Effect of thermal choking on ejection process in a rocket-based combined cycle engine

Rocket-based combined cycle (RBCC) engines show great potential for use on future reusable launch vehicles. By combining traditional rocket and ramjet into a single engine, RBCC engines can make use of the oxygen in atmosphere and reduce the amount of onboard oxidizer required. The induced air reacts with the secondary injection fuel in combustor and the heat release may develop a thermal throat, which has an impact on the upstream ejection process. Combustor-ejector interaction plays an important role in the performance analysis of RBCC engines, but it is often ignored in previous studies. In this paper, a quasi-one-dimensional model focused on the influence of thermal choking is developed. A fixed-geometry engine operating in ejector mode is simulated to investigate the ejector mode of a hydrogen fueled RBCC engine. With a series of results, the ejector mode is classified into four distinctive types. By analyzing the operating conditions and the performance, the relation between thermal choking and ejection process is revealed. A deeper understanding of the working principle and the mode transition of RBCC engines can be gained, which may be useful for design and optimization of RBCC engines.