Burnt Gas Flow Stability of Limit Flames in Vertical Tubes

Stability of gas flows generated by steady near-limit flames propagating in vertical tubes is studied numerically. Basic scenarios of the burnt gas flow evolution are identified in relation to the thermal gas expansion parameter and the normal flame speed. It is shown that the implementation of a specific scenario essentially depends on the stagnation zone width as well as on the distance travelled by the gas from the flame front to the tube end. In particular, it is found that for sufficiently short distances, the burnt gas flows are stable provided that the stagnation zone width is less than half the tube diameter. Otherwise, an unstable flow evolution can lead to the appearance of recirculation domains and acoustic perturbations.