Experimental Study On Flame Characteristics Under Trench And Slope Conditions

Flame attachment is an important reason for the acceleration of fire spread.In previous studies,people seldom paid attention to the process of flame development from oblique to attachment under slope conditions,and the influence of the degree of air entrainment restriction on the flame side on the development of flame shape.In order to study the flame attachment process,this paper adopts a trench combustion experiment platform,uses a propane burner with a length-to-width ratio of 6 to generate a gaseous fire,and installs baffles(tempered glass panels,heat-insulating fire-proof panels)on both sides of the experimental platform to simulate the trench condition,carry out combustion experiments with different slopes(0-40°),aspect ratios(0,0.1,0.3,0.5,1)and flame heat release rate(14.52?58.09 kW).The experiment obtains different average flame shape parameters through image processing,uses thermocouples and pitot tubes which are distributed along the center of slope to obtain the pre-fire temperature and flow velocity distribution data,and analyzes the change law of flame combustion characteristics.In terms of flame shape,under different aspect ratio conditions,the flame tilt angle shows a downward trend with the increase of the slope.Under the same slope condition(15-30°),the flame tilt angle decreases with the increase of the aspect ratio.When the heat release rate is 29.05 kW and the aspect ratio is 1,the critical slope angle of complete attachment of the flame is about 20°.The critical slope angle decreases with the increase of the aspect ratio and increases with the increase of the heat release rate.Under the conditions of different heat release rates,the flame attachment length increases with the increase of the slope.When the slope was higher than 15°,the flame attachment length increases with the increase of the aspect ratio.The flame height shows a downward trend as the slope increases.When the aspect ratio is higher than 0.3 and the slope is greater than 25°,as the aspect ratio increases,the rate of decrease of the flame height increases.In terms of flame combustion characteristics,there is a well linear relationship between flame attachment length and horizontal flame length.The increase in flame attachment length is mainly caused by the pressure difference on both sides of the flame.With the aspect ratio increases,the proportion of flame attachment length in horizontal flame length increases.Under the condition of no baffle,when the slope is 0° and 40°,the dimensionless flame length and the non-dimensional heat release rate satisfy the power law relationship.Compared with the slope of 0°,the flame length increases more slowly with the rate of heat release when the slope is 40°.When the aspect ratio is 1 and the slope is 0°,the exponential power relationship is consistent with the condition of no baffle.At 40°,the power exponent is higher than the condition of no baffle,and the flame length increases faster with the heat release rate.When the aspect ratio is 1,compared with the condition of no baffle,the rate of increase of enter temperature with the slope has been increased,in front of the fire,there is a reverse air entrainment flow under the condition of a lower slope.When the flame is completely attached,the flow velocity which in front of the fire increases significantly.