AN INFLUENCE OF METHANE/HYDROGEN PROPORTION IN FUEL BLEND ON EFFICIENCY OF CONVERSION ENERGY IN SI ENGINE

Abstract

The relations between methane/hydrogen proportions in fuel blend are presented in this paper. The research cycle carried out contains results of dynamometer chassis tests complemented with mathematical model calculations. An object of X16SZR engine installed in Opel Astra I was investigation. The engine has been equipped with additional CNG feeding system where fuel is being injected into intake manifold under low pressure. 8 fuel blends were tested with variable methane/hydrogen volume proportion (%): 100/0, 95/5, 90/10, 85/15, 80/20, 70/30, 60/40 and 50/50. The feeding and ignition systems were controlled by nominal drivers. In every measuring series engine was tested in the following steady states: on idle, high speed without load and full power at discrete variable speed in range 1500…3500 rpm. The main aspect of the analysis was to identify the influence of hydrogen share on engine parameters such power, fuel consumption, in-cylinder pressure, temperature and exhaust gas composition. Very significant ecological fact possibility of CO 2 emission reduction has been identified. Result of increasing content of hydrogen in fuel mixture is engine knocking. Analysis carried out on the basis of results allowed it to the point on methane/hydrogen proportion in fuel blend considering a total efficiency, emission and heat flux in parts of combustion chamber in engine.

Full text

Journal of KONES Powertrain and Transport, Vol. 19, No. 3 2012
AN INFLUENCE OF METHANE/HYDROGEN PROPORTION
IN FUEL BLEND ON EFFICIENCY
OF CONVERSION ENERGY IN SI ENGINE
Marek Flekiewicz, Grzegorz Kubica
Silesian University of Technology
Faculty of Transport
Zygmunta Krasinskiego Street 8, 40-019 Katowice, Poland
e-mail: marek.flekiewicz@polsl.pl
grzegorz.kubica@polsl.pl
Abstract
The relations between methane/hydrogen proportions in fuel blend are presented in this paper. The research cycle
carried out contains results of dynamometer chassis tests complemented with mathematical model calculations. An
object of X16SZR engine installed in Opel Astra I was investigation. The engine has been equipped with additional
CNG feeding system where fuel is being injected into intake manifold under low pressure. 8 fuel blends were tested
with variable methane/hydrogen volume proportion (%): 100/0, 95/5, 90/10, 85/15, 80/20, 70/30, 60/40 and 50/50.
The feeding and ignition systems were controlled by nominal drivers. In every measuring series engine was tested in
the following steady states: on idle, high speed without load and full power at discrete variable speed in range
1500…3500 rpm. The main aspect of the analysis was to identify the influence of hydrogen share on engine
parameters such power, fuel consumption, in-cylinder pressure, temperature and exhaust gas composition. Very
significant ecological fact possibility of CO2 emission reduction has been identified. Result of increasing content of
hydrogen in fuel mixture is engine knocking. Analysis carried out on the basis of results allowed it to the point on
methane/hydrogen proportion in fuel blend considering a total efficiency, emission and heat flux in parts
of combustion chamber in engine.
Keywords: methane/hydrogen blend, low-carbon fuel, total efficiency, SI engine
1. Introduction
Application of methane blended with hydrogen as a fuel in SI engine can be considered a next
step toward implementation of universal clean energy sources. In terms of the low emission
hydrogen is a perfect fuel, however many mechanical problems still exist. In the current situation
of energy-fuel industry natural gas is very important fuel. Significant economic-ecological
advantages of this fuel are stimulating constant progress, both in the area of its application as an
alternative fuel considering together the infrastructure and feeding system. However, in SI engines
the natural gas is still considered an alternative. The engine construction and operating parameters
nominally are being designed for petrol. Differences in the combustion cause certain disadvantages
in case of feeding with the natural gas. A basic difference is extension of the period of flame
development. However, in the second phase the speed of energy release is increasing while
air/petrol mixture combustion is proceeding in this period rather evenly (Fig. 1). The second
important difference is a lower calorific value (in relation to petrol) of air/methane mixture. In
a consequence of these differences in-cylinder pressure course changes (IMEP and engine power
are lower), the temperature of exhaust gases is rising (NOx emission is greeter). Presented results
are based exactly on the existing agreement, that methane is a main component of natural gas
(usually more than 96%). The addition of hydrogen is giving the possibility of obtaining to the
higher efficiency of the conversion energy, and the considerable reduction of CO2 emission.
Preliminary tests conducted by authors [2-4], as well as in other research centres [5-9], confirmed
the rightness of this thesis.
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Fig. 1. Sample differences in the course of the in-cylinder pressure and the function of heat release for petrol and gas
fuels. Engine speed - 2500rpm, WOT – 100%

2. An investigation
2.1. Object and range of research
A 1600ccm 4-in line cylinder X16SZR engine was the object of investigation. The engine
has been equipped with multipoint simultaneous CNG injection system. A car with tested
engine has been placed on dynamometer chassis. The test-bench has been additionally
equipped with the in-cylinder pressure measurement and the registration system. Nominal
engine regulation parameters remained unvaried during the tests, except for the EGR system,
which has been disabled.
Conducted tests included measurement series of engine performance parameters, individual for
each of the fuels. Each series included examinations of engine working at steady conditions: on
idle, without load with speed c.a. 4000rpm and at full load with speed varying from 1000 to
3500rpm, increasing discretely about 500rpm.
2.2. An influence of the hydrogen share on the quantity of energy delivered in the filling
process
Stream of energy delivered to the cylinder, in case of applying different fuels, depends on the
calorific value and the density of A/F mixture, which determines mass of charge in the given
cycle/cylinder.
Primary data of fuel blends prepared for tests has been shown in the Tab. 1. Whereas change of
the lower calorific value of fresh charge Wu, depending on the hydrogen share, presented in the
form of a graph (Fig. 2), was calculated according to the following relation:
a
d
uL
W
Wu
O
1. (1)
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An Influence of Methane/Hydrogen Proportion in Fuel Blend on Efficiency of Conversion Energy in SI Engine
Tab. 1. Characteristic parameters of tested fuels
CH4 / H2 mass proportion [%] Wd [MJ/kg] La [kgA/kgF] ȡ [kg/m3]
100/0 50.050 17.482 0.717
95/5 50.430 17.596 0.685
90/ 10 50.910 17.720 0.653
85/ 15 51.435 17.860 0.622
80/ 20 52.016 18.010 0.590
70/ 30 53.388 18.370 0.526
60/ 40 55.137 18.826 0.463
50/ 50 57.442 19.424 0.400
Fig. 2. Lower heating value of A/F mixture in function of hydrogen share
2.3. Transformations inside engine cylinder
Results registered during stand tests were used for calculation with the application of the
mathematical model of combustion. The model calculations are based on equations of energy
balance in a closed combustion chamber and were done on the base of the registered in-cylinder
pressure course.
The model calculations are supplementary to conducted measurements. Graphs presented
below (Fig. 3) show the influence of the hydrogen content in the fuel on basic parameters, which
describe the combustion process in the investigated engine.
2.4. The results of power on wheels measured
Power measured on wheels Pw is one of main functional parameters. The measurements were
made on chassis dynamometer at the engine set speeds for WOT (Fig.4). For the purposes of
engine output power estimation, it is necessary to take into consideration transmission efficiency.
For configuration of transmission in the investigated car a correction ratio of k=0.946 (according
to EEC standard) has been assumed.
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Fig. 3. The characteristic parameters of energy conversion in depend of variable methane /hydrogen proportion.
Engine speed - 2500rpm, WOT – 100%

Fig. 4. Power on wheels measured in steady operating, in relation to variable hydrogen share
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An Influence of Methane/Hydrogen Proportion in Fuel Blend on Efficiency of Conversion Energy in SI Engine
3. Discussion
3.1. Differences in heat release process
A chemical energy of the charge closed in a combustion chamber is released during
combustion process. The speed and the energy profiles are closely dependent on the fuel type.
General aim of adding hydrogen to methane is to minimize disadvantageous occurrences, which
are accompanying the combustion of A/F mixture created on the basis of the natural gas or pure
methane. Because of the differences of selected properties of methane and hydrogen, an
improvement of the conditions for the initiation of a flame and shortening the period of charge
heating are expected. Minimum ignition energy of hydrogen is 0.02 mJ; and of methane 0.28 mJ.
It can also be noticed that, speed of flame spread of hydrogen is 2.9 m/s; and of methane 0.38 m/s
[1]. Taking into consideration the increase of lower calorific value of fresh mixture (Fig. 2) also an
overall quantity of the energy released in combustion process increases. Changes of the duration of
the combustion period depending on the amount of the hydrogen share were appointed on the basis
of tests results obtained at fixed speeds. The chart below (Fig. 6) presents the duration of the main
phase of the combustion process (10 %< MFB<90%).
3.2. Temperature and exhaust gas composition
The basic factors that significantly influence the composition of the exhaust gases are the fuel
composition as well as temperature of the combustion process and physico-chemical
transformation occurring right after. A very significant fact related to the use of methane/
hydrogen blends is the possibility of a significant CO2 emission reduction (Fig. 5) [3]. This is due
to the reduced share of the carbon in the fuel through the introduction of the hydrogen. In tests that
have been carried out an additional simulation has been completed, which led to appointing the
course of the temperature of the gas in a closed combustion chamber, from the moment of the intake
valve closure until exhaust valve opening. The temperature of the gas at that point (open of the
exhaust valve) marked Tex, and named temperature of the exhaust gases leaving the combustion
chamber. Direction of changes of this temperature allows forecasting the change of shares of
individual elements in the emitted exhaust gases, including emission of NOx. Obtained Tex values
have been shown in the graph (Fig. 7). Analysis of presented relations shows the possibility to
reduce exhaust gas temperature for a certain proportion of the composition of fuel blend.

Fig. 5. The level of emission CO2 in depend on H2 share, compared with Petrol and CNG
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M. Flekiewicz, G. Kubica

Fig. 6. Combustion duration (10%<MFB<90%) in function
of H2 share for fixed engine speed
Fig. 7. An influence of H2 share on temperature of the
exhaust gases leaving the combustion chamber

Fig. 8. Changes of ge obtained for variable fuel composition and speed of engine
3.3. Efficiency of energy conversion
An individual fuel consumption ge [g/kWh] is one of universal indicators representing the level
of the efficiency of energy conversion in the IC engine. The value of this indicator has been
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An Influence of Methane/Hydrogen Proportion in Fuel Blend on Efficiency of Conversion Energy in SI Engine
calculated on the basis of the results of the measurements of fuel consumption and engine power
obtained in the course of executing stand tests. Measurements of fuel consumption were done in
a weight analysis mode, with the use of an external fuel tank placed on an electronic weight
platform. Registration of fuel mass loss was made in the engine steady operating point, with the time
coordination. Obtained results made it possible to estimate ge in function of fuel composition
(Fig. 8). Presented results show that ge decreases with the increase of hydrogen content in the fuel,
thus increases the effective efficiency of engine, and therefore becomes inversely proportionate.

3.4. Limitations of hydrogen in the fuel
Limitations of methane enrichment with hydrogen are connected with knocking combustion. The
presence of this phenomenon is visible in recorded signal of the in-cylinder pressure and becomes
audible in emitted sound. What can also be noticed is variation in the rate of pressure rise during the
combustion process. The sudden increase in the maximum value of this parameter can be observed at
maximum engine power and speed above 3000rpm, for blends with more than 30% of hydrogen (Fig. 9).
Fig. 9. The maximum value of the rate of pressure in function of the H2 share in the fuel, Ȝ=1.00
4. Conclusions
In the summary of the research process and analysis of the obtained results, it can be concluded that:
1. Increasing the content of hydrogen in a hydrocarbon-originated gas fuels (e.g. methane, natural
gas), significantly affects the improvement of the efficiency of energy conversion in the SI
engine, without interfering with the original feeding and ignition systems algorithms.
2. Basic changes in the course of the heat release function are ensued the shorten period of
burning initiation and increase the amount of energy supplied to the cylinder in the filling
process, due to the higher calorific value of charge.
3. As a result of these changes higher engine power and reduction of ge can be achieved. An
effective increase in power on wheels has been measured for fuel blends containing: 30% and
40% of hydrogen, which ranged from 11% (1500 rpm) to 3% (3500 rpm). While ge decreased
respectively from 16% to 8% in this range of speed.
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M. Flekiewicz, G. Kubica
4. Moreover, because of the necessity of global reduction of the greenhouse gas emissions, it is
important to significantly reduce CO2 emission. In comparison with the petrol, the level of
emissions has been reduced by 37%, for a blend of 70%CH4/30%H2.
5. The changes of course and the duration of combustion process, caused by a greater hydrogen
share in fuel, influence as well the temperature of charge. It has been proved that earlier
occurrence of maximum value, lowers exhaust gases temperature, which determines the
content of toxic components.
6. Further increasing of hydrogen share in the fuel, at nominal settings, is limited because of the
presence of signs of knocking combustion at full load of engine. Therefore, further research
should be primarily oriented on estimation of a reasonable proportion of methane and
hydrogen, and then on the optimization of settings, in order to eliminate negative phenomena’s.
Abbreviations
ge Individual fuel consumption
IC Internal combustion
CNG Compressed Natural Gas
IMEP Indicated Mean Effective Pressure
ʄAir excess ratio
Wu Mass heating value of stoichiometric mixture
Wd Mass heating value of fuel
La Stoichiometric air to fuel ratio
ȡ Density of fuel
Pw Wheel power measured
Tex Temperature of exhaust gases at opening exhaust valve
MFB Mass Fraction Burned
WOT Wide-open throttle.
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