Evaluation of SCCI potentials in comparison to HCCI and conventional DICI combustion using n-heptane

This work investigates the potential of stratified charge compression ignition (SCCI) to extend the high-load limits of homogeneous charge compression ignition (HCCI) engine. Engine experiments were conducted on a single-cylinder diesel engine equipped with an electrical port fuel injection system. When the n-heptane fuel amount of port injection and in-cylinder direct injection was calibrated, partial fuel stratification was created and three different combustion modes as SCCI, HCCI, and direct injection compression ignition (DICI) were achieved. The premixed ratio (r(p)) was used to indicate the partial fuel stratification, and the effects of premixed ratio on SCCI combustion were examined. It was found that SCCI could achieve a staged combustion event of reduced pressure-rise rates, thus offering good potential to expand the operating range of the HCCI engine. Also, the engine performance and emission characteristics of SCCI were evaluated, focusing on the comparison with the HCCI and conventional DICI combustion. The results show that, with suitable partial fuel stratification, SCCI has the capability to achieve lower CO and HC emissions in comparison to HCCI and keep the NOx emissions on a low level within 50 ppm while maintaining good efficiency equivalent to DICI.