Flame Structure and Propagation Through an Interface of Layered Gases

An experimental study on flame propagation through an interface between layered methane and air, propane and air, and methane and oxygen in inert baths has been made with a combustor having a length of 10 cm. Detailed flame structure was investigated by means of schlieren photography and a hot wire anemometer. The premixed flame, the diffusion flame, and the convection flame just like those propagating in line appeared in the limited combustor space, but one after another with some time lags in between. The diffusion flame appeared about 80 msec after the premixed flame passed, which equivalently corresponds to about 10 cm of space existing between the premixed flame and the forefront of the diffusion flame. An anomalous structure was observed in the premixed flame. That is, a post burning occurs immediately behind the conventional flame front which forms double flame fronts. The temperature in between these is flat, and the separated gap width increases towards lean and rich mixtures. Steady flame propagation was consistently established for all test conditions and flame speeds were measured for a variety of conditions. It was found that they vary in an exponential manner with inert bath concentrations.