Abstract:

To systematically reveal the effects of injection control parameters on the combustion and emission characteristics of a methanol-diesel dual direct injection internal combustion engine across a wide load range, this study carried out experiments on a methanol-diesel dual direct injection single-cylinder engine test system with a methanol substitution rate above 90%. The influences of methanol injection pressure, as well as methanol and diesel injection timings, on combustion and emission performance were investigated under low, medium and high load conditions. The results indicate that increasing methanol injection pressure accelerates methanol heat release and improves indicated thermal efficiency. Nevertheless, excessively high injection pressure under high load will drive the maximum pressure rise rate beyond the allowable limit and trigger engine knock. Retarding methanol injection timing linearly delays the CA50 combustion phasing, resulting in a substantial decline in indicated thermal efficiency but a reduction in NO_x emissions. Advancing diesel injection timing causes the peak heat release rate of methanol to first decrease and then increase, while indicated thermal efficiency and combustion duration exhibit a trend of first rising and then falling. The engine delivers the optimal balanced performance between thermal efficiency and emissions when diesel injection timing is set slightly earlier than methanol injection timing.

Key words: duel direct injection, high methanol substitution rate, diffusion combustion, thermal efficiency, emission characteristics