Shock Impinging Effect on Ethylene Flameholding

Abstract

The flameholding characteristics of ethylene in supersonic crossflows were investigated experimentally. Shock-tunnel experiments were conducted at a flow total enthalpy of 1.78MJ/kg, with a fuel-air equivalence ratio of 0.2. A contoured wedge model with a wall cavity and a cowl was used. To investigate the shock impinging effect on flameholding, different cowl locations were considered, varying from the upstream of the injection to the cavity ramp. Shadowgraph and CH* chemiluminescence optical images were obtained for each location. The experimental data showed that flameholding can be categorized as three distinct types of interaction. The first interaction, with the cowl shock impinging upstream of the fuel injection, showed a gradual quenching of CH* radical in the cavity during steady flow, and flameholding was not maintained. The second interaction, with the cowl shock impinging at the cavity ramp, showed flameholding in the shear layer above the cavity and downstream throughout. The third interaction, with the cowl shock impinging directly at the fuel injection, showed flameholding in the entire cavity and the downstream region. It was shown that, depending on the cowl location, ethylene flameholding could be achieved at a much lower enthalpy than a recent finding of flow total enthalpy of 2.05MJ/kg.