Research on thermal and central flame spread behaviors over insulation material EPS in different concave structure cases

The effect of different depth-width ratios (?) on the flame spread over molded polystyrene (EPS) at the central place ignition was studied. The variation laws of characteristic parameters such as flame structure, flame height, flame spread rate, flame temperature and mass loss rate were analyzed. The experimental results show that at the central flame spread, the extinction, re-ignition and re-burning were found for the upward flame except at ? = 1.5,while the downward flame didn?t have these phenomena. At ? = 1.5, the stability of upward flame spread was the best, as the extinction didn?t occur, and the flame spread rate was the fastest. When ? <1.5, the extinction of upward flame could be sorted to flame instability, while when ? >1.5, the extinction could be attributed to the more hot smoke effect. If the average flame height of upward increased, the average flame height of downward decreased, and vice versa. Inner flame pressure model was built, which could better explain the characteristics of mutual inhibition between upward and downward flame heights.