THE TRANSITION FROM NON-SOOTING TO SOOTING COFLOW ETHYLENE DIFFUSION FLAMES

Abstract

Laminar, sooting, ethylene-fueled, coflow diffusion flames at atmospheric pressure have been studied experimentally and theoretically as a function of fuel dilution by inert nitrogen. The flames have been investigated experimentally using a combination of laser diagnostics and thermocouple-gas sampling probe measurements. Numerical simulations have been based on a fully-coupled solution of the flow conservation equations, gas-phase species conservation equations with complex chemistry, and the dynamical equations for soot spheroid growth. Predicted flame heights, temperatures, and the important soot growth species, acetylene, are in good agreement with experiment. Benzene simulations are less satisfactory and are significantly under predicted at low dilution levels of ethylene. As ethylene dilution is decreased and soot levels increase, the experimental maxima in soot moves from the flame centerline toward the wings of the flame. Simulations of the soot field show similar trends with decreasing dilution of the fuel and predicted peak soot levels are in reasonable agreement with the data. Computations are also presented for modifications to the model that include: (i) a revised inception model; (ii) a maximum size limit to the primary particle size and (iii) estimates of radiative optical thickness corrections to computed flame temperatures.