The combustion of diesel fuel in internal combustion engines faces challenges associated with excessive emissions of pollutants. A direct solution to this issue is the incorporation of cleaner energy sources. In this study, a numerical model was constructed to investigate the characteristics of ammonia–diesel dual-fuel application in a medium-speed diesel engine. Effects of ammonia–diesel blending ratios on engine performance and emissions were investigated. The results indicate that for this engine model, the optimal diesel energy ratio is about 22%. When the diesel energy ratio is less than 22%, the engine’s output performance is significantly affected by the diesel energy ratio, while above 22%, the influence of the intake becomes more pronounced. When the diesel energy ratio is below 16%, the cylinder cannot reach combustion conditions. Diesel energy ratios below 22% can cause ammonia leakage. With increasing diesel energy ratio, the final emissions of carbon oxides increase. With a higher diesel energy ratio, NO emissions become lower. When the diesel fuel energy ratio exceeds 22%, the N₂O emissions can be almost neglected, while below 22%, with poor combustion conditions inside the cylinder, the N₂O emissions will increase.

As a hydrogen-rich and carbon-free fuel, ammonia is regarded as a promising carrier and storage medium for clean energy. By mixing methane with ammonia, the emission of carbon dioxide is also significantly reduced, which is of great significance for reducing greenhouse gas emissions and protecting the environment. However, ignition studies of ammonia/methane mixtures are still limited. In this paper, by means of numerical simulation with detailed chemical reaction mechanism, the effect of ammonia replacing methane on combustion was analyzed. Characteristics of explosion limit under different temperature (750-850K), equivalent ratio (0.5, 1.0 and 2.0) and ammonia mixing ratio (0-90%) were studied. The results show that the explosion limit decreases with the increase of temperature and equivalence ratio. When the proportion of NH3 is around 10%, the explosion limit shows a turning point. When the mole fraction of NH3 is higher than 50%, the explosion limit shows obvious increasing tendency with ammonia addition. Moreover, sensitivity and rate of production were also analyzed to expand the understanding of explosion limit for premixed ammonia-methane fuel blends.

Methanol and ammonia are considered promising low‐carbon fuel blends for engine applications; however, achieving stable ignition under compression–ignition conditions remains challenging. As a result, a small quantity of n‐heptane can be introduced as a highly reactive pilot fuel to initiate the combustion process. In this study a detailed mechanism is firstly constructed by combining the n‐heptane mechanism with the methanol/ammonia mechanism. In order to reduce the computational cost for the simulation of the engines, the mechanism is then reduced. This results in a reduced mechanism containing 171 species and 1307 reactions being developed. The consistency between detailed mechanisms and reduced mechanisms were evaluated through validation against experimental data. It is shown that the developed mechanisms can predict ignition delay time and laminar flame speed with good accuracy. Three‐dimensional simulation study is performed on a methanol/ammonia/n‐heptane compression ignition engine using the developed mechanisms. Results show that an increase in the ammonia blending ratio leads to a reduction in engine power, while significantly decreasing CO ₂ emissions. A shorter pulse width generally leads to slightly elevated peak pressure and temperature, and contributes to lower CO emissions. The two mechanisms exhibit good consistency in predicting cylinder pressure, peak average temperature, peak temperature, NO, N ₂ O, CO ₂ , et cetera. Overall, the developed reduced mechanism can be used for engine simulations with good computational efficiency.

The implementation of methanol-ammonia dual-fuel engines has the potential to contribute to a reduction in carbon emissions in the environment. The present study employs numerical simulations of the methanol-ammonia dual-fuel engine to investigate methanol direct injection pre-injection strategies. The impact of pre-main injection time interval and pre-injection quantity was investigated on output power, output torque, cylinder pressure and exhaust emissions such as NO_X, HC, CO, and CO₂. The results show that compared with the single methanol injection strategy, increasing the pre-injection strategy can effectively reduce soot emissions. Under certain pre-injection conditions, NO_X and soot emissions can also be significantly reduced. Compared with low pre-injection quantities, by using high pre-injection quantities, soot and NO_X emissions can be reduced by 36.91% and 35.31%, respectively. Under high pre-injection quantities, increasing the pre-main injection time interval can also significantly reduce NO_X emissions. Compared with the single methanol injection strategy, the pre-injection strategy leads to an increase in cylinder pressure peak and an advance in peak timing. As the pre-main injection time interval increases, both output power and output torque decrease. It is found that when the pre-injection quantity is 6 mg and the pre-main injection time interval is 25 °CA, with no substantial reduction in output power and output torque, the engine’s soot emissions can be reduced by 34.67%, and NO_X emissions can be reduced by 30.31%.