Soot growth in laminar premixed flames.

The objectives of the present investigation were to study soot processes in laminar premixed flames. Both experimental and computational methods were used: the experiments involved observations of the flame and soot properties of laminar premixed flames stabilized on flat-flame burners at atmospheric pressure, the computations involved predictions of flame structure using detailed mechanisms of transport and chemical kinetics as well as predictions of soot surface growth rate using existing mechanisms in the literature. The experiments considered soot-containing ethylene/air flames having fuel-equivalence ratios of 2.34--2.94 and soot-containing methane/oxygen flames having fuel-equivalence ratios of 2.20--2.60. The following properties were measured along the axes of the test flames: soot volume fractions, soot primary particle diameters, soot and gas temperatures, concentrations of major gas species, H atom concentrations, concentrations of condensable hydrocarbon species and gas velocities. Flame structure was predicted using the detailed chemical mechanisms of Frenklach and coworkers (1992) and Leung and Lindstedt (1995). Predictions of flame structure in the soot growth region were in good agreement with measurements. Prediction of H atom concentrations were also in good agreement with the measurements and showed that H atom was in local thermodynamic equilibrium. Present measurements were used to find soot surface growth rates and primary particle nucleation rates along the axes of the flames. These results were used to evaluate the Hydrogen-Abstraction/Carbon-Addition (HACA) soot growth mechanisms of Frenklach and coworkers (1995) and Colket and Hall (1994). The agreement between measured and predicted soot growth rates was excellent for both HACA mechanisms. These results imply that reduced soot surface growth rates with increasing residence time were mainly caused by reduced rates of surface activation due to reduced H atom concentrations as temperatures decrease from radiative heat losses; therefore, temperature reductions due to radiative heat losses from soot itself ultimately controls maximum soot concentrations in these flames.Ph.D.Aerospace engineeringApplied SciencesChemical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131820/2/9929982.pd