Measurements of flame propagation velocities and blast wave pressures for methane/oxygen gas mixtures

The flame propagation and the blast wave behaviors of methane/oxygen gas mixtures have been investigated. The mixtures were charged into spherical transparent rubber balloons and ignited at its center. The flame propagation behaviors were recorded by a high-speed video camera and the blast wave pressures were measured by several piezoelectric sensors. Although different scale experiments were conducted, the flame propagation behaviors for the same equivalence ratio are similar to each other. and the velocity increased continuously during the flame propagation. The pressure-time histories showed a continuous rise of pressure immediately after the blast wave was formed in air. However, as the blast wave traveled. a discontinuity appeared which resulted in the formation of a shock wave. Eventually. the blast wave lost its discontinuity at long distances. Trinitrotoluene (TNT) equivalents for the mixtures were evaluated by comparing the peak pressures and the impulses with those for TNT. It was found that TNT equivalents near the explosion source are smaller than those at long distances. while they can be considered as constant if evaluated using the impulse at a sufficiently long distance.