Effect of stretch rate

It can also be noted that the slope of the S , .,f-Ka plot reflects the combined effect of stretch rate and non-equidiffusion on the flame speed. Figure 4.1.6 clearly shows that the flame response with stretch rate variation differs for lean and rich mixtures. In particular, as Ka increases, the S for stoichiometric and rich mixtures increases, but decreases for the mixture of equivalence ratio = 0.7. This is because the effective Lewis numbers of lean w-heptane/ air and lean /so-octane/air flames are... 

The effects of stretch rate on stress-strain behavior can be seen from Fig. 3. In the range between 85 °C to 95 °C, the stress level increases with the increase of stretch rate. At 105°C the stress-strain curves in three stretch rates are almost overlapped. It indicates that the effect of stretch rate on stress-strain behavior is small. This case can be explained as follows. There are two molecular chain motion mechanisms one is the molecular orientation the other is the chain relaxation. The different stress-strain behavior is the result of these two mechanisms completeness. At fast stretch rate and low temperature the molecular relaxation is inhibited. In other words the rate of molecular chain relaxation can not keep up with that of orientation, and therefore the stress level is high. Owing to the fast rate of quiescent crystallization, at 105°C, quite a few quiescent crystallization existed before stretching results the high stress level and lessen the effect of stretch rates. 

---