An appearance of asymmetrically spreading flames in narrow combustible channel

Abstract

This paper numerically investigated the detail process to appear the asymmetrically spreading flames in narrow channel consisted of combustibles. We have successfully reproduced the transient process to form asymmetrically arranged spreading flame first ever in this work. 2-D, time-dependent mass and energy transport process as well as one-step chemical process in gas-phase is considered. Thick solid combustible plates (PMMA) are placed at both sides, then exactly the same ignition operation is made to initiate symmetrical processes. Pure oxygen is fed into the channel at the fixed rate to promote the spreading. Oxidizer velocity and channel height are varied as numerical parameters in this study. After the forced ignition, the combustibles are pyrolized via one-step reaction to evolve the fuel gas into the gas phase to form the opposed-mode flame spreading. Results show the distinctive three spreading modes (two-symmetric flames spreading, two-asymmetric flames spreading and one flame spreading) and transient process from one to the other mode is successfully simulated, which is hardly achieved in experiment. The asymmetric flame spreading mode appears under the limited combination of channel height and velocity. Moreover the distance between two leading edges of the flame varies depending on the imposed condition. Flow patterns are found to be sinus motion, thus the heated and accelerated oxidizer flow may enhance the reaction in the downstream. In this way, it is suggested that the flowing oxygen is effectively used to burn two fuel slabs. It is obvious that the asymmetrical configuration gives temporary stable condition. To study the details further, systematic study is demanded.