Fulltext: english,
Strojarstvo 52 (5) 577-587 (2010)
M. PUŠKÁR et. al., Output
Performance Increasing...����
ISSN 0562-1887
UDK 621.432.4.053/.057
Output Performance Increase of Two-stroke Combustion
Engine with Detonation Combustion Optimization
Michal PUŠKÁR and Peter BIGOŠ
KKDal SjF TU Košice,
Letná 9, 040 01 Košice
Slovak Republic
Preliminary note
All high-efficiency engines are inclined to destruction tendencies resulting
from detonation combustion. Most often the producers of engines solve this
problem with limitation of maximum output performance but, in this, there is
an efficiency decrease of fuel utilization. However, detonation combustion can
also be useful because if it is kept to a certain level, then detonation combustion
helps considerably in an additional increase of output performance. This article
defines the termination expressed in a number of detonation units per overridden
distance of track carried out by a single-track vehicle. Just for this limit, there is
a detonation combustion beneficial to increase an output performance and not
cause destruction in the engineering parts of an engine. The limit gives an idea
about the influence of individual factors on detonation combustion as well as
the influence on this combustion in obtaining maximum values and behaviours
of engine output performance and torque with dependence on engine speed.
Povećanje performansi dvotaktnog Otto motora optimiranjem
detonacijskog izgaranja
Detonation combustion
Engine output performance
Ključne riječi
Detonacijsko izgaranje
Izlazne performanse motora
Received (primljeno): 2010-03-08
Accepted (prihvaćeno): 2010-07-25
Prethodno priopćenje
Svi visoko učinski motori naginju detonacijskom načinu izgaranja. Mnogi
proizvođači motora rješavaju taj problem ograničavanjem maksiomalnih
izlaznih performansi motora, a što ima za posljedicu smanjenje stupnja
iskoristivosti tog motora. No ipak detonacijsko izgaranje može biti i od
koristi, jer ako se ono podržava na stvarnoj razini, tada takav način izgaranja
omogućava primjetno povećavanje izlaznih performansi motora. Ovaj članak
definira ograničenje broja detonacijskih jedinica nad cjelokupnim putanjom,
koje je prešlo vozilo. Upravo za to ograničenje postoji benefit detonacijskog
izgaranja u smislu povećavanja izlaznih performansi, a pri čemu ne dolazi do
oštećivanja bilo kojeg drigog dijela motora. To ograničenje daje ideju o utjecaju
pojedinačnih faktora na detonacijsko izgaranje, kao i utjecaj ovakvog načina
izgaranja na dobivanje maksimalnih vrijednosti kao i na ponašanja izlaznih
performansi motora i momenta ovisno o brzini motora.
1. Introduction and Aims
An arrangement of combustion space and plug
replacement influence the shape and distribution
of flame; therefore, they also influence heat and
cylinder pressure developments. In petrol engines, the
preparation of mixture begins at the time of a cylinder
filling and continues during compression and finishes
close before combustion. An ignition rate depends on a
kind of mixture, combustion development and mixture
movement. By means of the shape of combustion space
it is possible to whirl up a mixture and so regulate
combustion development. This shape influences an
indicated pressure, efficiency and hard running engine.
An advantage for shape of combustion space is evaluated
together with a critical compression ratio, resulting in a
detonation resistance. The value of a critical compression
ratio should be as high as possible from the point of view
of output performance and thermal efficiency of engine.
At a high level of mixture compression a faster and more
perfect fire-through occurs, creating a higher effective
pressure on a piston and, thus, it is possible to reach a high
engine speed. That is why antiknock spacings (squishes)
are used for combustion spaces. The basis is the antiknock
spacing of approximately 0.4 to 1.2 mm. This spacing is
between a piston and a cylinder head, if a piston is in
TDC. At the end of a compression stroke, the spacing
is reduced quickly and a mixture leaks from this place
in the direction of the piston centre. The intense flow is
evocated with this. The flow accelerates combustion and
prevents a detonation occurrence. There are also other
influences impacting the critical compression ratio, as for
example: cooling, the shape of ignition curve and others.
If compared, these impacts have to be kept as constant or
optimal value.
A normal combustion is a controlled one through a
mixture of fuel and air in a combustion chamber. It is a
M. PUŠKÁR et. al., Output Performance Increasing...
stable combustion, which develops at a spark plug and
continues in a combustion chamber in a three-dimensional
A detonation is a phenomenon, which is classified
as an abnormal combustion. It is an auto-ignition of a
residual tresh mixture in a combustion chamber. It occus
after normal combustion. At an initial phase, there is
normal mixture combustion, then under the influence of
high pressure and heat there are spontaneous ignitions, so
detonation combustion occurs.
Detonations induce high pressure in a combustion
chamber. This pressure takes a very short-time. In a
combustion chamber, the pressure behaviour seems
to be normal with an increasing development and then
the pressure increases evidently. The rapid increase of
pressure is indicated as excess compared with a normal
one. These excesses exemplify the pressure, caused
detonation combustion. Also this rapid increase of
pressure evocates forces in a combustion chamber, which
induces resonance in an engine construction. These
resonances are characteristic in detonation combustion.
The noise or vibrations present the phenomenon, which
is recorded which a detonation counter.
It is important to know that detonation need not be
necessarily destructive. Many engines operate with
a certain number of detonations. Some engines can
withstand strong detonations a very long time without
destruction. The controlled detonation combustion is
useful because it increases engine output performance.
The aim of this contribution is to find a limit where
an tested engine produces the highest performance,
but detonation combustion does not damage its design
components. Furthermore, the influence of detonation
combustion on maximum values of output performance
and torque as well as their behaviours depending on an
engine speed, are taken into consideration.
Strojarstvo 52 (5) 577-587 (2010)
of detonation ignition, which causes a melting down of
the piston and combustion space materials.
For this reason it is difficult to determine theoretically
the limit for detonation combustion and then to prove its
authenticity for a two-stroke petrol engine. Although
there is software for a modelling of processes inside a
cylinder and in an exhaust system during combustion,
the real results are performed seriously. That is why
the experiment was used to achieve the main goal.
It is necessary to choose the experimental model for
measurements. The development was carried out with
this experimental model. Further, there is a need to
choose the measurement devices (to provide feedback,
to give information about real output proposition for
concrete change in detonation combustion).
2.1. Experimental Models
The motorcycle Aprilia RS 125 with a racing
modification was used as the experimental model. This
single-track vehicle is equipped with a two-stroke engine
ROTAX 122 (Figure 1). In Table 1 there are the basic
technical parameters for this engine.
2. Experimental Models and Devices
Detonations influence the design of a combustion
chamber (shape, size, geometry, replacement of spark
plug), compression ratio, the proportion of air and fuel in a
combustion mixture, shape of ignition curve, atmospheric
conditions and octane number of fuel. If the surface of a
piston or the combustion space is damaged or destroyed,
detonation combustion also starts in such conditions,
which are not critical, but this damage affects directly as
an initiator of detonation combustion. The engines, which
are exposed to incodased detonation combustion, tend to
overheat, which initiates an avalanche effect. With higher
temperature, there is faster detonation combustion and
faster destruction. The piston absorbs a great deal of heat;
on four sides tit dilates, caouseing dilatation destruction.
The combustion temperatures are very high at the moment
Figure 1. Engine ROTAX 122
Slika 1. Motor ROTAX 122
As results of long-time experience and motorcycle
firms’ research, the compact semi-spherical combustion
space is the most suitable. This shape, with small
differences, is used for the large spectrum of motorcycle
series as well as special two-stroke racing vehicles. For
the requirements of the measurement, this shape was also
applied in the combination of a standard piston with a
The combustion development is presented in the
introduction of paragraph 1.
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M. PUŠKÁR et. al., Output
Performance Increasing...����
Table 1. Technical Parameters of Engine ROTAX 122
Tablica 1. Tehnički parametri motora ROTAX 122
Type / Tip
Single-cylinder, two-stroke engine,
liquid cooled, membrane filled, an
electrical-controlled exhaust power
valve / Jednocilindričan, dvotaktni
motor, hlađen tekućinom, punjen u
membranama, električno kontroliran
ventil ispuha
volume / Stapajni
124.8 cm3
Bore x Stroke /
Promjer x hod
54 x 54.5 mm
Carburator /
Dell’Orto PHBH 28 BD
In Table 2 the compression ratios are given. The
variations of antiknock spacing (paragraph 1) achieved
the differences. The compression ratio, used in the article
(Table 2), represents an effective compression ratio,
which is calculated according to the relation:
where: VC – compression volume
VS – stroke volume
An ignition curve, the shape of which is given with
a graphic representation by means of the pre-ignition
degrees depending on engine speed, was developed
considerably. The newest and the latest shapes of ignition
curves are common curves, which eliminate inadequacies,
e.g. problems with filling for the concrete mode of
an engine speed. For the needs of the experimental
measurements the SP curve (declared by a producer) was
used. It is provided for this motorcycle as a special part.
This curve is very similar to the serial-one provided for
the motorcycle since the 2006 year of production.
2.2. Experimental Devices
Two testing and measuring devices were developed
for the experimental measurements.
Engine Watch and Control System – EW&C
That is a data-recording system, i.e. a device which
scans and stores information during a motorcycle ride
(in real conditions, in real loading). This device enables
a diagnosis of parameters of a two-stroke combustion
engine: an output performance, a torque and their
behaviours, a temperature of exhaust system and its
behaviour and other characteristics. A number and a
kind of scanned parameters are related to the types and a
number of sensors, which are installed on the combustion
In Figure 3 there is the block diagram for data
measurement, operating and evaluation. The engine
activity record with dependence on time is the result of
this system. The principle of EW&C system is in the
measurement of the engine is instantaneous speed, an
instantaneous temperature of exhaust system and scanning
of an active speed gear or further parameters. The system
does a functional record of engine activity on the basis of
scanned and entered data (a wheel circumference, gear
ratios of individual speed gears, a curve of air resistance
and a motorcycle weight).
This record is stored in the memory of the EW&C
system. After finishing the measurement, it is possible to
copy the record by means of the parallel port into PC
(Figure 2). On PC display (Figure 8) there is a record
of engine activity with dependence on a time axis,
graphically presented (by means of the software which
is a component of EW&C system). Every point of the
record covers an instantaneous speed, a temperature of
exhaust system and an output at a crankshaft end.
Table 2. Input conditions
Tablica 2. Ulazni uvjeti
Atmospheric Conditions /
Atmosferski uvjeti
No. /
Ratio / Omjer
Temperature /
Pressure / / Relativna
Tlak, kPa vlažnost,
Figure 2. Engine watch and control aystem
Slika 2. Nadzorni i upravljački sustav motora
M. PUŠKÁR et. al., Output Performance Increasing...
Strojarstvo 52 (5) 577-587 (2010)
Figure 5. Detonation area in “saw-tooth” type diagram
Slika 5. Područje detonacije u dijagramu tipa ''Saw-tooth''
Figure 3. Block diagram of EW&C system
Slika 3. Blok-dijagram kočnice motora
Detonation Counter
In Figure 4 there is the detonation counter, which
was used for the measurement of detonations. It was
developed and produced by the racing department of
Honda HRC company. The detonation counter sensor
picks up an irregular combustion as the detonations in
the engine and provides a number of detonation units. In
Figure 9 this number on the display is displayed.
As shown in Figure 5, the 5th and the 6th gears provide
less acceleration than the 1st and 2nd gears where there is
extended use of these detonation range speeds. A, B, C, D,
E and F are the sectors of detonation combustion for the
relative concrete speed gears. For this reason, the circuits
with more acceleration and deceleration frequencies give
less detonation occurrence than circuits, where there is
extended use of a wide-open throttle operation using the
5th and 6th gears.
The frequent use of low ratio and 11.500 rpm and over,
resulting from ratio selections will control propensity
toward the detonation. Also, the distinct behaviour of
driving will result in less detonation associated with a
partial throttle opening.
In the engine output characteristics (Figure 6), peak
speeds are changing, depending on the wide-open throttle
to the partial throttle. Accordingly, detonation occurrence
ranges can vary with the throttle opening. The detonation
can suddenly take place when returning the throttle from
fully wide-open throttle at 10.000 rpm.
Legend: 1. Detonation Counter / Brojač detonacije, 2.Plug Cap
/ Kapa svjećice, 3.Spark Plug / Svjećica, 4. Sensor Assy / Assy
osjetnik, 5. Detonation Counter Unit Stay / Jedinica brojača
detonacije, 6. Washer / Podloška, 7. Wire Harness / Žičani
spojevi, 8. Sub Harness / Pomoćni žičani spojevi.
Figure 4. Detonation counter kit
Slika 4. Oprema za brojanje detonacije
The detonation will occur at, before or after, the
maximum output speeds (if peak speed is 11.250 rpm,
the detonation occurrence ranges from 11.000 to 11.500
rpm). The detonation seldom occurs outside these speed
ranges (Figure 5).
Figure 6. Detonation area with engine output characteristics
Slika 6. Područje detonacije s izlaznim karakteristikama
The counting at fully wide-open ranges tends to lead
to damages, but the counting at partial range will lead
to less damages. Accordingly, it is recommended that a
proper basis is found because the counts are different
from the rider’s behaviours to the course of lay outs.
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M. PUŠKÁR et. al., Output
Performance Increasing...����
The criteria for a detonation counter
Honda HRC producer of the device recommends two
units for an overridden kilometre of a race track.
In Japan on Suzuka Circuit a device was tested with
twelve units for one circuit, which is approximately
six kilometres in length. Certainly, this is only the
recommendation and it is enough apart from a limit
where detonation combustion reaches a limiting value
and has not damaged an engine design yet.
3. Experimental Results
The performed measurements are intended for the
analysis of the detonation combustion influence with an
output characteristic in consideration of the defined aim.
The aim of consecutive measurements determined
the limit, expressed in a number of detonation units per
overridden kilometre, where the combustion is beneficial
and helps to increase output performance and does
not cause destruction in the design components of an
In the experimental model the diagnostic devices were
applied, described in the above-mentioned paragraph. The
measurements were performed for two racing circuits:
the Hungaroring in Hungary and the Autodrom Most
in the Czech Republic. The obtained results, which are
presented in this paragraph, were verified with multiple
consecutive measurements to prevent a potential random
In the introduction of previous paragraph the factors
which influence detonation combustion are described.
They are the design of a combustion chamber (shape,
size, geometry, replacement of spark plug), compression
ratio, the proportion of the combustion mixture, shape
of ignition curve, the atmospheric conditions and octane
number of a fuel.
In paragraph 2.1 the used shape of an ignition curve
and the design shape of a combustion space are described
in detail. These shapes are equal for all measurements.
Unleaded petrol with the octane number 100 was applied
as a fuel. In Table 2 the atmospheric conditions for each
of four measurements as well as the used compression
ratios are scheduled. In Table 3 are illustrated numerically
the fuel maps which in Figure 7 there are recorded.
Table 3 contains four fuel maps. In the upper row there
the percentage positions of throttle is given. In the left
column, there is a consecutive number of measurements,
so every row represents one map. The numerical value,
given for the concrete position of the throttle, represents
a flow space. Through this flow space fuel flows into a
carburator diffusor. Subsequently in the diffuser there
is an influent fuel mixed with air. These values help in
a comparison of various alternatives for fuel maps. If
a value is higher then an overricher alternative for the
concrete carburator setup and, represented on the other
hand, if a value is lower then the mixture is weakened.
The fuel maps for the measurements No.1 and No.2 are
equal. In the case of the map No.3 the mixture is weaker
at the throttle position up to 40 %. At the throttle position
over 80 % the mixture isoverricher than for maps No.1
and No.2. Map No.4 is fuel-overricher in a whole range
of openings with the throttle position from 30 %. The fuel
volume at the complete opening of throttle position is
regulated by means of a main jet, which was 3 % smaller
at measurements No.3 and No.4 than it was at thefirst
Table 3. Fuel maps
Tablica 3. Mape goriva
Throttle Position / Regulator pozicije, %
Broj 0÷20 30 40 50
106 132 160
265 289
106 132 160
265 289
130 160
267 292
109 137 165
269 293
Legend: The wetted cross-section is a dimensionless parameter
and represents a value of flow space trough, which fuel flows
through, referred in the special unit, [mm2·100].
Figure 7. Fuel maps
Slika 7. Mape goriva
In Figure 7 the fuel maps are illustrated. This diagram
was drawn on the basis of numerical data from Table 3.
This graph enables a more integrated view of the fuel
supplies at all kinds of measurements to be obtained.
A horizontal axis represents the throttle position
and a vertical axis is given for the wetted cross-section.
Fuel flows through this flow space in the carburator at
a determined time. Its value is referred to in absolute
numbers. From the curve for measurement No.3 it is
evident that at the throttle position up to 40 % the mixture
M. PUŠKÁR et. al., Output Performance Increasing...
is weakened. Measurement No.1 was done during the first
testing day in the racing circuit Hungaroring. In Table 2
the input conditions of the measurement are scheduled
and the fuel maps are given in Table 3 as well as in Figure
7. In Figure 8 the record of EW&C system is illustrated.
In Figure 8 the record of engine activity and the
behaviour of engine performance with dependence on a
time axis is illustrated. A time axis is represented in the
bottom part of the figure. The engine activity record is
represented with an upper curve (saw-tooth type). On the
right side of every top of this curve a gear position, which
is active in the determined moment is illustrated.
On the left side there is an axis, which represents
engine speed (revolutions); therefore it is possible to
define the range of operating speed which the engine
operates in. The axis of temperature in the exhaust
system is on the right side. The temperature behaviour is
represented by a curve given in the lower section of the
figure. In this case, the illustrated curve is almost a line
because a relevant sensor was inactive.
The concrete extent of an activity engine record was
selected. This extent was terminated on both sides (with
dash vertical lines), then was analysed with regard to
output performance. This analysis is illustrated in the
left window. The horizontal axis belongs to the engine
speed (revolutions) and the vertical axis is for the output
performance. There is an upper curve which represents
output performance behaviour with dependence on
Strojarstvo 52 (5) 577-587 (2010)
engine speed axis and the bottom curve belongs to the
torque behaviour.
The output performance analysis was done for
all measurements at the forth speed gear. According
to experience, it is just this speed gear where output
performance is the highest.
In Figure 9 the display of detonation counter after
one of the testing rides is illustrated. The number 1545
indicates a total number of detonation units during the
whole ride. It is necessary to calculate the total number
per one overridden kilometre. In Table 3 there is a recalculated number of detonation units per overridden
kilometre for all four measurements.
Analysis of the output data from the EW&C system
and the detonation counter Table 4 was built up, where
the number of detonation units per overridden kilometre
as well as all the measured output values are stated. For
the measurement No.1 maximum output performance
was 27 kW and maximum torque 23 N·m. The number
of detonation units was 8 per one overridden kilometre.
After the complete analysis, it is evident that detonation
combustion is out of the limit at this measurement. This
fact is also obvious in Figure 10 on which a piston is
displayed. This piston does not have any marks of damage
or any black deposition. The output characteristics were
Figure 8. Activity record and output behaviour of engine at measurement No.1
Slika 8. Bilježenje aktivnosti i ponašanje izlazne snage motora prilikom prvog mjerenja
Strojarstvo 52 (5) 577-587 (2010)
Figure 9. Display of detonation counter
Slika 9. Displej brijača detonacije
Figure 10. Undamaged piston
Slika 10. Neoštećeni stap
M. PUŠKÁR et. al., Output
Performance Increasing...����
On the next testing day the measurement No.2 in
the same racing circuit was done. The conditions for the
measurement No.2 are referred to in Table 2, Table 3
and in Figure 7. In Figure 11 there is the engine activity
record. Maximum output performance was 29.5 kW and
maximum torque 27 N·m. The number of detonation
units is 30 per one overridden kilometre. Other measured
data are in Table 4. The output parameters were stable
which means that they did not decrease during the test
ride. In the middle of Figure 11, there is the example of
an analysis, which is possible to perform with a touch
cursor for any point of the engine activity record. This
analysis was done for the lowest point of the curve and
in the small window it is possible to see the values of
speed, an engine speed and a temperature in an exhaust
system (a sensor was inactive, therefore it was a constant
imaginary value).
This setup was characterized by the large range of
exploitable speed. The engine was set much better than
No.1, which is documented with higher maximum output
performance and torque as well as their ranges.
After disassembling, more significant damage of
the piston was not evident, Figure 12. But the black
deposition indicates that detonation combustion was at
a limit and, therefore, the engine was set optimally and
performed the stable output performance.
The following measurement No.3 was performed
an effort to determine whether it is possible to load the
engine with an even greater rate of detonation combustion
and what influence therewill be on the engine output
parameters as well as potential damage. Likewise,
the testing circuit was the Hungaroring and the input
conditions as well as the shape of fuel map are stated in
Table 2 and Table 3 and in Figure 7.
Figure 11. Activity record
and output behaviour of
engine at measurement
Slika 11. Bilježenje
aktivnosti i ponašanje
izlazne snage motora
prilikom drugog mjerenja
M. PUŠKÁR et. al., Output Performance Increasing...
Figure 12. Piston with black deposit
Slika 12. Stap sa crnim depozitom
Strojarstvo 52 (5) 577-587 (2010)
is evident at the edge of piston, there where a pointer
shows. This wear indicates that detonation combustion
has already a destructive character.
During measurement of No.4 the engine was exposed
to extreme detonation combustion. This measurement
was performed in the racing circuit Most in the north of
the Czech Republic. In Table 2 there are conditions for
performance of the measurement No.4. In Table 3 as well
as in Figure 7 there is the fuel map. In Figure 15 there
is the record from the EW&C system. Maximum output
performance was 29.5 kW and maximum torque 26 N·m.
The number of detonation units is 56 per one overridden
kilometre. Other measured data are in Table 4. The range
of exploitable speed was very short. The engine reached
these values only at the initial phases of the testing
ride then when significant overheating and expressive
Figure 13. Activity
record and output
behaviour of engine
at measurement No.3
Slika 13. Bilježenje
aktivnosti i
ponašanje izlazne
snage motora
prilikom trećeg
In Figure 13 there is the engine activity record.
Maximum output performance was 32 kW and maximum
torque 27 N·m. The number of detonation units is 44
per one overridden kilometre. Other measured data are
in Table 4. Maximum output performance increased in
comparison with the previous measurement, which was
caused by abnormal detonation combustion. It is important
to know that this performance is transient and the engine
reached it only at the beginning of measurement. During
the next kilometres, there was engine overheating,
small damage of the piston (Figure 14) and the loss of
output performance. Also, the range of exploitable speed
decreased significantly.
In Figure 14 there is the black deposition of the piston
similar to Figure 12. But the moderate abrasive wear
Figure 14. Piston with moderate damage
Slika 14. Stap s umjerenim oštećenjem
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Table 4. Measurement Results
Tablica 4. Rezultati mjerenja
Number of
(NDU)/ Broj
29.5 / 10.800
27 / 10.300
32 / 10.900
27 / 10.800
29.5 / 11.100
26 / 11.050
Maximum output
engine speed /
Maksimalna izlazna
snaga/broj okretaja
Range of speed for
output over 25kW
/ Područje broja
okretaja za izlaznu
snagu iznad 25 kW,
torque engine speed /
Maksimalni moment/broj
okretaja motora,
Range of speed for torque
over 20 N·m / područje
broja okretaja motora za
moment iznad 20 N·m,
27 / 11.200
23 / 11.100
Figure 15. Activity
record and Output
Behaviour of Engine at
Measurement No.4
Slika 15. Bilježenje
aktivnosti i ponašanje
izlazne snage motora
prilikom četvrtog
bottom. The pointer shows the place with great damage
where the material was melted down with detonation
combustion. Similarly the combustion space and an
upper section of the cylinder are also damaged. Like that
damaged design components are not applied in practice
any more.
4. Conclusions
Figure 16. Piston with great damage
Slika 16. Stap s velikim oštećenjem
destruction occurred there. The output performance was
transient in maximum extent.
In Figure 16 a piston is illustrated which is
considerably damaged with detonation combustion. The
black deposition is throughout the surface of the piston
The measurements, intent on detonation combustion,
have brought many interesting observations.
In paragraph 2 it is described that a design
of combustion chamber, combustion ratio, fuelair proportion in mixture, shape of ignition curve,
atmospheric conditions and fuel octane number have an
influence on detonation combustion. Changes were made,
in the field of a compression ratio and the atmospheric
conditions (Table 2), the proportion of air and a fuel in
a combustion mixture (Fuel Map) Table 3 and Figure 7,
M. PUŠKÁR et. al., Output Performance Increasing...
for the requirements of measurements. The other factors
were equal. The first three tests were performed in the
racing circuit Hungaroring and the forth test an the racing
circuit Autodrom Most. This reality did not influence the
results because the atmospheric conditions were taken
into account for each of these experiments.
On the basis of all information it is possible to review
the results of the measurement No.1 as follows:
In Table 2 the conditions are scheduled for the
measurement. In Table 3 and in Figure 7 there is the fuel
map which is drawn from the wetted cross-sections in
the carburator, through which fuel flows into the diffusor,
where is mixed with air. Maximum output performance
was 27 kW and maximum torque was 23 N·m (Table 4).
The engine output - torque characteristic is stable with
continuous development of performance what provides
easy steering control of this single-track vehicle. The
number of detonation units per overridden kilometre was
8. On the basis of complete evaluation it is possible to state
that the engine achieved very good output characteristics.
But detonation combustion was over the limit, which the
piston bottom also indicates (Figure 10). This bottom is
without any marks of damage and black deposition.
The results of the measurement No.2 are evaluated
as follows:
In Table 2, in Table 3 and in Figure 7 conditions for
measurement are scheduled and illustrated. It is evident
from these tables that the compression ratio was changed
only slightly and the fuel maps become the same.
Maximum output performance was 29.5 kW
maximum torque was 27 N·m (Table 4). The engine
output - torque characteristic is stable with large range
of exploitable speed, where the output performance is
kept constan almost in maximum value. The number of
detonation units per overridden kilometre was 30. On the
basis of complex evaluation it is possible to state that the
engine reached the excellent output characteristics. After
disassembling there was no evidence of more significant
damage of the piston, Figure 12. But the black deposition
indicates that detonation combustion was at a limit and
therefore the engine was set optimally. It is interesting
that no change of the engine setup occurred in spite of
the fact that the output characteristics had been changed
greatly. This change occurred because the atmospheric
conditions had been changed in comparison with the
measurement No.1 when the temperature decreased and
the pressure increased considerably, Table 2.
The next measurement No.3 was performed with an
effort to find out whether it is possiblepotential to still
shift a limit of detonation combustion without damage to
the engine construction. It is possible to summarize the
results for the following observations:
Resulting from Table 2 it is necessary to significantly
increase a compression ratio because of the atmospheric
Strojarstvo 52 (5) 577-587 (2010)
pressure depressurized, the temperature decreased greatly
and the humidity increased, which caused the engine
to become more detonation-resistant. By means of the
change for a carburator setup, the fuel map was modified
as well. The mixture was weakened up to 40 % of throttle
position and again was overrich above 80 %. Maximum
output performance increased to 32 kW and maximum
torque reached the value 27 N·m (Table 4). The increase
of maximum output performance caused abnormal
detonation combustion but the range of exploitable speed
decreased. The engine reached this output performance
only at the beginning of the measurement; that is why
it is transient. During the next kilometres there was
engine overheating, moderate damage of the piston and
the loss of output performance. It is evident from the
point where the pointer shows in Figure 14. The black
deposition is similar to that in Figure 12 but with visible
moderate abrasive wear, which indicates that detonation
combustion is already destructive.
The last measurement No. 4 characterised extreme
detonation combustion which the engine was exposed
to. It was caused by the predominately high value of
compression ratio (Table 2). In Table 2 and in Table 3
there are the atmospheric conditions and the modified
fuel map. The fuel map was changed because the mixture
was overrich in the whole process of throttle opening
over 30 %. Maximum output performance increased to
29.5 kW and maximum torque reached the value 26 N·m
(Table 4).
The range of exploitable speed was very short. This
output performance was transient and the engine reached
it only at the initial phases of the testing ride. Then
there occurred significant overheating and expressive
It is possible to suppose theoretically that the higher
extent of detonation combustion provides even greater
output performance at least in the initial phase of the
testing. However, the results indicate that neither the
output performance nor the torque was increased.
On the contrary, these values were decreased
in comparision with the measurement No.3 where
detonation combustion was weaker. This phenomenon
is caused by the fact that much energy is consumed for
negative work. This work is spent on breaking down of
resistances such as a high compression ratio. In Figure
16 there is a piston, which is significantly damaged with
detonation combustion. Throughout the whole surface
of piston bottom there is the saturated black deposition.
The pointer shows the place with great damage with
detonation combustion. Similarly the combustion
space and an upper section of the cylinder are already
Resulting from data of the measurements it is
necessary to keep detonation combustion at a certain
Strojarstvo 52 (5) 577-587 (2010)
M. PUŠKÁR et. al., Output
Performance Increasing...����
level. According to these results there are 30 detonation
units per overridden kilometre. This value is possible to
reach with various ways and combinations of elements
which influence detonation combustion.
At this value the engine reached permanently a high
output performance, the large range of exploitable speed
and detonation combustion did not cause the engine
destruction. The utilization of detonation combustion for
the increase of an output performance is considerably
hazardous. Therefore the measurements show that
by means of the change of atmospheric conditions
the combustion can occur. However, the combustion
will be destructive. Detonation combustion a the great
significance, which is also evident from the difference
between the measurement No.1 and No. 2 (Table 4). By
means of detonation combustion for measurement No.2
maximum output performance and torque in principle
were higher than for measurement No.1.
The value of 30 detonation units per overridden
kilometre is different from the value which is presented
by a producer of this detonation counter although it is
obvious the producer keeps certain reserves to minimize
some engine failure.
At the present time the problem of increasing for output
parameters of two-stroke combustion engine is solved in
the framework project VEGA 1/0146/08 Material Flows
and Logistics, Innovation Processes in Construction of
Manipulation and Transport Devices as Active Logistic
Elements with the Aim of Reliability Increasing.
[1] BIGOŠ, P.; PUŠKÁR, M.: Influence of Cylinder
Shape and Combustion Space on Engine Output
Characteristic of Two-stroke Combustion Engine,
Zdvihací zařízení v teorii a praxi, 3 /2008, ISSN
[2] BIGOŠ, P.; PUŠKÁR, M.: Optimal Value of
Compression Ratio, Strojarstvo, 12/2008, ISSN
[3] BIGOŠ, P.; PUŠKÁR. M.: Influence of Atmospheric
Conditions on Output Performance Characteristic
for Two-Stroke Combustion Engine, Zdvihací
zařízení v teorii a praxi, 1/2007, ISSN 1802-2812.
[4] BIGOŠ, P.; PUŠKÁR, M.: Influence of Ignition
Curve on Output Characteristic for Two-Stroke
Combustion Engine, Acta Mechanica Slovaca,
3/2008, ISSN 1335-2393.
[5] BLAIR, G., P.: The Design of Modern Two-stroke
Engines, Engine Power Products International,
[6] FERENC, B.: Combustion Engines – Carburators
and Fuel Injection, Computer Press, Brno, 2006.
[7] HUSÁK, P.: Motorcycle with Two-stroke Engine,
Praha, 1978.
[8] Ikrinský, A.; Patek, P.; Tichý, J.: Theory of
Vehicles, SjF STU Bratislava, 2007.
[9] KOVAŘÍK, L.; Ferencey, V.; Skalský,
R.; Částek, L.: Design of Vehicle Combustion
Engines, Naše vojsko, Praha, 1992.
[10]KOŽOUŠEK, J.: Computation and Design of
Combustion Engines, SNTL, Praha, 1983.
[11] KOŽOUŠEK, J.: Theory of Combustion Engines,
SNTL/ALFA, Praha, 1971.
[12]MACEK, J.; SUK, B.: Combustion Engines I.,
ČVUT Praha 1993, ISBN 80-01-00919.
[13]PUŠKÁR, M.: Contribution to Effect of Higher
Compression Ratio on Power in Racing Two-stroke
Engines, Transcom 2007, Žilina, ISBN 978-808070-696-8.
[14]PUŠKÁR, M.: Output Performance Increasing
of Two-stroke Combustion Engines by Means of
Change of Compression Ratio, Bezpečnosť-KvalitaSpoľahlivosť, Košice, 2007, ISBN 978-80-8073828-0.
[15]PUŠKÁR. M.: Increasing of Output Performance
Parameters for Single-Track Vehicles, Strojárstvo
2/2008, ISSN 1335-2938.
[16]RAUSCHER, J.: Combustion Engines, VUT Brno,
[17]ŠTOSS, M.: Equipment of Combustion Engines,
VUT Brno, 1992.
[18]Trnka, J.; Urban, J.: Combustion Engines,
Bratislava, Alfa, 1992.
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