@article{25121,
  keywords = {Buoyancy, Burner rotation, Lewis number, Microgravity, Premixed flame},
  author = {Hiroshi Gotoda and Kazuyuki Maeda and Toshihisa Ueda and Robert K Cheng},
  title = {Periodic motion of a Bunsen flame tip with burner rotation},
  abstract = {<p>Effects of burner rotation on the shapes and dynamics of premixed Bunsen flames have been investigated experimentally in normal gravity and in microgravity. Mixtures of CH<sub>4</sub>-air and C<sub>3</sub>H<sub>8</sub>-air are issued from the burner tube with mean flow velocity <em>U =</em> 0.6 m/s. The burner tube is rotated up to 1400 rpm (swirl number <em>S</em> = 1.58). An oscillating flame with large amplitude is formed between a conical-shape flame and a plateau flame under the condition of Lewis number <em>Le</em> &gt; 1 mixtures (rich CH<sub>4</sub>-air and lean C<sub>3</sub>H<sub>8</sub>-air mixtures). In contrast, for <em>Le</em> ≤ 1 mixtures (lean CH<sub>4</sub>-air and rich C<sub>3</sub>H<sub>8</sub>-air), asymmetric, eccentric flame or tilted flame is formed under the same swirl number range. Under microgravity condition, the oscillating flames are not formed, indicating that the oscillation is driven by buoyancy-induced instability associated with the unstable interface between the hot products and the ambient air. The flame tip flickering frequency ν is insensitive to burner rotation for <em>S</em> &lt; 0.11. For <em>S</em> &gt; 0.11, ν decreases linearly with increasing <em>S</em>. As <em>S</em> exceeds 0.11, a minimum value of axial mean velocity along the center line <em>u<sub>j,m</sub></em> due to flow divergence is found and it has a linear relationship with ν. This result shows that <em>u<sub>j,m</sub></em> has direct control of the oscillation frequency. When <em>S</em> approaches unity, the flame oscillation amplitude increases by a factor of 5, compared to the flickering amplitude of a conical-shape flame. This is accompanied by a hysteresis variation in the flame curvature from positive to negative and the thermo-diffusive zone thickness varying from small to large. With <em>S</em> &gt; 1.3, the plateau flame has the same small flickering amplitudes as with <em>S</em> = 0. These results show that the competing centrifugal and buoyancy forces, and the non-unity Lewis number effect, play important roles in amplifying the flame-tip oscillation.</p>},
  year = {2003},
  journal = {Combustion And Flame},
  volume = {134},
  pages = {67-79},
  month = {07/2003},
  doi = {10.1016/S0010-2180(03)00082-8},
  language = {eng},
}