Effect of wall parameters on impinging combustion and soot emission characteristics of heavy-duty diesel engine at low temperature

The effect of wall parameters on combustion and soot emission characteristics remains to be revealed so far, especially in the case of spray impingement at low temperatures. Therefore, the visualization experiments are carried out in a constant volume combustion chamber using the Mie scattering and direct photography techniques, and the two-color method was used to extract the flame temperature and soot volume. The results show that increased wall distance and wall angle contribute to fast and stable ignition, but result in more soot production. In addition, the lower the ambient temperature, the more prominent the above characteristics are. At T_amb = 820 K, as the wall distance increases from 40 mm to 60 mm, the liquid spray impingement changes to the vapor impingement, so the ignition delay shortens, and the flame area and natural luminance increase significantly. At lower T_amb = 770 K, a complete misfire is observed at L_w = 40 mm but the ignition remains stable at L_w = 60 mm. The variation of the ignition characteristic parameters with the wall angle is similar to that of the wall distance. Under P_inj = 40 MPa, as the wall angle increases from 0° to 70°, the time to reach luminance saturation advances from 0.60 ms to 0.27 ms. Under higher P_inj = 100 MPa, a complete misfire occurs at θ =0° but bright flames are observed at θ =30-70°. With the increase of wall distance, the mean flame temperature increases due to reduced wall cooling. Coupled with the expanded flame area and combustion duration, the high-temperature region (>1800K) of soot distribution and KL factor increase significantly, especially in the range of L_w = 40-50 mm.