Structural design and performance analysis of a novel helium heater for precooled air-breathing combined engines

To address the issues of high weight and structural complexity of the helium heater in precooled combined engines, a novel design of combustion heat exchange integrated helium heater is put forward. A numerical model validated by experimental data is developed to predict its performance. The flow and heat transfer characteristics of the helium heater are analyzed in detail. The crucial influence of structural design parameters on helium heater performance is thoroughly revealed. And the variations of heater performance with deviations in working fluid parameters are explored. The conclusions can be made as follows: The proposed design integrates the combustion and heat exchange components, eliminating the need for complex gas delivery pipelines and active thermal protection systems, thereby reducing weight and complexity. The heat transfer coefficient increases as the helium is heated. The difference between the maximum and minimum values of the heat transfer coefficient can reach up to 1500 W/m²·K. The transverse pitch has a greater impact on the heat transfer and flow resistance performance than the longitudinal pitch, with an optimal transverse pitch (S₁/d) of 2.0. As the number of radial layers in the helium heater increases, the total heat transfer coefficient is accordingly enhanced, which in turn reduces the required number of axial layers. The reduction in axial layers has a greater impact than the increase in radial layers, resulting in a reduction in helium heater weight. Compared to the heat transfer coefficient, the total pressure recovery coefficient on the helium side is more sensitive to changes in helium flow rate. Considering the temperature tolerance of the walls, an excess air coefficient between 3.5 and 4 is recommended.