Effect of blending ratio and equivalence ratio on combustion process of ammonia/hydrogen rotary engine

Ammonia/hydrogen mixed fuel is considered one of the ideal alternative fuels for internal combustion engines and can effectively reduce greenhouse gas emissions. This study investigates the effects of hydrogen blending ratio and equivalence ratio on the combustion characteristics and emission process of ammonia/hydrogen rotary engines through experiments and numerical simulations. The hydrogen blending ratio ranges from 5 % to 80 %, and the equivalence ratio varies from 0.8 to 1.2. The results show that when the hydrogen blending ratio is 5 %, the ammonia/hydrogen rotary engine fails to ignite. When the hydrogen blending ratio is more than 20 %, the combustion performance is significantly better. As the hydrogen blending ratio increases, the peak in-cylinder pressure gradually rises, and the timing of the peak pressure occurs earlier. The instantaneous heat release rate also increases progressively. When the hydrogen blending ratio reaches 80 %, the peak pressure reaches 1.92 MPa, and the peak heat release rate reaches 66.12 J/degrees CA. During the early combustion stage, the formation rates and amounts of NO, NO2 and N2O in the cylinder increase with the hydrogen blending ratio. However, as combustion progresses, ammonia is almost completely combusted for high hydrogen blending ratios, and the NO formation decreases after reaching its peak value. Furthermore, as the equivalence ratio increases, the in-cylinder pressure of the rotary engine gradually increases. However, when the equivalence ratio exceeds 1.1, excessive fuel leads to a decrease in oxygen concentration within the combustion chamber, causing incomplete combustion of the fuel. This results in a reduced heat release, a decrease in in-cylinder pressure, and a gradual reduction in NO formation. This study provides novel insights into optimizing the combustion performance of ammonia/ hydrogen rotary engines, presenting a unique approach to enhancing engine efficiency and emission reduction. The findings offer practical guidance for future engine design and strategies to address environmental concerns.