Study on Combustion Simplification Mechanism and 3D Simulation of Ammonia/Diesel Dual-Fuel Engine

To accurately describe the combustion process of ammonia/diesel dual-fuel, this paper develops a simplified kinetic mechanism for ammonia/diesel dual-fuel based on the decoupling method and a modular approach, comprising 212 components and 620 elementary reactions. The diesel component is represented by four components: n-heptane, n-hexadecane, isohexadecane, and α-methylnaphthalene. The mechanism was validated using shock tube experimental data. The results indicate that the developed mechanism can accurately predict key parameters such as ignition delay time and laminar flame speed under different ammonia-blending ratios, showing good agreement with experimental values. Single-component ignition delay prediction error ≤ 6%; laminar flame speed deviation error ≤2%; CFD validation metrics (e.g., peak cylinder pressure error within 1.35%) Furthermore, the mechanism was coupled with 3D CFD software to validate the cylinder pressure and heat release rates, using a six-cylinder, heavy-duty diesel engine with a bore of 114 mm, a stroke of 145 mm, a displacement of 8.9 L, and a compression ratio of 16.6 as the study subject. Based on the validation of the model and the feasibility of the mechanism, further studies were conducted on combustion and emission patterns under different load conditions and ammonia substitution rates. The results indicate that at low ammonia substitution rates, as the load decreases, the combustion rate slows down and thermal efficiency declines, while the indicated thermal efficiency first decreases and then increases; load primarily influences ignition and combustion processes by altering the thermodynamic state within the cylinder. At ammonia substitution rates of 20–60%, the heat release rate exhibits a “bimodal” pattern under different load conditions. NO, NO2, and N2O emissions first increase and then decrease with increasing ammonia substitution rate, peaking in the 40–60% range; CO2 emissions gradually decrease as the ammonia substitution rate increases.