Predicting the effects of the presence of diluents with methane on spark ignition engine performance

The presence of diluents with methane, which is often encountered in practice, brings about significant changes in the combustion process in engines and undermines performance. This paper describes an analytical approach for predicting the effects of the presence of diluents with methane on spark ignition engine performance. Calculated values of power output for a range of diluent concentrations in the fuel mixtures are shown for various operating conditions. The agreement between predicted and the corresponding experimental values was found to be especially good when the fractional concentration of the diluent in the fuel is lower than about 50%. Better agreement was also obtained with cases involving nitrogen relative to those with carbon dioxide.