Effect of variation in gas distribution on explosion propagation characteristics in coal mines

In order to investigate the effect of variation in the distribution of gas on explosion propagation characteristics in coal mines, experiments were carried out in two different channels with variation in gas concentration and geometry. Flame and pressure transducers were used to track the explosion front velocity. The flame speed (Sf) showed a slight downward trend while the methane concentration varied from 10% to 3% in the experimental channel. The peak overpressure (Pmax) dropped dramatically when compared with normal conditions. As well, the values of Pmax and Sf decreased when the methane concentration dropped from 8% to 6%. The flame speed in the channel, connected to a cylinder with a length varying from 0.5 to 2 m, was greater than that in the normal channel. The peak overpressure was also higher than that under normal conditions because of a higher flame speed and stronger pressure piling up. The values of Pmax and Sf increased with an increase in cylinder length. The research results indicate that damage caused by explosions can be reduced by decreasing the gas concentration, which should be immediately detected in roadways with large cross-sections because of the possibility of greater destruction caused by more serious explosions.

Effect of roadway turnings on gas explosion propagation characteristics in coal mines

In order to reveal the effect of turnings on explosion propagation, experiments were performed in three different pipes （single bend, U-shaped pipe and Z-shaped pipe）. Flame and pressure transducers were used to track the velocity at the explosion front. When the pipes were filled with methane, the explosion strength was significantly enhanced due to the turbulence induced by increasing the number of turnings, while the flame speed （Sf） and peak overpressure （ΔPmax） increased dramatically. In addition, the strength of the explosion increased in violence as a function of the number of turnings. However, when the bend was without methane, the turnings weakened the strength of the explosion compared with the ordinary pipe, shown by the decrease in the values of ΔPmax and Sf. In addition, the propagation characteristics in a U-shaped pipe were similar to those in a Z-shaped pipe and the values of APmax and Sf were also close. The results show that the explosion propagation characteristics largely depend on gas distribution in the pipes and the number of turnings. The different directions of the turnings had no effect.

Experiment study on the propagation laws of gas and coal dust explosion in coal mine

The experiment of gas and coal dust explosion propagation in a single lanewaywas carried out in a large experimental roadway that is nearly the same with actual environmentand geometry conditions.In the experiment,the time when the gas and coal dustexplosion flame reaches test points has a logarithmic function relation with the test pointdistances.The explosion flame propagation velocity rises rapidly in the foreside of the coaldust segment and comes down after that.The length of the flame area is about 2 timesthat of the original coal dust accumulation area.Shock wave pressure comes down to therock bottom in the coal dust segment,then reaches the maximum peak rapidly and comesdown.The theoretical basis of the research and assemble of across or explosion is suppliedby the experiment conclusion.Compared with gas explosion,the force and destructiondegree of gas and coal dust explosion is much larger.

Methane–air explosion characteristics with different obstacle configurations

To investigate the flame and overpressure characteristics of methane–air explosion with different obstacle configurations,an experimental study has been conducted,taking account of the number of obstacles,obstacle distance from ignition source,and stream-wise and cross-wise obstacle positions.The results show that the flame speed and peak overpressure increase with the increasing number of obstacles,while the time to reach the peak is not fully determined by it.And the configuration having the farthest obstacle produces a higher overpressure and takes a longer time to reach the peak,but a slower flame propagation speed is obtained.Similar explosion characteristics are also observed in the configurations with two obstacles fixed at different stream-wise positions.Furthermore,the experimental results demonstrate that the peak overpressures and flame speeds in configurations with central or staggered obstacles are relatively higher,which should to be avoided in practical processes to minimize the risk associated with methane–air explosion.

Detonation Propagation Characteristics of Superposition Explosive Materials

In order to investigate detonation propagation characteristics of different charge patterns,the detonation velocities of superposition strip shaped charges made up of a detonating cord and explosives were measured by a detonation velocity measuring instrument under conditions of different ignition.The experimental results and theoretical analysis show that the maximum detonation propagation velocity depends on the explosive materials with the maximum velocity among all the explosive materials.Using detonating cord in a superposition charge can shorten detonation propagation time and improve the efficiency of explosive energy.The measurement method of detonation propagation velocity and experimental results are presented and investigated.