The Speed and Temperature of an Edge Flame Stabilized in a Mixing Layer: Dependence on Fuel Properties and Local Mixture Fraction Gradient

摘要

Edge flames are of fundamental importance to the attachment and stabilization of diffusion flames in many practical devices, and serve as transient structures for establishing combustion in locally-quenched regions of turbulent diffusion flames. In this study, we consider an edge flame sustained in the mixing layer of two streams, one containing fuel and the other oxidizer, and examine its structure and its thermal and dynamic properties over a wide range of flow conditions, using a diffusive-thermal (constant-density) model. In addition, we allow for the fuel Lewis number to vary from sub- to super-unity values, corresponding to light and moderately heavy fuels, or fuels suitably diluted by inert species, with unity oxidizer Lewis number as appropriate for combustion in air. Two regimes have been identified and examined; a thermal-interaction regime where there is appreciable heat loss from the edge flame to the splitter plate, and a freely-standing regime where the edge flame lifts off considerably and the plate plays no role on its stabilization. The objective is to correlate important edge-flame properties, including standoff distance and edge speed and temperature, with global parameters such as overall flow rate and total heat conducted from the flame to the plate, and local parameters such as local mixture fraction gradient at the edge of the flame.