Experimental study on effects of pilot injection strategy on combustion and emission characteristics of diesel/methanol dual-fuel engine under low load

In order to explore the optimization scheme of injection strategy for dual-fuel engine at low load, diesel/methanol dual-fuel combustion mode was conducted on a turbocharged intercooled engine. Effects of methanol ratio, main and pilot injection parameters on combustion process, emission characteristics and fuel economy of dual-fuel engine were systematically studied at 30% load of 1800r/min. Results show that with the addition of pilot injection strategy, dual-fuel combustion process gradually changed from two-stage to single-stage with methanol ratio increasing, the upper limit of methanol ratio was increased from 40% to 60%, the cyclic coefficient of variation (COV) and HC emissions decreased, and the brake thermal efficiency (BTE) increased. While the heat release was delayed with the advance of pilot injection timing, the peak heat release rate increased, and the combustion duration, soot emission and COV decreased. Additionally, the increasing pilot injection quantity would make heat release rate curve evolve to bimodal distribution, resulting in advanced CA05 and CA50, and the increased BTE, NOx and soot emissions along with the decreased HC and CO emissions were also observed. Dual-fuel engine with optimized pilot/main injection strategy could achieve the BTE of 47.34% and the COV of 1.4% at 50% methanol ratio condition.