The Precooled Turbine-Based Combined Cycle (PCTBCC) synergistically integrates precooled turbine engine with bypass ramjet, establishing itself as a pivotal hypersonic propulsion solution. This study systematically analyzes the thermodynamic parameters coupling mechanisms and optimizes the precooling strategy of PCTBCC, demonstrating a 33.6% improvement in specific impulse. Based on unified parametric benchmarks, the critical Mach numbers and propulsion performance of methane, hydrogen, ammonia, and methanol fuels are evaluated, which quantitatively elucidates the impact mechanisms of fuel thermophysical properties on propulsion performance. The results reveal that PCTBCC exhibits a 45.2% performance advantage over ramjets. Furthermore, this research establishes mapping relationships between fuel combinations’ thermophysical properties and propulsion performance/storage requirements, delineating the theoretical performance ceiling for multi-fuel PCTBCC. The results indicate that specific fuel combinations achieve a 25% reduction in storage volume compared to pure hydrogen while maintaining balanced performance parameters, including a critical Mach number of 4.03 and a specific impulse of 2191 s.

The coupling effects among the flow field, temperature distribution and structural deformation in a turbine cannot be ignored, particularly during flight cycles when the turbine experiences varied operational states. Relying solely on steady-state solutions cannot predict the detrimental effects caused by hysteresis. Consequently, this paper employs a quasi-steady-state fluid-thermal-structure multidisciplinary coupling solution method, integrating transient solid heat conduction with steady-state flow field and static structural deformation solutions. After conducting a numerical simulation of a three-dimensional, five-stage, low-pressure turbine air system, the following conclusions are drawn: when boundary conditions attain high-power states through processes that are numerically identical but in opposite directions, slight variations in solid deformation significantly impact the flow field; when boundary conditions attain high-power states through processes that are directionally consistent but have different numerical values, the influence of the boundary condition change rate on the flow field surpasses that of solid deformation. In terms of turbine design parameters, a large difference in stage-reaction between adjacent stages at the lower radius of the turbine can lead to significant changes in the disc cavity flow field during flight cycles. The difference in the stage-reaction of 0.23 at 10% blade height in adjacent stages may induce severe gas ingress in the stator disc cavity. Thus, it is crucial to minimize this difference and to appropriately extend the duration of the deceleration phase to ensure the turbine’s safe operation.