ディーゼル機関におけるエタノール混合軽油のEGR燃焼解析

概要

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Utilization of bio-ethanol as an alternative fuel for diesel engines is one of the effective strategy for suppression of global warming because of its high thermal efficiency. In order to realize a premixed compression ignition (PCI) engine by utilizing the ethanol blend fuel, the effects of ethanol blend ratio and exhaust gas recirculation (EGR) ratio on combustion and exhaust emission were investigated experimentally in a direct injection diesel engine. According to the experimental results, in the case of ethanol blend fuel with the blend ratio larger than 40%, smoke density could be reduced in spite of increase in EGR ratio without deterioration of thermal efficiency. The combustion of two components fuel blended with ethanol and tetradecane instead of gas oil were simulated by means of the numerical code KIVA-3V in order to elucidate the reason for reduction in smoke density by EGR. It is shown that if the smoke density reduces by increase in EGR ratio, the mass fraction of the local unburned mixture having high equivalence ratio decreases in the combustion region with increase in EGR ratio by promotion of the premixed condition based on the longer ignition delay due to ethanol blend and EGR.