Counterflow premixed flames limits

This section emphasizes on flame quenching by stretch, as well as highlights and separately discusses the four aspects of counterflow premixed flame extinction limits, including (1) effect of nonequidiffusion, (2) influence of different boundary conditions, (3) effect of pulsating instability, and (4) relahonship of the fundamental limit of flammability. 

In Chapter 6.3, C-J. Sung examines extinction of counterflow premixed flames. He emphasizes flame quenching by stretch and highlights four aspects of counterflow premixed flame extinction limits effect of nonequidiffusion, parf played by differences in boundary conditions, effect of pulsating insfabilify, and relation to the fundamental limit of flammability. 

It is well known that in a jet flame blow-out occurs if the air-fuel mixture flow rate is increased beyond a certain limit. Figure 18.3 shows the relationship between the blow-out velocity and the equivalence ratio for a premixed flame. The variation of blow-out velocity is observed for three different cases. First, the suction collar surrounding the burner is removed and the burner baseline performance obtained. Next, the effect of a suction collar itself without suction flow is documented. These experiments show that for the nozzle geometry studied, the free jet flame (without the presence of the collar) blows out at relatively low exit velocities, e.g., 2.15 m/s at T = 1.46, whereas for > 2 flame lift-off occurs. When the collar is present without the counterflow, the flame is anchored to the collar rim and blows out with the velocity of 8.5 m/s at T = 4. Figure 18.4a shows the photograph of the premixed flame anchored to the collar rim. The collar appears to have an effect similar to a bluff-body flame stabilizer. The third... 

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