Spray-wall interaction on n-dodecane spray combustion and soot formation under different wall temperatures

To investigate the effect of the wall on soot formation during spray combustion and to explain the existence of contradictory results, the vapor-phase, ignition, combustion, and soot formation of free- and impingement-spray with different wall temperatures were studied in comparison using optical diagnostic techniques. Results reveal that, compared to free spray, the impingement spray's vapor-phase spray tip penetration is reduced, and its vapor-phase spray volume is increased by about three times. At conditions where only the vapor-phase impinges on the wall, the impingement spray has a shorter ignition delay time (IDT) for various wall temperatures. Furthermore, the soot formation of the impingement spray combustion is approximately one-third of the free spray, and the increase in air entrainment accounts for this phenomenon. In a comparison of different wall temperature conditions, the higher wall temperature facilitates the spray ignition process with a shorter IDT, and the ignition location is further away from the wall. However, the relationship between wall temperature and soot formation is not linear. The soot formation varies in a pattern of reducing and then increasing as the wall temperature increases due to the high wall temperature accelerating both the generation and oxidation rate of soot.