Performance and emission characteristics of hydrogen enriched CNG in a dual fuel diesel engine: An experimental and numerical research

Diesel engines are widely utilised thanks to their high thermal efficiency and low emissions of hydrocarbons (HC) and carbon monoxide (CO). However, they produce significant nitrogen oxides (NOx) and particulate matter (PM) in operation, necessitating alternative strategies like dual-fuel combustion with natural gas (NG) and hydrogen enrichment to improve performance and reduce emissions. While previous research has primarily focused on performance and emission characteristics, limited attention has been given to combustion behaviour and its direct relationship with engine performance. This study aims to investigate the combustion characteristics of a diesel engine operating in dual-fuel mode with hydrogen-enriched CNG. It uniquely explores the relationship between hydrogen addition and engine performance, which has not been thoroughly addressed in existing literature. Experiments were conducted with hydrogen fractions of 20 and 30 % by volume in CNG. Combustion characteristics, such as in-cylinder peak pressure and the Coefficient of Variation of Indicated Mean Effective Pressure (COVIMEP), were analysed, alongside energy conversion efficiency with respect to different engine speeds and loads. The results showed significant improvements in combustion, particularly during the premixed phase. In-cylinder peak pressure increased, reaching 4.1 bar at 20 % load. Combustion stability was enhanced, with COVIMEP remaining below 10 % across all hydrogen test blends. Performance improvements included a maximum thermal efficiency of 10.2 % and a minimum fuel consumption of 236 g/kWh, comparable to diesel operation. The findings highlight the promising potential of hydrogen-enriched CNG as a sustainable and efficient alternative to conventional diesel engines. This study provides new insights into the combustion behaviour of dual-fuel engines and underlines the role of hydrogen enrichment in enhancing both combustion stability and engine performance.