Parametric Investigation of Two-Stage Pilot Diesel Injection on the Combustion and Emissions of a Pilot Diesel Compression Ignition Natural Gas Engine at Low Load 2020-01-5056

The purpose of this study is to evaluate the impact of two-stage pilot injection parameters on the combustion and emissions of pilot diesel compression ignition natural gas (CING) engine at low load. Experiments were performed using a diesel/natural gas dual-fuel engine, which was modified from a six-cylinder diesel engine. The effect of injection timing and injection pressure of two-stage pilot diesel were analyzed in order to reduce both the fuel consumption and total hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. The results indicate that, because injection timing can determine the degree of pilot diesel stratification, in-cylinder thermodynamic state, and the available mixing time prior to the combustion, the combustion process can be controlled and optimized through adjusting injection timing. Earlier first start of injection timing (SOI1) and moderately early second start of injection timing (SOI2) can realize sequential combustion of pilot diesel and controlled combustion process, while start of combustion (SOC) is decided by SOI2 and duration of combustion (DOC) is decided by SOI1. Injection pressure has great effect on the first injection pilot diesel. For enhanced flame combustion, higher thermal efficiency, and lower THC and CO emissions, the injection condition of SOI1=55°CA BTDC and SOI2=25°CA BTDC with moderate higher injection pressure were preferred, but they had an adverse effect on oxides of nitrogen (NO_X) emissions.