Study On Gas Explosion Characteristics And Inert Gas Explosion Suppression Of Urban Utility Tunnel

With the advancement of modernization,corridor and intensification of urban pipelines in China,utility tunnel has become an important public infrastructure in new urban areas.However,due to the limited space characteristics of utility tunnel,once the gas explosion accident occurs,it will bring great challenges to urban public safety.Therefore,this paper explores the dynamic characteristics of gas explosion in utility tunnel and the influence analysis of inert gas under explosion suppression conditions by building a small size utility tunnel explosion experimental platform and combining with numerical simulation method,aiming at proposing explosion prevention and control schemes for gas cabins in urban utility tunnel.The main contents and conclusions are as follows:First of all,through the methane-air explosion characteristics experiment of small-scale narrow and long pipeline,the influence of three influencing factors on overpressure characteristics and flame structure was analyzed,including different premixed concentration,number of relief outlets and number of obstacles.The experimental results show that when the methane concentration is 9.5%,the overpressure waveform curves of the open working condition show a periodic oscillation trend compared with the closed space working condition.The reduction rates of the central overpressure peak are 47.5%,57.7%and 38.4%,and the reduction rates of the tail overpressure peak are 29.4%,54.5%and 35.2%,respectively.The explosion hazard of opening condition is lower than that of closing condition,and the explosion hazard is the smallest when there is a vent at the end.Therefore,adding explosion vents to the gas tank of the utility tunnel is beneficial to reduce the consequences of the explosion accident of the utility tunnel,and it is of great significance to the explosion prevention and anti-explosion of the gas tank of the utility tunnel.Then,taking the experimental data as the control group,the validity of Fluent numerical method for studying the combustion and explosion characteristics in narrow and long space was verified.Combined with the gas tank project of utility tunnel,the effects of premixed gas concentration and obstacles（including pipelines and supports）on the gas explosion characteristics of utility tunnel are analyzed.The numerical results show that when the methane concentration is 9.5%,compared with the smooth working condition,the peak overpressure rise rates in the middle and tail of the gas tank with obstacles（including pipelines and supports）are 1265.6%and 1320.7%,respectively,and the peak flame propagation velocity rise rate is182.8%.Obviously,the pipe and support in the gas cabin of the utility tunnel have a great influence on the flow field,and the peak overpressure on each wall and the flame propagation velocity increase in order of magnitude.Therefore,in the construction of gas cabin in the utility tunnel,the area of obstacles such as pipelines and supports should be reduced as much as possible,and the wall at both ends of the fire compartment should be protected.Finally,under the most unfavorable conditions（methane concentration of 9.5%,gas cabin containing obstacles）,the influence of different CO₂ spraying time on the gas explosion characteristics of the utility tunnel is analyzed.The results show that when the response time of the explosion suppression system is 100ms,and the CO₂ spraying time is 1min and 0.75min,the reduction rates of the peak overpressure at the tail are 88.7%and 86.7%,respectively,and the reduction rates of the flame propagation velocity are 83.4%and 92.1%,respectively.Both groups of conditions have obvious inhibitory effects on the gas explosion characteristics of the utility tunnel.Therefore,the high pressure pipe network full submerged CO₂ explosion suppression system is feasible for the explosion suppression of gas tank in utility tunnel.With the reduction of CO₂ emission time,the reduction rate of overpressure peak value decreases and the reduction rate of flame propagation velocity increases.