Experimental investigation on spray combustion characteristics and transient wall temperature in a swirl-guided combustion chamber of OP2S diesel engine

The opposed-piston two-stroke diesel engine exhibits high thermal efficiency but still suffers from insufficient fuel-air mixing and excessive piston wall thermal load due to its opposed configuration. Experimental investigations on transient wall temperature variations during combustion remain limited. In this study, optical diagnostics combined with transient wall temperature measurement were employed to investigate the swirl-guided spray combustion process. The results indicate that increasing the initial kinetic energy of the spray impinging on the swirl-guided wall directs the inner-chamber flame toward the injector side and the outer-chamber flame toward the chamber center, thereby expanding the flame distribution area and accelerating the combustion rate. The flame distribution remarkably affects near-wall heat transfer. When the ambient density increases from 12.3 to 20.5 kg/m³, the combustion duration extends by 26 %, and the near-wall flame region becomes larger. Higher ambient density strengthens the near-wall combustion zone and temperature gradient, resulting in a wall temperature rise exceeding 80 %. As the injection pressure increases from 120 to 160 MPa, the combustion duration decreases by 10.3 %. The increased near-wall flow velocity enhances convective heat transfer, leading to temperature rises of 12.3 % and 9 % at the inner-pit and outer-ridge locations, respectively. When the nozzle diameter increases from 0.12 to 0.16 mm, the ignition delay first decreases and then increases, while the combustion duration extends by 11.1 %. The spatial flame region expands, whereas the near-wall flame region diminishes. The enlarged nozzle diameter promotes wall fuel adhesion, reducing the flame-wall temperature difference and weakening the wall heat transfer intensity.