ON THE BURNING VELOCITY OF STRETCHED FLAMES

The term "burning velocity" is commonly defined as the velocity of the gas ahead of and relative to the flame. This definition is appropriate for a one-dimensional flow because the mass flow rate across the flame is constant. In more general circumstances, however, this definition becomes ambiguous because the mass flow rate varies with distance through the flame. Thus, the reference position becomes important when measuring flame speed of stretched flames. As a consequence of the different definitions used by various investigators, there are conflicting results, with respect to the dependence of the flame speed on stretch, between experimental data and experimental and theoretical studies. In this article we provide an explanation for these differences. Expressions for the burning rate, valid for weak stretch, are given based on various definitions that are or could be used in experiments.