Flame acceleration in tube explosions with up to three flat-bar obstacles with variable obstacle separation distance

Abstract

The effect of obstacle separation distance on the severity of gas explosions has received little methodical study. It was the aim of this work to investigate the influence of obstacle spacing of up to three flat-bar obstacles. The tests were performed using methane-air (10% by vol.), in an elongated vented cylindrical vessel 162 mm internal diameter with an overall length-todiameter, L/D, of 27.7. The obstacles had either 2 or 4 flat-bars and presenting 20% blockage ratio to the flow path. The different number of flat-bars for the same blockage achieved a change of the obstacle scale which was also part of this investigation. The first two obstacles were kept at the established optimum spacing and only the spacing between the second and third obstacles was varied. The profiles of maximum flame speed and overpressure with separation distance were shown to agree with the cold flow turbulence profile determined in cold flows by other researchers. However, the present results showed that the maximum effect in explosions is experienced at 80 to 100 obstacle scales about 3 times further downstream than the position of maximum turbulence determined in the cold flow studies. Similar trends were observed for the flames speeds. In both cases the optimum spacing between the second and third obstacles corresponded to the same optimum spacing found for the first two obstacles demonstrating that the optimum separation distance does not change with number of obstacles. In planning the layout of new installations, the worst case separation distance needs to be avoided but incorporated when assessing the risk to existing set-ups. The results clearly demonstrate that high congestion in a given layout does not necessarily imply higher explosion severity as traditionally assumed. Less congested but optimally separated obstructions can lead to higher overpressures.

Turbulent flame propagation with pressure oscillation in the end gas region of confined combustion chamber equipped with different perforated plates

“…Based on the above theory fundamentals including the flame acceleration and flame-shock interactions, a number of experimental studies [12,13,[28][29][30] have demonstrated the influence of obstacle spacing or scale on the flame propagation process. The work by Ciccarelli et al [31] demonstrated that the detonation initiation due to shock reflection is roughly the same for the different blockage ratio (BR) reflector perforated plates tested.…”

“…In other work by Abdulmajid [28], the effects of obstacle scale with the same BR on the flame speed and overpressure were investigated. The obstacle with two flat bars obtained maximum overpressure compared with that with four flat bars.…”

Experimental study of low‐concentration gas explosion in large‐scale pipeline

“…On the other hand, when the explosion spreads throughout the pipeline, the propagation of shock waves is restricted by the sealing of the pipeline outlet. The reflection and superposition of shock wave rapidly occurred, causing a further increase in explosion pressure …”

Numerical Simulation of Premixed Methane–Air Explosion in a Closed Tube with U-Type Obstacles

“…Gubba et al [19] found that the flame propagation could be influenced by the number of obstacles and its blocking rate and low pressure areas could appear [12] around the next plates, whereas its blocking rate decreased during the experiment of combining the block shape with plates. In addition, Na'inna et al [20] suggested that it can cause higher pressure for appropriate blocking rate and separation distance of obstacles. After experimentation, Li et al [21] suggested these obstacles could have a great influence on the explosion overpressure and the flame propagation based on the different shapes of trapezoid, circle, square and rectangle.…”