There was no significant difference between larger section and smaller vacuum chambers in degree of maximum peak value overpressure and specific impulse declining, except that quenching fire effect of the former was superior to the latter.
When the vacuum chamber was not connected to the tunnel, detonation would happen in the tunnel at methane volume fraction from 9.3% to 11.5%, with flame propagation velocity exceeding 2000 m/s, maximum peak value overpressure reaching 0.7 MPa, and specific impulse of shock wave running up to 20 kPa s.
When the vacuum chamber with 5/34 of the tunnel volume was connected to the flank of the tunnel, gas explosion of the same concentration would greatly weaken with flame propagation velocity declining to about 200 m/s, the quenching distance decreasing to 3/4 of the tunnel length, maximum peak value overpressure running down to 0.1 0.15 MPa and specific impulse of shock wave below 0.9 kPa s.
However, under a single number of obstacles, the peak overpressure and the maximum combustion rate increase firstly and then decrease as VBR increases and reach the highest at the VBR of 0.74, which indicated that the intensity of vapor cloud explosion reach a peak at a certain VBR in the middle instead of the largest.
When the height-width ratio is 0.5 (the corresponding geometrical shape is 4 m × 4 m × 2 m), the explosion peak overpressure reaches the maximum of 1.57 bar, which is 3.6 times of that (0.44 bar) for the 2 m × 2 m × 8 m vapor cloud.
Based on the results and analysis, it is found that the peak overpressure and the maximum combustion rate rise with the increase of the number of obstacles for a single VBR, which indicated that the vapor cloud explosion of more obstacles was more dangerous for a single VBR.
With increasing distance from the ignition source, the peak overpressure formed by shock wave, the flame propagation speed, the maximum combustion rate, the maximum density, and the maximum gas velocity increased gradually, but the peak overpressure formed by sonic compression wave and the maximum temperature decreased gradually.
Interestingly, for the stoichiometric and rich mixtures, the peak overpressure reached the maximal when the obstacle was at the middle position.
