Experimental Simulation Study On Flame Attachment Under Slope Condition

Eruptive fire is an extreme fire behavior in which rate of fire spread increases sharply in a short period of time.In wildland fires,eruptive fires often result in serious threat to the safety of human life and property.Previous studies have shown that flame attachment may be an important reason of flame acceleration in trench fires,but due to the complex coupling effects of combustion,heat transfer and flow in the fire spread,there is lack of unified view on the mechanism of the flame attachment.In order to achieve deep understanding on the flame attachment in eruptive fires,this paper designs a gas fire test bench with adjustable slope to simulate the flame in trench fire spread.The experimental method produces continuous and stable flames,and thus the flame geometry characteristic parameters under different experimental conditions are obtained.By the experimental studies,the physical mechanisms and processes of flame attachment are systematically investigated.This paper carries out gas burner experiments under different slopes and aspect ratios,using propane as the fuels and mainly focusing on the flame geometry parameters,flame attachment characteristics and heat transfer ahead of the flame.The slope of the bench in experiments varies from 0° to 45°,and different aspect ratios of 0,0.2,0,6,and 1,respectively were used.According to the experimental results,slope is the key factor causing the flame attachment in the upslope fire and the effect of side wall is just to restrict the air entrainment of flame sides and enhance the fire-induced wind which can strengthen the asymmetry of the entrainment and accelerate the rate of flame tilting.There is a critical slope for the occurrence of the flame attachment.The critical slope does not depend on the aspect ratio.Under the experimental conditions of this work,the critical slope for the occurrence of flame attachment is 10?15°.The fire when side wall is present will eventually form a "sheet" structure burning closely to the fuel bed surface as the slope increases.At this time,the flame can be considered to be in a completely attached state.There is another critical slope for the completely attached fire,but the slope does not depend on the aspect ratio.The attached flame involves obvious pulsation and intermittency,and the pulsation and intermittency will be enhanced with the increase of slope.The presence of side wall can significantly aggravate the pulsation characteristics of the flame.However,the increase of the height of side wall does not have a significant effect on the pulsation characteristics of the flame.