A preliminary study for applying the Atkinson cycle on the 2-stage injection type PCCI engine

Abstract

It is well known that diesel engines generate a large amount of NOx and PM because of locally excessive richness and overall lean combustion. Recently, a premixed charge compression ignition (PCCI) engine has received attention for its attractive advanced combustion process because this combustion system can reduce NOx and PM simultaneously. However, PCCI engines have a disadvantage that the combustion efficiency is relatively low when the PCCI strategy is applied to conventional diesel engines, the combustion takes place before TDC due to the spontaneous pre-ignition property of diesel. Many researchers have been trying to overcome the drawback by retarding the ignition timing with low compression ratios. In this study a modified cam having the fixed opening timing of the intake valve and the 30° retarded closing timing was employed to reduce the effective compression ratio. Although the Atkinson cycle with a retarded cam leads to a low in-cylinder pressure in the compression stroke, the engine work can increase through the compensation of the max pressure. On that account, we applied various advanced second injection timings to raise the max pressure up to the same pressure as the original cam's.