Experimental study on flame spread over poplar plywood in inclined trench: phenomenon of flame injection

Abstract

A series of experimental tests were conducted to investigate the flame spread over poplar plywood in inclined trench. Considering the influence of the inner space between fuel and trench floor on combustion, poplar plywood was kept parallel to trench floor during the text. The effects of fuel position and inclination angle on trench fire behaviors were considered. The temperature inside trench was measured, and flame spread characteristics were recorded. The results demonstrate that a typical behavior of flame injection occurred during the flame spreading in trench, which mainly induced by the combined effects of thermal buoyancy and expansion force of pyrolysis gas, causing the flame to accelerate violently. What’s more, the larger the inclination angle is, the more violent the flame injection would be. And the fuel position has a significant influence on flame injection, both angles used in experiment exist a critical fuel position, at which the flame injection phenomenon is most obvious. Specially, the flame propagation velocity of poplar plywood varies obviously from bottom to top inside trench and the maximum value appeared in the middle of trench. Moreover, the flame spread process roughly could be divided into four stages according to the flame propagation acceleration, and flame injection starts in the second stage near the middle region of trench. Additionally, the temperature in trench increased sharply when the flame injection occurs, and temperature distribution indicates that the flame attachment toward poplar plywood is more likely to occur in larger inclination angle.