Effect of hydrogen enrichment strategy on performance, combustion and emission characteristics of dual-fuel diesel engine: recent progress, challenges and opportunities

Hydrogen-enriched combustion in dual-fuel diesel engines has emerged as a promising strategy to enhance efficiency and reduce emissions while addressing global energy sustainability challenges. However, the practical implementation of hydrogen enrichment presents challenges such as NO_x emissions, combustion instability, and backfire risks. This review critically examines recent advancements in hydrogen enrichment strategies, focusing on injection techniques, combustion characteristics, and emission control methods. A comparative analysis of port-fuel injection, direct injection, and manifold injection is provided, highlighting their respective impacts on engine performance and emissions. Key findings indicate that optimized hydrogen injection timing and exhaust gas recirculation can mitigate NO_x formation while improving combustion stability. Additionally, this review synthesizes data from various studies to identify emerging trends, limitations, and research gaps in hydrogen-enriched combustion. Future research directions, including advanced injection strategies, hybrid combustion models, and economic feasibility assessments, are outlined to support the broader adoption of hydrogen in internal combustion engines. This study contributes to the growing body of knowledge on hydrogen-based sustainable energy solutions by offering insights that can guide technological advancements and policy developments.