Thermodynamic analysis of the influential mechanism of fuel properties on the performance of an indirect precooled hypersonic airbreathing engine and vehicle

Abstract

Fuel indirect precooled engines are promising power to realize the vision of greener and faster air transportation. Efficient operation of the engines relies critically on sophisticated energy management schemes, within which the fuel plays a decisive role. Research here intends to make clear the mechanism of how the energy conversion process of this innovative cycle is driven by properties of the fuel. A unified engine model was developed for analysis, through which it indicates that besides the properties commonly known, the triple point temperature and stoichiometric heat capacity (SHC) of the fuel are also crucial to efficient engine operation. Numerical engine method and the Concorde airplane were proposed to evaluate the synthetic influence of the multiple properties on engine and vehicle performance, with four seemingly promising fuels, i.e., the methane, n-decane, methanol and hydrogen were selected for further assessment. Experiments were performed to evaluate the contribution of chemical endothermic effect (CEE) to SHC. On account of the results, the impacts of the CEE and the quantitative significance of fuel properties on engine and vehicle performance are revealed. Also, it indicates that the system fueled with hydrogen shows superior performances in engine specific impulse and specific thrust, in spite that the corresponding flight range of the vehicle is extremely poor. On the contrary, the systems using hydrocarbon fuels (i.e., methane, n-decane or methanol) exhibit better performance in vehicle flight range, but their related engine-level performances such as the specific impulse/thrust are usually lower than that using hydrogen. Considering this complementary feature, it implies that combined use of several fuels (for instance, hydrogen + kerosene) may provide more balanced and better overall performance than that of the single fuel scheme.