Effects of hydrogen doping on combustion and emissions of ammonia-diesel dual-fuel marine engine with different energy ratios

In order to achieve the goal of low-carbonization in the shipping industry, ammonia-diesel dual-fuel (ADDF) engines are widely researched. However, the higher ammonia energy ratio (AER) could significantly worsen the combustion environment and thus limited the use of high AER to cut down carbon emissions produced from diesel fuel. To address these issues, hydrogen fuel is introduced to enhance the combustion of ADDF. This study focuses on a large-bore six-cylinder, four-stroke marine diesel engine. The comprehensive impacts of hydrogen energy ratio (HER) ranging from 0 % to 20 % on ADDF operating with ammonia energy ratio of 40 %, 50 %, 60 %, and 70 % were studied, respectively. The aim is to analyze the effects of hydrogen doping on the performance of ADDF engines. The findings show that the inclusion of hydrogen significantly improves the in-cylinder combustion environment, facilitating a better combustion. When the HER exceeds 5 %, emissions of unburned NH 3 and N 2 O almost zero. Greenhouse gas emissions have been significantly reduced. Additionally, the indicated thermal efficiencies of ADDF engine are significantly improved to more than the levels of pure diesel mode, especially in the high AER substitution of more than 50 %. It can be also found that hydrogen doping has less effect on the ADDF operation when HER is higher than 10 %, which indicates that the optimal hydrogen ratio strongly depends on the combustion completion degree of in-cylinder ammonia fuel.