Effects of Pressure on Mechanisms of Soot Surface Growth and Oxidation in Laminar Non-Premixed Flames at 1.0-8.0 atm

摘要

The flame and soot structure, including primary soot particle surface growth and oxidation properties, of round laminar diffusion flames were studied experimentally at pressures of 1.0-8.0 atm. Ethylene/helium mixtures were used at pressures from 1.0 to 8.0 atm in oxygen/helium coflow. The following properties along the flame axes were measured as a function of distance from the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using transmission electron microscopy (TEM), concentrations of major stable gas species by isokinetic sampling and gas chromatography, concentrations of radical species (H, OH, O) by deconvoluted Li/LiOH atomic absorption, and flow velocities by laser velocimetry. It was found that local primary soot particle surface growth rates could be correlated effectively using Hydrogen-Abstraction/Carbon-Addition (HACA) soot surface growth rate mechanisms regardless of pressure, and that local primary soot particle surface oxidation rates using OH/O_2 mechanisms were consistent with earlier measurements at atmospheric and sub-atmospheric pressures.