Transient flow excursion of cracking hydrocarbon fuel in parallel cooling channels

Cracking hydrocarbon fuel is usually used as coolant of the regenerative cooling in scramjet engines. However, the drastic thermophysical property changes in the pyrolysis and trans-critical transitions may induce flow instabilities such as flow excursion, leading to flow maldistribution and thermal deviation. The structural safety is threatened. In this work, to investigate the flow excursion of cracking hydrocarbon fuel, a transient flow excursion model based on hydrodynamic curves was developed and validated. Stability analysis of multi-solution flow distribution was conducted, identifying flow distribution solutions and the stability under three heat flux levels (1125, 750, and 375 kW/m²). Flow distribution solutions are found to be unstable when two or more channels operate in negative slope regions. Whereas, flow distribution including one single negative slope region solution exhibits only partial stability. Regarding the transient flow excursion, under high and medium heat flux, usually it terminates when drifting from negative slope region into the positive slope region. While under low-heat-flux conditions, large-span excursion from the trans-critical negative slope region to the pyrolysis region. The flow maldistribution is much more severe (deviation coefficients up to 0.6185 and temperature differences exceeding 400 K). This study is expected to provide the theoretical foundation for predicting instability thresholds and optimizing the design of scramjet cooling systems under extreme thermal loads.