Impact of pilot injection quantity and fuel composition via pressure difference control in a same-needle diesel-methanol dual-fuel injector on engine performance

• Self-developed ΔP method controlled same needle DMDF injector. • When PIQ = 1.7 mg/cycle, both COV IMEP and soot are minimized. • The MPPDQ must be strictly limited to ≤ 15 %. • The impact of VDMI on the combustion process is minor. • Synchronous control: PIQ, MPPDQ and VDMI to achieve ultra-low emissions. This study investigated the effects of pilot injection quantity (PIQ), methanol proportion in pilot diesel quantity (MPPDQ), and volume of diesel in main injection (VDMI) on the combustion, energy distribution, conventional, and unconventional emissions of a diesel-methanol dual-fuel (DMDF) engine, using a self-developed, pressure difference (ΔP) controlled same-needle DMDF injector. Experimental and numerical simulation results indicated that PIQ had an optimum value of 1.7 mg/cycle. At this level, combustion stability and emissions were optimal. Values lower or higher than this optimum value caused combustion deterioration and increased emissions. MPPDQ was recommended to be controlled below 15 %. Excessively high MPPDQ was found to suppress pilot injection combustion, prolong the ignition delay period, lead to increased incomplete combustion losses, exacerbate combustion roughness and emission deterioration, and even trigger engine misfire. VDMI exhibited no significant effect on combustion characteristics within the range of 0.2–0.6 μL, only causing a slight increase in NO x and a minor increase in soot. The overall impact was not particularly significant. Therefore, to achieve efficient and stable operation of the DMDF engine while reducing emissions, it is necessary to balance the PIQ and keep the MPPDQ below 15 %.