On the flame propagation in a rotating flow field

Using a glass tube into which a combustible mixture is tangentially injected from one end, the phenomenon of flame propagation in a rotating flow field has been experimentally investigated. The regions for the flame propagation are mapped as functions of the fuel concentration and the flow velocity, and the flame speeds are also determined. The results show that, when the tangential injection velocity is small, the propagation range in the fuel concentration becomes narrower with an increase of the flow velocity, whereas when the injection velocity is large, and thereby the rotation is strong, the range becomes wider as the flow velocity is increased; an axisymmetric flame, convex towards the oncoming mixture, is formed at the open end, and it projects into the glass tube eventually to the closed end. An interesting point is that the concentration limit is extended by the flow rotation to that for a quiescent mixture in lean methane or rich propane mixtures, but not in rich methane or lean propane mixtures. In the former mixtures, the head of the flame is intensified in burning, whereas in the latter mixtures, the head is weakened. In addition, it is found that the flame speed almost linearly increases with an increase of the tangential velocity. These results are discussed on the basis of the vortex bursting mechanism proposed by Chomiak and Lewis number considerations.