Nitrogen Jet Array for Ignition Enhancement in a Rocket-Based Combined Cycle Combustor

In a rocket-based combined cycle combustor operating at scramjet mode, the size of the cavity recirculation flow might be reduced when the cavity is subjected to an expansion fan, which is detrimental to ignition. To address this challenge, a method based on a nitrogen jet array is proposed and evaluated in a combustor with a Mach 2.92 inflow. Nitrogen is supplied through injectors in the cavity. In the case without nitrogen injection, the cavity recirculation flow is so small that the spark plug cannot ignite the combustor. In stark contrast, the interaction between the supersonic inflow and the nitrogen jets on the cavity ramp significantly elevates the pressure in the cavity, and it enlarges the cavity recirculation flow. During the ignition process, the enlarged cavity recirculation flow is essential to holding the weak self-sustained flame. The heat, hot products, and radicals generated by the weak self-sustained flame elevate the pressure in the cavity and further enlarge the cavity recirculation flow, which paves the way for a successful ignition. Once a successful ignition is achieved, turning off the nitrogen jet array does not lead to flame extinction. Compared to the mass flow rate of the inflow, the nitrogen consumption for ignition enhancement is minor.