Flame establishment and flameholding modes spontaneous transformation in kerosene axisymmetric supersonic combustor with a plasma igniter

Plasma is considered as a potential method to promote the establishment of supersonic flame and has been investigated wildly. This paper provides the establishment process of flame with a plasma igniter (PI) in axisymmetric kerosene combustor under the conditions of Ma=3 and T_t=1680 K, and finds that proposes several typical modes of flameholding during the establishment process, as well as investigates the main factors on the flameholding modes. The results showed that during the establishment process of flame, a phenomenon that a weak flame will spontaneously transform to a stronger flame in a pure supersonic flow will occur. To understand the reason inducing spontaneous transformation, four types of flameholding are classified. The four types of flameholding modes are partial oxidation, weak flame, strong flame and cone-strut flame. Each type of flameholding modes has unique color, brightness, shape and size. The excitation current of plasma igniter, the feedstock flow rate of the plasma igniter, and the fuel equivalent ratio will determine which flame is formed. A simple analysis model including the heat release rate, which is proposed to explain the experimental results, indicates that the heat release rate and flame temperature of flame front are the key factors affecting flameholding modes, and the thermal congestion induced by the heat release maybe the reason causing spontaneous transformation.