Experimental Research On Combustion And Propagation Characteristics Of Diesel And Blended Fuels In Tunnel

In recent years,with the rapid development of transportation,tunnel has played an increasingly important role in transportation.However,with the number and length of tunnels increasing,people are paying more and more attention to tunnel fire.Liquid fire is a common type of tunnel fire.In general,liquid has the characteristics such as fluidity,thermal expansion,and evaporability.Immediately after the leak occurs,it will spread on the ground to form pools of different sizes.Once ignited,a pool fire with various shapes will be formed.Flame spread on liquid surface is a very important phenomenon in the development of liquid fire to form stable pool fires.Tunnel has a special narrow and relative closed structure,which will affect the development of liquid fire.Therefore,studying the flame propagation behavior of liquid surface has important practical significance for exploring the rule of liquid fire spread in tunnels and fighting oil fire.Considering the characteristics of the ventilation methods commonly used in tunnels,this paper chooses 0 # diesel fuel as the experimental object,and analyzes the effects of different wind speeds(0m/s-1.6m/s)on the flame spread of diesel under concurrent and opposite longitudinal ventilation conditions.The important parameters of liquid fire spread are analyzed,including flame spread phenomenon,mass loss rate,main flame spread speed and trajectory,flash flame pulsation frequency and wavelength,oil surface temperature distribution.The main conclusions are as follows:(1)Under the condition of positive ventilation,with the increase of ventilation wind speed(v0),the diesel fire spreading speed can be divided into four stages:linear rising stage,rapid rising stage,descending stage and stable stage.Under the condition of opposite ventilation,the influence of wind speed on flame spread is not significant.In general,it plays a certain role in suppressing the flame spread.(2)Under both forward and reverse ventilation conditions,the frequency of flame pulsation increases with the increase ofventilation speed,while the wavelength presents the opposite change.(3)In the process of flame spreading,the opposite ventilation speed has little effect on the oil surface temperature.The concurrent ventilation speed will increase the heating rate.Once the temperature exceeds the flash point,the air velocity has little effect on the heating rate.In order to study the difference of diesel and mixed fuel spread characteristics,n-butanol,which has high compatibility with diesel fuel,is selected and the propagation characteristics of butanol-diesel blended fuel with different proportions are analyzed.The conclusions are summarized as follows: When the proportion of n-butanol reaches 20%,which is the turning point for changes in the law of spread,the pulsation wavelength of flash flame decreases linearly to gradually stabilize,and the temperature rising rate of liquid surface of blended fuel increases gradually to remain unchanged.Moreover,the spreading speed of main flame changes from linearly increasing with to basically stable and close to the spreading speed of n-butanol.In addition,the main flame changes from a periodic propagation mode of "forward-backward-forward" to an alternating change of "crawling" and "jumping".Flash flame shows different changing rules from main flame.When the mixing ratio of n-butanol is in the range of0%-10%,the flashing flame presents the rule of "appearance-disappearance-appearance";when the mixing ratio reaches the range of 15%-30%,the flash flame persists and presents a periodic change of "forward-backward-forward"...