Combustion enhancement subjected to the inlet distortion in a cavity-based supersonic combustor

Abstract

The present study experimentally investigates the effect of inlet distortion on the combustion process in a direct-connect test environment. A blockage by introducing physical intrusions with three heights (H = 2.5 mm, 3.2 mm, and 4 mm) was mounted at the entrance of the isolator to mimic the inlet distortion. Cases without blockage were used as a comparison. Schlieren visualization synchronized with high-speed CH* chemiluminescence imaging and pressure measurements were employed to characterize the flowfields. The results show that the blockage mounted at the entrance of the isolator could reasonably mimic distortion generated at the inlet. The combustion enhancement is achieved in all cases with blockage, and the lean blowoff limits could be widened in the combustor with blockage (H = 2.5 mm and 3.2 mm). In the cavity stabilized combustion mode and transition mode (Φ=0.159∼0.689), the stronger oblique shock wave emanating from the cavity leading edge and the additional background shock wave created by the inlet distortion are the chief causes of combustion enhancement in cases with blockage. The combustion enhancement gradually recedes with the increase of blockage height. It could be speculated that the relatively concentrated impinging of the incoming shock waves induces a more remarkable combustion enhancement. In the jet-wake stabilized combustion mode (Φ=0.848∼1.325), the effect of blockage height on combustion enhancement is significantly suppressed. As the equivalence ratio rises to 1.06, the regularity that the effect of blockage height on combustion enhancement is completely reversed. That is, the combustion enhancement attenuates with the decrease in blockage height. It could be inferred that in these cases, the dominance of combustion enhancement is the incoming flow velocity upstream of the reaction zone instead of the impinging sparsity of the incoming shock waves.