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.

Ammonia is a promising alternative fuel, which is considered to have the potential to substitute conventional fossil fuels. In the present work, auto-ignition characteristics of ammonia substitution on methane are investigated both experimentally and numerically. The auto-ignition procedure of ammonia-substituted methane/air mixtures are measured behind the reflected shock wave in a shock tube experiment system over temperatures from 1355 to 1877 K, pressure up to 5 atm and an equivalence ratio from 0.5 to 2. Numerical simulation studies using a detailed kinetics mechanism are also performed to gain a deep insight into the auto-ignition procedure of ammonia-substituted methane fuel mixtures. The established numerical model is verified with the measured auto-ignition delay time data by experiments. Then, the auto-ignition delay times are predicted under a wider range of conditions such as equivalence ratio, pressure, temperature, etc. In this way, combustion characteristics of such mixtures are investigated. It is found that adding ammonia fuel to methane will not change the autoignition delay time of methane a lot, while it can effectively benefit the reduction of carbon emissions. Finally, sensitivity analyses are performed to provide essential information for the elementary reaction sensitive to the ignition characteristics. The results present in this work can provide fundamental information for combustion application of ammonia-based fuels.

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.

Utilizing ammonia (NH₃) as a zero-carbon alternative fuel requires a deeper understanding of its combustion characteristics, with ignition delay time (IDT) serving as a critical descriptive parameter. To investigate the effects of propane (C₃H₈) addition on NH₃ ignition at high temperatures, the ignition delay times of NH₃/C₃H₈ blends were systematically measured using a shock tube over a wide range of conditions: temperatures of 1263–2117 K, pressures of 0.14–0.5 MPa, equivalence ratios of 0.5–2.0 and propane mole fractions of 5–70%. The results indicate that propane addition significantly promotes ammonia ignition. Under stoichiometric and 1.4 atm pressure conditions, the addition of C₃H₈ to pure NH₃ reduces the ignition delay time by approximately fivefold, allowing auto-ignition to occur at a lower temperature. Furthermore, detailed chemical kinetic mechanisms from the literature were adopted for numerical simulations and validated against the newly acquired experimental data. Kinetic analysis reveals that the propane addition does not alter the main oxidation pathways of ammonia, while it triggers C-N cross-reactions at higher blending ratios (>30%). The active radicals generated during the early stages of propane oxidation accelerate H-abstraction reactions, serving as the key mechanism responsible for the shortened ignition delay times and promoted ignition.