Effect of specific heat ratio on heat release analysis in a spark ignition engine

The specific heat ratio used in heat release calculations plays a crucial role in the determination of combustion parameters. In this study, the effects of assumed specific heat ratio on the heat release analysis of engine pressure data are studied in a spark ignition engine, using natural gas and gasoline fuels. The experiments were carried out with the spark timing adjusted to the maximum brake torque timing, at an equivalence ratio of ϕ=1ϕ=1 and a speed engine of N=3300rpm. The combustion parameters are obtained from the heat release rate, which obtained from the first law of thermodynamics during a cycle. The results show that the combustion parameters have high sensitivity to the variation and first derivative of the specific heat ratio. The results also show that the influence of the first derivative of the specific heat ratio on the combustion parameters for natural gas operation is higher than that for gasoline operation. Moreover, the first derivative of the specific heat ratio for determination of combustion parameters should not be ignored.