Combined effects of obstacle position and equivalence ratio on overpressure of premixed hydrogen–air explosion

Gas explosion flame propagation over various hollow-square obstacles

Scale effects on premixed flame propagation of hydrogen/methane deflagration

An experimental study has been conducted to investigate the effects of hydrogen addition on the fundamental propagation characteristics of methane/air premixed flames at different equivalence ratios in a venting duct. The hydrogen fraction in the methane–hydrogen mixture was varied from 0 to 1 at equivalence ratios of 0.8, 1.0 and 1.2. The results indicate that the tendency towards flame instability increased with the fraction of hydrogen, and the premixed hydrogen/methane flame underwent a complex shape change with the increasing hydrogen fraction. The tulip flame only formed when the fraction of hydrogen ranged from 0 to 50% at an equivalence ratio of 0.8. It was also found that the flame front speed and the overpressure increased significantly with the hydrogen fraction. For all equivalence ratios, the stoichiometric flame ( Φ  = 1.0) has the shortest time of flame propagation and the maximum overpressure.

Effects of hydrogen addition on propagation characteristics of premixed methane/air flames

In many practical applications, the comprehensive measures are needed to suppress the gas explosions, and lining the channel walls with porous materials before a special installation for flame resistance is an effective choice. The aim of the present work is to investigate the effect of porous materials on the premixed flame propagation process in a closed combustion tube. Experiments are carried out to examine the flame dynamics for the stoichiometric methane/air mixtures both in the empty tube and in the presence of porous materials. The results demonstrate that the flame propagation can be divided into five typical stages, and a tri-tulip flame is observed during the development of the classic tulip flame. The inversion distance L of the flame front is selected to characterize the tulip flame evolution. It is worth to notice that the flame tip fronts travel faster with smaller porous densities PPI(pores per inch) from the finger shape stages to flat shape stages. The explosion severity parameters, including peak pressure and maximum pressure growth rates, are compared for all configurations, and the porous density plays an important role on the explosion severity. The maximum rate of pressure rise decreases linearly with the porous densities. It is deduced that the metal foam meshes with the larger porous densities PPI have more significant impacts on suppressing the tulip formation. The coupling of the flame front with the pressure wave plays a significant role in the onset and evolution of the tulip flame. As a whole, the metal foam meshes can reduce the overpressures can reduce the overpressures by33.3%–46.6%, while they have little effect on the flame tip speeds and shapes.

Effects of metal foam meshes on premixed methane-air flame propagation in the closed duct

Porous media quenching behaviors of gas deflagration in the presence of obstacles

A vented chamber, with internal dimensions of 150 mm × 150 mm × 500 mm, is constructed in which the premixed methane–air deflagration flame, propagating away from the ignition source, interacts with obstacles along its path. Three obstacle configurations with different cross-wise positions are investigated. The cross-wise obstacle positions are found to have significant effects on deflagration characteristics, such as flame structure, flame front location, flame speed, and overpressure transients. The rate of flame acceleration, as the flame passes over the last obstacle, is the highest at the configuration with three centrally located obstacles, whereas the lowest is observed at the configuration with three obstacles mounted on one side of the chamber. Compared with the side configuration, the magnitude of overpressure generated increases by approximately 80% and 165% for the central and staggered configurations, respectively. Furthermore, flame propagation speeds and generated overpressures for both the central and staggered configurations are greater, which should to be avoided to reduce the risk associated with turbulent premixed deflagrations in practical processes.

Effects of cross-wise obstacle position on methane–air deflagration characteristics

In this paper, simulations of methane–air deflagration inside a semi-confined chamber with three solid obstacles have been carried out with large eddy simulation (LES) technique Three sub-grid scale (SGS) combustion models, including power-law flame wrinkling model by Charlette et al, turbulent flame speed closure (TFC) model, and eddy dissipation model (EDM), are applied All numerical results have been compared to literature experimental data It is found that the power-law flame wrinkling model by Charlette et al is able to better predict the generated pressure and other flame features, such as flame structure, position, speed and acceleration against measured data Based on the power-law flame wrinkling model, the flame–vortex interaction during the deflagration progress is also investigated The results obtained have demonstrated that higher turbulence levels, induced by obstacles, wrinkle the flame and then increase its surface area, the burning rates and the flame speed

Large eddy simulation of methane–air deflagration in an obstructed chamber using different combustion models

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.

Methane–air explosion characteristics with different obstacle configurations

The utility model provides a quick-resetting and locking standby explosion door for a coal mine ventilation shaft, which is a set of independent standby explosion door for the coal mine ventilation shaft that is added without changing the existing explosion door structure and function of the coal mine ventilation shaft, and includes a square wall, a standby explosion door, a base plate, a traveling device, track-mounted bracket, a sealing gasket, a locking device and an awning. When the explosion door is damaged by the explosion air current, the standby explosion door and the base plate are driven to quickly and transversely move to the position above the ventilation shaft opening; the ventilation shaft opening is closely sealed through the square wall and the sealing gasket fixed below the base plate device; and in case of the inverted ventilation of the ventilation shaft, the explosion door is tightly locked through the locking device between the standby explosion door and the base plate device. The utility model has the effect and the benefits that the quick-resetting and locking standby explosion door can isolate the underground air current and the air above the ground in case that the existing explosion door is damaged, so as to ensure the normal operation of the ventilating system of the coal mine ventilation shaft; and in case of the inverted ventilation of the ventilation shaft, the standby explosion door is tightly locked by the locking device, so as to prevent air current short circuit.

Xiaoping Wen

Papers

Porous media quenching behaviors of gas deflagration in the presence of obstacles

Effects of cross-wise obstacle position on methane–air deflagration characteristics

Large eddy simulation of methane–air deflagration in an obstructed chamber using different combustion models

Methane–air explosion characteristics with different obstacle configurations

Quick-resetting and locking standby explosion door for coal mine ventilation shaft