Relaxation combustion of gas mixture in a tube: Paradox piston motion

The pattern of the propagation of the propane-air flame front and a piston from a closed tube end to an open end that is investigated experimentally. It is shown that the tube length and the coefficient of the tube being filled up by a combustible mixture are determining conditions for generation of oscillations of the piston and the flame front. It is found that the velocities of the piston and the flame front are directed oppositely to each other in definite phases of oscillations. Gas oscillations in the tube trigger a relaxation combustion mode at which the velocity of the flame front effects a variation in the amplitude-frequency characteristics. The time dependences of a periodic variation in coordinates of the piston and the flame front are represented. A physical explanation of the phenomenon of mutual approaching of the flame front and the piston is proposed.