Effect of the gas state equation on the thermodynamic diagnostic of diesel combustion

The effect of considering the gaseous fuel as ideal gas during the diagnostic procedure from experimental cylinder pressure signal from a Diesel engine is analysed. After the chemical characterization of the fuel and the estimation of the thermodynamic properties, the compressibility factor of the fuel was quantified under engine operating conditions, the prediction capability of four cubic state equations was tested, and finally their application was extended to the whole gaseous mixture throughout the engine cycle. One of the tested equations was finally selected and used to compare the main results of the combustion diagnostic procedure (mean cylinder temperature and heat release) with those obtained with the ideal gas state equation, under two selected operating modes. Although the obtained differences are relatively small, the deviations in the gas temperature around the top dead centre may be important in case that these results are used for predictions of heat radiation and pollutant formation.