Studies on Micro Structure and Dynamic Behavior of Stretch-Controlled Flames

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Numerical computations of laminar flames have been conducted taking into account detailed chemical kinetics and multi-component diffusion. Diffusion flames, flat premixed flames and spherical flames considered of different stretch rate.In the diffusion flames, (1) There are two types of extinction, the intermittent and the perfect extinction. (2) Extinction occurs slightly in down stream where local stretch rate is the largest. (3) The local stretch rate is much affect the extinction. (4) The convection flow along the flamelet changes the extinction limit.In the flat premixed flame, (1) Symmetrical twin flame is formed As the counter velocity increases, the peak of the heat release rate comes to the central part. (2) The burning velocity increases with increasing the stretch rate, but the burning rate decreases with increasing the stretch rate.The effects of the stretch rate are investigated on the burning velocity in three kind of hydrogen/air flames, that is, outwardly propagating (OPF), inwardly propagating (IPF) and stationary (SF) spherical Direction of the flame propagation and radius of the flame change the stretch rate.(1) The burning velocity is changed for the smaller radius than 5mm. For the IPF, the flame velocity becomes large for the equivalence ratio ¢ larger than 0.7. But, for the smaller Φ, the results is opposite. The change is opposite for the OPF and IPF. (2) The stretch rate of the SF is zero, but the burning velocity has a wide range. (3) The burning velocity is dominated by not only the stretch rate but also the Lewis number, because the burning velocity has the opposite results assuming different diffusivities.