| Abstract:A constant-volume combustion bomb was used to simulate the thermodynamic states of a heavy-duty diesel engine when operating at altitudes of 0m, 3000m and 4500m, respectively. Based on the use of multiple imaging technologies to visualize the spray wall impingement combustion process, the effect of different altitudes on high temperature ignition, flame propagation, and soot formation characteristics of spray wall impingement combustion were studied. Results showed that as altitude increased from 0m to 4500m, the ignition delay during the spray wall impingements extended from 0.55ms to 0.88ms, and the ignition distance increased from 20.38mm to 26.87mm, indicating that high altitude had a significant suppression effect on ignition process. At this time, the burning flame assumed a disk-like shape. When the flame development entered a quasi-steady stage, the height, width and area of flame expansion rose with altitudes due to the increase of vortex intensity in flame front area. However, at the early stage of flame development, the flame size began to decrease after altitude reaches 4500m due to the cooling effect of spray impinged surface. In addition, the space-integrated flame luminosity and time-integrated luminosity rose with increased altitude, and both of soot formation and oxidation rate would increase accordingly when altitude rises to 4500m. |