Transient flow excursion of cracking hydrocarbon fuel in parallel channels under varying inlet total mass flowrates

As flight Mach number increases, scramjet encounters thermal limit, where regenerative cooling systems utilizing cracking hydrocarbon fuel serve as the critical solution. To investigate the effects of flow excursion on the mass flow path of parallel channels under different inlet total mass flow rates, a transient flow excursion model is developed based on hydrodynamic characteristic curves. The flow distribution solutions and their stability in parallel dual channels are systematically analyzed under three heat flux levels (1125, 750, and 375 kW/m²). Compared with high heat flux conditions, additional flow distribution solutions with greater flow deviations are discovered under medium and low heat flux levels. The effects of heat flux and variation rate of total mass flow rate on the transient flow trajectories, particularly flow excursion, are systematically investigated using the transient model. The results demonstrate that flow excursion is triggered through two distinct modes: (i) initiated by perturbations or pump-driven perturbations within unstable solution regimes, (ii) induced by pump actuation that drives the total mass flow rate to transit directly from the multiple solution regime to the unique solution regime. Hysteresis phenomenon is observed in the mass flow rate paths. The overlap region of stable deviation solutions and stable uniform solutions decides the minimum hysteresis width. Prior to flow excursion, the hysteresis distance along mass flow rate paths of the unstable solutions governs the ultimate hysteresis width. The heat sink waste is analyzed and the efficiency of heat sink may drop to 58.48% with the large–deviation solutions. This investigation is expected to provide the guidance for the design of regenerative cooling channels.