Pressure and Flow Residence Time Effects on Soot Properties in Counterflow Non-Premixed Hydrocarbon-Air Flames

Abstract

Numerous studies have reported the adverse health, environmental, and climatic effects of aerosol or soot particulate emissions from the combustion of hydrocarbon fuels in boilers, furnaces, gas turbines and other internal combustion engines. Considering the significant dependence that our modern society places on hydrocarbon fuels, it is of ethical interest to reduce or mitigate the resulting pollutants. With advanced laser based diagnostic techniques under development, the potential for future regulation on particulate emissions provides further motivation. While production of some pollutant species is well understood, knowledge of soot particulate nucleation and growth remains in its infancy. Precise synthesis of flame generated carbon nanoparticles may also prove useful as an industrial and technical commodity to increase efficiency and reduce cost for a variety of applications. One of the most elementary and important effects on soot formation and growth relevant to modern combustion engines is that of pressure. Utilizing the simple laminar, steady counterflow burner configuration, the goal of this work is to investigate the effect of elevated pressure on the soot nucleation, growth, and oxidation mechanisms of hydrocarbon combustion over a wide range of flow residence times. An absolute irradiance calibrated two-color time resolved Laser Induced Incandescence (LII) technique was developed and utilized to collect quantitative soot incandescence data for determination of soot particle temperature, primary particle size, soot volume fraction, and number density. The approach requires a comprehensive LII nano-scale heat transfer model with coupled extinction and elastic light scattering submodels. Thermophoretic soot

Determining fractal properties of soot aggregates and primary particle size distribution in counterflow flames up to 10 atm

“…Values of fractal dimension of soot in current study range from 1.61 to 1.67 at different pressures with uncertainty of 0.05 (95% confidence) for the mean value. A thorough search of literature revealed the only information about fractal properties of soot in pressurized counterflow flames was reported in the doctoral thesis of Sarnacki [32], where the measured fractal dimension and fractal prefactor are 1.41 and 2.9, respectively at 8.45 atm. Lower fractal dimension and high fractal prefactor of soot may be due to an insufficient number of aggregates analyzed.…”