Experimental study on the thermoacoustic oscillation of the uncracked and cracked hydrocarbon fuel under supercritical pressure

This study investigates the flow and heat transfer instability of hydrocarbon fuels under supercritical pressure via experimental methods, focusing on the pressure range of 2.5–5.0 MPa and mass flow rate of 0.5–3 g/s for the regenerative cooling system of engines like Scramjet. Key parameters, including back pressure, mass flow rate, and working fluid types (n-Decane and RP-3 kerosene), are examined to analyze their effects on instability phenomena. The results demonstrate that thermoacoustic oscillations in the trans-critical region are primarily induced by the combined effects of inlet disturbance and pseudo-boiling effect. When the working fluid enters the pyrolysis temperature zone accompanied by oxidative coking reactions, the strong coupling between chemical reactions and flow heat transfer significantly exacerbates system instability. Increasing the back pressure or mass flow rate remarkably suppresses the instability by enhancing the flow inertia and inhibiting phase-change-induced disturbances. Compared with RP-3 kerosene, n-Decane is more prone to induce flow-heat transfer instability under supercritical conditions due to its lower thermal stability and higher reaction activity.