Acting mechanism of inner chamber structure of the asymmetric swirl-induced combustion system on the combustion and heat transfer of the OP2S diesel engine

The Opposed-Piston Two-Stroke engine shows great potential for high-power-density applications. However, side fuel injection limits the further thermal efficiency improvement. Furthermore, the exhaust-side piston is subjected to prolonged scouring by high-temperature combustion gases, making it susceptible to thermal ablation failure. To address this, an asymmetric combustion system with an intake-side swirl profile and exhaust-side flat top using exclusive intake-side injection is proposed. This study investigates the influence of inner chamber configuration on spray combustion and piston heat transfer. The results indicate that the ridge position alters fuel mass distribution, leading to inner-chamber dominated (P1), outer-chamber dominated (P5), and dual-zone synergistic (P3) mixing modes. Specifically, the P3 configuration generates a velocity field of appropriate intensity and direction in both inner and outer chambers, driving uniform fuel distribution. Consequently, P3 achieves a peak air utilization of 55.5%, compared to 53.3% and 49.9% for the P1 and P5 configurations. This optimized mixing mode improves the spatial distribution of flame and shortens the post-combustion period to 6.6 °CA, boosting indicated thermal efficiency to 51.30% and power to 15.51 kW. In contrast, P1 and P5 are limited by prolonged combustion, yielding lower efficiencies of 50.60% and 49.64%, and power outputs of 15.16 kW and 14.47 kW. Finally, this asymmetric system facilitates a thermal load transfer from the exhaust to the intake side, leveraging fresh charge cooling to prevent thermal overload. Consequently, the intake-side piston bears a peak heat flux of 7311.72 kW/m2, while the exhaust-side flux is restricted to 3925.42 kW/m2.