SURFACE-PROPERTIES OF TURBULENT PREMIXED PROPANE AIR FLAMES AT VARIOUS LEWIS NUMBERS

Surface properties of turbulent premixed flames including the wrinkled flame perimeter, fraction of the flame pocket perimeter, flame curvat ure, and orientation distributions have been measured for propane-air flames at Lewis numbers ranging from 0.98 to 1.86 and u'/S(L) = 1.42-5 .71. The wrinkled flame perimeter is found to be greater for the therm odiffusively unstable Lewis number (Le < 1) by up to 30% in comparison to the most stable condition (L3 = 1.86) tested, while the fraction o f the flame pocket perimeter shows a similar tendency to be greater fo r Le < 1. The flame curvature probability density functions are nearly symmetric with respect to the zero mean at all Lewis numbers througho ut the range of u'/S(L) tested, and show a much stronger dependence on the turbulence condition than on the Lewis number. Similarly, the fla me orientation distributions show a trend from anisotropy toward a mor e uniform distribution with increasing u'/S(L) at a similar rate for a ll Lewis numbers. Thus, for turbulent premixed propane/air flames for a practical range of Lewis number from 0.98 to 1.86, the effect of Lew is number is primarily to affect the flame structures and thereby flam e surface areas and flame pocket areas, while the flame curvature and orientation statistics are essentially determined by the turbulence pr operties.