Research on the substitution rate and main injection timing and ultra-low emission mechanism under diesel-methanol dual-fuel injector controlled by pressure difference

This study was based on a pressure difference (ΔP) controlled same-needle diesel-methanol dual-fuel (DMDF) injector, which systematically revealed the mechanisms of methanol substitution rate (MSR), main injection timing (SOImain), and composition on engine combustion and emissions. The results indicated that at high MSR (ΔP = 6–9 MPa), CA50 was delayed and brake thermal efficiency (BTE) decreased. The moderate MSR (ΔP = 10–12 MPa) balanced the oxygen content of methanol and the ignition ability of diesel, leading to the forward movement of CA50, shortened combustion duration, and achieved the highest BTE. Soot emissions meet emission regulations (0.01 g/kW · h) when MSR ≥50 %. Optimization analysis of the SOImain showed that DMDF mode had a faster combustion rate and CA50 was closer to the top dead center (TDC), ultimately enhancing BTE by 3.76 % relative to D mode operation. Soot and NOx emissions were reduced by 99.8 % and 74.4 % respectively compared to D2. Research on composition showed that the high oxygen content, OH oxidation characteristics and uniform mixture of methanol effectively promoted soot oxidation, while the temperature suppression effect in-cylinder reduced NOx emissions. Research had shown that moderate MSR and SOImain can improve BTE and achieve ultra-low emissions, providing theoretical and engineering support for near zero emission engine technology.