Exploring the influence of mixture formation methods on combustion and emissions of hydrogen/ammonia dual-fuel engines at part loads and excess air coefficients

This study investigates hydrogen and ammonia as promising alternative fuels for decarbonizing internal combustion engines during the energy transition. The research addresses challenges in combustion efficiency and emission performance of hydrogen/ammonia dual-fuel engines, focusing on mixture distribution deterioration. By examining the effects of direct hydrogen injection timing, three mixture formation methods are analyzed: homogeneous charge (HC), mild stratified charge (MSC), and severe stratified charge (SSC). Experimental results demonstrate the MSC method achieved the highest peak cylinder pressure and the most concentrated heat release. In contrast, the SSC method exhibited significant instability, with a 1.85 % higher coefficient of variation of indicated mean effective pressure (COVIMEP) at IMEP = 4 bar and λ = 1.4 compared to MSC. In terms of emissions, SSC resulted in elevated NH3 emissions, while HC and MSC produced increased NOx emissions. Energy analysis revealed that the HC and SSC methods reduced exhaust loss power (PEL) and heat loss power (PHL), respectively. However, MSC achieved the highest effective power (37.4 %) at IMEP = 7 bar and λ = 1.4, due to the lowest combined PEL and PHL. These findings highlight the potential of MSC as a superior strategy for improving combustion stability and efficiency in hydrogen/ammonia dual-fuel engines.