Flame dynamics in a heated meso-scale radial channel

Abstract

Combustion dynamics in a heated meso-scale radial channel made of quartz glass were experimentally investigated. Wall temperature profiles were generated by an external heat source to simulate the practical situation of heat-recirculating type mini-combustors. It was found that asymmetric stable flames appeared in the radial channel at lower inlet velocities. Moreover, the height of the flame front was less than the gap distance of the radial channel, indicating fuel leakage from the channel exists. At larger inlet velocities, the asymmetric flame front became very unstable. Stochastic transitions between asymmetric unstable flame and spiral-like flame were observed and captured with an image-intensified high-speed video camera. The movie recordings demonstrated that the formation of the spiral-like flame originates from local splitting in the unstable flame front. The inner flame front moved upstream and ignited the fresh fuel close to it, while the outer one can survive by burning the leaked fuel from the gap between the inner flame and the top disc. Thus, a rotating spiral-like flame was formed. Due to the unbalance between the radial component of flow velocity and the flame speed, the inner flame front was pushed outward and merged with the outer one, which led to the regression from the spiral-like flame to asymmetric unstable flame. Numerical study on the flow fields revealed that flow field grows unstable at larger inlet velocities. The unstable flow field and flame quenching near the top wall surface are expected to play key roles in those flame dynamics.