An effort to enhance methanol energy in a diesel engine under dual fuel mode using pilot injection strategy coupled with exhaust gas recirculation

The methanol/indirect coal to liquid (ICTL) dual fuel mode was realized by direct injection of ICTL as high-reactivity fuel to ignite methanol as low-reactivity fuel in a diesel engine. However, HC, CO and the coefficient of variation of pressure (COVp) increases significantly with the increase of methanol alternative ratio (MAR) under low speed and light load condition. Based on methanol/ICTL dual fuel test bench, the effects of MAR and pilot injection strategy coupled with exhaust gas recirculation (EGR) on engine performances at a constant engine speed of 1000r/min and 60Nm were assessed to improve engine performance as well as to reduce cyclic fluctuation rate. The results display that ignition delay (ID) is prolonged, combustion duration (CD) is decreased, the corresponding crank angle of 50 % (CA50) is advanced, maximum cylinder pressure and heat release rate (HRR) decrease, SOOT and NOx emission are decreased, but HC and CO emission increase with the increase of MAR, and the COVp reaches 4.8 % when the MAR is 15.2 %. When the start of pilot injection (SOI_pilot) is −29 ^oCA and pilot injection quantity (PIQ) is fixed at 1.8 mg/cyc, SOOT, HC and CO emission are further reduced, but NOx emission is increased. Moreover, the pilot injection strategy can reduce COVp by shortening ID and CD to strengthen the control of the CA50 phase and improve the activity of mixture. With the appropriate EGR ratio combined with the optimized pilot injection strategy, the SOOT emission is decreased by 53.6 %, NOx emission is increased by 31.4 %, HC and CO emission are gradually increased but at a very low level, and COVp is decreased from 4.8 % to 2.99 %. The results in this paper can promote the diesel engine to low carbon emission and provide theoretical guidance for the application of methanol and ICTL.