Lean Mixture Operation of Hydrogen-Fueled Spark Ignition Engines

Tests have been carried out with a hydrogen fueled four-cylinder engine to determine the susceptability of a worn engine to preignition and subsequent flashback when operating with lean mixtures, and the effect of different spark plug and ignition system characteristics on the completeness of combustion of very lean mixtures. Flashbacks occurred at equivalence ratios as low as 0.4 in an engine with combustion chamber deposits thought to approximate those in a hydrogen-fueled engine with significant wear. The completeness of combustion of very lean mixtures was found to depend only on equivalence ratio and was not influenced by any of the ignition system changes performed. This suggests that slow flame propagation rather than inadequate ignition determines the lean limit of operation.