Thermodynamic Properties of Gas Generated by Rapeseed Methyl Ester-Air Combustion Under Fuel-Lean Conditions

Abstract

Biodiesel in the form of rapeseed methyl ester (RME) has been widely used for transportation as a partial (or complete) substitute fuel for compression ignition (diesel) engines. The properties of gas generated by the combustion of RME and air under fuel-lean conditions were studied. A simple analytical model was used to determine the burned gas composition. Firstly, the effects of relative air/fuel ratios on flue gas composition were studied theoretically, without exhaust gas recirculation (EGR). As the relative air/fuel ratios increased, carbon dioxide and water vapor decreased, while oxygen increased in the burned gases. The mass and molecular weight of the burned gas reduced with increasing relative air/fuel ratios. Secondly, the thermodynamic properties (i.e. specific heat, specific heat ratio, enthalpy and entropy) of the burned gas mixture, as they were affected by the relative air/fuel ratio, were calculated based upon the element concentrations of individual component in the chemical equilibrium state. The thermodynamic properties of RME-air combustion gas were plotted against relative air/fuel ratios under fuel-lean conditions and were compared to those from conventional diesel fuels. Under certain conditions, good agreement was found. This research produced primary data for further calculations regarding the thermochemistry of biodiesel-air combustion analysis.