Study on the flow and thermal performance of n-decane combined with supercritical CO2 in double-layer channels for scramjet engine

•N-decane and supercritical CO2 are utilized as coolants to absorb heat from the combustion chamber.•We develop a double-layer channel model to analyze the flow and heat transfer performance of the coolants through numerical simulation.•The co-directional flow pattern of coolants leads to a reduction in the average temperature of the heated wall, while the bi-directional flow pattern lowers the maximum temperature of the heated wall.•In the BDF pattern, the temperature difference between the maximum and average wall temperature on the heated wall is 35 K lower than the CDF pattern. This is advantageous for reducing thermal stress. Active cooling technology utilizes a coolant to absorb heat and prevent excessive wall temperature. This study employs numerical simulation to analyze the heat transfer performance of supercritical n-decane in conjunction with carbon dioxide within a cooling channel featuring a double-layer design. The findings reveal that augmenting the mass flow rate of n-decane or carbon dioxide results in diminishing wall temperatures and enhancing heat transfer performance, concurrently leading to a reduction in the friction factor. Moreover, the average temperature of the heated wall is 15 K lower in co-directional flow pattern compared to bi-directional flow pattern. Conversely, the bi-directional flow pattern yields a more uniform temperature distribution and reduces the maximum temperature at the heated wall by 20 K. In the BDF pattern, the temperature difference between the maximum and average wall temperature on the heated wall is 35 K lower than the CDF pattern. This is advantageous for reducing thermal stress.