Enhancement of chemical heat release in a generic scramjet combustor using plasma injection modules

The ability to achieve stable heat release from fuel injected into high-speed air-breathing propulsion systems (such as scramjets) operating at supersonic speeds across a wide range of inlet conditions is crucial for hypersonic applications. Energetic enhancement using plasma is an attractive method of active flameholding and provides the potential for enhancing combustion in scramjet systems. Plasma injection modules (PIMs) have been used previously for flameholding and flow control and this work extends the application of PIMs to combustion enhancement in a stably burning, axisymmetric scramjet combustor. A narrow range of operating conditions, where the engine had an excess of unburned fuel and was on the verge of transitioning from scram-mode to ram-mode operation, generated local conditions in the flameholder where improvements to a specific stream thrust metric of up to 42.1 % during actuation of the PIMs was possible. The requirement for low operating efficiency in the system in order to leverage energy from the PIMs to improve performance is discussed, as well as the effect of modifying the upstream fuel injection scheme. A comparison of the thermal power required to match the result of adding ∼8 kW of power from the PIMs is presented and indicates that the PIMs can successfully improve the performance of a stably burning scramjet combustor, albeit over a narrow range of inefficient operating conditions.