Experimental Study Of Soot Distribution In Laminar Diffusion Flames Of Liquid Fuels Under Low Pressures

The fire protection of plateau areas and high-altitude environment,of which the condition is hypobaric hypoxia,attracts most focus for years.Soot is the residual product of combustion,as well as an important parameter in studying burning behavior.It is of great importance in learning about the features of soot distribution in sub-atmosphere flames for the in-depth study of combustion behavior and fire protection under low-pressure areas.The research objects were laminar diffusion flames under low pressures.Flame appearances and soot distribution of typical combustion liquids were analyzed.A simulating chamber with an inner diameter of 240 mm and an inner height of 600 mm was employed,of which the pressure range is 40?101 kPa.The design of the burner imitated an alcohol burner.The experiments were conducted under 7 sub-atmosphere conductions,namely 40?50?60?70?80?90 and 101 kPa.8 combustible liquids,including 3 pure substances(n-hexane,n-heptane and n-octane),3 mixtures(mixture of pure substances with different mass ratio)and 2 commercial fuels(gasoline and RP-3 aviation kerosene)were confirmed as samples.The relationship between flame size and pressure was analyzed quantitatively under 40?101 kPa.As the pressure becomes higher,the flame height increases and the width decreases.Flame width has a negative pressure exponent,and the higher the carbon content,the slower the width decreased.A method of Laser Induced Incandescence was used in studying the relationship between soot distribution and pressure of the 8 combustible liquids.It is reported that soot volume fraction increases with the increasing of pressure,or with the increasing of carbon ratio.The position of high soot concentration transfers from a ring centered by the flame axis at small heights of flames to a point along flame axis at larger heights.Through a semi-quantitatively analysis of the peaks of local soot volume fraction in flames and a comparison with previous experiments,the conclusion that the peak is of exponent to pressure was drawn.The higher the carbon content is,the smaller the exponent is.