Numerical simulation on combustion emission of hydrogen-ammonia blended natural gas rotary engines

Abstract

To address the challenge of excessive carbon emissions from natural gas rotary engines, blending hydrogen and ammonia emerges as a promising low-carbon strategy. In this study, combustion strategies for ternary fuel blended rotary engines using hydrogen, ammonia and natural gas are proposed, and the effects of hydrogen/ammonia blending ratios on the combustion emission characteristics of natural gas rotary engines are investigated through three-dimensional numerical simulations. Three categories of blending strategies are examined: hydrogen blending, ammonia blending and hydrogen-ammonia blending. Results indicate that hydrogen blending intensifies the combustion reaction in the natural gas rotary engine, enhances engine performance and significantly reduces carbon emissions. At 40 % hydrogen blending ratio, CO₂ emission can be reduced by up to 34 % and CO emission by up to 98 %, although it also leads to higher NO_x emissions. Regards the ammonia blending, the combustion reaction decelerates, leading to decreased carbon emissions as well, yet causes incomplete combustion and increased NO_x emissions at high blending ratios. When the ammonia blending ratio is below 20 %, the maximum unburned ammonia fraction remains under 4.1 %, indicating an environmentally acceptable blending strategy. Hydrogen-ammonia mixture with 27.3 % hydrogen and 72.7 % ammonia exhibits combustion characteristics closely resembling those of pure natural gas. This ratio effectively mitigates the combustion deficiency of ammonia while maintaining a stable indicated mean effective pressure (IMEP) and reducing carbon emissions. These findings provide guidance for the design and optimization of low-carbon rotary engines using multi-fuel strategies, achieving emission reduction, and promoting the development of hydrogen economy.