Parametric effects on combustion, performance, and emissions of diesel-hydrogen dual-fuel compression ignition engines: A comprehensive review

Diesel‑hydrogen dual-fuel engines have attracted research interest because they can reduce carbon-based emissions while maintaining high thermal efficiency. Their combustion, performance, and emissions depend on several operating and design parameters. This review examines hydrogen addition strategies, including hydrogen energy share, hydrogen flow rate, volumetric and mass-based hydrogen addition, and fuel substitution. It also comprehensively examines the effects of engine load and speed, injection timing, duration, pressure and spray angle, compression ratio, piston bowl geometry, nano-additives, combustion strategies, exhaust gas recirculation, and water injection. Existing studies show that suitable hydrogen addition can improve combustion and brake thermal efficiency while reducing carbon monoxide, hydrocarbons, carbon dioxide, and soot emissions. However, higher hydrogen addition may increase nitrogen oxide emissions and knock risk, while poor hydrogen use and hydrogen slip can occur at low loads. Engine load, speed, injection settings, compression ratio, and combustion strategies also affect efficiency and combustion stability. Exhaust gas recirculation and water injection can help reduce nitrogen oxide emissions and knock but may reduce efficiency if used excessively. Beyond these individual effects, this review compares the major operating and design parameters and their reported study-specific favorable conditions and performance-emission trade-offs. The relative research intensity of these parameters is also assessed to distinguish well-investigated areas from those needing more research. Hydrogen storage remains a practical challenge, while long-term durability and operation under changing loads need further study.