• A combined premixing-direct injection strategy enhances methanol-hydrogen combustion. • Direct hydrogen injection reduces backfiring and forms controllable stratified mixtures. • Hydrogen blending (12%) increases peak cylinder pressure by 22.1%. The overuse of fossil fuels has intensified environmental challenges, highlighting the need for low-carbon alternatives in transportation. Methanol, a promising low-carbon fuel, is limited by its high latent heat of vaporization and low calorific value, while hydrogen offers high energy density and wide flammability limits, making it an effective combustion enhancer. This study adopts a methanol-air intake premixing combined with in-cylinder hydrogen direct injection strategy to mitigate backfire and enable stratified mixture formation. CFD simulations were conducted to investigate the effects of hydrogen energy ratios (3%–12%) and injection timings (140°CA, 180°CA, and 240°CA BTDC) on engine performance and emissions. Results show that optimizing injection timing reduces pressure loss by approximately 13% at 12% hydrogen ratio, and co-optimizing injection and ignition timing boosts combustion efficiency to over 90%. In terms of emissions, increasing hydrogen from 3% to 12% reduces CO by 23.08% and CO 2 by 8.43%, although NO X emissions rise from 0.7 × 10 − ⁶ kg to 1.1 × 10 − ⁶ kg under 12% hydrogen with 140°CA BTDC injection. Hydrogen supplementation effectively improves combustion efficiency and reduces carbon emissions, offering a viable pathway toward cleaner and more efficient low-carbon engines.
Li et al. (Sun,) studied this question.