Verhelst, S., Sierens, R., and Verstraeten, S., "A Critical Review of Experimental Research on Hydrogen Fueled SI Engines," SAE Technical Paper 2006-01-0430, 2006, doi:10.4271/2006-01-0430.
The literature on hydrogen fueled internal combustion engines is surprisingly extensive and papers have been published continuously from the 1930's up to the present day. Ghent University has been working on hydrogen engines for more than a decade. A summary of the most important findings, resulting from a literature study and the experimental work at Ghent University, is given in the present paper, to clarify some contradictory claims and ultimately to provide a comprehensive overview of the design features in which a dedicated hydrogen engine differs from traditionally fueled engines.Topics that are discussed include abnormal combustion (backfire, pre-ignition and knock), mixture formation techniques (carbureted, port injected, direct injection) and load control strategies (power output versus NOx trade-off). Attention is given to the most recent research by car manufacturers BMW and Ford, reporting hybrid control strategies (PFI+DI, lean burn + stoichiometric operation using EGR) to obtain power outputs equivalent to gasoline engines with extremely low emission levels. Recent results from experiments with EGR on a hydrogen engine at Ghent University are also given. Finally, a synthesis of hydrogen engine design features is given, that make the most of hydrogen's advantages and counter its disadvantages. Areas requiring further research are highlighted.