Identification of N2O formation in an ammonia/n-heptane dual-fueled compression ignition engine using numerical simulations
Year: 2024
Type: article
Abstract: Ammonia, as an alternative fuel to reduce harmful gas emissions from internal combustion engines, has gained increased interest during the last decade. However, the combustion of ammonia could lead to increased formation of nitrous oxide (N2O), a potent greenhouse gas that can offset the climate benefits of using a carbon-free fuel. N2O is an intermediate species that ideally gets reduced by thermal decomposition or reacting with atomic hydrogen in the later stage of the combustion, leaving low post-flame concentrations. This study investigates events leading to N2O formation and accumulation in a dual-fuel direct injection compression ignition engine operated with ammonia and diesel. The injection timing of diesel is fixed, while four different injection times of ammonia are investigated. The results reveal that N2O accumulation within the engine cylinder can be traced to phenomena that prevent complete combustion. The findings in this article show that accumulation of N2O occurs close to the cylinder walls, regions that are cooled down by the ammonia evaporation featuring elevated ammonia concentrations, and regions with slow oxidation of ammonia during the expansion stroke. A lower consumption of N2O in post-flame reactions is observed for early injection timings, linked to the lower temperatures outside the piston bowl caused by misdirected ammonia injection. Utilizing the pilot fuel to ensure interaction with the ammonia spray reduces the occurrence of phenomena resulting in N2O accumulation. Overlapping injections and directing ammonia spray toward the piston bowl avert these phenomena. The results of this study contribute to the understanding of N2O formation, consumption, and accumulation, facilitating the optimization of direct ammonia injection strategies.Ammonia, as an alternative fuel to reduce harmful gas emissions from internal combustion engine
Source: Fuel
Institution: Norwegian University of Science and Technology
Language: English
Subfield: Fluid Flow and Transfer Processes
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,200
OpenAlex ID: W4404237907