The effect of injection timing and intake valve close timing on performance and emissions of diesel PCCI engine with a full engine cycle CFD simulation

Abstract

A full-cycle computational fluid dynamics (CFD) simulation coupled with detailed chemical kinetics mechanism has been used to investigate the effect of start of injection (SOI) timing and intake valve close (IVC) timing on performance and emissions of diesel premixed charge compression ignition (PCCI) engine. By sweeping SOI timing from −35 to −5 °CA ATDC and IVC timing from −140 to −80 °CA ATDC with fixed 50% exhaust gas recirculation (EGR) and 1.8 bar intake pressure, the contour plots for ignition timing, nitric oxides (NO x ), soot, hydrocarbon (HC), carbon monoxide (CO), indicated specific fuel consumption (ISFC), and ringing intensity have been developed. The results indicate that the operating range can be divided into kinetically controlled region and mixing-controlled region, in which the ignition timing is solely controlled by IVC timing and SOI timing respectively. To Minimize HC, CO, NO x and soot emissions, SOI timing must be carefully adjusted within a limited range. With the retarded IVC timing, the operating range of SOI becomes wider for clean combustion. The IVC timing should be optimized with consideration of ignition timing and combustion efficiency at different SOI timing in order to improve fuel economy. For purpose of avoiding engine knock, the SOI timing around −20 °CA ATDC and early IVC timing are pursued.