Thermodynamic Analysis of the Second Fluid Brayton Cycle for Scramjet Engine

The burning chamber wall of the ramjet engine is facing an extremely thermal environment during normal conditions. Thermal protection measures must be taken on the wall surface of the combustion chamber. At the same time, the aircraft faces high-power electrical demand problems under high-speed cruising states. To address these issues, a second fluid-closed Brayton cycle system was introduced in this paper. Helium was utilized as the secondary fluid medium, while kerosene was used as the final heat sink. The ramjet engine chamber wall was cooled by the helium cycle system. At the same time, part of the heat absorbed by the helium cycle was transformed into electric power by a generator. This work proposes a new method of thermal management in a closed cycle. Unlike traditional methods, this proposal can regulate the mass flow rate of helium based on the requirement of heat load. A zero-dimensional numerical calculation method was established for thermodynamic analysis. The results show that as the equivalence ratio of 0.8~1.5 for the kerosene flow rate, the system can suffer the thermal load of 200~350 kJ/kg on the combustion chamber wall at the maximum kerosene allowable temperature. To ensure the normal operation of the circulating system, the mass flow ratio between the helium and the air changes from 0.02 to 0.045. Compared with the direct kerosene cooling method, the second fluid circulation method leads to the kerosene equivalent saving ratio by 2% to 14%; at the same time, such a system could generate 160~500 kJ/kg of electrical energy. This new thermal management method can achieve kerosene saving, electric power generating and suffering more thermal loads under the premise of satisfying normal work.