Flame modelling and burning velocity measurement

Abstract

Strictly, the term “burning velocity” is only meaningful in relation to planar flame frontsin one-dimensional flow systems. On the other hand, burning velocity measurements are obtained from flames which are frequently curved, and in systems where the flow diverges to a greater or lesser extent on approach to the reaction zone. Thus, in order to extract from an experimental arrangement a burning velocity which can validly be used in one-dimensional flame modelling, it becomes necessary to define an appropriate reference plane in the flame, and to estimate the gaseous mass flux (or some equivalent) at this plane. A computational method of defining such a plane is suggested, and has been used on a range of methane-air and hydrogen-air flames. Resulting reference plane temperatures and positions are presented. They almost coincide with the maximum reaction rates in the flames, and for practical purposes they may be identified in the case of methane flames with the leading edge of the luminous zone. The implications of the findings are discussed for both stationary and non-stationary flamemethods of measuring burning velocities. For mixtures initially at room temperature and atmospheric pressure, laminar burning velocities are presented graphically for a range of methane-air flames not too far from stoichiometric. The “best” value for the stoichiometric methane-air flame turns out to be around 37 or 38 cm s −1 .