Lifted Flames and the Effects of Inhibitors

Abstract

The blowoff and liftoff characteristics of lifted turbulent diffusion flames of liquefied petroleum gas and compressed natural gas are investigated with a range of burner diameters. Uninhibited flames as well as flames inhibited by either Bromotrifluoromethane, (CF3Br known as Halon-1301), N₂or Ar have been studied. The coflowing air stream is set at about 42cm/s. The inhibitor is either premixed with the fuel or introduced externally in the air stream via a circular injector positioned at the jet exit plane. The flames are videotaped and subsequently analysed.

It is found that, for the burner diameters investigated here, the liftoff height, H of uninhibited turbulent diffusion flames increases linearly with the jet Reynolds number, Rer The largest amount of inhibitor which must be injected to cause blowoff occurs when the flames have intermediate velocities in the range 20% to 60% of the uninhibited flame blowoff velocity. Halon-1301 acts chemically on the flame and hence is a far mote effective inhibitor than N₂ or Ar which act only thermally. The liftoff height, H increases with the addition of inhibitor and it is similar for flames inhibited with N₂ or Ar. His largest for the flames inhibited with halon. The results are independent of whether the inhibitor is introduced in the air stream or premixed with the fuel

Key Words:

• Lifted flames
• halons
• thermal inhibition
• chemical inhibition