Overview
The leading contributor of the various greenhouse gases is CO2, of which nearly all the additional concentration arrives from the combustion of fossil fuels, and to a lesser extent the burning of tropic rain forests. 56% of all the carbon dioxide formed from the combustion of hydrocarbons still remains in the atmosphere [2], with the rest sequestered by the ocean.
Currently, approximately 22×10^9 man-made tons of CO2 are emitted per year, contributing to the 25% increase since the 18th century. Of all the fossil fuels consumed in the United States, 18% of that goes toward transportation needs, and of that 63% toward motor fuels [4] for surface travel. In 1986, 187 million automobiles [5] were in operation in the U.S., contributing a large majority of the greenhouse gases and pollutants into the atmosphere. The fuel of choice is a mixture of hydrocarbons called gasoline. Several other fuels present themselves as alternatives to gasoline including gaseous hydrocarbons derived from coal, alcohols such as methanol, gasoline blends, and hydrogen. Only one of the alternative fuels mentioned above also has the feature of producing zero greenhouse gases when combusted with air: Hydrogen.
Hydrogen (H2) as an transportation fuel has its share of problems, including storage requirements, detonability, and production. Currently, industrial H2 comes from the water-gas shift reaction with coal, but other methods include electrolysis, thermal decomposition, thermolysis, thermochemical cycles, and photolysis (photo-electrolysis, catalytic photolysis, bio-photolysis). The thermal and electrical requirements in the production of H2 gas makes a natural link with either non-greenhouse gas processes such a fission/fusion and solar photovoltaics or solar thermal systems.
Currently two gaseous fuels vie for supremacy on the ladder of alternative fuels: methane and hydrogen [15]. Carbon based methane produces greenhouse gases along with an assortment of other toxic pollutants including carbon monoxide. Both gases still produce a significant amount of nitric oxide (NO) and nitrogen dioxide (NO2), whose concentration depends on the equivalence ratio (f) and unburned gas conditions. Hydrogen is the leader in reduced tailpipe NO formation, without complex de-NOx (combined NO and NO2 concentrations) apparatus, due to its wide flammability limits.
Internal Combustion Engine
Experimental results [10] with an IC engine fueled with a H2-air charge, revealed the lowest equivalence ratio to assure steady running without much misfire occurred at a equivalence ratio of 0.218, but reliable function occurred at f of 0.28 and above. Several papers report vast reduction of NO formation through direct fuel injection into the cylinder head or water injection [8, 10, 11] to keep the flame temperature down, yet the experimental setups vary considerably from gasoline converted to hydrogen engines, to exotic timed spark and manifold designs, yielding NOx concentration twice as high to fourteen times less [11] than gasoline. One undisputed repeatable results is the lean oxidation of hydrogen, with equivalence ratios bound between 0.3 and 0.6 values. Luckily, the maximum thermal efficiency under numerous observations occurred at f = 0.4 and has been reported as high at 55% [11], compared to a methane engine at 30% (gasoline).
Greater efficiency and power control of the engine is maintained through the use of the wide lean flammability limits, and use of fuel injection over a throttled carburated system. With the low LFL, quality regulation under unthrottled air intake can vary power output over the quantity regulation necessary for a hydrocarbon fuel [11]. Aspects of safety are no more stringent than those for gasoline, just different. Storage either as a compressed gas or liquid may pose difficult, but solvable. Consideration into managing other problems of backfire, flashback, and knock each has resolvable solutions slightly different to strategies association with carbon fuels. With all the combined efforts taken to perfect and refine the Otto-cycle petroleum based engine, the hydrogen engine has the opportunity to become the next chemical transportation fuel of choice.
Conclusion
Several thermochemical and kinetic factors make hydrogen attractive as the next industrial and transportation fuel. The wide flammability limits allow lower or comparable pollution emissions to carbon based fuels (methane). The additional problems of organic pollutants such as carbon monoxide, formaldehyde, sulfur (acid rain), and lead are eliminated with a H2-air combustion system. If the hydrogen is derived from a solar-hydrogen array, then problems of erosion and mining could be eliminated from coal production. In the era of the environment, where pollution and greenhouse gases are devaluing the quality of life for many on the earth, hydrogen poses a possible solution to our thirst for chemical fuels for transportation and goods.
Will the solar-hydrogen economy ever become a reality? The 400 billion dollars in equity in petroleum and gas exploration along with the coal industry signals that the transition will take a long time, as not to shock the present carbon-combustion economy. If the world starts today to take a pledge for change, as did several scientists and engineers in the Energy-Environment Resolution, when the supply or fossil fuels is still in full swing, the change over will be smoother, and we could all breath a little better.
Literature
[1]Skelton, L. W. The Solar-Hydrogen Energy Economy: Beyond the Age of Fire. Van Nostrand Reinhold Company, New York: 1984.
[2]Kellogg W. W. “Energy Generation: The Basic Cause of Current and Future Climate Change.” Hydrogen Energy Progress VIII. Edited by T. N. Veziroglu. Pergamon Press, New York: 1990. Volume 1, Pages 145-161.
[3]Winter, C. J. “Hydrogen and Solar Energy-Ultima Ratio: Avoiding a “Lost Moment in the History of Energy!”” Hydrogen Energy Progress VIII. Edited by T. N. Veziroglu. Pergamon Press, New York: 1990. Volume 1, Pages 3-47.
[4]Plass, H. J. “Economics of Hydrogen as a Fuel for Surface Transportation.” Hydrogen Energy Progress VIII. Edited by T. N. Veziroglu. Pergamon Press, New York: 1990. Volume 1, Pages 237-249.
[5]Chuveliov, A. V. “Fossil Fuels and Air Pollution in USA After the Clean Air Act: Markets for Hydrogen.” Hydrogen Energy Progress VIII. Edited by T. N. Veziroglu. Pergamon Press, New York: 1990. Volume 1, Pages 251-280.
[6]Das, L. M. “Abnormal Combustion in Hydrogen Engines: Causes and Remedies.” Hydrogen Energy Progress VIII. Edited by T. N. Veziroglu. Pergamon Press, New York: 1990. Volume 3, Pages 1379-1397.
[7]Eichert, H. “Dynamics of Combustion of Hydrogen-Air and Hydrogen-Methane-Air Mixtures.” Hydrogen Energy Progress VIII. Edited by T. N. Veziroglu. Pergamon Press, New York: 1990. Volume 3, Pages 1183-1195.
[8]Mathur, H. B. “Combustion Related Studies on a Timed Manifold Injection Hydrogen Engine.” Energy and Environmental Progress I- Hydrogen Energy and Power Generation. Edited by T. Nejat Veziroglu. Nova Science Publishers, New York: 1991. Volume D, Pages 223-240.
[9]Karim, G. A. “Some Considerations of the Lean Flammability Limits of Mixtures Involving Hydrogen.” Hydrogen Energy Progress IV. Edited by T. N. Veziroglu. Pergamon Press, New York: 1986. Volume 4, Pages 1685-1695.
[10]Mathur, H. B. “Hydrogen Fuelled Internal Combustion Engines.” Progress in Hydrogen Energy. Edited by R. P. Dahiya. D. Reidel Publishing Company, Boston: 1987. Pages 159-177.
[11]DeBoer, P. C. T. “Performance and Emissions of Hydrogen Fueled Internal Combustion Engines.” International Journal of Hydrogen Energy. Pergamon Press, Northern Ireland: 1976. Volume 1, Pages 153-172.
[12]Watson, H. C. “Reduction of Cyclic Variability and Lean Limit Operation of Alternative Fuels by Pilot Hydrogen in Unmodified SI Engines.” Hydrogen Energy Progress VIII. Edited by T. N. Veziroglu. Pergamon Press, New York: 1990. Volume 3, Pages 1263-1274.
Additional Background Information Resources
[13]Alternative Transportation Fuels: An Environmental and Energy Solution. Edited by D. Sperling. Quorum Books, New York: 1989.
[14]Fuels to Drive our Future. National Research Council Committee on Production Technologies for Liquid Transportation Fuels. National Academy Press, Washington D.C.: 1990.
[15]Gallopoulus, N. E. “Alternative Fuels for Reciprocating Internal Combustion Engines.” Alternative Hydrocarbon Fuel: Combustion and Chemical Kinetics. Edited by C. T. Bowman. Progress in Astronautics and Aeronautics Volume 62. American Institute of Aeronautics and Astronautics: 1970. Page 74-115.
[16]Ramage, J. Energy: A Guidebook. Oxford University Press, Oxford: 1983.
[17]Mustoe, J. E. H. An Atlas of Renewable Energy Resources. John Wiley & Sons, New York: 1984.
[18]McGown, L. B. How to Obtain Abundant Clean Energy. Plenum Press, New York: 1980.
[19]Stoker, H. S. From Source to Use: Energy. Scott, Forseman & Company. Palo Alto, CA: 1975.
[20]Namboodiry, E. V. S. “Liquid Hydrogen as a Fuel for Ground, Air, and Naval Vehicles.” Progress in Hydrogen Energy. Edited by R. P. Dahiya. D. Reidel Publishing Company, Boston: 1987. Pages 133-157.
[21]Peschka, W. “Hydrogen Combustion in Tomorrow’s Energy Technology” Hydrogen Energy Progress VI. Edited by T. N. Veziroglu. Pergamon Press, New York: 1986. Volume 3, Pages 1019-1036.
[22]Souche, I. “Some Aspects if Hydrogen Combustion and its Potentials Compared to Other Usual Fuels.” Hydrogen Energy Progress VI. Edited by T. N. Veziroglu. Pergamon Press, New York: 1986. Volume 3, Pages 1129-1144.
[23]Hoffman, P. The Forever Fuel: The Story of Hydrogen. Westview Press, Boulder, CO: 1981.
[24]Goodger, E. M. Alternative Fuels: Chemical Energy Resources. John Wiley & Sons, New York: 1980.
[25]Winter, C. J. Hydrogen as an Energy Carrier: Technologies, Systems, Economy. Springer-Verlag, Berlin: 1988.
[26]Burgess D. “The Flammability Limits of Lean Fuel-Air Mixtures: Thermochemical and Kinetic Criteria for Explosion Hazards.” ISA Transactions. Instrument Society of America, Pittsburgh, PA: 1975. Volume 14, Number 2, Pages 129-136.