Abstract:As a key transitional technology for the low-carbon transformation of energy systems, hydrogen dual-fuel engine technology utilizes the co-combustion of hydrogen with conventional or renewable fuels and demonstrates significant potential for improving thermal efficiency and reducing carbon emissions. This paper systematically reviews the combustion characteristics, performance impacts, emission control strategies, and engineering applications of hydrogen blended with diesel, gasoline, natural gas, and ammonia. A comparative analysis highlights differences in combustion regulation mechanisms among these fuel combinations, revealing a principle of "common synergy with individual adaptation" for hydrogen across various technical pathways. For hydrogen–diesel engines, hydrogen enhances premixed combustion and improves thermal efficiency; a hydrogen blending ratio of 7.5% increases power output by 17.2% and brake thermal efficiency by 23%. The NOx-soot trade-off necessitates synergistic optimization through exhaust gas recirculation, water injection, and advanced injection strategies. In hydrogen–gasoline engines, hydrogen extends the lean-burn limit from λ=1.45 to 2.55 and improves cold-start performance. With a hydrogen blending ratio of 20%, brake thermal efficiency reaches 34.2%, while HC and CO emissions are reduced by 40.0%–58.3%. Split-injection strategies enable active control of mixture stratification, thereby enhancing combustion stability under ultra-lean conditions. For hydrogen–natural gas engines, hydrogen accelerates flame propagation and broadens the lean-burn limit. Hydrogen injection timing has been identified as an independent parameter with a more pronounced effect on combustion than the blending ratio. In hydrogen–ammonia engines, hydrogen acts as an effective combustion promoter for ammonia. Increasing the compression ratio significantly reduces hydrogen consumption, while pre-chamber combustion and active hydrogen jet ignition enable stable combustion with a hydrogen energy fraction as low as 2.9%, achieving an indicated thermal efficiency of 42.5%. Despite these benefits, the high reactivity of hydrogen intensifies thermal NOx formation, particularly under medium to high loads. Its wide flammability range and low ignition energy introduce risks of backfire, pre-ignition, and knocking. Engineering challenges such as hydrogen storage, transportation safety, and system cost remain critical barriers to large-scale deployment. Future research should shift from static optimization to dynamic, multi-parameter coordinated control. To prevent abnormal combustion, active control systems based on precise injection timing, real-time in-cylinder pressure monitoring, and artificial intelligence are required. For safe storage and transportation, breakthroughs in hydrogen carriers that are stable under ambient conditions, such as ammonia and liquid organic hydrogen carriers, are essential. Advancing the green hydrogen industrial chain with full life-cycle carbon emission management will support large-scale applications in transportation, shipping, and power generation, positioning hydrogen dual-fuel technology as a key pathway toward carbon neutrality. Close-