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Natural gas is considered to be an alternative fuel for passenger cars, truck transportation and stationary engines that can provide both good environmental effect and energy security. However, as the composition of fuel natural gas varies with the location, climate and other factors, such changes in fuel properties affect emission characteristics and performance of CNG (Compressed Natural Gas) engines. The purpose of the present study is to investigate effects of difference in gas composition on engine performance and hydrocarbon emission characteristics. The results show that THC decreases with an increasing WI (Wobber Index) and MCP (Maximum Combustion Potential) of natural gas. The power is shown to be proportional to the total heat value of the actual amount of gas entering the cylinder. There is 20% power variation depending on the composition of gas when the A/F ratio and spark timing are adjusted and fixed for a specific gas.

Mixing characteristics of a Direct-Injection engine with liquefied petroleum gas were numerically investigated using a 3D unsteady Eularian-Lagrangian two-phase model. Numerical results were validated to the experimental data of heat release rate, pressure and mass flow rate of air. The numerical results and experimental data were in a good agreement. Simulations were conducted with various engine operation conditions to investigate the effects of supercharging on the mixing characteristics of the DI engine with LPG. The results showed that the fuel uniformities and evaporation rates of LPG are higher than them of gasoline. Fuel consumption rates and maximum cylinder temperatures of LPG were also higher than them of gasoline.