Spray combustion of ammonia–hydrocarbon blended fuels under high-pressure dual-fuel conditions in large engines: Numerical investigation

• 3D combustion CFD of spray combustion of ammonia–hydrocarbon blends under high-pressure dual-fuel conditions in large engines • CFD model validation: predicted ignition delays closely match experimental trends for pure ammonia and all blended fuels • High local equivalence ratios in the spray led to increased fuel residue during diffusion combustion and intensified afterburning • Post-injection afterburning is most pronounced in propane–ammonia blends, which may impair overall thermal efficiency • Methanol–ammonia blends improved ignition stability with lower risk of excessive post-injection afterburning • Detailed chemical kinetics (112 species, 641 reactions) coupled with RNG k-ε turbulence modeling enables comprehensive prediction of combustion and emissions Ammonia is a promising zero-carbon fuel for high-power internal combustion engines, but its inherently low reactivity poses significant challenges for stable and efficient combustion. To address these challenges, this study conducted three-dimensional computational fluid dynamics (CFD) of pure ammonia and ammonia–hydrocarbon blended fuels under high-pressure dual-fuel (HPDF) conditions, using a setup that replicates the configuration of the Rapid Compression Expansion Machine used in our previous experiments. The CFD model incorporated detailed chemical kinetics (112 species, 641 reactions) and was validated against experimentally measured heat release rate profiles. The simulations successfully captured key combustion phenomena, including ignition delay, combustion duration, flame structure evolution, and post-injection afterburning behavior. Hydrocarbon blending improved combustion stability by modifying the spray flame structure, with methanol–ammonia blending achieving a favorable balance of high combustion efficiency, shorter combustion duration, and moderate emission levels without severely increasing local equivalence ratios. In contrast, propane–ammonia blending broadened the high-equivalence-ratio region along the spray, degrading diffusion combustion and leading to undesirable afterburning. This resulted in enhanced oxidation of residual ammonia but also introduced potential drawbacks in thermal efficiency and emission behavior. These findings elucidate the strong influence of fuel composition on spray flame structure, combustion sustainability, and nitrogen-based emissions in ammonia-fueled HPDF systems, providing critical insights for optimizing ammonia-based fuel strategies for large engines.