THE VELOCITY OF A PREMIXED FLAME AS A FUNCTION OF THE FLAME STRETCH - AN EXPERIMENTAL-STUDY

We present an experimental study of the change in burning velocity of a premixed flame due to the flame curvature and (or) to the rate of strain tensor of the incoming fresh mixture. Three lean propane-oxygen-nitrogen mixtures are investigated. These experimental results are compared to the theoretical prediction of P. Clavin and G. Joulin. As predicted by this theoretical work, we found that the flame burning velocity is a linear function of both the flame curvature and the gradient towards the flame front of the normal component of the velocity profile in the incoming fresh mixture, and both contribute to the stretch that the flame undergoes. Particular attention is devoted to the experimental determination of (1) the flame burning velocity in nonuniform flow, i.e., in hydrodynamical situations where the velocity of the incoming fresh mixture has a different value at each point in space, and (2) the coefficient of proportionality between the reduced burning velocity and the reduced flame stretch, i.e., of the Markstein number.