希薄および過濃なメタン・空気,プロパン・空気乱流予混合火炎の火炎面の挙動(熱工学,内燃機関,動力など)  [in Japanese] Flamelet Movements in Lean and Rich Methane-air and Propane-air Turbulent Premixed Flames(Thermal Engineering)  [in Japanese]

3-D movement of flame fronts in lean and rich hydrocarbon-air turbulent premixed Bunsen flames, having the identical laminar burning velocities, were examined by a four-element electrostatic probe. Measurements were conducted at an off-axis position in turbulent flame brush. The probability distributions of the magnitude and of the direction cosines of the velocity vector of the flamelet were examined. The results showed differences between the lean and rich propane flames but not between the lean and rich methane-flame pairs. The lean propane flame has the same probability distribution of direction cosines as the methane flames. The probability distributions of the direction cosines for the rich propane flame are, however, quite different, that there is a much greater tendency for outward flamelet motion. Although these results for rich propane flame exhibit a larger most probable outward-motion direction cosine for burnt-to-unburnt passage than for unburnt-to-burnt passage, as has been found in all Bunsen-flame data and explained previously, this is the first example in Bunsen-flame data in which the most probable value of the direction cosine in the radial direction for unburnt to burnt passage is positive, that is, contrary to the other Bunsen-flame results, the average flamelet velocity direction is outward at this off axis position even for unburnt-to-burnt passage. The exceptional characteristics of rich propane were explained by nonlinear enhancement of the average flamelet burning velocity through preferential oxygen diffusion to turbulence-induced flamelet bulges convex towards the fresh mixture.