Investigation of charge preparation strategies for controlled premixed charge compression ignition combustion using a variable pressure injection system

Abstract

This paper uses a multi-dimensional computational fluid dynamics (CFD) code coupled with detailed chemistry, the KIVA-CHEMKIN code, to provide guidelines for solving problems with premixed combustion strategies, namely, lack of combustion phasing control, excessive pressure rise rate, and spray wall impingement due to early injections. A multiple injection concept is used to control combustion phasing and reduce the rate of peak pressure rise. To address spray—wall impingement, an adaptive injection strategy (AIS) using two-injection pulses at different injection pressures is employed. The combustion process considered is at a mid-load operating condition for the light-duty engine of the present study (nominal indicated mean effective pressure (IMEP) of 5.5 bar and high speed, 2000 r/min) and the effects of first and second pulse injection pressure and timing, swirl ratio, and spray targeting are explored. The investigation showed that an optimized low-pressure early cycle injection combined with a high-pressure near top dead centre (TDC) injection allows combustion phasing to be well controlled while achieving premixed compression ignition (PCI)-like emissions levels. An improved solution was found with near-zero nitric oxides (NO x) and soot, a net indicated specific fuel consumption (ISFC) of only 175 g/kW h, and a peak pressure rise rate of ∼8 bar/deg.