A Novel Gas Generator Concept for Jet Engines Using a Rotating Combustion Chamber

Abstract

A gas generator—consisting of a single-stage shrouded mixed-flow compressor without a diffusor, a rotating combustion chamber, and a vaneless single-stage shrouded centripetal turbine—is presented and analyzed here. All components comprise a coherent rotating device, which avoids most of the problems usually associated with small gas generators. In other words, the concept avoids all radial clearances; it is vaneless, shortens the combustion chamber, minimizes the wetted area, and enables ceramic materials to be used, due to compressive blade stresses. However, the concept faces severe structural, thermal, and chemical reaction challenges and is associated with a large Rayleigh-type total pressure loss. All these features and their implications are discussed and their benefits and drawbacks for several jet engines are quantified, mainly by means of thermodynamic cycle calculations. As a result, it has been demonstrated that the concept offers a thrust-to-weight ratio which is higher than the standard when incorporated into small unmanned aerial vehicles (UAV)-type jet engines. It also enables an attractive multistage and dual-flow, but fully vaneless design option. However, the concept leads to a decrease in thermal efficiency if these were to be accomplished in the (small) core of turbofans with highest overall pressure ratios (OPRs) and high bypass ratios. In summary, the paper presents a gas generator approach, which may be considered by designers of small jet engines with high power density requirements, like those used in UAV applications. But this has been proven not to be an option for high-efficiency propulsion.