Theoretical Criterion for Ignition of a Combustible Gas Flowing over a Wedge

Abstract

In relation to the criterion for ignition of a combustible gas flowing at high speed over a wedge at a high surface temperature, the method of large activation energy asymptotics was employed to investigate the characteristics of ignition and to derive an explicit expression for an ignition criterion including the effects of general Prandtl (Pr) number and wedge angle. Based on this criterion, the regions of ignition and lack of ignition were identified over the surface of the wedge for various wedge angles. The ignition criterion, which is defined in terms of a modified Damkohler number at ignition, depends analytically on the wedge angle, Pr number and the surface temperature of the wedge ([Ttilde]_w) for a given combustible flow. The magnitude of the dimensionless ignition distance (ζ_I,) increases as the wedge angle increases, but decreases for increasing Pr number and [Ttilde]_w. The variation of (ζ_I,) is increasingly sensitive to the Pr number for a larger wedge angle. Finally the relationship between the existence regions for ignition and the relevant parameters is discussed.