| Coal is the most basic energy source in China,and it occupies a dominant position in the energy production and consumption market.With the gradual increase of the current coal mining depth,the geological conditions are becoming more and more complex,while extremely serious accidents have occurred frequently,among which gas explosion disasters are the most prominent.The hazards of coal mine gas explosion accidents to personnel,equipment,and facilities mainly come from the explosive flame(high-temperature gas flow),shock waves,and toxic and harmful gases.The underground conditions of coal mines are complex and there are many structures,such as ventilation facilities,supporting facilities,transportation facilities,and lifting facilities.These structures have obvious differences in shape and size,which acted as obstacles during the explosion process and disturbed the explosion field.Once an explosion occurs underground,when the explosion flame and shock wave pass through obstacles,their propagation law will change due to the impact of obstacles.The flame propagation speed increases with the increase of turbulence intensity,causing greater harm.In addition,the interaction between flame and pressure wave also has important influence on the intensity and sweep range of explosion.The propagation and interaction of the wave mentioned above are typical mechanical problems.Therefore,whether from the perspective of coal mine safety production or social effects,research on the law of gas explosion propagation should be carried out to provide technical support for the prevention and control of underground coal mine gas explosion accidents on the basis of mathematical and mechanical analysis.In this paper,a combination of experimental research and numerical simulation was adopted,based on the study of the interaction mechanism between flame and pressure wave,the experiment of small pipe and large tunnel was connected in series.On the basis of the propagation law of gas explosion and the influence law of obstacles on flame and pressure wave,the influence process of pressure wave on flame structure and flame velocity as well as the influence process of flame on pressure wave was deeply analyzed.The main work content and conclusions are as follows:First of all,according to the characteristics of high reproducibility and easy to observation and testing of small pipeline experiments,a steel pipeline with a specification size of200mm×200mm×6500mm was used to conduct a deflagration propagation experiment under the condition that the entire pipeline is filled with gas.Using test methods such as schlieren,high-speed photography system,pressure sensor,flame sensor to study the propagation law of gas deflagration pressure wave and flame.Focusing on detailed analysis of the overpressure,flame propagation speed,and flame characteristics in the observation window area,etc.Visualizing the participation of deposited coal dust in the reaction process.The study found that under the same initial conditions,the maximum pressure peak value and the maximum pressure rise rate peak of ignition at the left end are the same as those in the middle,but slightly greater than the latter two;the process of gas deflagration during ignition in the middle(that is,the presentation time of each measuring point reaching the maximum pressure)is longer than the ignition process at the left end;the mutual game of turbulent flame,chemical reaction ability and reflected pressure wave is the main reason for the change of flame propagation speed.From the process of flame and pressure wave induced deposited coal dust to participate in the reaction,it was found that the rising of deposited coal dust is the result of the combined effect of the pressure wave and flame,the turbulent flame is the main force that induces the rising of coal dust,and the height of dust is directly related to the intensity of turbulence.This paper also discussed the maximum pressure rise rate formula under the experimental conditions.Secondly,a large-scale test roadway with a cross-section of 7.2 m~2 and a length of 896 m was used to carry out research work to study the propagation law of gas deflagration of different volumes,the scale effect,and the interaction mechanism of flame and pressure waves.The study found that the size of the gas volume determines the intensity of the deflagration reaction and also affects the propagation process of the deflagration pressure along the tunnel.The larger the gas volume,the stronger the deflagration power.The flame propagation velocity first gradually increases and then decreases during the deflagration process.The variation curve of the maximum pressure with the propagation distance is approximately a quaternary function relationship in the gas accumulation zone and the flame deceleration zone,and approximately a ninth-fold function relationship in the flame acceleration zone and the flameless zone.This is mainly related to the volume of gas and the interaction between flame and pressure wave.The study also found that in the initial stage of the deflagration reaction,the difference in the size of the tunnel and the pipeline device has little effect on the flame speed,and the maximum deflagration pressure gap is not large;but in the rapid development period of the deflagration,the scale effect begins to appear.The amount of combustibles involved in the reaction is different,and the turbulence formed by the internal structure of the experimental device is the main cause of the scale effect.Third,the propagation behavior of the deflagration flame when passing through the obstacles was studied experimentally by arranging three different types of obstacles such as rectangle,trapezoid,and spherical in the observation section of the pipeline.The study found that when the front of the deflagration flame reaches the second half of the observation window without obstacle,the front of the flame tends to be flat;when there are obstacles,the flame is divided into three situations:forward,center,and tail,the forward is the fastest and the tail is the slowest.There is a large lateral deviation distance?between the flame front and the tail,and?_R>?_S>?_T.When there are no obstacles,the flame propagation speed is related to the reflected pressure wave.The reflected pressure wave will induce a turbulent flame at the front of the flame and begin to fold and deform.Obstacles can cause a disturbance in the flow field.For the front and rear pressure peaks of the obstacle,the trapezoid is the lowest and the rectangle is the highest,but the spherical obstacle is the closest to the front and rear pressure peaks,with a difference of only 9.54 k Pa.The front measuring point of the rectangular obstacle reaches the pressure peak relatively earlier,while the pressure peak of the back measuring point of the trapezoidal and spherical obstacles is ahead of the measuring point in front of the obstacle.Finally,based on the ANSYS FLUENT software,this paper uses numerical simulation to study the influence of pressure waves on the flame propagation speed in the presence of obstacles and compares them with the experimental results.The turbulence model based on Reynolds Time Average(RANS)is adopted,the near-wall surface adopts a scaling wall function,the combustion model adopts a general finite rate model,the geometric model adopts a simplified two-dimensional model,and the solution of discrete equations adopts the SIMPLE algorithm.The study found that the flame propagation speed changes periodically when there are no obstacles,and the flame propagates backward,which is caused by the reflected pressure wave;when there are obstacles,the fluctuating characteristics of flame propagation are suppressed,the flame front spreads more smoothly to the unburned area,and the existence of obstacles accelerates the spread of flame at the obstacle.Under the conditions of obstacle-free and spherical obstacles,the pressure fluctuations in the whole process are relatively severe,and the amplitude of the pressure fluctuation follows the process of increasing-decreasing-increasing;under the conditions of square and trapezoidal obstacles,the pressure fluctuations in the initial stage are relatively large,after the flame passes the obstacle,the pressure wave amplitude decreases rapidly. |
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