Interaction of shock tube exhaust flow with a non-pre-mixed flame

Much of the discussion in the public domain relating to shockwave interaction with flames, and the use of high explosives to extinguish, for instance, oil and gas well fires, is anecdotal and outside of scientific literature. The result is a lack of consistent insight into the physical mechanisms involved. It has been proposed by several researchers that the shock waves and the strong vortex rings from detonations are effective in extinguishing large­scale fires (Akhmetov et al. 1980, 2001, 2009; Bliznetsov et al. 2001). To date, methodical laboratory shock tube work in controlled conditions for simple flame cases has not been reported. Therefore, a preliminary laboratory­scale study was devised to investigate, qualitatively, the interaction between the flow exhausting from an open­ended shock tube and a standard Bunsen burner flame. The shock tube was a basic, compressed air­driven device not capable of producing exactly the kind of temporal pressure profile associated with explosive events (i.e. a Friedlander­esque waveform) (Chandra et al. 2012). However, the flow fields obtained resulted in many interactions not previously observed and documented. This was possible due to the complex flow features emanating from the tube exit, including strongly rotating vortices and a central jet of flow following the initial shock wave (Jiang et al. 2003; Kashimura et al. 2000; Onodera et al. 1998). The flow from the shock tube was expected to be in the low­supersonic range within the immediate vicinity of the exit, with the leading shock and jet both dissipating significantly downstream with an accompanying reduction in planarity. Therefore, the effect of the exhaust flow on the Bunsen safety (yellow) non­pre­mixed flame was examined at 50 mm and 500 mm from the tube exit to investigate the range of interactions possible with this setup. Multiple stagnation pressures in the driver section (from 140 to 620 kPa) were used to examine the influence of Mach number at the exit (1.1–1.4). The shock tube had a 44 mm 9 47 mm rectangular cross­sectional exit, a 1,790 mm long driver section, and a 2,195 mm driven section. The visualization was captured at 6,000–10,000 fps using a Photron APX­RS, with an exposure time of 20 ls. A conventional z­type schlieren arrangement was utilized with a vertical knife­edge cutoff.