- Author
-
Okoh, C. I.
- Title
- Soot and Radiation in Free Boundary Layer Flames.
- Coporate
- California Univ., Berkeley
- Sponsor
- National Bureau of Standards, Gaithersburg, MD
Department of Energy, Berkeley, CA
- Report
-
LBL-18705
December 1984
133 p.
- Contract
- NBS80NAGE68393
DE-AC0376SF000098
- Keywords
-
flame research
- Abstract
- Soot volume fraction data on six fuels [C7H8,C6H10,C8H18,C6H12,C7H16, (C5H8O2)n] in free, radiating boundary layer, diffusion flames are presented along with approximate particle concentrations and size distribution used, and a brief discussion of the optical method employed to obtain them. A mathematical model also is presented for these flames. The soot and gas temperatures are shown to be locked, allowing the soot radiation to be included in the gas energy equation. The conservation equations are nondimensionalised and solved. Nine dimensionless parameters are found to control the solution. The effects of buoyancy are studied, and found to be pronounced in forced flow systems. Average transport and radiative properties are specified for the sooting flames studied, and rules are established for obtaining these properties. The absorption coefficient is presented for all the fuels. The values are consistent with the initial assumptions that the boundary layers examined are optically thin. Solutions are obtained for the temperature, species, and velocity fields and comparisons are made with corrected experimental thermocouple measurements. Gas streamlines are calculated, and thermophoresis is included in particle trajectory determinations. Soot mass conservation and carbon conversion are studied in the boundary layers. Soot mass flow rates and net generation rates are obtained. The normalized soot generation rates exhibit similarity near the flame. A simple Arrhenius correlation is introduced for calculating net generation rates and is found to sufficiently describe the temperature dependence of the soot growth over the temperature range 1700K < T < 2200K. The energy parameter is of 0(50 kcal/mole) and the pre-exponential is of 0(1GHz). The Arrhenius forms are integrated along trajectories to obtain predicted soot concentrations which agree well with experiment.