Ammonia blending in diesel is an efficient combustion strategy that overcomes the low reactivity of ammonia while maintaining high engine adaptability. A smaller and accurate chemical kinetic mechanism is crucial for exploring the application of ammonia/diesel in engine. Building upon a previously developed reduced mechanism, this study presents a newly developed four-component skeletal mechanism for ammonia/diesel dual-fuel combustion. The mechanism includes 123 species and 669 reactions, with 134 specifically identified as cross-reactions between fuel components. It was progressively validated and optimized through detailed kinetic analyses involving ammonia, n-dodecane, cyclohexane, toluene, diesel, and their ammonia/diesel mixtures. To investigate the impact of ammonia–diesel cross-reactions on engine emissions, a CFD model of an RCCI engine was established, demonstrating the applicability of the skeletal mechanism in three-dimensional simulations. The results show that incorporating cross-reactions significantly improves the prediction accuracy for in-cylinder pressure, heat release rate, and emission trends. Under 40% ammonia energy fraction, the presence of cross-reactions notably enhanced radical formation and chain-initiation processes, leading to advanced combustion phasing and higher in-cylinder temperatures. This, in turn, promoted the formation of NO2 and N2O, accelerated NH3 consumption and CO oxidation, but also intensified local soot formation due to incomplete combustion. The proposed skeletal mechanism offers a favorable balance between computational efficiency and predictive accuracy, providing a robust kinetic foundation for optimizing combustion and emission control in ammonia/diesel dual-fuel engines.
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