LES of kerosene spray combustion in RBCC ramjet/scramjet mode

Large-eddy simulation (LES) of kerosene spray combustion in a model supersonic combustor with cavity flame holder is carried out. Kerosene is injected through the ceiling of the cavity. Chamber wall pressure predicted from the LES is validated by experimental data reported in literature. The test case has a cavity length of 77 mm and the depth of 8mm. After liquid kerosene is injected through the orifice, most of the droplets are loaded with recirculation fluid momentum inside the cavity. Due to lower velocity of the carrier fluid inside the cavity, sufficient atomization and evaporation take place during the processes of droplets transportation, resulting in rich fuel mixture of kerosene vapor accumulating inside the cavity. These rich fuel mixtures are mixed with fresh air by the approach mixing layer at the front of the cavity, thus are involved in burning accompanied with the approach boundary layer separation extending towards upstream. The combustion flame in the downstream impinges onto the rear wall of cavity, and then is reflected back to the front of the cavity. During the recirculation of hot flow, heat is compensated for droplets evaporation. The circulation processes mentioned above provide an efficient flame holding mechanism to stabilize the flame. Comparisons with results from a shorter length of cavity (cavity length of 45mm) shows that, due to insufficient atomization and evaporation of droplets in the short distance inside the cavity, parts of droplets are carried out of the cavity through the boundary layer fluctuation, and evaporated in the hot flame layer, thus results incomplete air fuel mixing and worse combustion performance. The flow structures inside the cavity play an important role in the spray distribution, thus determine the combustion performance.