Ammonia-diesel cross-reactions in dual fuel engines: Emission impacts and kinetic analysis

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 NO 2 and N 2 O, accelerated NH 3 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.