Effect of Turbulent Intensity and Mixture Composition on Flame Velocity

2 Effect of Turbulent Intensity and Mixture Composition on Flame Velocity 

It follows from the observed results graphed in Fig. 3.6, that the attempts to extinguish the flame in the 10% H2 mixture were not successful, even at the maximum possible rotation speed of the fans (at u = 16 m/s). The same conclusions about near-limiting H2 + air mixtures were made in [10]. 

A further conclusion can be drawn on the basis of the measured turbulent flame velocities presented in Figs. 3.4 and 3.5. For this, let us plot the S y/Su ratio relative to the mixture composition at a fixed pulsating speed value. Values 5x at m = 2 m/s have been taken from Figs. 3.4 and 3.5 and supplemented with at m = 5 m/s from [1]. The diagram plotted in Fig. 3.7 shows that in the lean mixtures, at a fixed turbulent intensity value, the turbulent flame velocity exceeds the laminar flame velocity, but this ratio decreases with the increasing H2% content. 

The same conclusion can be made based on the turbulent flame velocities measured by the other method (in a rectangular burner) [11] and illustrated in Fig. 3.8. Let us note the high Sx/S ratio in the lean mixture with less than 13.7% H2 at a turbulent intensity u = 10 m/s. The attempt to summarize the measured results and to verify the possibility of natural turbulence generation by the flame was made in [11]. 

In accordance with [12], additional turbulence generated by the flame can be described as follows 

---