Combustion Diagnostics Laboratory

The atmospheric laminarflamespeeds of mixtures of air with ethylene, n-butane, toluene, ethylene-n-butane, ethylene-toluene, and n-butane-toluene were experimentally and computationally investigated over an extended range of equivalence ratios. Binary fuelblends with 1:1, 1:2, and 2:1 molar ratios were examined. Experimentally, the laminarflamespeeds were determined using digitalparticleimagevelocimetry (DPIV). Since the use of DPIV enables the mapping of the two-dimensional flow field adhead of the flame, the reference speed based on the minimum axial velocity point as well as the imposed strain rate can be identified simultaneously. The latter can now be unambiguously determined by the radial velocity gradient at the minimum velocity point. By systematically varying the imposed strain rate, the corresponding laminarflamespeed was obtained through nonlinear extrapolation to zero strain rate. The associated experimental accuracy of the DPIV measurements was also assessed and discussed. Computationally, the laminarflamespeeds were simulated for all single-component fuel/air and binary fuelblend/air mixtures with a detailed kinetic model. Comparison of experimental and computed flamespeeds shows generally good agreement. A semiempirical mixing rule was developed. The mixing rule which requires only the knowledge of the flamespeeds and flame temperatures of the individual fuel constituents, is shown to provide acurate estimates for the laminarflamespeeds of binary fuelblends under the conditions tested.