Effect of Saturation and Unsaturation of Fatty Methyl Esters on Biodiesel NOx Emission Characteristics

Abstract

Biodiesel is a renewable fuel and an attractive alternative to replace fossil diesel without major engine modifications. However, the emissions of oxides of nitrogen (NOx) from biodiesel fuelled engines are reported to be higher compared to diesel engine. The characteristics of biodiesel are known to depend on their fatty acid methyl ester (FAME) contents which vary with the feedstock. Thus the contribution of saturation and unsaturation of pure components of fatty acid methyl esters on NOx formation warrants a systematic investigation. This paper attempts to relate the composition of biodiesel with NOx formation. For this purpose, the NO formation from pure fatty acid methyl esters are predicted using extended Zeldovich reaction scheme. Also, the experiments are conducted for measuring oxides of nitrogen from a compression ignition engine operated using neat palm and karanja methyl esters and their blends providing biodiesel combinations of varying degree of saturation for investigation. The measured NOx concentrations are compared with the corresponding predictions to affirm the influence of fatty acid methyl ester on engine NOx characteristics. The results clearly indicate that the change in degree of saturation influences the NOx formation and an increase in the degree of saturation of biodiesel decreases the engine NOx emission.