Modeling the working process of a gas-diesel engine running on ammonia with the addition of hydrogen

BACKGROUND: Ammonia, as a carbon-free fuel, has attracted much attention from researchers in many countries and is considered as one of the promising alternative fuels that ensures reduction of greenhouse gas emissions. Despite the fact that the properties of ammonia have been widely studied, the practical application of this type of fuel remains difficult. Additional research is needed to overcome problems, including low combustion rate, high emissions of nitrogen oxides and unburned ammonia. To stimulate the combustion process in the cylinder, it is possible to use hydrogen additive as a combustion activator of the ammonia-air mixture. This paper is aimed at a computational study of the effect of replacing diesel fuel with ammonia on the characteristics and harmful emissions of an in-ternal combustion engine. OBJECTIVE: Computational study of the working process and harmful emissions from exhaust gases of an automotive and tractor gas-diesel engine when operating on ammonia with the addition of hydrogen. METHODS: The object of the study was the modern YaMZ-53415 automotive and tractor diesel engine. The calculations were carried out for the nominal operating mode of the engine. For three-dimensional modeling of the working process of a gas-diesel engine running on ammonia with the addition of hydrogen, the Ansys Forte software package was used, which was developed based on modern theoretical concepts of the physics of three-dimensional gas and liquid flows, fuel spray dynamics and combustion processes. RESULTS: Calculation of the working process of a gas-diesel engine running on ammonia with various ignition doses of diesel fuel showed that when the dose of diesel fuel is reduced from 100% to 5%, the engine power and efficiency are maintained, the maximum pressure in the cylinder is reduced by 26%, nitrogen oxide emissions and the amount of unburned ammonia increase. Calculation of the working process of a gas-diesel engine running on ammonia with hydrogen additive helped to determine the minimum hydrogen additive that ensures complete combustion of ammonia. CONCLUSIONS: Running a gas-diesel engine on ammonia results in a significant reduction in carbon dioxide emissions, more than an order of magnitude, i.e. ammonia can become an alternative to hydrocarbon fuel to achieve carbon neutrality. The use of a small hydrogen additive — 0.4% helps to significantly increase the combustion rate of the ammonia-air mixture and ensures almost complete combustion of ammonia. Nitrogen oxide emissions when replacing diesel fuel with ammonia increase more than twice. To reduce them, it is necessary to use known methods — exhaust gas recirculation, a SCR-neutralizer.