For spark ignition and compression ignition ammonia engines, a typical approach to ensure stable operation involves the blending of ammonia with hydrogen and diesel, respectively. For the ammonia/hydrogen fuel, in this study a comprehensive comparison was conducted firstly for the differences among existing chemical mechanisms according to the experimental data of ignition, oxidation, and flame propagation. The result indicates that the current reaction mechanisms for ammonia/hydrogen fuel exhibit high prediction accuracy only within limited condition ranges. Subsequently, considering the completeness of combustion reaction pathways for ammonia/hydrogen fuel, a chemical mechanism of ammonia and ammonia/hydrogen fuel was developed and optimized in this study, and the comprehensive validation demonstrates the accuracy of the developed mechanism. On this basis, the ammonia mechanism was integrated with the detailed n-heptane mechanism to derive a mechanism for ammonia/diesel fuel that includes 1351 species and 6227 reactions. The good performance of this mechanism was demonstrated in terms of the experimental data of ignition and oxidation. In addition, the ignition sensitivity and reaction pathways of ammonia/hydrogen fuel were investigated based on the constructed mechanism, and the significance of C₃–C₇/N reactions was also analyzed for the ammonia/diesel fuel ignition process.

One viable technical approach for achieving hydrogen-blended combustion in marine ammonia-fueled engines is to utilize online ammonia decomposition to produce hydrogen, which is then introduced into the engine for combustion. This work carried out ammonia decomposition experiments using various catalysts, examining the effects of temperature and space velocity on Ru/Ce_0.33Zr_0.58La_0.03Nd_0.03Pr_0.03O_2.09 and Ni/Ce_0.36Zr_0.64O₂ catalysts. Based on the experimental data obtained, the kinetic parameters of ammonia decomposition were fitted using four different models: mass action law, first-order reaction, Langmuir, and Temkin–Pyzhev kinetics across two catalysts, with the subsequent mechanistic analysis of catalytic reaction processes within the reactor. The results revealed that the NH₃ conversion rate of the Ru/Ce_0.33Zr_0.58La_0.03Nd_0.03Pr_0.03O_2.09 catalyst was superior to that of the Ni/Ce_0.36Zr_0.64O₂ catalyst, with temperature activity windows of 250–450 °C and 400–600 °C, respectively. Within the range of 2000–32,000 mL·g⁻¹·h⁻¹), an increase in space velocity led to a decrease in NH₃ conversion rate by approximately half. All four models were able to predict NH₃ conversion rates for the different catalysts with reasonable accuracy. The activation energies for Ru/Ce_0.33Zr_0.58La_0.03Nd_0.03Pr_0.03O_2.09 and Ni/Ce_0.36Zr_0.64O₂ catalysts were found to be 37.7 kJ·mol⁻¹ and 66 kJ·mol⁻¹, respectively. Targeting hydrogen requirements of 10–40% vol for ammonia engines, the corresponding catalytic temperatures for Ru/Ce_0.33Zr_0.58La_0.03Nd_0.03Pr_0.03O_2.09 and Ni/Ce_0.36Zr_0.64O₂ were above 267 °C and 500 °C, respectively.

1-Methylnaphthalene is a critical component for constructing fuel surrogates of diesel and aviation kerosene. However, the reaction pathways of 1-methylnaphthalene included in existing detailed chemical kinetic models vary from each other, leading to discrepancies in the simulation of ignition and oxidation processes. In the present study, reaction classes and pathways involved in the combustion of 1-methylnaphthalene were analyzed, and effects of rate constants of reactions related to 1-methylnaphthalene and its significant intermediates on ignition delay times and species concentration profiles were discussed, involving hydrogen abstraction and substitution reactions of 1-methylnaphthalene, oxidation, isomerization, and addition reactions of 1-naphthylmethyl, hydrogen abstraction and oxidation reactions of indene, as well as the oxidation of indenyl and naphthalene. On this basis, a new detailed chemical kinetic model for 1-methylnaphthalene was developed, which includes 1389 species and 7185 reactions. The validation of this mechanism shows that it can predict accurately the available experimental ignition delay times, species concentration profiles, and laminar flame speeds of 1-methylnaphthalene. Finally, reaction paths and sensitivity analysis of ignition delay times were performed using the proposed reaction mechanism, and the result shows that the conversion of 1-methylnaphthalene to 1-naphthaldehyde plays an important role in its ignition.

This study focuses on the power systems of inland waterway vessels in Chinese Yangtze River, systematically outlining the low-carbon technology pathways for different power system types. A comparative analysis is conducted on the technical feasibility, emission reduction potential, and economic viability of LNG, methanol, ammonia, pure electric and hybrid power systems, revealing the bottlenecks hindering the large-scale application of each system. Key findings indicate that: (1) LNG and methanol fuels offer significant short-term emission reductions in internal combustion engine power systems, yet face constraints from methane slip and insufficient green methanol production capacity, respectively; (2) ammonia enables zero-carbon operations but requires breakthroughs in combustion stability and synergistic control of NO_X; (3) electric vessels show high decarbonization potential, but battery energy density limits their range, while PEMFC lifespan constraints and SOFC thermal management deficiencies impede commercialization; (4) hybrid/range-extended power systems, with superior energy efficiency and lower retrofitting costs, serve as transitional solutions for existing vessels, though challenged by inadequate energy management strategies and multi-equipment communication protocol interoperability. A phased transition pathway is proposed: LNG/methanol engines and hybrid systems dominate during 2025–2030; ammonia-powered systems and solid-state batteries scale during 2030–2035; post-2035 operations achieve zero-carbon shipping via green hydrogen/ammonia.

The application of ammonia decomposition technology for hydrogen production enables hydrogen-enriched combustion in marine diesel-ignited ammonia engines. This study presents experimental and simulation investigations of a diesel-ignited ammonia engine operating with hydrogen-containing fuels derived from ammonia decomposition at various blending ratios. The combustion and emission characteristics of the engine were systematically examined, and a comparative analysis was conducted on the combustion behavior of the engine between using ammonia decomposition-derived hydrogen-containing fuel and pure hydrogen. The result shows that under constant engine output power, at 1200 rpm and 75% load, increasing the hydrogen energy rate results in largely unchanged cylinder pressure and heat release rate. The diesel substitution rate exhibits an initial increase followed by a decrease, while the energy consumption rate demonstrates the opposite trend. At 1500 rpm and 75% load, an increase in hydrogen enrichment leads to an earlier rise in cylinder pressure and heat release rate, a continuous increase in diesel substitution rate, and a consistent decrease in energy consumption rate. The early stage of in-cylinder combustion is dominated by diesel combustion, followed predominantly by the combustion of ammonia and hydrogen. Regarding the difference between using decomposition-derived hydrogen-containing fuel and pure hydrogen, within the hydrogen enrichment range of 0–20%, the discrepancies in intake composition and equivalence ratio between the two hydrogen-addition modes gradually widen but remain within 1.3%. Taking a hydrogen energy rate of 10.56% as an example, the differences in in-cylinder pressure and heat release rate between the two hydrogen-addition modes are not significant, indicating that the N₂ generated from ammonia decomposition has a relatively weak influence on the engine. With increasing hydrogen enrichment, NH₃ emissions gradually decrease, while NO emissions increase. For N₂O, hydrogen enrichment promotes its consumption, resulting in lower emissions. Under various hydrogen enrichment conditions, equivalent greenhouse gas emissions are mainly influenced by CO₂ emissions.

With the rapid development of data science, machine learning has been widely applied to research on pollutant emission prediction in internal combustion engines due to its excellent responsiveness and generalization ability. This article introduces Lightgbm (LGB), which belongs to ensemble learning, to predict the pollutant emissions from a low-speed two-stroke marine engine. The dataset used to train LGB was derived from a one-dimensional performance simulation model of the engine, which was rigorously verified for its reliability by experimental data. To further improve the forecast performance of the LGB model, we used Harris Hawks Optimization (HHO) to automatically optimize the hyperparameters of the model, and finally, we analyzed the importance of the model features. The results show that changes in engine control parameters have significant influences on NOx and soot emissions from the engine, which can serve as the basis for the selection of the LGB model features; the LGB model was able to accurately predict pollutant concentrations from the engine with much higher accuracy than a single decision tree (DT) model; combining with HHO, the predictive ability of the LGB model was significantly improved, such as for the validation set prediction results, the mean absolute error (MAE) was reduced by about 20%, the mean squared error (MSE) was reduced by about 30%, and the coefficient of determination (R²) was increased by about 0.005; and the importance analysis of the model features indicated that the combustion condition of the fuel was highly correlated with the generation of the pollutants, and the fuel injection phases can be adjusted in practice to achieve highly efficient and low-emission processes of combustion. The results of this study can provide references for the development of a new generation of highly efficient and low-pollution marine engines.