Simplified Approach to Identify Thermal Choking Limits of a Dual-Mode Variable Area Combustor

Asimplified analytical model was developed to predict the thermal choking limits of a variable-area duct in a dual-mode supersonic combustor. Specifically, a quasi-one-dimensional model was used to predict the operability limits of ethylene-air mixtures at conditions relevant for the UVA supersonic combustion facility. Reasonable agreement between the predicted and experimentally observed equivalence ratio limits associated with thermal choking conditions supports the model assumptions. It was also shown that, for low-equivalence-ratio mixtures, the neglect of product gas dissociation in estimating heat release has negligible effect on predicted thermal choking limits because of lower combustion temperatures. On the other hand, for equivalence ratios above 0.4, the dissociation of product gas mixture has a significant effect on the heat-release estimates, and hence, also on the thermal choking limit predictions. Although experimental data on thermal choking limits were available for only the Mach 2 nozzle, the model predictions have shown that use of a higher Mach number nozzle can yield broader range of operating conditions.