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One of the main features of methane fueled spark ignition engines is their relatively slow flame propagation rates in comparison to liquid fuel applications which may lead to relatively lower power output and efficiency with increased emissions and cyclic variations. This is especially pronounced at operational equivalence ratios that are much leaner than the stoichiometric value. The addition of some hydrogen and oxygen to the methane may contribute towards speeding the combustion process and bring about significant improvements in performance and emissions. It has been suggested that the addition to the methane of products of water electrolysis generated in situ on board of a vehicle may produce such improvements.

There are distinct operational mixture limits beyond which satisfactory spark ignition engine performance can not be maintained. The values of these limit mixtures which depend on the mode of their determination, are affected by numerous operational and design factors that include the type of engine and fuel used. Simple approximate methods are presented for predicting these limits. Good agreement is shown to exist between the calculated and the corresponding experimental values over a range of operating conditions while operating on the gaseous fuels: methane, propane and hydrogen. The experimentally observed operational limits deviate very substantially from the corresponding accepted flammability limit values for quiescent conditions evaluated at the average temperature and pressure prevailing at the instant of the spark passage.

The current rapidly growing interests on utilization of various alternative fuels, including low heating value fuels such as land filled gases and biogases, are prompted due to the energy security concerns and the environmental advantages. It is nevertheless augmented due to the recent high price of the conventional petroleum based fuels. Generally, the low heating value (Btu) fuels contain substantial amounts of the diluents such as carbon dioxide, nitrogen, water vapor and other trace gases in the fuel composition. This paper describes the results of the investigation of knock in a single cylinder variable compression ratio spark ignition engine fueled with gaseous fuels such as natural gas, methane and hydrogen in the presence of different amounts of diluents specifically carbon dioxide in the fuel mixture in order to represent closely the general composition of land filled and biogases in practice.