ディーゼルPCCI燃焼における噴射条件の選択に関する研究（確率過程論燃焼モデルによる検討）

摘要

ディーゼル機関の低負荷域における排気特性改善のため，予混合圧縮自着火（PCCI）燃焼の原理を活用する試みが行われている．最近では，比較的圧縮上死点に近い噴射時期を選択して潤滑油希釈を防ぎながら，有効圧縮比の低下と大量EGRにより着火時期の適正化と窒素酸化物（NO_x）排出の抑制を狙った燃焼方式に関する研究が盛んに行われている．%To obtain a strategy for combustion control to achieve low NO_x emission with high thermal efficiency in DI-PCCI operation of diesel engines, numerical study was conducted using a combustion model including a stochastic-PDF mixing model with a reduced chemical kinetic scheme. Effects of injection conditions on heat release and NO_x formation processes were investigated. The results indicate that the combustion model successfully describe the trends of NO_x, maximum pressure rise rate and thermal efficiency. The mechanisms which control pressure rise rate and NO_x formation were discussed paying attention to the effects of fuel-air mixing.