The effects of aspect ratio on CH4/air flame stability in rectangular mesoscale combustors

The effects of aspect ratio (alpha = 1, 2, 3 and 4) of mesoscale rectangular channels on CH4-air flame stability were numerically studied. The results show that at relatively high inlet velocity, the flame is convex (with respect to the upstream) when alpha <= 3; instead it shifts to a W-shaped appearance at alpha = 4. In addition, the flame blowout limit exhibits a non-monotonic variation and it peaks at alpha = 3. Our analysis reveals that when alpha is raised from 1 to 3, both of the heat loss ratio and hydrodynamic perturbation rate are reduced, which favors a larger blowout limit. However, for the channel with alpha = 4, the perturbation rate of hydrodynamic instability is significantly increased at the flame tip because of the increased wave number, which results from the W-shaped flame front. Consequently, the intensified hydrodynamic instability will lead to a reduction in the flame blowout limit of the channel with alpha = 4. (C) 2019 Energy Institute. Published by Elsevier Ltd. All rights reserved.