HYDROGEN-FUELED SPARK IGNITION ENGINE--ITS PERFORMANCE AND EXHAUST EMISSION CHARACTERISTICS
By
PRITHVI RAJ KHAJURIA
A Thesis
aubmitted in fulfilment of the requirements of the degree of
DOCTOR OF PHILOSOPHY in the Faculty of engineering
Department of Mechanical Engineering
INDIAN INSTITUTE OF TECHNOLOGY, NEW DELHI (INDIA)
July, 198,1
ii
CERTIFICATE
I, the undersigned, certify that the thesis entitled, 'Hydrogen-Fueled Spark Ignition Engine - Its Performance and Exhaust Emission Characteristics' which is being sub- mitted by Mr. P.R. Khajuria, in fulfilment of the require- ments fol.‘ , the award of the degree of 'Doctor of Philosophy' in the Faculty of Engineering of the Indian Institute of
Technology, New Delhi, is a record• :of candidate's own bona- fide research work carried out under my guidance. The matter embodied in this thesis has not been submitted in part or full, elsewhere for the award of any degree.
(Dr. H.B.athulf-cT-- Professor and He ad
Department of Mechanical Engineering, Indian Institute of Technology, Delhi.
ACKNOWLEDGEMENTS
The author is extremely grateful to Dr. H.B. Mathur, Professor and Head of Mechanical Engineering Department, for his able guidance, encouragement, fruitful suggestions and helpful attitude during the course of this research work.
The valuable help extended by Dr. M.K. G. Babu of Centre of Energy Studies during computational and experimental work is gratefully acknowledged.
Sincere thanks are due to the technical staff of the 'Engines and Unconventional Fuels Laboratory' of Centre of Energy Studies and the 'I.C. Engines Laboratory' of Mechanical Engineering Department for their valuable assistance during
experimental work. Thanks are also due to Mr. V.P. Gulati for typing the manuscript and to Mr. N.K. Choudhary for making drawings.
The financial assistance made available under Q.I.P. by the Ministry of Education, Government of India, is gratefully acknowled ged.
Finally, the author wishes to offer sincere gratitude and appologies to his family for patiently enduring certain
difficulties wkiich resulted from his long absence from home for completing this research work.
(P. R. KHAJURI A )
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ABSTRACT
V
The economic and industrial growth of a nation is greatly dependent upon modern means of surface transport.
This is all the more so for developing countries like India where the demand for automobiles and other light vehicles is growing rapidly with the pace of economic development and industrralization. These vehicles are powered by spark
ignition engines which are quite reliable and efficient. In fact presently there is no other power-plant in sight for light vehicles which can compete with spark-ignition (S.I.) engine in cost, size, flexibility and reliability. It
appears that at least for next few decades the S.I. engines will continue to have monopoly in the field of automobiles and other light vehicles,.
The S.I. engine uses gasoline as fuel which was both plentiful and reasonably cheap in the world market upto
1973. The situation has since drastically changed and gaso- line prices have incre ased manifold causing great scarcities and an unbearable strain on the economy of developing coun- tries which have been depending on. imports to meet their motor fuel requirements. Moreover, the resources of petroleum fuels are fast depleting, making the availability of gasoline
supplies in future a matter of serious concern.
Apart from their irreplaceable nature, and growing scarcity another problem associated with the use of petroleum
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based fuels is the nature of their combustion products which cause environmental pollution. Gasoline powered vehicles are the main contributors to atmospheric carbon monoxide pollution in metropoliton cities. The hazardous effects of automobile exhaust pollution on human health, plant and animal life are well known.
These problems of fast dwindling resources of petroleum fuels and the hazard of environmental pollution caused by
their combustion have focused the attention on the task of finding alternate 'clean' burning renewable fuels for use in automobiles. Broadly two types of alternative fuels have been under investigation for use in automobiles. These are the two types of alcohols (ethanol, methanol) and hydrogen.
Alcohols are conveniently handled liquids and are already operational fuels. They can be obtained from
renewable store of raw materials, organic matters including lignite, wood, coal, oil shale, natural gas and indirectly from punicipal and farm wastes. However, their wide spread use in chemical industry makes it difficult to spare them for burning in automobiles on a large scale.
From many technical and economic considerations hydro- gen seems to be the most suitable candidate fuel to substitute
gaPotine . Hydrogen can be manufactured from nuclear
energy through electrolysis or thermal, decomposition of water
vii
and it has been suggested as the most feasible future fuel.
Tasteless, Odourless and non—toxic by itself, hydrogen produces just clean energy- and water vapours upon combustion
with air, thus restoring quantitatively to the environment the water from which it is produced. Hence, there would never be a 'resource depletion' when hydrogen is burned as a fuel.
Hydrogen would be a particularly good fuel for spark ignition engines, because its wide flammability limit would permit high efficiency and unthrottled engine operation.
Engine emissions of hydrocarbons, c arb onmonoxide and carbon dioxide would be completely eliminated,
Hydrogen mixes easily with air and the mixture is quite stable at room temperature, however, the ignition energy of hydrogen is low compared to other gaseous and liquid fuels
and it is ignitable at very low equivalence rati os. The
flammability limits of hydrogen vary between 4 and 74 per cent by volume in air at room temperature and pressure. One of the consequences of this is the wide range of flame speeds and temperatures obtainable from hydrogen—air mixture.
3:I, engines using gasoline as fuel must be run very close to stoichiometric or richer mixtures thus producing conditions favourable to the formation of nitrogen oxides, unburned hydrocarbons and carbon monoxide in the exhaust.
Hydrogen, on the other hand, may be burned so lean as to
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ireduce peak temperatures to values at which dramatically less NO is produced and of course it is no source of hydrocarbons
or carbon monoxide.
In addition to the favourable aspects of the properties of 'hydrogen noted above, its exceptionally high flame velocity le 3d6'` to such rapid combustion that the linstant-combustion' idealization of the Otto cycle is approached, which should lead to higher thermal efficiency. However, it could also cause rough running of the engine, and result in other
associated combustion problems. These and other aspects of hydrogen utilisation as spark ignition engine fuels are matters of considerable current research interest.
In the work reported here, detailed analytical and experimental investigations of hydrogen as an S.I. engine fuel have been carried out. The analytical study involves
application of a combustion model to predict combustion
characteristics of hydrogen and a nitric oxide emission model to predict emission characteristics. The experimental
investigations have been carried out using a single-cylinder, Varimax variable compression ratio engine modified to run on hydrogen. Both aspects of investigation have focused parti- cular attention on the unthrottled pre-mixed hydrogen engine.
Model calculations and experimental results are described and compared.
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An engine combustion model has been formulated to
determine the combustion rate with hydrogen fuel. Using this model the cylinder pressures and temperatures have been pre- dicted and cylinder pressure crank angle traces have been compiled.
In the formulation of the combustion model the cylinder has been divided into two zones, one composed of burnt gases in chemical equilibrium and the other composed of unburned fuel air mixture along with residual gases. The flame front area has been found by assuming spherical propagation outward from the ignition point. By applying mass and energy balance equations, the temperature and pressure after each increment of flame advance have been determined for each zone. Temper- ature and composition dependent thermodynamic properties have been used and all processes except combustion have been assumed
to be isentropic.
This combustion model has been employed to account for the hydrogen-air combustion process over a wide range of
stoichiometry and spark advance for the Varimax engine oper- ating at various speeds and compression ratios. Based on the computed results various graphs have been plotted showing the variation of combustion crank angle and flame speed with fuel air equivalence ratio, engine speed, compression ratio, etc.
In addition pressure-time traces for various fuel-air e qui-
valence ratios and compression ratios have been prepared.
Plots for peak pressure and temperature variations across the cylinder for various equivalence ratios have also been obtained.
Although a spark ignition engine fueli with hydrogen would be free from carbon monoxide and hydrocarbon emissions, nitric oxide (NO)would still be a potential exhaust pollutant
requiring control. In order to estimate the exhaust nitric oxide concentration an analytical model has been evolved.
This is based on the experimental observations of Zeldovich and his co—workers, that the NO formation rate is much slower than the combustion rate and that most of the NO formation is after the completion of combustion. Using the 'frozen'
expansion concept, the exhaust nitric oxide concentration has been computed by integrating the chemical rate equation. The burnt gases have been assumed to remain unmixed and they have been divided into a series of discret adiabatic zones of
equal pressure but different temperature. The nitric oxide production has been computed for each zone during the entire expansion stroke till the opening of the exhaust valve. At this point the exhaust NO concentration has been arrived at by summing the contribution from all zones. On the basis of
this model exhaust nitric oxide emissions for hydrogen fueled spark ignition varimax engine have been calculated for a wide variety of engine operating conditions, and variations of
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exhaust NOx emissions with equivalence ratio at various speeds have been plotted.
In order to check on the analytical re sults and to know how to ad apt spark ignition engine s for operation of hydrogen fuel detailed experimental investigations have been carried
out using Vari max research engine. The engine performance data over its entire operating range of speeds and loads has been collected at different compression ratios , spark timings,
etc. using hydrogen as fuels. various graphs show-
ing the nature of engine performance characteristics wi th hydrogen fuel have been plotted.
Experimental plots of the rmal efficiency variation with equivalence ratio at different engine speeds and compression rati os show that use of hydrogen as fuel can result in signi- ficantly higher cycle efficiencies. Hydrogen' s extremely broad le an flammability limit enables power output regulation by mixture control rather than by throttling. Graphs showing
the variation of me an effective press ure wi th equivalence ratio and specific fuel consumpti on have been plotted for
different engine speeds and compression ratios. They indicate the feasible range of engine speeds and compression ratios for best results with hydrogen operation of the engine.
In order to assess the NO/NOx emission characteristics of the engine extensive experiments have been carried out
xii
using a chemiluminescent NO/NOx analyser. The experimental results have been plotted showing variation of exhaust NO/NOx
with equivalence ratio and compression ratio. It has been found that NO emission is maximum at an equivalence ratio of around 0.8 and it is extremely low for very lean mixtures.
NO formation process depends upon the available oxygen and the prevailing temperatures, and they occur in post flame gases. The type of fuel used effects the flame temperatures and through the stoichi ome try the available oxygen. For equivalence ratios lower than 0.8 the NO formation is controlled by quenching of formation reactions during the expansion stroke, while for richer mixtures NO concentrations are primarily determined by the quenching of decomposition reactions during the expansion process. The experimentally determined trends of NO/NOx emissions are in good agreement
with the theoretically predicted results.
On the basis of the work reported here, it can be safely concluded that hydrogen—fueled S.I. engine is a feasi- ble proposition. Such an engine having quality governing
can operate with very lean mixtures giving much higher efficiency as compared to gasoline engine. It would have the additional advantage of emitting a cleaner exhaust free from hazardous carbon containing pollutants and as much as
about ninety per cent lower exhaust NO emissions.
At higher outputs and higher equivalence ratios, charge dilution is one of the measures to ensure smoother
operations. Narrower spark plug gap would have to be employed to account for hydrogen' s 'low quench' distance and low
ignition energy-. These coupled with deposit free combustion chamber could ensure smoother operation without the problem
of flashback past the intake valve an.d preigniti on during compression.
=00=
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CON NT.S m•-•-1.-•■••••■••••■ PAGE Certificate
Acknowledgements
Abstract .. • •
Contents xiv
List of Figures xviii
CHAPTEA-1 1.1
IN TRODUC TI ON
Energy Crisis and Internal
.. 1-10 Combustion aagines • • 2 1.2 Alternate Engine Fuels .. 3 1.3 Hydrogen as a S.I . Engine Fuel .. 4 1.4 Statement of Problem .. 9 CHAPTER-2
2.1 2.2 2.3
HYDROGEN AS S . I . ENGINE
.. 11-38
.. 16 FUEL
. • .12 Historic al Review
Current Status of Hydrogen Combustion Characteristics of
Hydrogen .. 21
2.4 Problems Connected with Hydrogen
..
2.4 . 1 On Board Storage of Hydrogen i
2276
2.4.2 Safety Consideration
.. 32
2.4.3 Cost Benefit An
..
2.5 Concludin: Remarks .. 37
XV
PAGE CHAPTER-3 ,,_,-...._ THEORETICAL ,. IN YES TI GAT IONS
ANDCOiskUTATI ON AL TECHNI .20 39-84 . 3.1 Basic Appro ach and Equations • • 40
3.1.
1 Temperature Derivative • •41 .
3. 1. 2 Heat Transfer Coefficient • • 44 3. 2 Engine C omb us ti on Model • • 46 3. 2. 1 Expression for Flame Velocity . • 50
3.2.
2 Expression for He at Rele as e .. 53 3.2.3 Expression for the Rate of Changein Unburnt Gas Temperature • •
55.
3.2.4 Expressi on for the Rate of Burnt
Volume Change • • 56
3.2.5 Expressi on for the Rate of Change of Burnt Mass
. •
3. 2.6 Expression for the Rate of Change of Pressure
3. 2. 7 Expressi on for the Burnt Volume 3. 2.8 Es ti mati on of the Rate of Pressure
rise and Rate of Change of Mass 3.3 Expansion Process
3. 3. 1 Computation of Equilibrium Gas Composi ti on
3.3.
2 Red uc ti on in Number of Equati ons3.3.3
Mole Fractionn Computati on Equati ons3.3.4
Initial Estimation of Mole Fractions..
• •
• •
• •
• •
• •
• •
• •
• •
56
59 60
61 63
63 66
67
69
XVi
PAGE 3.3.5 Partial Derivatives of Mole
Fr ac ti on s • • 71 3. 3. 6 Enthalpy and Internal Energy ••• 74 3.4 Oxides of Ni Urogen Formati on
Model • • 7 6
3.5 Computer Program • • 80 CHAPTER.4 EXPERI TAI, EsnalEN
AN- D • • 85
-1 10
4.1 Introduction • • 86
4. 2 The Variable aompression Engine
System .. 8 6
4.2.1 Vari max Engine • • 86 4. 2. 2 Engine Dynamometer • • 93 4.2.3 Fuel and ai r-Fl ow Measurement • • 94 4.2.4 Cylinder Pressure Me asuring Setup .. 97 4.2.5 Crank Angle Timing Marker • • 9 7 4.3 Instrument for Measuring NO
Emission x
• • 97 4.3.1 Chemiluminescent NO Analyser • • 97
4.4 Experimental Technique • • 103
4.4.1 Performance a:-ad Fuel Economy
Tests , • 103
4.4. 2 Exhaust Emission Tests • • 107
Appendix to Chapter-4 • • 108
xvii
CHAPTER-5
--____ DISCUSSION OF RESULTS
PAGE Tp. w. MI
111-211
5.1 Introduction • • 112
5.2 Engine Performance • • 113
5.3 Engine Emissi on . • • 149
5.4 Analytical Results • • 168
C H AP TER. -6 CONCLUSIONS • • 212- 21 7
REFERENCES • • 218-229
