Experimental study was made to investigate the flame propagation within methane/air mixture with periodic concentration fluctuation in a stagnation flow. The following results were obtained: (1)Burning velocity differences between the flames propagating upstream and propagating downstream were larger than those estimated at the burner exit, meaning that the mixture concentration fluctuation in front of the flame was enlarged. (2)In some cases, giving a concentration fluctuation to the mixture outside the flammable region made the frame possible to propagate.
