Effect of air-injection mode on mainstream-forced entrainment and combustion characteristics of a cavity-based combustor

Abstract

The trapped vortex combustor (TVC) has shown promise for use in advanced aircraft engines due to its high combustion efficiency, excellent stability, compact geometry, and low pressure loss. However, the mainstream-forced entrainment phenomenon presents a significant challenge to implementing the TVC. This study conducted experimental and numerical investigations to examine the effect of different cavity-air-injection modes on mainstream-forced entrainment. The results indicate that the entrainment of mainstream air into the cavity is greatly affected by the cavity-air-injection mode, subsequently influencing the combustion performance of the TVC. Compared to the front/rear air-injection mode (case 1) or the front air-injection mode (case 3) of the cavity, the rear air-injection mode (case 2) can effectively reduce the entrainment of the main flow into the cavity, creating a stable large-scale single vortex flow structure. Additionally, the fuel distribution in the cavity is somewhat influenced by the cavity's air-injection design. The local equivalence ratio of the cavity in case 1 is higher than that of cases 2 and 3, which benefits lean ignition and blowout performance. Case 1 demonstrates superior ignition and blowout performance compared to case 2, which exhibits the poorest ignition–blowout performance. Cases 1 and 3 share similar ignition processes, although case 3 has a significantly longer ignition time than case 1. In contrast, case 2 experiences ignition with the flame primarily concentrated in the mainstream area due to its air-injection mode. The cavity's air-injection mode leads to a rapid influx of fuel into the mainstream area, resulting in the lowest combustion efficiency observed in case 2.