Eco-diesel engine fuelled with rapeseed oil methyl ester and ethanol. Part 2: comparison of emissions and efficiency for two base fuels: diesel fuel and ester

A comparison has been made of the efficiency and emissions from a single-cylinder naturally aspirated direct injection compression ignition engine when fuelled either with diesel fuel (DF) or rapeseed oil methyl ester (RME) and additionally with ethanol in different proportions injected into the inlet port during the suction stroke. Investigations were performed at two constant loads, high and low. At each load the proportions of ethanol and base fuel were changed in such a way that the load was held constant. At each load the engine operated at a constant speed and for three injection timings. The obtained results were similar for both fuels, but in the case of RME there were lower carbon dioxide and smoke emissions and in some operating conditions NOx emission was observed. The aim of the ethanol injection, which was produced with air premixed with a homogeneous mixture in the cylinder, was to promote and accelerate combustion of DF/RME droplets, resulting in shorter combustion of the total fuel. The second objective of ethanol addition was to decrease the emissions of smoke and carbon dioxide, because as ethanol burns its combustion products have more H2O and less CO2. The aim was to provide a sufficient effective energetic fraction of ethanol in order to reach a satisfactory decrease in emissions, which was found to be about 25 per cent for RME and about 20 per cent for diesel fuel.