Abstract
The extinction of stretched premixed flames propagating in a stagnation-point flow under the influences of dilute fuel spray, preferential diffusion and upstream external heat loss is analyzed using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. The liquid fuel loading and the initial droplet size of the spray indicate the internal heat gain and heat loss for the lean and rich sprays, respectively. The flow stretch coupled with Lewis number (Le) intensifies the burning intensity of the Le>1 flame, but weakens that of the Le<1 flame. It is found that theLe>1 flame can be quenched with or without external heat loss, and that both the external heat loss and the flow stretch strongly dominate the trend for flame extinction characterized by a C-shaped extinction curve. In the absence of external heat loss, no extinction occurs under the influence of flow stretch for the Le<1 flame enduring completely prevaporized burning sprays. However, it can be extinguished by the external heat loss characterized by a C-shaped extinction curve if the flow stretch is small. Under the condition of Le<1 flames experiencing a small flow stretch and enduring a partially prevaporized spray composed of a large enough liquid loading and sufficiently large droplet size, a W-shaped extinction curve is obtained. The W-shaped extinction curve in distinction from the C-shaped one points out that the flame extinction is governed by the internal heat loss.
