ONBOARD GENERATION OF HYDROGEN-RICH GASEOUS FUELS - A REVIEW

- A Review International Journal of Hydrogen Energy Vol.19, No.7, pp. 557-572, 1994,
Received for publication 1 September 1993  By: Y. Jamal and M.L.Wyszynski *

School of Manufacturing and Mechanical Engineering University of Birmingham, Birmingham B15 2TT, UK.

* Author to whom correspondence should be addressed.
 
 

Hydrogen has a good potential as an alternative fuel for spark ignition engines. It can extend the lean flammability limit of conventional fuels in order to achieve higher thermal efficiency and lower exhaust emissions.

This paper reviews the use of hydrogen and hydrogen-enriched gasoline as a fuel for SI engines and the techniques used to generate hydrogen from liquid fuels such as gasoline and methanol, on-board the vehicle. The processes of thermal decomposition, steam reforming, partial oxidation and exhaust gas
reforming are evaluated.
A considerable amount of both theoretical and experimental work has been done in this field. Predictive and experimental results of the various investigators are reviewed and summarised.

The scarcity of fossil fuels and the associated pollution problems have attracted the attention of researchers towards the search for alternative fuels. With any alternative fuel, its availability of the source, as well as the emissions of pollutants are most important from the aspect of energy preservation and environment, respectively, while its potential effects on the engine performance and the form of storage will be significant issues from the stand point of the engine and vehicle technologies.

An alternative energy carrier that has great environmental advantages is hydrogen. It is a clean fuel, when burned in air, produces non-toxic exhaust emissions except at some equivalence ratios, where its high flame temperature results in significant NOx levels in the exhaust products. The use of gaseous fuels inducted with air does, however, limit the total power output of the engine due to the reduction of volume of air aspirated.
     The current approach for the reduction of emissions relies on three-way catalytic converters. An alternate and more basic approach to the emissions problem is to modify the initial combustion process in the engine by using lean mixtures. The primary advantage of lean burn is that it increasingly reduces NOx and CO. The problem with it is that engine power declines rapidly, while unburned hydrocarbon emissions increase because of misfire [1]. Unfortunately, an engine still produces unacceptably high NOx exhaust
pollutants near the lean flammability limit of gasoline. In a practical sense, lean-burning engines are limited by the onset of engine misfiring as the lean flammability limit of any fuel is approached. For this reason
emission standards for NOx could not be achieved in the engine by operating lean, using only gasoline. Mixtures of hydrogen and gasoline, on the other hand, can burn lean enough to meet this requirement [2].
Hydrogen may be used to extend the lean limit of conventional fuels in order to achieve higher efficiency and lower pollutant emissions. Because of its wide flammability limits and high flame speeds the Hydrogen-rich fuel lends itself readily to ultra lean combustion and should allow the use of higher
compression ratios. Combining the increase in heating value, the recovery of waste energy from the engine exhaust, lean operation and higher compression ratios provides potentially high increase in thermal efficiency for the hydrogen-enriched fuels over that of the conventional fuels.
   However, there are significant problems associated with the use of hydrogen,especially concerning production and storage. Hydrogen is commercially produced by electrolysis of water and by coal gasification. These methods are not widely used because they are more expensive than steam reforming of
natural gas or partial oxidation of heavy oils [3]. Most of the worlds hydrogen is currently derived from hydrocarbons such as oil or natural gas, via the catalytic steam reformation [4, 5]. There are generally three ways to store hydrogen in an automobile: as a gas dissolved in a metal (metal hydride), as a cryogenic liquid or as a compressed gas. Hydride storage is the simplest and the safest, but it
increases vehicle weight and results in a severe fuel economy penalty.
Liquid hydrogen is light, but due to its low energy density occupies three times as much volume as gasoline. Storage as a compressed gas is inexpensive and provides for ease of operation but its weight and bulk is the main problem.
    One solution to the storage problem is the onboard hydrogen generation from a suitable high energy density patent fuel such as gasoline or methanol. With this form of storage, the technical problem is how to generate the hydrogen. There are a number of methods to generate hydrogen from such
fuels. The most common amongst those are partial oxidation, steam reforming, thermal decomposition and exhaust-gas reforming. Partial oxidation is not usually considered to be attractive in terms of efficiency because it is an exothermic process, and the resulting hydrogen containing fuel gas has a lower calorific value than that of original feed stock. However, it is an interesting means of generating free hydrogen gas
for use as a charge supplement in ultra lean combustion exercises [6]. On the other hand, steam reforming is an endothermic process, the fuel gas thus produced has higher calorific value than the feed stock, and the efficiency of the process is quite favourable, particularly if the heat energy requirement is supplied from a source which would otherwise be wasted, like hot engine exhaust gases [7]. Thermal decomposition of hydrocarbons results in the formation of hydrogen and carbon. The difficulty of gasifying or handling the solid carbon makes hydrocarbon decomposition not suitable for on board hydrogen generation. Methanol can be catalytically decomposed into hydrogen and carbon monoxide at temperatures of the order of 250oC [8]. The reaction is endothermic and requires a heat source to provide energy. This energy can usually be supplied by the engine exhaust gas. In exhaust gas reforming fuels are reformed catalytically by direct contact with a portion of hot products of combustion utilising the fact that exhaust gases contain a certain quantity of steam. The fuel gas thus generated contain quantities
of hydrogen, carbon monoxide and nitrogen, thus providing a potential for lean combustion leading to lower emissions and higher engine thermal efficiency than conventional fuel [9]. The objective of this paper is to review the use of hydrogen as a fuel for gasoline engine, in particular as a supplementary fuel, and to discuss the different methods of onboard hydrogen generation. The main parts of the paper:

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CONCLUSIONS

1. Spark ignition engine can be operated efficiently at light loads using hydrogen fuel alone.

2. Some charge dilution to avoid knock is essential to permit operation with hydrogen at higher power output.

3. Hydrogen supplementation of gasoline combustion has been shown to yield reduction in fuel consumption.

4. Hydrogen-rich gaseous fuels can be burned under ultra lean conditions to yield very low NOx emissions without running into lean flammability limit problems.

5.The lean burning conditions give possibilities for very low CO emissions.

6. Enrichment by pure hydrogen does not appear to be a sufficient means of reducing HC emission as measured by total HC methods.

7. Consideration of the hydrogen/gasoline/air combustion process, coupled with the observation of steady state test-bed performance, suggested the possibility that the hydrogen and gasoline oxidation processes are independent and may result in two flames.

8. Onboard hydrogen generation from liquid fuels, either hydrocarbons or alcohols, is technically feasible.

9. The economy benefit from running lean almost compensates for the energy requirements for making hydrogen from gasoline in an atmospheric reactor.

10. Some of the waste heat from the vehicle exhaust gas can be reclaimed by converting it to chemical energy in the fuel.

11. Optimum performance of a reforming reactor occurs at the lowest possible excess oxidant factor just short of the soot formation limit.

12. The use of a catalyst in the reforming reactor allows a closer approach to equilibrium H2 yields.

13. The use of reformed fuel (compared to liquid raw fuel) may result in higher engine thermal efficiency in the low power range, with the improvement due to the increase in the heating value of the gaseous fuel
resulting from the reforming reaction.

14. Use of reformed fuel (compared to liquid fuel) in a spark ignition engine may result in lower exhaust emissions, particularly of the heavier and aromatic hydrocarbons and NOx.

15. In all cases considered, a considerable loss in maximum power capacity of the engine occurs as a result of the use of gaseous fuels and by operating under lean conditions. Effective utilisation of onboard hydrogen generation calls for lightweight high displacement engines to overcome this disadvantage.

16. An automobile could not be operated over the required power range when it was fed exclusively with reformed fuel. A supplementary fuel supply would be required to reach the higher loads.

1. C. Cragg, Cleaning up Motor Car Pollution New fuels and Technology. Financial Times Management Report, FT Business Information, London, 1992.

2. F. W. Hoehn and M. W. Dowdy, Feasibility Demonstration of a Road Vehicle Fueled with Hydrogen Enriched Gasoline. SAE Paper No. 749105, Presented at the Ninth Intersociety Energy Conversion Engineering Conference, San Francisco, California ,August 26-30, 1974.

3. C. A. Kukkonen, Hydrogen as an Automotive Fuel. SAE Transaction Paper 810349, (SP-480), Vol. 90, Section 2, 1981.

4. M. Steinberg and H. C. Cheng, Modern and Prospective Technologies for H2-Production from Fossil-Fuels. International Journal of Hydrogen Energy, Vol. 14, No. 11, pp 797-820, 1989.

5. N. C. Thomas, The Role of Hydrogen as a Future Fuel. Science Progress, Vol. 72, No. 285, pp 37-52, 1988.

6. J. Houseman and D. J. Cerini, Onboard Hydrogen Generator for a Partial Hydrogen Injection Internal Combustion Engine. SAE Paper 740600, Presented at The National West Coast Meeting of the Society of Automotive Engineers, Anaheim, California, August 12-16, 1974.

7. M. R. Jones, J. W. Dunn and M. L. Wyszynski, Thermodynamic Feasibility Studies of the Exhaust-Gas Reforming of Hydrocarbon Fuels. I Mech E International Conference: Automotive Power Systems Environment and Conservation, Paper No. C394/014, Chester, England, September 10-12, 1990.

8. J. Houseman and G. E. Voecks, Hydrogen engines based on liquid fuels, a review. Hydrogen Energy Progress, Proceedings of 3rd World Hydrogen Energy Conference, Vol. 2, pp 949-968, Tokyo, Pergamon Press, Oxford, 1981.

9. M. R. Jones, Feasibility Studies of the Exhaust Gas Reforming of Hydrocarbon and Alcohol Fuels, PhD Thesis, Automotive Engineering Centre, School of Manufacturing and Mechanical Engineering, University of Birmingham, April 1992.

10. C. A. Amann, Future Automotive Fuels from a United-States Standpoint. International Journal of Vehicle Design, Vol. 13, No. 5-6, pp 407-427, 1992. 11. M. A. Deluchi, Hydrogen Vehicles: An Evaluation of Fuel Storage, Performance, Safety, Environmental Impacts, and Cost. International Journal
of Hydrogen Energy, Vol. 14, No. 2, pp 81-130, 1989.

12. Karl S. Young, Hydrogen fuel storage using activated carbon for vehicles. SAE Paper No. 911703 (P-245), 1991.

13. C. A. Amann, The Passenger Car and the Greenhouse Effect. International Journal of Vehicle Design, Vol. 13, No. 4, pp 305-334, 1992.

14. Ennio Peres Da Silva, The UNICAMP experiments with hydrogen vehicles. SAE Paper No. 911704 (P-245), 1991.

15. John Templeman, Fill Er Up - With Hydrogen, Please. Business Week (Industrial/Technology Edition), Iss. 3202, pp 62-63, March 4, 1991.

16. Bill Siuru, R & D in the Fast Lane. Mechanical Engineering, Vol. 111, Iss. 10, pp 62-67, Oct 1989.

17. R. H. Thring, Alternative Fuels for Spark Ignition Engines. SAE Transaction Paper 831685, (SP-559), Vol. 92, Section 4, 1983.

18. T. N. Veziroglu and F. Barbir, Hydrogen - The Wonder Fuel. International Journal of Hydrogen Energy, Vol. 17, No. 6, pp 391-404, 1992.

19. T. Petkov, T. N. Veziroglu and J. W. Sheffield, An Outlook of Hydrogen as an Automotive Fuel. International Journal of Hydrogen Energy, Vol. 14, No. 7, pp 449-474,1989.

20. Ematage, A. L., Microprocessor Engine Management applied to Hydrogen / Petrol Operation. PhD Thesis, University of Technology, Loughborough, United Kingdom, 1987.

21. R. F. Stebar and F. B. Parks, Emission Control with Lean Operation Using Hydrogen-Supplemented Fuel. SAE Transaction Paper 740187, Vol. 83, Section 1, G M Research Laboratories, Paper presented at SAE Automotive Engineering Congress, Detroit, Michigan, February 25 - March 1,1974.

22. Laurence O. Williams, Hydrogen Power An Introduction to Hydrogen Energy and its Application., Pergamon Press, London, 1980.

23. H. B. Mathur and L. M. Das, Performance Characteristics of a Hydrogen Fueled SI Engine Using Timed Manifold Injection. International Journal of Hydrogen Energy, Vol. 16, No. 2, pp 115-127, 1991.

24. Bob Johnstone, Research & Innovation: Stepping on the Gas. Far East Review, Vol. 155, Iss. 24, pp 90, June 18,1992.

25. J. G. Finegold and W. D. Van Vorst, Engine Performance with Gasoline and Hydrogen: A Comparative Study. Paper Presented at The Hydrogen Economy Energy (THEME) Conference, Miami Beach, Florida, March 18-20, 1974.

26. E. M. Goodger, Alternative Fuels Chemical Energy Resources Macmillan Press, London, 1980.

27. M. D. Marton, Gaseous Automotive Fuels from Steam Reformed Liquid Hydrocarbons. SAE Paper 780457, 1978.

28. J. F. Cassidy, Emissions and Total Energy Consumption of a Multicylinder Piston Engine Running on Gasoline and Hydrogen-Gasoline Mixture. NASA Technical Note D-8487, Lewis Research Centre, Cleveland, Ohio, May 1977.

29. G. Yu, C. K. Law and C. K. Wu, Laminar Flame Speeds of Hydrocarbon + Air Mixtures with Hydrogen Addition. Combustion and Flame Vol. 63, pp 339-347, Elsevier Science Publishing,, New York, 1986.

30. B. E. Milton and J. C. Keck. Laminar Burning Velocities in Stoichiometric Hydrogen and Hydrogen-Hydrocarbon Gas Mixtures. Combustion and Flame Vol. 58: 13-22, Elsevier Science Publishing, New York, 1984.

31. R. Bresheas, H. Cotrill and J. Rupe, Partial Hydrogen Injection into Internal Combustion Engines Effect on Emissions and Fuel Economy. Presented at the First Symposium on Low Pollution Power Systems Development, Ann Arbor, Michigan, October 14-19,1973.

32. F. B. Parks, A Single-Cylinder Engine Study of Hydrogen-Rich Fuels. SAE Transaction Paper 760099, Vol. 85, Section 1, 1976.

33. M. J. Rauckis and W. J. McLean, The Effect of Hydrogen Addition on Ignition Delays and Flame Propagation in Spark Ignition Engines. Combustion Science and Technology, Vol. 19, pp 207-216, 1979.

34. G. G. Lucas and W. L. Richards, The Hydrogen/Petrol Engine S The means to give good part load Thermal Efficiency. SAE Paper No. 820315, 1982.

35. E. Sher and Y. Hacohen, On The Modelling of a SI 4-Stroke Cycle Engine Fueled with Hydrogen-Enriched Gasoline. International Journal of Hydrogen Energy, Vol. 12, No. 11, pp 773-781,1987.

36. D. Sfinteanu and N. Apostolescu, Efficiency, Pollution - Control and Performances of Hydrogen-Fueled Passenger Cars. International Journal of Hydrogen Energy, Vol. 17, No. 7, pp 539-542, 1992.

37. Fukutani and N. Kunioshi, Fuel Mixing Effects on Propagation of Premixed Flames. 1. Hydrogen Plus Carbon Monoxide Flames. Bulletin of the Chemical Society of Japan, Vol. 65, No. 10, pp 2569-2572, 1992.

38. S. J. Yoo and C. I. Lee, Feasibility Evaluation of Reformed Methanol Usage to Spark Ignition Engine. SAE Paper No. 871166, 1987.

39. G. E. Voecks, S. Dawson and J. Houseman, Operation of a Catalytic Methanol Decomposition Reactor for Vehicular Use. Jet Propulsion Laboratory, Proceedings, 4th International Symposium on Alcohol Fuels Technology, Guaruja, Brazil, October 5-8,1980.

40. L. Pettersson and K. Sjostrom, Onboard Hydrogen Generation by Methanol Decomposition for the Cold Start of Neat Methanol Engines. International Journal of Hydrogen Energy, Vol. 16, No. 10, pp 671-676, 1991.

41. T. Sakai, I. Yamaguchi, M. Asano, T. Ayusawa and Y. K. Kim, Transient Performance Development on Dissociated Methanol Fueled Passenger Car. SAE Paper 871169, 1987.

42. T. Sato, M. Tanaka and K. Agawa, A Study on the Reformed-Methanol Engine., SAE Paper 861237, 1986.

43. D. M. McCall, T. R. Lalk, R. R. Davison and W. B. Harris, Performance and Emissions Characteristics of a Spark Ignition Engine fueled with Dissociated and Steam - Reformed Methanol. SAE Transaction Paper No. 852106, Vol. 94, (SP - 638), 1985.

44. N. D. Brinkman and R. F. Steber, A Comparison of Methanol and Dissociated Methanol Illustrating effects of fuel properties on Engine efficiency Experiments and Thermodynamics Analysis. SAE Transactions Paper No. 850217, Vol. 94, 1985.

45. I. Yamaguchi, T. Takishita, T. Sakai, T. Ayusawa and Y. K. Kim, Development Research on Dissociated Methanol Fueled Spark Ignition Engine.  SAE Paper No. 852201, (P-169), Proceedings of 4th Joint Symposium on Internal Combustion Engines, January 1984.

46. R. L. Bechtold and T. J. Timbario, The Theoretical limits and Practical Considerations of Decomposed Methanol as a Light-duty vehicle Fuel. Paper A-5, Proceedings VI International Symposium on Alcohol Fuels Technology, Ottawa, Canada, May 21-25, 1984.

47. E. Anthonissen and J. J. Wallace, Dissociated Methanol Engine Testing Results Using H2-CO Mixtures. Proceedings of the 18th Intersociety Energy Conversion Engineering Conference, Orlando, (SAE 839091), Florida, August 21-26, 1983.

48. B. Lindner and K. Sjostrom, Operation of an Internal Combustion Engine under Lean Conditions With Hydrogen Produced in an Onboard Methanol Reforming Unit. V International Alcohol Fuel Symposium on Alcohol Fuels Technology, Auckland, New Zealand, May 1982.

49. Martin V. Twigg, ICI, Catalyst Handbook. 2nd Edition, chapter 5, Wolfe Scientific, London, 1989.

50. J. Houseman and D. J. Cerini, Onboard Hydrogen Generation for Automobiles. 11th Intersociety Energy Conversion Engineering Conference, SAE Paper 769001, New York, Presented at the 11th IECEC, Proceedings, pp 6-15, 1976.

51. M. S. Newkirk and J. L. Abel, The Boston Reformed Fuel Car. SAE Transactions Paper No. 720670, Vol. 81, 1972.

52. J. Houseman and F. W. Hoehn, A Two-Charge Engine Concept: Hydrogen Enrichment. SAE Transactions Paper No. 741169, Vol. 83, Presented at the International Stratified Charge Engine Conference, Troy, Mich., October 30 - November 1, 1974.

53. F. W. Hoehn, R. L. L. Baisley and M. W. Dowdy, Advances in Ultra lean Combustion Technology using Hydrogen-Enriched Gasoline. Proceedings of the 10th Intersociety Energy Conversion Engineering Conference, SAE Paper 759173, 1975.

54. Jet Propulsion Laboratory California Institute of Technology, Hydrogen Enrichment Concept Preliminary Evaluation. Final Report, US Energy Research and Development Administration, Technical Information Centre TEC-75/007, JPL Document 1200-237, Prepared for EPA under Interagency Agreement EPA-IAG-D4-0548, December-15, 1975.

55. F. L. Kester, A. J. Konopka and E. H. Camara, Onboard Steam Reforming of Methanol to Fuel the Automotive Hydrogen Engine. Intersociety Energy Conversion Engineering Conference, SAE Paper 759175, New York, 1975. (p 1176)

56. J. G. Finegold, Reformed Methanol Vehicle System Considerations. Proceedings of the 18th Intersociety Energy Conversion Engineering Conference (IECEC), Orlando, Florida, , SAE Paper 839092, 557, August 1983.

57. J. W. Jenkins of Johnson Matthey plc., Catalytic Generation of Hydrogen from Hydrocarbons. European Patent Publication No. 0 262 947,1988.

58. O. B. Lindstrom, Fuel Treatment for Combustion Engines. USA Patent 3918412, 1975.

59. K. Sjostrom, Sren Eriksson and G. Landqvist., Onboard Hydrogen Generation for Hydrogen Injection into Internal Combustion Engines. SAE Paper 810348, (SP-480), 1981.

60. R. Jones and M. L. Wyszynski, Exhaust-Gas Reforming of Hydrocarbon Fuels. SAE Paper No. 931096 (P-263), presented at the SAE - IMechE Conference: Vehicle Thermal Management Systems, Columbus, Ohio, 28 March - 1April 1993.

61. Bradley and C. G. W. Sheppard, Combustion Tests with Reformed Fuel. Ref.Exp, 1992. (Unpublished report, University of Leeds).

62. C. R. Ferguson, Internal Combustion Engines Applied Thermosciences. J Wiley & Sons, New York, 1986.

63. E. Sher and N. Ozdor, Laminar Burning Velocities of n-butane/air Mixtures Enriched with Hydrogen. Combustion and Flame, Vol. 89, No. 2, 214-220, 1992.

64. H. West, The On-line Characterisation of Hydrocarbon Species in Engine Exhaust Gases using a Mass Spectrometer, with Applications to the Reduction of Harmful Hydrocarbon Species by Fuel Reforming. PhD Thesis, School of Manufacturing and Mechanical Engineering, University of Birmingham, April
1993.

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