Investigating the use of ammonia- and methanol-diesel blends in reactivity controlled compression ignition mode for marine engines

There is a need to adopt low-carbon fuels such as ammonia and methanol to decarbonize the marine fleet. The higher autoignition temperatures of ammonia and methanol make it challenging to use these fuels in conventional diesel engines. Previous studies have demonstrated that operating a conventional diesel engine in the Reactivity Controlled Compression Ignition (RCCI) mode has the potential to utilize low-carbon fuels without compromising engine performance or emissions. This study comprehensively compares the RCCI engine characteristics when methanol-diesel and ammonia-diesel are used as fuels. Experiments were conducted in a 6.7 L Cummins ISB engine for the methanol-diesel RCCI. A 3D CFD numerical engine model was developed in the Converge software and validated with experimental data. The ammonia-diesel RCCI was studied by replacing the methanol-diesel blend with the ammonia-diesel blend for the same fuel energy. The premixed energy ratio was varied from 5 % to 95 % for the constant fuel energy, keeping all other engine operating parameters the same. Best cases for RCCI combustion were chosen based on maximum gross indicated thermal efficiency and minimum greenhouse gas emissions. The maximum gross indicated thermal efficiency for the methanol-diesel RCCI (obtained by substituting 83 % diesel mass with methanol) was 20 % higher than that of ammonia-diesel RCCI (obtained by substituting 65 % diesel mass with ammonia) and 13 % higher than that of conventional diesel combustion. Overall, this study provides directions on using methanol and ammonia as sustainable fuels for marine engines, selecting the optimal premixed energy ratios to achieve efficient RCCI combustion.