Simultaneous reduction in cloud point, smoke, and NOx emissions by blending bioethanol into biodiesel fuels and exhaust gas recirculation

摘要

Palm oil has the important advantage of productivity compared with other vegetable oils such as rapeseed oil and soybean oil. However, the cold flow performance of palm oil methyl ester (PME) is poorer than other vegetable-oil-based biodiesel fuels. Previous research by the current authors has shown that ethanol blending into PME improves the cold flow performance and considerably reduces smoke emission. The reduced smoke may be expected to allow an expansion in the exhaust gas recirculation (EGR) limit and lead to reduced oxides of nitrogen (NOx). This paper experimentally analyses the influence of EGR on smoke and NOx emissions with ethanol-blended PME. The results show that the combination of ethanol blending and EGR is effective in reducing NOx and smoke simultaneously without the thermal efficiency deteriorating. The smoke reduction can be attributed to an improved fuel–air mixing by an increased ignition delay owing to the low cetane number of ethanol and by a promoted fuel spray atomization caused by the low boiling point of ethanol. The increase in the oxygen content also leads to lower soot emission. The decrease in local equivalence ratio by ethanol blending was also suggested by the flame observation in which flame with high luminosity, high temperature, and high KL factor shrinks.