Figure 3 Flame appearances of R123 (a) and R125 (b) recorded by
using a high-speed camera.
For clearly observing the process of fire extinguising, the flame
behavior in the last 0.3 s before the fire was extinguished was recorded
(in Figure 3). R123 and R125
extinguished the cup-burner flame both through the process of
oscillation-separation-extinction. As the concentration reached the
extinction limit, the flame oscillated frequently, and the flame root
began leaving the rim of the cup-burner. Due to the sudden increase in
the distance between the root of the flame and the burner at a certain
point, the flame cannot return to the edge of burner, the
two agents eventually cause the
flame to blow out.
The addition of two extinguishing agents weakened the adhesion of the
flame with the rim of cup, causing the flame to vibrate continuously.
However, it was also found that R123 (Figure 3a) made the flame
oscillation more obvious than R125 (Figure 3b) before extinguishing.
For
co-flow diffusion flame in the cup burner, the reaction kernel provides
a continuing ignition source in the flame base, which can consume the
new incoming reactants fast and maintain combustion, thereby the
trailing diffusion flame in the flow can keep holding in
succession[28, 29]. However, when the flame root starts appearing
the separation from the rim of cup, the reaction kernel which was at the
flame base was weakened by the addition of extinguishing agents, thus
the phenomenon of flame oscillation was occurred. It is indicated that
the influnce of R123 on the reaction kernel is greater than R125, the
addition of R123 may make the phenomenon of flame oscillation more
obvious.