They stated that hydrogen combustion had a shorter
combustion period due to its higher burning velocity than methane. They observed
that the combustion chamber wall temperature tended to increase with an advance
in ignition timing for both fuels. They noted that the apparent rate of heat release
in hydrogen combustion was greatly influenced by the cooling loss. They
attributed this higher cooling loss of hydrogen combustion to a thin temperature
boundary layer thickness on the combustion chamber wall due to a shorter
quenching distance. They also stated that the high burning velocity of hydrogen
combustion might also have caused intense convection between the burning gas
and the wall, it resulted in an enhancement of the heat transfer. They further
noticed that in combustion of both fuels, the cooling loss ratio tended to increase
with an advance in ignition timing. This was significantly higher in hydrogen
combustion than methane combustion at the same ignition timing. The cooling
loss tended to decrease with the retardation of ignition timing for both hydrogen
and methane combustion. They confirmed this trend by taking instantaneous heat
flux measurements at a representative location in the cylinder head. They obtained
lower thermal efficiency in hydrogen combustion than that of methane
combustion in throttled conditions. This was due to higher cooling loss ratio and
the higher degree of constant volume cooling in hydrogen combustion. They
86
concluded that to improve the thermal efficiency of hydrogen-fuelled engines, it is
essential to reduce the cooling loss.
Saravanan & Nagarajan (2009) investigated the effect of hydrogen
addition on diesel engine performance and emission characteristics, by injecting
hydrogen in timed manifold injection, port timed injection and carburetion
technique along with reduced cooling water flow rate of 75% in order to decrease
the percentage of cooling loss. They conducted their experiments in a singlecylinder, four-stroke, water-cooled, direct-injection diesel engine running at a
rated power of 3.78 kW coupled to an electrical generator. Their results showed
that the brake thermal efficiency for hydrogen with diesel as an ignition source in
timed port injection technique was 27.3% at full load and 26.2% in manifold
injection whereas in the diesel combustion it was 23%. NOX emission in timed
port injection technique was 34% higher and in carburetion technique, it was 8%
higher compared to baseline diesel. With timed port injection technique, the
smoke level varied from 2.1 BSN to 3.5 BSN with a reduction of 45% at full rated
load compared to diesel fuel. The HC emission was lower at full load compared to
the base line diesel, the maximum being 0.047 g/kWh and 0.039 g/kWh in the
case of timed manifold and port injection technique respectively. In carburetion
technique, the HC emission was 0.106 g/kWh at full load compared to base line
diesel fuel of 0.12 g/kWh. Their study very clearly gave a direction that by
changing the cooling water parameters, the performance as well as emission
characteristics of the engine could be enhanced.
Shudo (2005) reported about the cooling loss of internal combustion
engine when hydrogen was used in the combustion process. For his study, he
chose a 4-cylinder, 4-stroke, spark-ignition engine having a bore and stroke of 85
mm and 88 mm, respectively. He measured the hydrogen with a mass-flow meter
Oval F203S and he continuously supplied hydrogen to the intake pipe of the
engine. He kept the engine speed as fixed at 1500 rpm, excess air ratio at 1.0 and
87
volumetric efficiency at 35% including the fuel gas. He measured the in- cylinder
pressure data with a piezoelectric type pressure transducer AVL GM12D installed
in the cylinder head. For calculating the apparent rate of heat release and the incylinder gas temperature, he averaged the cylinder pressure data for 50 cycles. He
observed larger changes in the composition and the thermo-physical properties of
the in-cylinder gas. He related this to larger burning velocity of hydrogen than
hydrocarbons. He calculated the heat transfer coefficient from the rate of cooling,
which was estimated by the apparent rate of heat release and Wiebe function.
Then he calculated representative velocity of the in-cylinder gas derived from the
turbulent heat transfer equation for pipe flows by using the obtained heat transfer
coefficient. He proved that by adjusting the velocity term in the widely used
equation of Woschni, the equation might calculate better results for hydrogen
combustion.
Shudo (2007) proved that a direct injection stratified charge is an
effective technique to improve the thermal efficiency of hydrogen combustion
engines. For his study he used a spark ignition engine fueled with hydrogen with a
bore of 85 mm, a stroke of 88 mm, and a compression ratio of 8.5. He maintained
the engine speed at 1500rpm, and charged the engine with a homogenous mixture
of hydrogen and air through the intake pipe of the engine. He set the mixing ratio
to stoichiometric which resulted in higher cooling losses than leaner mixture
conditions. He carried out the experiments at different spark ignition timings of
the engine. In order to avoid backfire from the engine particularly with
stoichiometric mixture, he controlled the volumetric efficiency to 50% by using a
throttle valve. He measured the combustion pressure with a piezoelectric type
pressure transducer AVL GM12D installed in the cylinder head and averaged over
ust
after the end of combustion, and this signified that a part of heat released by the
combustion was transferred to the combustion chamber walls. He concluded that
88
retardation in the spark ignition timing could decrease the cooling loss by
lowering the maximum combustion temperature. However this method also
decreased the degree of constant volume and did not lead to effective thermal
efficiency improvements. He proved that the increase in the apparent heat release
fraction effectively led to improvements in thermal efficiency, because the
stratified charge reduced the cooling loss without lowering the degree of constant
volume. Therefore, a method that reduces cooling loss without lowering the
degree of constant volume will be effective to improve the thermal efficiency of
internal combustion engines.
Sudheesh & Mallikarjuna (2010) made an experimental investigation
on the acetylene-fueled engine operated in homogeneous charge compression
ignition (HCCI) mode to study the effect of cooling water flow direction on intake
charge temperature, heating requirements, and performance of the engine. They
conducted their study in a single-cylinder, water-cooled, CI engine operated in
HCCI mode with acetylene as fuel. They used an external electrical heater to heat
the intake charge to achieve HCCI combustion. They kept engine speed and
cooling water outlet temperature as constant. In their study, they changed the
coolant water flow direction in HCCI mode from bottom-up to top-down flow.
They did this in order to reduce heat transfer from cylinder liner to cooling water
so that higher cylinder liner temperature would be maintained. They operated the
engine also in the conventional CI mode to find the effect of HCCI mode with the
conventional and reverse cooling water flow directions using different intake
charge temperatures at different loads. Their results showed that the reverse
cooling water flow direction showed about 14% to 50% reduction in external
intake charge heating at different load conditions as compared to the conventional
cooling water flow direction. The brake thermal efficiency got improved by about
5% to 10% at different load conditions. Nitric oxide (NO) and smoke emissions
were very low in both cases. However, hydrocarbon (HC) and carbon monoxide
(CO) emissions were higher than conventional CI mode in both the cases. In
89
conventional flow direction, peak heat-release occured at about 364 CAD,
whereas for reverse flow direction, it was at about 358 CAD. In reverse flow
direction, the combustion phase occured closer to TDC. Whereas, in conventional
case it occured far away after compression TDC. This reduced the net work
output. They attributed this to higher cylinder liner temperatures with reverse flow
direction in which heat transfered into cylinder gases. Also, peak heat release in
former case was about 80 J/CAD, whereas in later case, it was about 150 J/CAD.
They concluded that by reducing heat transfer from cylinder liner to cooling
water, the performance and emission characteristics of the engine could be
improved.
Torregrosa et al (2006) investigated about the influence of coolant and
inlet charge temperature on the emissions and performances of a DI diesel engine.
For their study, they used a unique test rig which could control the important
operational parameters of the engine. They converted multi-cylinder engine to
single cylinder operated engine. They selected three operating points to represent
the European homologation cycle and tested the engine. They controled the
temperature of the coolant leaving the engine block by regulating the tap water
flow through the shell and tube heat exchanger. The tap water valve was regulated
by a PID controller which used the temperature measurement at the exit of the
engine. They used an external screw compressor with a dryer to supply the
required air. They conveyed the dry air to the test bench where it passed through a
heater. Their experimental results showed that the coolant temperature influenced
the combustion process through the temperature of the combustion chamber walls.
When they raised the coolant and inlet charge temperature, they witnessed
diminishing effect in hydrocarbon emissions and increasing effect in NOX
emissions. At low load these effects were more pronounced. The NO X emissions
got increased significantly with increasing air temperature. They stated that as
NOX formation was a thermally activated process and thus when the air
temperature was higher, NOX formation was enhanced. They observed increase in
90
HC emissions when the temperatures of wall and the inlet air were lower. They
related this to enhanced flame quenching and increase in the ignition delay period.
They further observed that at low loads, more HCs were emitted when the walls
were colder. They related this to incomplete combustion. They concluded that by
optimizing the cooling water and the inlet air temperatures, the emissions from the
engine could be greatly reduced.
2.14
COMBUSTION UNDER VARIOUS INJECTION PRESSURE OF
DIESEL FUEL
Rao et al (2011) made an experimental investigation on LPG, a byproduct of petroleum refining process to use it as a supplementary fuel for diesel
engine. They used four-stroke, single-cylinder diesel engine, most widely used in
agricultural sector for their experimentation. They varied fuel injection pressure of
diesel by adjusting the spring stiffness of the fuel pump. Their experimental set up
consisted of a single-cylinder, four-stroke diesel engine connected to an eddycurrent dynamometer for the loading of the engine. It was provided with necessary
instruments for combustion pressure and crank angle measurements. The signals
were interfaced to a computer through an engine indicator to obtain pressure-crank
angle diagram. They also made provision for interfacing air flow, fuel flow,
temperatures and load measurement. They measured the fuel injection pressure by
using a mechanical type of hand operated pressure gauge. They varied the
injection pressure of diesel fuel in the range of 180 bar to 220 bar with a step of 10
bar. Their results showed that the brake thermal efficiency of the engine at low
engine load of 20% was found to decrease with an increase in the LPG content.
They related this to poor combustion characteristics of air-LPG mixture at low
load conditions. High auto-ignition temperature of LPG might be the basis for the
poor combustion characteristics of air-LPG mixture. At low engine load of 20%,
at an injection pressure of 180 bar, the brake thermal efficiency was found to be
13.5% on diesel fuel mode, and reduced to 9.1% on dual-fuel mode with 50%
91
LPG energy. At mid engine load of 60%, the fuel injection pressure had a
significant effect on the brake thermal efficiency of the engine. On diesel fuel
mode of operation, it got increased from 21.1% at an injection pressure of 180 bar
to 22.3% when the fuel was injected at 200 bar. At 80% engine load, on dual-fuel
mode of operation with 20% LPG energy, it was found to be 25.7% when the fuel
injection pressure was 180 bar, and increased to 26.8% when fuel was injected at
200 bar. They observed decrease in smoke density with an increase in the fuel
injection pressure on both the modes of operation. They obtained lowest smoke
when the fuel injection occurred at 220 bar. The smoke of 8.8 HSU of diesel
operation got decreased to 2.9 HSU on dual-fuel mode with 50% LPG. They
related this to better combustion of air-LPG mixture. They further observed that
the emissions of NO got increased with an increase in the fuel injection pressure
on both the modes of engine operation. They concluded that at lower engine loads,
the engine performance on dual-fuel mode was found to be inferior compared to
that of the diesel fuel mode. At mid and higher engine loads, the dual-fuel mode of
operation was found to be superior compared to that of the diesel fuel mode of
operation. At low engine loads, the engine might be operated on the diesel fuel
mode, and at higher engine loads, the engine could be switched over to the dualfuel mode.
Bakar et al (2008) reported about the effects of fuel injection pressure
on engine performance of a diesel engine with four-cylinder, two-stroke, direct
injection. They investigated engine performance values such as indicated
pressure (IP), indicated horse power (IHP), shaft horse power (SHP), brake
horse
power (BHP),
break mean effective pressure (BMEP) and fuel
consumption both of variation engine speeds - fixed load and fixed engine speed variation loads by changing the fuel injection pressure from 180 bar to 220 bar.
They ran the engine in the range of 600 rpm to 1600 rpm with the interval of
200 rpm and the fuel injection pressure setting from 180 bar to 220 bar with
the interval of 10 bar. In their second phase of experiments, the diesel
92
engine loads were tested in 55% to 80% of the rated load with the interval of
5% and they fixed the engine speed as 1600 rpm. Their experimental result
showed that the engine performance parameters like IP, IHP, SHP, BHP, and
BMEP got increased when the injection pressure of the fuel was increased. They
related this to excellent mixing of fuel and air in the combustion chamber. This
also resulted in less un-burnt fuel than the lower injection pressure combustion
operation. In the second phase of experiments on fixed engine speed and
variation
engine
loads,
they obtained highest engine performance at
the
injection pressure 220 bar. They observed increase in the specific fuel
consumption when the engine speed was increased. They found economical
specific fuel consumption at the injection pressure of 200 bar. They observed
enlargement in fuel particle diameters when the fuel injection pressure was low.
This also resulted in an increase in ignition delay period and an increase in
cylinder pressure. On the otherhand, they witnessed a decrease in ignition delay
period when the injection pressure was increased. This also resulted in an increase
in the performance of the engine. They ascribed this to a decrease in the fuel
particle diameters and an increase in the degree of formation of homogeneous
mixture of fuel and air. They also noticed that if the fuel injection pressure was
too higher, ignition delay period became shorter. So, the possibilities of
homogeneous mixing got decreased and combustion efficiency got reduced. They
attributed this to more energy needed to drive the injection system by
reducing the leak flow and by dynamically adjusting the maximum pressure to
the actual needs of the engine.
Siebers & Pickett (2002) investigated about the effects of injection
pressure and orifice diameter on soot in diesel fuel jets under quiescent, directinjection (DI) diesel engine conditions. They carried out these investigations in a
constant-volume combustion vessel with complete optical access. The injector
used was an electronically-controlled, common-rail injector. They considered
injection pressures between 40 MPa and 190 MPa and orifice diameters between
93
501.1m and 180 µm. They measured the soot with a line-of-sight laser extinction
technique and visualized with planar laser-induced incandescence. They
determined flame lift-off lengths used in the analysis of the soot measurements
with time-averaged OH chemiluminescence imaging. Their results showed that
the peak soot in a fuel jet decreased with increasing injection pressure and
decreasing orifice diameter. The decrease in soot with increasing injection
pressure was linear with increasing injection velocity (i.e., the square-root of the
pressure drop across the injector orifice). The decrease in soot with decreasing
orifice diameter was such that for the smallest orifice diameter considered (50
table for the ambient gas and injector conditions
considered. These direct measurements of soot within a fuel jet, coupled with
estimates of the amount of air entrained relative to the amount of fuel injected,
confirmed that air entrainment and fuel-air mixing upstream of the lift-off length
had an important role in determining the soot levels within a diesel fuel jet.
Ghazikhani et al (2007b) conducted an investigation on the soot
emission level on an OM314 DI diesel engine. The engine used for their
investigation was a four-cylinder, four-stroke, direct injection, naturally aspirated
diesel engine with a peak power of 63 kW and peak torque of 235 Nm at 1830
rpm. This was a 2006 production engine Daimler OM314 with a compression ratio
of 17:1, bore and stroke of 97 mm and 128 mm and displacement volume of 3.784
L. They installed and operated the engine on a 112 kW DXF Heenan & Froude
hydraulic dynamometer. They used AVL 415 smart sampler to measure soot
emission levels in the exhaust gas. They mounted an electrical speed meter on the
engine flywheel to measure the engine speed. During the tests, they operated the
engine at three different conditions, naturally aspirated, LIMP turbocharged and
elevated injection pressure from 200 bars to 240 bars. In each stage, in order to
investigate the soot contents, they tested the engine under ECE-R49, 13 mode
standard test. They observed that the naturally aspirated engine had acceptable
performance characteristics but needed urgent attention in view of the soot
94
emission levels. LIMP turbocharged engine had reduced the soot emission level to
the extent of 35%. They related this to the higher pressure and temperature of
intake-air and reduction of ignition delay which improved the soot burnout
process. When the injection pressure was elevated, they observed that the specific
soot pollution decreased by about 26% less than the turbocharged engine. They
stated that this was due to smaller fuel particles diameter and better formation of
mixing fuel to air. They further observed that the soot emission level of the engine
was 21% less than the Euro I stndard level but it did not match with the Euro II
standard level.
Ghazikhani & Darbandi (2010) studied the effects of injection pressure
on BSFC and exhaust emissions on a direct-injection turbocharged diesel engine.
They measured emissions and engine BSFC values in 13 speed and load
conditions based on ECE-R49 test by changing injection pressure from 200 to 300
bars. The engine used for their test was OM314 turbocharged diesel engine
equipped with a waste gate supported by Borg Warner Company to convert the
naturally aspirated engine to a turbo-charged diesel engine. The test rig was
equipped with a 112 kW DXF Heenan & Froude hydraulic dynamometer. They
measured engine emissions using a Plint-RE205 gas analyzer for unburned
hydrocarbons as C6H14, CO, CO2 and O2. Their experimental apparatus
composed of AVL-415 smoke meter, thermocouples type K by using an interface
connected to a PC, volumetric fuel meter, air meter, pressure gauges and electrical
engine speed meter. Their results showed that the specific HC emission got
reduced when the injection pressure was increased. They related this to a better
mixing of air and fuel. They also stated that if injection pressure is too high, the
HC emission got increased because of impinging on the body of the cylinder and
cooling loss. The oxygen emission got reduced when the injection pressure was
increased due to lower ignition delay and higher combustion rate at better fuel air
mixing. The CO emission got increased when the injection pressure was too high.
They reasoned this to higher exhaust gas temperature which caused for the
95
dissociation of CO2 to CO and O2 with higher injection pressures. The amount of
specific CO2 emission got increased upto moderate rise in injection pressure. They
attributed this to better mixing of fuel and air which in-turn increased combustion
efficiency. They further observed that the specific O 2 emission got decreased with
rise in injection pressures. The specific NOX emission was almost constant inspite
of variation of injection pressures. They related this to not much change in peak
temperature. They noticed that the smoke level got reduced when injection
pressure was increased to 235 bars; after that smoke level got increased when
injection pressure was increased to 300 bars. They stated that this was due to
lower ignition delay and better combustion rate. But, when the injection pressure
was increased to more than 235 bars, the ignition delay period became shorter
because of increase in cylinder temperature. This in-turn decreased possibility of
homogeneous mixing and resulted in increase in smoke level. They obtained
improvement in engine specific fuel consumption with higher injection pressure
due to lower ignition delay and higher combustion rate at better fuel air mixing.
They concluded that variable injection pressure was a better one than the constant
injection pressure.
2.15
COMBUSTION UNDER VARIOUS INLET AIR
TEMPERATURES
Paykani et al (2011) made an experimental investigation on a Lister 8-1
dual fuel (diesel - natural gas) engine to examine the simultaneous effect of inlet
air pre-heating and EGR on performance and emission characteristics of a dual
fuel engine. As the use of EGR at high levels was unable to improve the engine
performance at part loads, they combined EGR with pre-heating of inlet air for
their experiments. Their results showed that there was a slight increase in thermal
efficiency, CO and HC emissions got reduced by 24% and 31%, respectively. The
UBHC emission also got reduced to some extent. The NOX emissions got
decreased by 21%. They related this to the lower combustion temperature due to
96
the much inert gas brought by EGR and decreased oxygen concentration in the
cylinder. They observed that when the intake temperature of air was increased, the
flame was propagating successfully through the gaseous fuel air mixture. They
further observed that when the inlet charge temperature was increased, it resulted
in decrease in ignition delay period and eventually improved the combustion
process. They witnessed a close trend of CO emission variation with intake
mixture temperature. When the inlet air charge temperature was increased, the CO
emission got decreased. They stated that this was due to an increase in the reaction
rate of the fuel mixture and resulted in widened flammability limits.
Shahadat et al (2005) conducted the experiment in a four-stroke DI
diesel engine to evaluate its characteristics when preheated air was inducted in a
combustion process. The engine used for their analysis was a single cylinder, 4stroke, water cooled diesel engine having a bore of 95 mm and stroke of 115 mm.
It produced rated output of 10 kW at a rated speed of 2000 rpm and having a
compression ratio 20:1. They used conventional diesel fuel and diesel-kerosene
blend as fuels for their experiments. They preheated the inlet air from 32°C to
55°C and 60°C by taking heat from the exhaust gases. Their results showed that
there was a significant reduction in NOX emission when the air was preheated.
They obtained the NOX emission of 125 ppm, 360 ppm, 460 ppm, and 465 ppm
when the air was not preheated in diesel fuel mode for the speeds of 900 rpm, 950
rpm, 1000 rpm, and 1150 rpm respectively. When air was pre-heated to 55oC, the
NOX emissions got reduced to 100 ppm, 125 ppm, 175 ppm, and 210 ppm for the
above mentioned speeds. They attributed this remarkable reduction to reduction in
ignition delay which in-turn reduced engine emissions. For the above mentioned
speeds the CO emission got reduced from 625 ppm to 390 ppm, 550 ppm to 325
ppm, 500 ppm to 275 ppm and 425 ppm to 250 ppm respectively. They reasoned
this to increase in combustion rate of unburnt hydrocarbons. The brake thermal
efficiency also got increased when the air was pre-heated. When the inlet air
temperature was increased from 32oC to 45oC, 55oC, and 60oC, they obtained
97
increase in brake thermal efficiency from 22% to 26%, 27%, and 28%
respectively. They related this increase in brake thermal efficiency to increase in
the degree of constant volume combustion. They concluded that by increasing the
inlet air charge temperature, the brake thermal efficiency of the engine could be
increased with reduction in emissions.
Murayama et al (1971) investigated the effect of inlet air preheating on
in-cylinder combustion and exhaust emissions of a diesel engine when various
fuels of low cetane number were used. The engine used for their study was single
cylinder, vertical type, water cooled, four stroke diesel engine having a stroke
volume of 780 cc and compression ratio of 19:1. They pre-heated the inlet air in
the range of 20oC to 100oC by using electrical heater of capacity of 2 kW inserted
into a inlet manifold of the engine. The multiple fuels used in their study were gas
oil, undoped gasoline, regular gasoline and premium gasoline. Their results
showed that the combustibility of engine could be improved remarkably by using
pre-heated air. The heat release rate, rate of pressure rise, and peak cylinder
pressure got decreased. They related this to decrease in ignition lag period. This
was more pronounced when the injection time was advanced. The specific fuel
consumption and the brake thermal efficiency got increased. They related this to
increase in specific heat of combustion mixture and reduction of excess air factor.
They observed decrease in smoke level when inlet air was pre-heated. They
concluded that by pre-heating the inlet air, the low cetane number fuels could be
comfortably burnt in a diesel engine.
Naber & Siebers (1998) investigated the auto-ignition and combustion
of hydrogen in a constant volume combustion vessel under simulated directinjection (DI) diesel engine conditions. The parameters varied in the investigation
included: the injection pressure and temperature, the orifice diameter, and the
ambient gas pressure, temperature and composition. They conducted experiments
in a constant volume combustion vessel using a high pressure gaseous fuel
98
injector. The vessel had a disk-shaped combustion chamber (114 mm diameter
and 28.6 mm width) with sapphire windows at each end to permit full field lineof-sight optical access. They designed the combustion vessel for the study of an
extended range of ambient conditions including combustion pressures to 35 MPa.
They used a modified version of fuel injector developed by Diesel Technology
Corporation for a natural gas DI compression ignition engine with an electronic
control. For their experiments, they supplied high purity gaseous hydrogen from a
gas cylinder and boosted to injection pressures by an oilless pump. Their results
showed that the ignition delay of hydrogen under DI diesel conditions had a
strong, Arrhenius dependence on temperature of inlet air condition which reflected
the importance of chemical kinetics; however, the dependence on the other
parameters examined was small. For gas temperatures greater than 1120 K with
oxygen concentrations as low as 5% (by volume), they observed ignition delays of
less than l.0 ms. They measured ignition delays for two different initial hydrogen
temperatures of 450 K and 410 K. When comparing the data of the above two
temperatures, they found that the ignition delay got increased with a decrease in
the fuel temperature. And, they also found that in comparison to the effect of
change in ambient gas temperature, the effect of a change in the fuel temperature
was small. They concluded that compression ignition of hydrogen was possible in
a diesel engine at reasonable TDC conditions.
Alam et al (2005) conducted experiments to study the effects of
changing the inlet air temperature on the performance and emission characteristics
of a Cummins 5.9L, turbocharged, water cooled, six-cylinder, 4-valves per
cylinder direct injection (DI) diesel engine. The other specifications of the test
engine were: rated power of 235 hp at 2700 rpm, bore and stroke of 102 mm and
120 mm, compression ratio of 16.3:1, displacement volume of 5.9 L, injection
system of Bosch VP-44 rotary distributor pump, and swirl ratio of 2.45. Their
experimental system consisted of an engine, dynamometer, controller, combustion
analysis instrumentation, and different emissions analyzers. They fitted the engine
99
with an ECM that monitored engine performance and controled different events
automatically, especially the start of injection (SOI), injection timing advancement
or retardation. As the engine was fitted with a turbocharger, they cooled the
compressed hot air coming out from the turbocharger in an aftercooler to control
the inlet air temperature. They manipulated water circulation to the aftercooler to
control the inlet manifold air temperature. They varied the inlet manifold air
temperature between 30 oC and 60oC. They collected all the combustion,
performance and emissions data in each and every temperature of inlet air by
keeping the engine speed as constant at 1408 rpm with an external load of 5.12
kNm. Their experimental results showed that a small decrease of cylinder pressure
was observed with an increase in inlet air temperature. However, the peak
pressures were observed at the same crank angle. The intake air temperature
affected the ignition delay due to its effect on charge conditions during the delay
period. They observed decrease in ignition delay with an increase in inlet air
temperature. They attributed this to the increase in vaporization of fuel-air mixture
to make a combustible mixture. They witnessed earlier start of combustion when
the inlet air temperature was increased. On the other hand, the higher the inlet air
temperature, the lower the premixed and diffusion burning peaks. It was also true
that the premixed combustion stage decreased with shorter ignition delay. They
further observed that average in-cylinder temperature increased with an increase
in inlet air temperature. When the inlet air temperature was changed from 30 oC to
60oC, the average cylinder temperatures got increased by 150K. They witnessed
higher NOX emissions when the temperature of the inlet air was increased due to
increase in average cylinder temperatures. The air flow rate decreased with
increase in inlet air temperature. Similarly, specific fuel consumption got
decreased with an increase in inlet air temperature which was confirmed with the
higher exhaust gas temperature. CO emissions got increased and hydrocarbon
emissions got decreased with an increase in inlet air temperature. They related this
to the decrease in air-fuel ratio with an increase in inlet air temperature.
100
2.16
COMBUSTION UNDER PREHEATED FUEL
Shepherd (1982) patented an invention related to apparatus associated
with a fuel injection of a diesel engine. This apparatus preheat the fuel prior to
injection into engine. Thus, the general object of his invention was to increase the
fuel efficiency. The system and apparatus of his invention was based on storing,
preheating and delivering preheated fuel to a conventional fuel injection diesel
truck engine. A conventional fuel pump was arranged to draw the fuel through a
conventional fuel filter from an insulated fuel preheat tank which in turn received
the fuel by gravity feed both from a pair of vented fuel tanks as well as from an
auxiliary overflow fuel tank arranged to store excess fuel pumped to the engine.
The preheat tank was equipped with a series of coils inside the tank through which
hot engine coolant was bypassed and returned to the engine cooling system. He
found that the optimum fuel temperature should be in the range of 140oF to 150oF.
If the temperature of the preheated fuel exceeded over 150oF, he controlled the
temperature by the conventional thermostatic coolant control of the diesel engine
employed to power the truck/tractor unit. He also provided an additional
temperature control which stoped flow of the hot coolant from the engine to the
fuel preheat tank whenever the temperature of the fuel being supplied to the
engine exceed 150oF. At any time, if the temperature of the fuel being admitted to
the engine droped below 140oF, the invented apparatus restored flow of hot
coolant to the fuel preheat tank. By this invented apparatus, he proved that the fuel
economy of the diesel truck engine could be improved without sacrificing the
efficiency of the engine.
Rowley & Gonzalez (2012) patented an invention related to pre-heating
fuel such as gasoline, alcohol, kerosene, diesel or ethanol before pumping the
super heated fuel into a fuel rail system on mechanical or electronic fuel injected
internal combustion engines. They used free heat or scavenged heat from the
coolant system and/or circulating oil from the crankcase of an internal combustion
101
engine to preheat the fuel. They connected the fuel preheater device physically to
part of the engine cooling water circulating system and/or hoses connecting
circulating crankcase oil. They maintained about 125°F to 200°F of temperature in
a fuel preheater chamber to superheat the fuel. In this temperature range most of
the liquid fuels got superheated. Then, this superheated fuel was made to travel
across a metal catalyst in the form of rods and/or a thin flexible multi-layer
sandwich of different types of metal ribbons/wires which further broke down long
hydrocarbon chains into shorter hydrocarbon chains. This galvanic reaction took
place among the different metal types coming into contact with each other. This
reaction acted as a catalyst and injected metallic ions into the fuel that passed over
the metal rods/ribbons/wires. Then, the superheated fuel with the metal ions was
made to pass to the injector pump which forced the partially vaporized fluid to the
fuel rail and then to the individual fuel injectors which mixed with the incoming
air from the intake manifold. They repeatedly tested the engine with this invented
apparatus and found an increase of 10% to 20% in fuel economy and reduction of
20% in greenhouse gases emission in highway driving conditions.
Crowther & Crowther (2012) patented an invention related to a device
for warming diesel fuel before it was injected into the engine. The fuel warming
device comprised a cylindrical housing for heating the fuel. The housing had a
first end, a second end, an inner surface, and an outer surface which altogether
enclosed in an inner compartment. They installed the housing in a vehicle near the
engine. The housing was constructed using copper. A copper coil tube had a first
end and a second end. It spanned through the length of housing in the inner
compartment. The first end of the copper coil tube extended outwardly through the
first end of the housing and the second end of the copper coil tube extended
outwardly through the second end of the housing. They allowed fuel to enter
through first end and exit through second end. The fuel exiting the copper coil
tube was subsequently injected into the engine of the vehicle. A heating fluid was
disposed in the inner compartment of the housing. The heating fluid filled the
102
inner compartment of the housing and surrounded the copper coil tube. The
heating fluid helped to transfer heat quickly and evenly distributed the heat in the
inner compartment of the housing. The heating fluid helped to hold heat in the
housing. A heating element was disposed in the inner compartment of the housing.
The heating element was for increasing the temperature of the heating fluid that
surrounded the copper coil tube. When the heating element was activated, the
temperature of the heating fluid got increased, which warmed the copper coil tube.
Fuel that ran through the copper coil tube was then warmed by the copper coil
tube. They provided the heating element of a 12-volt submersible heater. The
heating element was operatively/electrically connected to an electrical connection
component. They concluded that by using fuel warming systems to warm fuel
before the fuel was injected into the engine; the efficiency of the combustion
inside the engine got increased. They also reported that their fuel warming system
could be used for both gasoline and diesel fuel.
2.17
COMBUSTION UNDER OXYGEN ENRICHED AIR
Wartinbee (1971) made an engine dynamometer study to determine the
effects of oxygen enriched air on exhaust emissions. His results indicated that
compared to operation with lean air-fuel mixtures, hydrocarbon emissions were
reduced substantially, carbon monoxide emissions were similar, and oxides of
nitrogen emissions increased significantly. He also found that octane requirements
and fuel consumption were higher with oxygen enrichment. He concluded that
these emissions and performance characteristics were due to the higher peak
combustion temperatures associated with high oxygen concentrations.
Maxwell et al (1993) evaluated the effect of oxygen enriched air on
engine performance and exhaust emissions of a single-cylinder, 4-stroke, sparkignition engine. They evaluated with both gasoline and natural gas. They varied
the oxygen content of the intake air between 20.9% (ambient air) and 25%. Their
103
test results indicated that the use of oxygen enriched air produced a significant
increase in power output, improved fuel conversion efficiency, lower specific fuel
consumption, higher exhaust gas temperature and a significant reduction in carbon
monoxide and hydrocarbon emissions when the engine was fueled with either
gasoline or natural gas.
Ng et al (1993) tested a production spark ignition engine powered
vehicle (3.1-L Chevrolet Lumina, model year 1990) with oxygen- enriched intake
air containing 25% and 28% oxygen by volume to determine any difficulties in
running the vehicle and to evaluate emissions benefits. They tested the engine
with Standard Federal Test Procedure (FTP) emissions test cycles. Their results
showed that the engine ran satisfactorily without vehicle performance anomalies.
The emissions of carbon monoxide and hydrocarbons got reduced significantly in
all three phases of the emissions test cycle, compared with normal air (21%
oxygen). Carbon monoxide emissions from the engine with the three-way catalytic
converter removed were significantly reduced in the cold-phase of the test cycle.
The catalytic converter also had improved carbon monoxide conversion efficiency
under the oxygen-enriched air conditions. The detailed results of hydrocarbon
speciation
indicated
large
reductions
in
1,3-butadiene,
formaldehyde,
acetaldehyde, and benzene from the engine with the oxygen-enriched air. They
also observed that the catalytic converter out ozone got reduced by 60% with the
25% oxygen-content air. But, they observed significant increase in NOX emissions
on all percentages of oxygen enrichment. They concluded that adding oxygen to
the intake air was a better method than adding it to the fuel.
Ghojel et al (1983) studied the effect of the partial pressure of O in the
intake charge of an I.D.I. diesel engine on the various operating parameters and
the exhaust emissions. They varied oxygen content in the intake between 21% and
40% by volume. They evaluated the engine performance and emissions at constant
engine speed and injection timing. Their research revealed that enriching the
104
intake air with oxygen led to a large decrease in ignition delay and reduced
combustion noise. The fuel economy, the power output and the exhaust
temperature remained almost constant. HC and CO emissions decreased and
smoke levels dropped substantially, while NOX emissions increased in proportion
with the O added.
105
2.18
SUMMARY OF THE LITERATURE REVIEW
From the above literature review, the following preliminary
conclusions have been arrived at. The technical facts based on these conclusions
have been integrated in the present experimental investigation. The important
conclusions are:
Hydrogen is one of the primary sources which can fulfill the future energy
requirements.
Hydrogen is the possible energy which can cause least harm to the
environment.
The stringent future emission norms could be met easily only with use of
hydrogen.
A modification of the fuel is the best way to reduce engine-out emissions
without modifying the present configurations of the engines.
Hydrogen can be used in the engines by way of inducting in the inlet
manifold, inducting in the inlet port and also by direct injection into
cylinders.
While using hydrogen, care should be taken because of its nature of back
firing.
The literature clearly shows that hydrogen can be used in a diesel engine
and in the gasoline engines without any modification to the present
configurations of the engine.
106
As a whole, using hydrogen as a fuel / additive in an engine, due to its fast
flame velocity, high diffusion rate, low activation energy, low quenching
distance resulted in an increase in brake thermal efficiency, decrease in all
engine-out emissions except NOX emission. This happens because when
hydrogen is used, the premixed burning phase of combustion gets
increased. This in-turn increases the in-cylinder pressure and temperature
and also heat release rate.
At low load conditions of the engine, the hydrogen is not an active
participant in combustion process. This is because the self ignition
temperature of hydrogen is more. It needs an ignition starter to start its
combustion. At low load conditions, the temperatures are always low. This
resulted in high hydrogen emission in the exhaust of the engine at low load
conditions.
Limited studies were found in hydrogen / oxygen enriched hydrogen gas.
Mostly, they were based on varying the flow rates of the gas without
modification to the operating parameters of the engine.
From the above literature review, it is evident that more work is needed
to optimize the combustion of hydrogen / oxygen enriched hydrogen in diesel
engines. The research problem for the present work was selected based on the
above literature review. The following chapter briefly elucidates the problem its
definition, its objectives, and scope of the present work.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Related manuals

Download PDF

advertisement