Soot generation within radiating diffusion flames

Abstract

C 7 H 16 and (C S H 8 0 2 )n] in free, radiating, boundary layer, diffusion flames are represented analytically. Approximate particle concentrations and size distributions, determined with previously reported optical techniques, are used. These sizes, r -30 nm, indicate the particles are in the free molecular flow regime, Kn -10, so that the thermal boundary layer thickness around the particle approaches zero and the particle temperature is locked to the local gas temperature. Based on this coupling and the experimental -soot fv -1 ppm, the optically thin approximation is valid for incorporating soot radiation in the gas boundary layer equations. The pertinent fields, i.e. tpmperature, velocity and species, are reported. Thermophoretic forces are included in particle trajectory calculations. The local soot mass flow rates within the boundary layer are derived and net soot mass generation rates are obtained for these well characterized laminar flames. An Arrenhius expression appears to suffice to describe the temperature dependence of the soot growth rate over a 400 0 K temperature range, 19S0 < T < 23S0K. Toluene has Ea = 108 kcal/mole while all the other fuels examined have Ea = 86 kcal/mole, very close to H3C -C6HS and C-C bond energies, respectively. Consistent with the goal of fire radiation prediction, calculated temperatures and velocities were used to obtain these empirical energies. Temperature and velocity measurements are in progress. Future work will include mixed flow boundary layer systems where control over the free stream oxygen mass fraction in a combustion tunnel configuration provides greater flame stability and a wider temperature range.

Heat transfer blockage in small scale combustion of polymers

“…(1) Experimental studies and data accumulations, such as an experimental study of radiative heat feedback and blockage on vertical wall fires [13], measurements on absorptivity and emissivity of fuel vapors [14,15], various models on soot formation, transfer and consumption within flames as well as soot radiation [16][17][18][19][20], measurements of heat of gasification/vaporization for small scale polymer samples [21,22] and experimental simulation and measurement on radiative heat feedbacks using gas flames [23] etc.…”