Effects of injection angles and ignition timing on combustion characteristics in a hydrogen/ammonia dual direct injection rotary engine based on orthogonal analysis

The potential application of hydrogen-ammonia blended fuel in rotary engines and the critical role of in-cylinder dual direct injection technology in fuel distribution and combustion control are well-recognized. However, the coupling effects of hydrogen/ammonia injection angles and ignition timing remain unclear. To identify the most significant injection strategy and ignition strategy affecting engine combustion parameters, this study investigates the impacts of hydrogen injection angle (θ2_H2), ammonia injection angle (θ1_NH3), and ignition timing (IT) on combustion characteristics and emission performance using an orthogonal experimental design based on CONVERGE three-dimensional simulations, with the accuracy of the numerical model validated through experimental verification. Results indicate that the order of influence on in-cylinder pressure, quantified by range (R) and variance analysis, is θ2_H2 (R = 1.1269) > θ1_NH3 (R = 0.7002) > IT (R = 0.4835). Using the normalization method, the optimal parameter combination is determined as θ1_NH3 = −60°, θ2_H2 = 0°, and IT = 10 °CA before the top dead center. Hydrogen exhibits a significant influence with a contribution rate of 51.14%. This optimal combination reduces NOx emissions by 62.6%, yields a maximum in-cylinder pressure of 3.05 MPa, and increases the combustion heat release rate by 32.5%. It clarifies the effect of parameter optimization on ammonia-hydrogen stratified combustion and pollutant formation, thereby providing strategies for the engineering design of injection systems.