Numerical Investigations on Formation Process of N ₂ O in Ammonia/Hydrogen Fueled Pre-Chamber Jet Ignition Engine 2023-01-7023

Ammonia is used as the carbon-free fuel in the engine, which is consistent with the requirements of the current national dual-carbon policy. However, the great amount of NOx in the exhaust emissions is produced after combustion of ammonia and is one kind of the most tightly controlled pollutants in the emission regulation. Nitrous Oxide (N₂O) is a greenhouse gas with a very strong greenhouse effect, so that the N₂O emissions needs to be paid close attention. In this paper, the CFD simulation of the N₂O formation and emission characteristics during combustion is carried in the ammonia/hydrogen fueled pre-chamber jet ignition engine. The simulation results show that the turbulent kinetic energy (TKE) around the orifices of the pre-chamber is enhanced due to the local temperature difference between the main-chamber and the pre-chamber, and then the residual ammonia/hydrogen fuel in the crevice or near the cylinder wall is trapped in the high temperature zone of the main chamber, leading to the occurrence of secondary combustion phenomenon and the N₂O secondary stage formation peak around 30°CA ATDC. With the increasing of equivalence ratio (phi), the value of N₂O secondary stage formation peak will decrease and the influence of the secondary stage peak on the N₂O concentration at EVO moment will also be weakened. And the influence is minimizing at the equivalence ratio of 1.1. With the increasing of ammonia dissociation degree (α), the value of N₂O secondary stage formation peak will decrease caused by the reduction of residual fuel, which is due to enhancement of the efficient combustion. When α=0.3, the secondary combustion phenomenon will disappear, and the N₂O secondary stage formation peak also disappears synchronously. The concentration of N₂O at EVO moment is almost zero at α=0.4. Therefore, ammonia dissociation can effectively reduce the emission of N₂O.