Embed Size (px)
Citation preview
Knock rating of gaseous fuels in a single cylinder spark ignition engine
C. Rahmounia, G. Brecqb, M. Tazeroutb, O. Le Correb,*
aCreeD, 291 Avenue Dreyfous Ducas, 78520 Limay, FrancebEcole des Mines de Nantes, Department of Energy and Environment System, 4 Rue A. Kastler, BP 20722, 44307 Nantes Cedex 3, France
Received 25 February 2003; revised 7 July 2003; accepted 7 July 2003; available online 6 August 2003
Abstract
This paper presents the determination of knock rating of gaseous fuels in a single cylinder engine. The first part of the work deals with an
application of a standard method for the knock rating of gaseous fuels. The Service Methane Number (SMN) is compared with the standard
Methane Number (MN) calculated from the standard AVL software METHANE (which corresponds to the MN measured on a Cooperative
Fuel Research engine). Then, in the second part, the ‘mechanical’ resistance to knock of our engine is highlighted by means of the Methane
Number Requirement (MNR). A single cylinder LISTER PETTER engine was modified to run as a spark ignition engine with a fixed
compression ratio and an adjustable spark advance. Effects of engine settings on the MNR are deduced from experimental data and compared
extensively with previous studies. Using the above, it is then possible to adapt the engine settings for optimal knock control and
performances. The error on the SMN and MNR stands beneath ^2 MN units over the gases and engine settings considered.
q 2004 Elsevier Ltd. All rights reserved.
Keywords: Knock rating of gaseous fuels; Service methane number; Methane number requirement
1. Introduction
The composition of natural gas depends on the feed stock
location [1]. For instance, the methane concentration in
natural gas supplied in Europe ranges from about 80 to 98%
[2]. When natural gas is used to run an internal combustion
engine, these variations can induce knock occurrence and
lead to increasing emissions and decreasing engine
efficiency. Knock is due to auto-ignition of the end-gas
ahead of the propagating flame. When this auto-ignition
takes place in the cylinder, the chemical energy contained in
the end gas is released very rapidly. Beyond a certain burn
rate, it causes the propagation of shock waves across the
combustion chamber that is then forced to resonate at its
natural frequencies. This can lead to high frequency shock
waves hitting the cylinder walls and causing irreversible
damages.
The indicator generally used to characterise changing
composition is the methane number (MN). It is similar to the
octane number (ON) used for liquid fuels. MN characterises
the tendency to knock of gaseous fuels measured on a
Cooperative Fuel Research engine (CFR engine) [3–5].
Methane, which is the least detonating hydrocarbon, has a
conventional MN of 100. At the opposite scale, hydrogen,
which is the most detonating gas [6], has a conventional MN
of 0. It is however possible to get a MN over 100 for gases
mainly composed of methane and inert compounds like
nitrogen and carbon dioxide (biogas for instance) [3].
Shrestha and Karim [7] and Brecq et al. [8] have
investigated the effect of inert gases on the knock rating
of gaseous.
Combined heat and power (CHP) engines run at knock
limit for optimal efficiency and environmental perform-
ances in order to reduce the pay-back period [9]. Because of
environmental and economical concerns, engines are set
with high compression ratios. Consequently, optimal
operating conditions are generally very close to those of
knock occurrence.
Human ear was for a long time the unique mean of knock
detection. This method is still taken as a reference in recent
works carried out by Kalghatgi in 1996 [10]. ON was
frequently determined using this specific ‘knock detection’
[11]. But, because of subjectivity (human ear is incapable of
measuring knock intensity), it was necessary to define a
knock indicator capable of characterising its intensity and
determining its threshold in a reliable and reproducible
manner.
0016-2361/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/S0016-2361(03)00245-X
Fuel 83 (2004) 327–336
www.fuelfirst.com
* Corresponding author. Tel.: þ33-2-518-58257; fax: þ33-2-518-58299.
E-mail address: [email protected] (O. Le Corre).
Several knock detection methods exists in both industry
and research [12]:
† Wall losses. When knock occurs, wall losses are clearly
more important. Syrimis and Assanis [13,14] are the
main authors whose work deals with the link between
heat transfer and knock. Trapy also provides lots of
results in this field [15].
† Ion current. Along with the propagating flame (presence
of ions), to the spark plug neighbourhood, the electrical
conductivity changes and so far the current intensity.
There is a correlation between the ion current intensity
and the value of the cylinder pressure [16,17]. Therefore,
the high frequencies contained in the ion current signal
can be used to detect knock [18–21]. That technique is
however not yet reliable because of a high noise level.
† Engine vibrations. By means of an accelerometer fixed
onto the outer surface of the engine cylinder head. The
high noise level is the main drawback of this technique
[12,22], especially for high speed running engines.
† Cylinder pressure. That old technology, found in
previous works [23], is based on the fact that cylinder
pressure is directly linked to knock via shock waves.
Because this technique is based on the real nature of
knock, it is much more reliable than the one using engine
vibrations. Many authors advise it [12,24,25]. However,
these sensors are very expensive and not adapted for
industrial purpose. It mainly remains a research tool.
The two first techniques are not commonly used. The
first one is still a principle and the second is efficient and
interesting but is still known as an emerging technology.
The last two techniques are much more used: acceler-
ometer technique is mainly employed in industrial engines
because of a cost-effective sensor. The cylinder pressure
measure is mainly employed in research fields because of
the quality of the results and the high cost of pressure
probes. Advantages and drawbacks of each technique are
presented in Ref. [26].
Most of knock indicators that can be used to quantify
knock strength (that is knock intensity) are based on
cylinder pressure measurement:
† Direct evaluation from cylinder pressure (peak pressure
analysis, for instance) [3,27–29];
† Filtered pressure analysis (MAPO,IMPO,…) [4–6,12,
29–34,38–45,54];
† Pressure derivatives analysis [29,35–37].
There are numerous existing means to determine knock
limit in spark ignition engines. These means result from
three different choices: the choice of probes, the choice of
knock indicators and the choice of analytical methods to be
employed. Thus, the definition of knock limit is a relative
notion because it depends on these three choices. There are
different couples ‘indicator-method’ according to many
authors to define knock limit in SI engines. The synthesis of
these different indicators with the corresponding methods is
given in Table 1.
IMPO and MAPO. There are two knock indicators, based
on a high frequency analysis of cylinder pressure data,
commonly used in the literature. The first one is the integral
of modulus of pressure oscillations (IMPO), representing
the energy contained in the high frequency oscillations of
the cylinder pressure signal (including noise). The second
one is the maximum amplitude of pressure oscillations
(MAPO), related to the peak of the pressure oscillations due
to knock.
IMPO and MAPO are obtained for N consecutive cycles
and are expressed by the following relations:
MAPO ¼1
N
XN1
maxui ;uiþW
l~pl ð1Þ
IMPO ¼1
N
XN1
ðuiþW
ui
l~pldu ð2Þ
Nomenclature
IMPO integral of modulus of pressure oscillations,
bar.CA
MAPO maximum amplitude of pressure oscillations, bar
KLCR knock limited compression, –
KLER knock limited equivalence ratio, –
KLEP knock limited exhaust pressure, Pa
KLIP knock limited intake pressure, Pa
KLIT knock limited intake temperature, K
KLSA knock limited spark advance, 8CA
KLST knock limited spark timing, 8CA
KLVE knock limited volumetric efficiency, %
SA spark advance, CA
ST spark timing, CA
MN methane number, –
SMN service methane number, –
MNR methane number requirement, –
T temperature, K
PKC percentage of knocking cycles, %
KC knocking cycles
Greek symbols
D variation, –
f equivalence ratio, bar
hv volumetric efficiency, –
C. Rahmouni et al. / Fuel 83 (2004) 327–336328
N represents the number of computed cycles, ui the crank
angle corresponding to the beginning of the window of
calculation, W the value of the window of calculation and ~p
the filtered in-cylinder pressure.
Percentage of knocking cycle (PKC). A general method,
based on a statistical analysis of the in-cylinder peak
pressure (PP) and angle of peak pressure (APP) during
combustion was presented in Ref. [26]. Studies of Brecq
et al. [26,55] showed that over a great number of cycles
(about 400 cycles), two separated groups of cycles can be
distinguished: group A of non-knocking cycles and group B
of knocking cycles (Fig. 1). In this paper, an analysis, first
outlined in Ref. [26], concerning the evolution of the PKC
with spark advance showed that a threshold of knocking
cycles fixed at 50% gives a knock limit close to that given
by standard knock indices (Figs. 2 and 3). This indicator was
then used in all the experiments carried out because of its
versatility and its accuracy.
Indicators for knock rating of gaseous fuels. An
adaptation of engine settings to changing gas composition
is then necessary in order to ensure a safe running of the
engine. Schiffgens et al. [46] have already used a sensor to
adapt the engine to variable composition by means of a
measure of MN.
MN is directly linked to knock in SI engines. Numerous
authors [3,4–6,28,33,47–50] have observed interconnec-
tions between knock limited engine parameters and engine
settings on the one hand, and between knock limited engine
Table 1
Knock detection methods
Knock indices
Method Raw pressure Filtered pressure Pressure derivative
Constant threshold
method
Checkel and Dale [27],
Russ [28], Chun and
Kim [29]
Millo and Ferraro [12], Thomas et al. [30],
Dubel et al. [31], Chun and Kim [29],
Lee et al. [32], Westin et al. [33],
Attar and Karim [6],a Brunt et al. [34],
Brecq et al. [44], Worret et al. [45]
Checkel and Dale [35], Ando et al. [36],
Dhall and Beans [37], Chun and Kim [29]
Updated threshold
method
Ortmann et al. [38],a Schmillen and
Rechs [22], Ryan et al. [4],a Lee et al. [32],
Callahan et al. [5],a Ferraro et al. [39]
Trend-intersection
method
Checkel and Dale [27] Najt [40], Ho and Kuo [41], Dubel et al. [31],
Abu Qudais [42],a Goto and Itoh [43]a
a Indicators not given explicitly.
Fig. 2. Evolution of the % of knocking cycles versus spark advance (SA).
Fig. 1. Knocking-cycle distinction by PP analysis. Fig. 3. Value of PKC to determine the onset of knock.
C. Rahmouni et al. / Fuel 83 (2004) 327–336 329
Table 2
Effect of þ10 MN units variation on critical engine parameters
Leiker [3] Douaud [51] Ryan [4] Schiffgens [46] Ho [49] Russ [28] Faure [50] Attar [6] Westin [33]
KLST þ1 to þ38CA þ4 to þ58CA þ3 to þ68CAa þ48CA þ68CA þ2 to þ38CAb
KLCR þ0.5 to 0.8 þ0.9 þ0.7 þ0.6b þ1.2 þ0.6
KLIT þ10 to þ14 8C þ40 to þ130 8C þ20 to þ25 8Cb þ40 8C þ40 8C
KLCT þ150 to þ210 8C þ48 to þ60 8C
KLIP þ13 to þ16 kPa þ15 to þ20 kPa
KLEP þ180 kPa þ110 to þ180 kPa
KLER ^0.17c ^0.15c
Speed 240%
Operating conditions according to authors
Engine CFR – CFR FEVa Cat. G3505 FEV CFR CFR Mitsubishia
Fuel Natural gas Gasoline Natural gas Natural gas Gasoline Gasoline Gasoline Binary gases Gasoline
No of cylinder 1 4 1 1 – 1 1 1 4
Displacement (cm3) 677 1289 677 <2000 4300 676 677 677 572
Compression ratio – 9.5 11–15 9.4–13 8–11 9.1–12.5 – 8.5–11 8.95
Speed (rpm) 375 3000 900 1500 1400 1500 – 900 3500
Spark timing – – 158CA 5 to 308CA – 1 to 118CA 128CA 158CA –
Equivalence ratio 1.0 1.2 1.0 1.0 < 0.6 and 0.8 1.17 1.1 0.8 and 1.0 < 1
Intake temperature (K) 298 <300 294 313 and 353 330 < 300 313 and 353 300 313
a Valid for 40 , MN (turbocharged engines).b Valid for 40 , MN , 80.c Sign ‘ þ ’ in lean mixtures and sign ‘ 2 ’ in rich mixtures.
C.
Ra
hm
ou
ni
eta
l./
Fu
el8
3(2
00
4)
32
7–
33
63
30
parameters and knock rating indicators (MN, ON) on the
other hand. Among them, Russ [28] managed to find
relations between knock limited parameters of the engine,
via a variation of ON. Douaud [51] has also given
prominence to numerous dependencies between knock
limited parameters and ON. Leiker et al. [3] have linked
some knock limited parameters to a variation of þ10 MN
units. The effect of a variation of þ10 MN units on the
different knock limited parameters has been performed
(Table 2). As many authors have used ON instead of MN, a
conversion between these two indicators has been applied so
that comparisons can then be possible. By adding lead
tetraethyl to iso-octane, it is possible to estimate the ON of
gaseous fuels up to 120.3 ON units [52]. This method has
been applied by Kubesh et al. [52] in order to measure ON
of gaseous fuels. They also obtained a ON value for pure
methane of about 140. Besides, Daverat [53] and Dimpel-
feld and Foster [47] have as well measured ON of heavy
hydrocarbons like ethane, propane and n-butane. Thus,
using the composition tested by Kubesh [52], Daverat [53]
and Dimpelfeld [47] and the software developed by AVL for
the calculation of MN from composition, a relation between
ON and MN can be established (Fig. 4). The link between
the work carried out on liquid fuels and those carried out on
gaseous fuels is realised by the connecting relation between
MN and ON (þ5.7 ON units corresponds to þ10 MN
units).
Globally, there is a good agreement of the results,
summed up in Table 2, among the different authors.
The most important differences between authors result
from the KLIT (knock limited intake temperature).
However, the study of the impact of the KLIT on the
KLST results in the identification of the following trends:
† Russ [28], 27 K/8CA
† Faure [50], 27 K/8CA
† Leiker [3], 26 K/8CA1
† Schiffgens [46], 210 to 25 K/8CA
† Douaud [51], 214 K/8CA2
The differences observed in Table 2 result from the mean
of calculation, based on the KLST variation of Russ [28]
which is relatively important (þ5.7 ON units corresponds to
þ10 MN units).
The aim of this work is to define a knock indicator in a
single cylinder spark ignition engine, taking into account
gas composition and engine tunings. Two main points have
been tackled in this study:
† Capability of the MN to characterise the tendency to
knock of gaseous fuels, from different critical parameters
(equivalence ratio, volumetric efficiency, spark
advance);
† Measurement of the methane number requirement
(MNR) of the engine from different engine para-
meters (equivalence ratio, volumetric efficiency,
spark advance) and comparison with the results of
Table 2.
The influence of temperature on knock limited spark
advance is also presented in order to outline the temperature
dependence of all the results.
2. Material and methods
Test bench. The test bench is composed of a naturally
aspirated single-cylinder SI gas engine of Lister-Petter
make. Table 3 gives the main characteristics of this
engine. The engine is connected to an electrical generator,
which maintained the speed at 1500 rev/min (to generate
50 Hz electrical power). Engine and main measurements
are presented in Fig. 5. The engine is based on a DI
Diesel engine, with bowl chamber and flat-faced cylinder
head. It is adapted to SI operation by reducing its
compression ratio and by connecting a spark plug in the
injector location. The data acquisition system of cylinder
pressure is composed of
† Sensor AVL QH32D, gain 25.28 pC/bar, range
0–200 bar;
† Piezo amplifier AVL 3066A0, gain 400 pC/V with no
pressure reference;
† Piezo resistive pressure sensor fixed inside the inlet
manifold, range 0–2.5 bar.
The acquisition frequency of the in-cylinder pressure is
90 kHz. It corresponds to a resolution of 0.1 CA.
Fig. 4. Relation between IM and IO for gas mixtures [52] and pure gases
[47,53].
1 Average value calculated from the effect of the variation of MN on
KLST and KLIT.2 Average value calculated from the mean effect of the variation of
þ18CA of spark advance on ON.
C. Rahmouni et al. / Fuel 83 (2004) 327–336 331
Exhaust gases are analysed by a COSMA Cristal 500
analyser. Experiments were carried out with synthesised
natural gas fuel. A matrix of nine pure gases (CH4, C2H6,
C3H8, C4H10, CO2, N2, O2, H2, CO) simulates various
natural gas compositions accounting for the main constitu-
ents of natural gas encountered in stationary applications.
The gas composition was determined from the mass flow
rates and checked by gas chromatography.
Knock rating of gaseous fuels is determined by varying
the engine spark advance unlike Leiker [3] who used the
compression ratio. Authors have made this choice because
spark advance is the main adjustable parameter in stationary
gas engine.
Determination of knock limited spark advance (KLSA).
The knock limit is determined by increasing gradually the
SA until the occurrence of knock (Fig. 2), materialized by
oscillations of the in-cylinder pressure. The other engine
parameters (equivalence ratio and volumetric efficiency)
must remain constant during this operation. The knock limit,
corresponding to the onset of pressure oscillations in the
cylinder, is set using the PKC [3,6]. The threshold of knock
was fixed at 50% of knocking cycles (Fig. 3). We can notice
that the threshold of knock, fixed at 50% PKC, gives a
knock limit close to that obtained by the MAPO analysis
(Fig. 2).
3. Results and discussion
Experiments were divided into two distinct stages: First,
a matrix of different gas composition was established [54].
The service methane number (SMN) [3] of these gases is
measured. The relation between the SMN and the standard
MN calculated by the METHANE software developed by
AVL is performed. Finally, various specified operating
conditions were tested to calculate the MNR of the engine.
This allows us to obtain the variation of the MNR from
engine parameters. The methodologies for the determi-
nation of the SMN and the MNR are also described in Ref.
[54]. Table 4 gives the values of the engine parameters
considered. The fuel used is the synthesised Abu Dhabi gas,
whose composition is 82% of methane, 16% of ethane and
2% of propane. The MN of this gas is 69.1 (AVL).
Measurement of the SMN using spark advance as critical
parameter. The measurement of the SMN, for different
gaseous fuels, is based on a test gas matrix suggested by the
work carried out by Klimstra [5]. This database includes 21
gases of different compositions (binary, ternary gases or
more) [54]. Technical limitations on the mass flow rates
leaded in a limited range of pure gases as given in Ref. [54].
Despite these limitations, a large range of SMN has been
covered, from 70 to 110. Results are given in Fig. 6. A
comparison between the SMN, determined with spark
advance as critical parameter, and the standard MN,
determined in a CFR engine with compression ratio as
critical parameter, is made (Fig. 6). The link between knock
Fig. 5. Test rig and main sensor locations.
Table 3
Engine technical features
Type Spark ignition
Bore 95.3 mm
Stroke 88.9 mm
Displacement 633 cm3
Compression ratio 12.37:1
Cooling system Forced air circulation
No. of cylinders One
Table 4
Operating conditions for the first stage
T 288, 293, 298 and 310 K
f 0.7, 0.8 and 0.9
hv 60 and 70%
Fig. 6. KLSA versus SMN and standard MN (AVL) for the 21 gases of the
test matrix.
C. Rahmouni et al. / Fuel 83 (2004) 327–336332
in engines and knock resistance of fuels is here highlighted.
We can thus notice that SMN, as well as MN, is a good
indicator for knock resistance of gaseous fuels (reflected by
KLSA), whatever the engine used as reference.
Measurement of the SMN using equivalence ratio and
volumetric efficiency as critical parameters. SMN can also
be determined by varying the equivalence ratio or the
volumetric efficiency (other parameters remaining constant)
using the same methodology as for the spark advance. From
Table 5, the SMN is determined for different critical
parameters. Thus, let us consider a gas of given compo-
sition. For an equivalence ratio of 0.8 and a volumetric
efficiency of 70%, the KLSA is 18.88CA and for a
volumetric efficiency of 70% and a spark advance of
158CA, the KLER is 0.86. Whatever critical parameter
chosen, the SMN remains 83. These results ascertain the
standard methodology used to determine knock rating of
gaseous fuels and show that the critical parameters chosen
have no effects on the measured SMN. As a consequence,
the work carried out on knock rating of gaseous fuels by
Leiker et al. [3] (KLCR) and Attar and Karim [6] (KLSA
and KLCR) should give similar results. Besides, the
determination of SMN is independent of the engine settings
considered.
Measurement of the MNR. By definition, at knock limit,
the MNR is equal to the SMN of the consumed gas. Each
engine tuning is associated with a MNR. For its determi-
nation, the engine is supplied with a reference blend of
methane and hydrogen. At each engine setting, the
volumetric percentage of hydrogen is modified so as to
reach the knock limit, corresponding to 50% of knocking
cycles. The MNR then corresponds to the volumetric
percentage of methane in the reference blend.
An experimental plan was established in order to
determine the effect of each engine parameter on the
MNR. Two levels of variation are fixed. The mean effect of
each engine parameter was calculated to determine the
influent factors on the MNR. The plan quantifies the main
effects and their interactions on the MNR, which then results
in a regression model capable of taking into account MNR
variation. The levels of variation and the range of validation
of the engine settings considered are given in Table 6. We
are looking for a relation between the engine parameters and
the gas composition in order to define a global index to run
the engine at knock limit.
Predictive model of the MNR. The mean effect of each
engine parameter is obtained thanks to an experimental plan
[56]. Table 7 gives the mean effect of each engine
parameters and its interactions.
By arbitrarily fixing a significant threshold of 1 point for
the MNR, we noticed that the mean effect of each parameter
taken alone is more significant than the effect of double
interactions. The contribution of each parameter is fairly the
same. The effect of double interactions is also significant.
Interactions 3 to 3 are not significant. A correlation, between
the MNR, the main factors and their double interactions, is
established
MNR ¼ C1h2v þ C2f2 þ C3SA2 þ C4hvfþ C5hvSA
þ C6fSA þ C7hv þ C8fþ C9SA ð3Þ
where Ci are coefficients obtained by the least square
method [54], where
C1 ¼ 25:9 £ 1022; C2 ¼ 2:0 £ 102
; C3 ¼ 23:7 £ 1023;
C4 ¼ 2:4; C5 ¼ 10:3 £ 1022; C6 ¼ 13:0; C7 ¼ 6:0;
C8 ¼ 214:7 £ 102; C9 ¼ 214:1
The global behaviour of the MNR, displayed in Fig. 7, is
well predicted by correlation (3). The mean absolute error is
then lower than 3 MNR units and the global trend of MNR
variation is satisfactory for our application. In order to
obtain a more general relation, it is necessary to extend the
range of variations of the engine parameters.
Link between SMN and engine parameters. In order to
find a relation between engine parameters and gas
composition, the effect of a variation of composition
(here, SMN) on critical parameters such as the KLSA, the
equivalence ratio and the volumetric efficiency is brought
out in Tables 8 and 9. A variation of þ10 SMN units
corresponds to a variation contained between þ2 and þ4
CA in term of KLSA, a variation of þ0.029 in term of
equivalence ratio and a variation of þ5.5 points in term of
Table 5
SMN of Algerian gas for various critical engine parameters
r f SA SMN
KLSA 70 0.8 18.8 83
70 0.7 30.8 83
KLER 70 0.86 15 83
70 0.74 25 83
KLVE 77.8 0.70 25 82
Table 6
Levels of variation (experimental plan) and range of validation (corre-
lation) of engine parameters
Engine parameters Levels of variation Range of validation
T (K) 298 298
SA 10 and 158CA 10–308CA
f 0.8 and 0.9 0.7–0.9
hv 60 and 70% 60–70%
Table 7
Mean effect of each engine parameter and its interactions on MNR
Factor Main factors Interactions
SA f hv SAf SAhv fhv SAfhv
Mean effect 8.0 8.8 7.0 2.0 1.8 1.5 20.8
C. Rahmouni et al. / Fuel 83 (2004) 327–336 333
volumetric efficiency. From Table 2, other authors [3,4,6,
28,33,46,49–51] have quantified the effect of a variation of
þ10 MN units on critical engine parameters and noted that
the corresponding variation in term of KLSA ranges
between þ1 and þ6 CA. These values depend on the
operating conditions according to authors and on the kind of
engine used. The values obtained from the Lister-Petter
engine are similar to those obtained by Leiker et al. [3] or
Attar and Karim [6], which ascertains the methodology
employed using KLSA.
Influence of ambient temperature on KLSA. The effect of
ambient temperature on the occurrence of knock is studied
for various engine settings. For each temperature, the engine
parameters are fixed. The SA is modified until KLSA is
reached.
Measurements show that temperature has an appreciable
effect on KLSA whatever engine settings. An increase of the
ambient temperature leads to a decrease in KLSA (Figs. 8
and 9). Knock appears much earlier when the equivalence
ratio and temperature are important. The dependence of
KLSA, in term of relative variation ðDrKLSAÞ; with the
absolute variation of ambient temperature ðDTÞ can be
observed in Fig. 10. It can be noted that DrKLSA is
proportional to DT whatever is the engine tuning. Thus,
an increase of the ambient temperature leads to a decrease of
KLSA. Ambient temperature has a double effect on the
inner charge temperature:
† First, it directly changes the air/fuel mixture temperature;
† Second, it has an influence on wall heat transfer.
The different tests show that:
† Temperature has a great role in the variation of the
KLSA. When temperature increases, KLSA decreases;
† The error on KLSA is estimated to be about ^0.5 CA
and the error on the ambient temperature to be about
^0.2 8C. The slope of the curve is 21.7. An error of
2.2% was calculated on this coefficient;
Fig. 7. Measured MNR versus calculated MNR for 15 engine tunings.
Table 8
Engine settings considered for the measure of the effect of a þ10 SMN
units variation on critical parameters
Engine set Tuning No. 1 Tuning No. 2 Tuning No. 3 Tuning No. 4
SA 10 15 10 25
w 0.8 0.8 0.9 0.7
hv 70 70 70 70
KLSA 18.8 18.8 12.6 30.8
KLER 1.02 0.858 .1.05 0.743
KLVE .75.7 .77 .76 78.1
MNR 52.7 70 71 68
SMN 83 83 83 83
Table 9
Effect of a þ 10 SMN units variation on critical engine parameters
Tuning No. 1 Tuning No. 2 Tuning No. 3 Tuning No. 4
KLSA 2.98CA 2.98CA 2.28CA þ3.98CA
KLER 0.073 0.045 – 0.029
KLVE – – – 5.5 points
Fig. 8. Effect of the ambient temperature on KLSA ðhv ¼ 70%Þ:
Fig. 9. Effect of the ambient temperature on KLSA ðhv ¼ 60%Þ:
C. Rahmouni et al. / Fuel 83 (2004) 327–336334
† A þ10 8C increase in the temperature between two
tests corresponds to a decrease of approximately
17 ^ 0.4% on the relative variation of the KLSA.
Depending of the KLSA, one obtains a variable trend
ranging between 21.5 K/8CA (for very low knocking
conditions) and 210 K/8CA, reflecting a noticeable influ-
ence of the intake temperature compared to other studies
(25 to 214 K/8CA). It can be explained by the double
influence of the ambient air also used to cool the engine.
4. Conclusions
1. Knock has been studied in a natural gas fuelled SI engine.
2. A database of 21 different gases was established and their
SMN was measured. We calculated the SMN of gases,
using Leiker’s methodology by varying SA.
3. A remarkable result is that the SMN is a very good
indicator of knock rating of gaseous fuels.
4. The measured SMN is highly correlated with the MN,
derived from the AVL software METHANE. MN is also
a good indicator for the knock rating of gaseous fuels.
5. An experimental plan was established to obtain the
influence of engine parameters (equivalence ratio, volu-
metric efficiency and spark advance) on MNR. This latter
was determined from 15 different engine tunings.
6. A correlation between the MNR and the engine
parameters was deduced from experimental data using a
least square method. Optimal operation of the engine
(knock-free operation) is then possible by adapting engine
parameters to variation of gas quality.
7. The determination of the SMN was proved to be
independent of the critical parameters chosen.
8. Experiments confirm the role of temperature and highlight
an influence twice as much important in the case of a
cooled air engine.
9. This work should be expanded for other gas engines in
order to confirm the results and to control knock whatever
engines.
References
[1] BT104. Gaseous combustibles and combustion principles. Gaz de
France; 1993. [in French].
[2] Klimstra J, Hernaez AB, Bouwman WH, Gerard A, Karll B, Quinto V,
Roberts GR, Schollmeyer H-J. Classification methods for the knock
resistance of gaseous fuels: an attempt towards unification. ASME
(ICE) Fall Tech Conf 1999;33-1:127–37.
[3] Leiker M, Christoph K, Rankl M, Cartellieri W, Pfeifer U. Evaluation
of antiknocking property of gaseous fuels by means of methane
number and its practical application to gas engines. ASME Paper No.
72-DGP-4. p. 1–16.
[4] Ryan III TW, Callahan TJ, King SR. Engine knock rating of natural
gases-methane number. ASME, J Engng Gas Turbines Power 1993;
115:769–76.
[5] Ryan IIITW, Callahan TJ, Buckingham JP, Kakockzi RJ, Sorge G.
Engine knock rating of natural gases-expanding the methane number
database. Proceeding of the 18th Annual Fall Technical, Conference
of ASME, ICE-vol. 27-4. International Combustion Engine Division;
1996. p. 59–64.
[6] Attar A, Karim GA. Knock rating of gaseous fuels. Fall Tech Conf
ASME 1998;31-3:41–7. Paper No. 98-ICE-149.
[7] Bade Shrestha SO, Karim GA. Predicting the effects of the presence of
diluents with methane on spark ignition engine performance. Appl
Therm Engng 2001;21:331–42.
[8] Brecq G, Bellettre J, Tazerout M, Muller T. Knock prevention of gas
SI engine by adjunction of inert gases to the fuel. Proceedings of
IJPGC (International Joint Power Generation Conference) of the
ASME (2002-26112); June 24–26, 2002. ISBN 0-7918-3602-9.
[9] Le Corre O, Brecq G, Tazerout M. Thermoeconomic analysis based
on energy structure for CHP. Appl Therm Engng 2002;22:561–6.
[10] Kalghatgi GT. Combustion chamber deposits and knock in a spark
ignition engine: some additive and fuel effects. SAE Technical Paper
No. 962009; 1996.
[11] Heywood JB. Internal combustion engine fundamentals. New York:
McGraw-Hill; 1988.
[12] Millo F, Ferraro CV. Knock in SI engines: a comparison between
different techniques for detection and control. SAE Technical Paper
No. 982477; 1998.
[13] Syrimis M, Assanis DN. The effect of the location of knock initiation
on heat flux into a SI combustion chamber. SAE Technical Paper No.
972935; 1997.
[14] Syrimis M. Characterisation of knocking combustion and heat transfer
in a spark ignition engine. PhD Thesis. Rice University (1990) and
University of Illinois (1992); 1996.
[15] Trapy J. Les transferts thermiques dans le moteur a allumage
commande: conception et mise au point d’un modele specifique du
coefficient d’echange gaz-parois (Heat transfer in SI engines:
conception and development of a specific model for wall heat transfer
coefficient). SFT (Societe Francaise des Thermiciens); 1985.
[16] Winch RF, Mayes FM. A method for identifying preignition. SAE
Trans 1953;61:453–68.
[17] Collings N, Dinsdale S, Eade D. Knock detection by means of the
spark plug. SAE Technical Paper No. 860635; 1986.
[18] Auzins J, Johansson H, Nytomt J. Ion-gap sense in misfire detection,
knock and engine control. SAE Technical Paper No. 950004; 1995.
[19] Asano M, Kuma T, Kajitani M, Takeuchi M. Development of a new
ion current combustion control system. SAE Technical Paper No.
980162; 1998.
Fig. 10. Effect of ambient temperature on DrKLSA for the Abu Dhabi gas
(MN ¼ 69.1).
C. Rahmouni et al. / Fuel 83 (2004) 327–336 335
[20] Eriksson L, Nielsen L, Nytomt J. Ignition control by ionisation current
interpretation. SAE Technical Paper No. 960045; 1996.
[21] Schneider D, Chia Lai M. An investigation of the impact of cycle-to-
cycle variations on the ionic current signal in SI engines. SAE
Technical Paper No. 2000-01-1943; 2000.
[22] Schmillen KP, Rechs M. Different methods of knock detection and
knock control. SAE Technical Paper No. 910858; 1991.
[23] Draper CS. The physical effects of detonation in a closed cylindrical
chamber. Technical Report 493, NACA; 1935.
[24] Pauzinauskas PV. Examination of methods used to characterise
engine knock. SAE Technical Paper No. 920808; 1992.
[25] Burgdorf K, Denbratt I. Comparison of cylinder pressure based knock
detection methods. SAE Technical Paper No. 972932; 1997.
[26] Brecq G. Contribution a la caracterisation du cliquetis dans les
moteurs a gaz fonctionnant en melange pauvre (Contribution to the
thermodynamic characterisation of knock for gas engines: application
to new methods of detection). PhD Thesis. Universite de Nantes; 2002
[in French].
[27] Checkel MD, Dale JD. Testing a third derivative knock indicator on a
production engine. SAE Technical Paper No. 861216; 1986.
[28] Russ S. A review of the effect of engine operating conditions on
borderline knock. SAE Paper No. 960497; 1996.
[29] Chun KM, Kim KW. Measurement and analysis of knock in a SI
engine using the cylinder pressure and block vibration signals. SAE
Technical Paper No. 940146; 1994.
[30] Thomas JR, Clarke DP, Collins JM, Sakonji T, Ikeda K, Shoji F,
Furushima K. A test to evaluate the influences of natural gas
composition and knock intensity. ASME ICE 1994;22:149–59.
[31] Dubel M, Schmillen K, Wackertapp H. Influence of gas composition on
the knocking behaviour of spark-ignited gas engines. In International
Gas Research Conference Transactions; 1983. p. 952–63.
[32] Lee JH, Hwang SH, Lim JS, Jeon DC, Cho YS. A new knock-detection
method using cylinder pressure block vibration and sound pressure
signals from SI engine. SAE Technical Paper No. 981436; 1998.
[33] Westin F, Grandin B, Angstrom HE. The influence of residual gases
on knock in turbocharged SI-engines. SAE Technical Paper No. 2000-
01-2840; 2000.
[34] Brunt MFJ, Pond CR, Biundo J. Gasoline engine knock analysis using
cylinder pressure data. SAE Technical Paper No. 980896; 1998.
[35] Checkel MD, Dale JD. Computerised knock detection from engine
pressure records. SAE Technical Paper No. 860028; 1986.
[36] Ando H, Takemura J, Koujina E. A knock anticipating strategy basing on
the real-time combustion mode analysis. SAE Paper No. 890882; 1989.
[37] Dhall SN, Beans EW. Correlation of knock with engine parameters
for ammonia/nitrous oxide mixtures. SAE Technical Paper No.
912360; 1991.
[38] Ortmann S, Rychetsky M, Glenser M, Groppo R, Tubetti P, Morra
G. Engine knock estimation neural networks based on a real-world
database. SAE Technical Paper No. 980513; 1998.
[39] Ferarro CV, Marzano M, Nuccio P. Knock-limit measurement in high
speed SI engines. SAE Technical Paper No. 850127; 1985.
[40] Najt PM. Evaluating threshold knock occurrence and intensity in
multicylinder engine. SAE Technical Paper No. 820074; 1982.
[41] Ho SY, Kuo TW. A hydrocarbon autoignition model for knocking
combustion in SI engines. SAE Technical Paper No. 971672; 1997.
[42] Abu Qudais M. Exhaust gas temperature for knock detection and
control in spark ignition engine. Energy Conversion Mgmt 1996;37:
1383–92.
[43] Goto S, Itoh Y. Development of lean burn high-output spark-ignited
gas engines (experimental study in lean gas engines). In: Nippon
Kikai Gakkai Ronbunshu, editor. Transactions of the Japan Society of
Mechanical Engineers, Part B, vol. 63.; 1997. p. 1055–61.
[44] Brecq G, Bellettre J, Tazerout M. A new indicator for knock detection
in gas SI engines. Int J Therm Sci 2003;42(5) S23–S32.
[45] Worret R, Bernhardt S, Schwarz F, Spicher U. Application of different
cylinder pressure based knock detection methods in spark ignition
engines. SAE Technical Paper No. 2002-01-1668; 2002.
[46] Schiffgens HJ, Endres H, Schrey E, Wackertapp H. Concept for the
adaptation of SI engines to changing methane number. Trans ASME, J
Engng Gas Turbine Power 1994;116:733–9.
[47] Dimpelfeld PM, Foster DE. The prediction of auto-ignition in a spark-
ignited engine. SAE Technical Paper No. 841337; 1984.
[48] Ryan WT, Callahan JT. Effects of gas composition on engine
performance and emissions. Topical Report GETA 91-13, NTIS,
Southwest Research Institute, San Antonio, TX; December 1991.
[49] Ho S, Amlee D, Johns R. A comprehensive knock model for
application in gas engines. SAE Technical Paper No. 961938;
1996.
[50] Faure E, Montagne X. ORI: assessment methodology and influence of
engine running parameters. SAE Technical Paper No. 972933; 1997.
[51] Douaud A. Elements d’analyse du cliquetis et de ses effets (Elements
for the analysis of knock and its effects). Revue l’Inst Francais Petrole
(IFP) 1983;38(5).
[52] Kubesh J, King SR, Liss WE. Effect of gas composition on octane
number of natural gas fuels. SAE Technical Paper No. 922359; 1992.
[53] Daverat P. Moteurs a gaz et cogeneration (Gas engines and
cogeneration). Revue Generale de Thermique No. 383; 1993.
[54] Brecq G, Rahmouni C, Taouri A, Tazerout M, Le Corre O. Service
methane number as a mean to avoid knock in natural gas fuelled spark
ignition engines. Salzburg, Austria: Internal Combustion Engine
Division of the ASME; May 11–14, 2003. ICES2003-573.
[55] Brecq G, Ramesh A, Tazerout M, Le Corre O. An experimental study
of knock in a natural gas fuelled spark ignition engine. SAE Technical
Paper No. 2001-01-3562; 2001.
[56] Sado G, Sado M-C. Les plans d’experiences: De l’experimentation a
l’assurance qualite (Experimental plans). AFNOR Technique; 1991.
ISSN: 0297-4827.
C. Rahmouni et al. / Fuel 83 (2004) 327–336336
