Opposed-flow flame spread across n-propanol pools

Abstract

A computational study is made of the effects of forced, opposed air flow on pulsating and uniform flame spread across n -propanol pools at either normal or zero gravity conditions. The numerical model incorporates finite-rate chemical kinetics, variable properties, and an adaptive gridding scheme in the direction of flame spread. In zero gravity, the combination of forced, opposed flow and thermocapillary-driven concurrent flow can cause a gas-phase recirculation cell to form ahead of the flame and thus lead to flame pulsations. The pulsation mechanism, in this case, is essentially the same as that previously detailed for pulsating flame spread in normal gravity without forced flow [1]. In either normal gravity or zero gravity, increasing the opposed air speed ( U opp ) causes a transition from uniform flame spread to pulsating flame spread. The value of U opp that corresponds to this transition increases with initial pool temperature ( T c ). Unlike with normal gravity flame spread, the mean flame spread rate ( Ū fl ) in zero gravity decreases significantly because of this transition for T c <21°C. As U opp is increased further, both Ū fl and the pulsation frequency increase in zero gravity but change only slightly in normal gravity. For high values of U opp , Ū fl varies little with gravity level. For low values of U opp , the flame spread rate in zero gravity is sensitive to the initial profile of fuel vapor in the gas phase.