Effect of in-cylinder flow on the combustion and flame propagation characteristics of an ammonia/diesel dual-fuel engine

This numerical study investigates the effect of in-cylinder flow, regulated by combustion chamber (CC) geometry and swirl ratio (SR), on the combustion and flame propagation characteristics of an ammonia/diesel dual-fuel engine. First, a 3-D computational model considering flame propagation was constructed by fitting the parameters of Gulder model for ammonia. Then, four different CCs, namely shallow depth CC (SCC), petal type CC (PTCC), toroidal CC (TCC), and toroidal re-entrant CC (TRCC), were designed based on the original CC (OCC). Simulations of the designed CCs were performed under different SRs. The results show that OCC, PTCC, and SCC exhibit weak swirl and strong reverse squish, while TCC and TRCC feature strong swirl and weak reverse squish. The strong swirl of TCC can significantly enhance the diffusion combustion stage, resulting in the highest indicated thermal efficiency of 44.2 % with an SR of 0.978. Increasing SR can further enhance the swirl and displace it towards the bowl, which enhances combustion in the bowl region and subsequently leads to a significant increase in the heat loss through the piston bowl. However, increasing SR also leads to a further weakening of the reverse squish, resulting in a shorter flame propagation distance in the squish region.