An Investigation on Combustion and Heat Transfer Characteristics of Spray Wall Impingement Under High-Altitude Simulation Conditions

The extreme operating conditions of low temperature and low pressure at high altitudes can easily trigger a serious spray wall impingement in an engine combustion chamber, causing wall-attached combustion and pool fires, which are some of the important causes of ablation damage to the piston and combustion chamber wall. However, the mechanism of spray wall impingement, wall-attached combustion, and wall heat transfer at high altitudes is not completely understood. In this study, the characteristics of spray wall impingement, wall-attached combustion, and wall heat transfer under high-altitude simulation conditions were investigated based on a constant-volume bomb combined with the multidimensional numerical simulation method. The results indicated that background pressure plays a dominant role in liquid spray wall impingement by affecting the spray penetration ability, and background temperature plays a significant role in the evolution of fuel film by affecting fuel evaporation. The mass and evaporation rate of the fuel film considerably affect the combustion characteristics of the pool fire. The mass of the fuel film is small, and the evaporation rate of the fuel film is increased under high temperature and high pressure, resulting in pool fires with early appearance time, highest peak intensity, and shortest duration. The mass of the fuel film is the largest and the evaporation rate of the fuel film is the slowest under low temperature and low pressure conditions, which makes the pool fire appear late, with the smallest peak intensity and the longest duration. The appearance time, peak intensity, and combustion duration of pool fires at high temperature and low pressure and at low temperature and high pressure are between those under the two conditions aforementioned. Moreover, the fuel film and pool fire significantly enhance the heat transfer from the flow field to the wall in the constant-volume bomb. The flame on the wall keeps the wall surface in a state of high heat flux density and high temperature for a long duration. The heat flux density and temperature distribution of the wall surface in the pool fire zone are uneven and change drastically because of the difference in fuel film distribution and evaporation rate, and the resulting thermal fatigue may be an important cause of wall ablation. © 2023 Tianjin University. All rights reserved.