Evaluating the potential performance of methane in lean conditions and examining the variations in combustion in a gasoline direct injection engine

The present work investigates the effect of methane addition on a direct injection spark-ignition engine's performance, combustion, cycle-to-cycle variation, coefficient of variation, and emission characteristics. Equivalence ratio of the engine is varied from λ = 1.0, 1.02, 1.08, 1.15, and 1.22. Methane addition for the equivalence ratios (λ = 1.0, 1.02, and 1.08) close to the stoichiometric condition does not support the methane addition. Decrease in peak pressure is seen in minimum to the maximum methane addition of 19.5 %. Adding the gaseous fuel to the intake manifold causes charge displacement, as the fuel is inducted at the suction top dead center. This effect is consistent with the increase in flame initiation and combustion durations. The same methane addition fraction for the equivalence ratios of λ = 1.15 and 1.22 provides better combustion stability and efficiency. The peak pressure attainment for λ = 1.22 is a 25 % increment with the maximum methane addition. Emission formation of carbon monoxide and unburnt hydrocarbons drops as the fuel is leaner towards λ = 1.22, even with the addition of methane. The oxides of nitrogen emissions decrease initially for the equivalence ratio close to the stoichiometric condition but increase for the leaner equivalence ratio with the methane addition fraction.