Operating Mode Influence on Heat Release in an Axisymmetric Dual-Mode Ramjet

A thermally perfect, one-dimensional model that is capable of evaluating flow properties along the isolator and combustor of a dual-mode ramjet operating in either a ramjet or scramjet mode is described. The model is incorporated into a multistage optimizer that computes an estimated fuel-burning profile for a given experimentally measured static pressure profile, and this solution is used to infer information about additional flow properties and the combustion process. Measurements obtained in a 1X-scale, ethylene-fueled, axisymmetric dual-mode ramjet are used with this optimizer to determine how combustion efficiency and heat addition vary with respect to different parameters. It is determined that there is a statistically significant difference in the heat release distribution between ramjet and scramjet operating modes, with the rate of heat release near the entrance of the combustor being larger for ramjet modes. Combustion efficiency in ramjet operating modes is found to be dependent on combustor residence time and velocity at the combustor entrance, whereas combustion efficiency in scramjet operating modes is largely independent of combustor flow properties and is instead primarily dependent on flameholder geometry.