ディーゼル機関の排出未燃炭化水素に及ぼすリエントラント燃焼室の影響

Abstract

The effects of re-entrant combustion chambers on emissions of particulates and unburned hydrocarbons were investigated in a high speed small direct-injection diesel engine. From our study, it has been already suggested that the fuel or the fuel-air mixture can become an important origin of unburned hydrocarbon emissions when they intrude into the narrow space between the piston and the cylinder head. In this work, especially noticing this point, the trends of THC and SOF were examined changing the injection timing and the top clearance.The results show that the re-entrant combustion chamber reduces THC emissions, but increases SOF emissions compared with the deep bowl chamber at the advanced injection timing. On the other hand, at the late injection timing, THC and SOF are simultaneously reduced. When the injection timing and the top clearance are optimized for the re-entrant combustion chamber, it is possible to reduce not only smoke and NOx but also THC and SOF.