Soot Formation in Partially Premixed Diffusion Flames at Atmospheric

Fabian Mauss, Bernhard Trilken, Hermann Breitbach

Abstract

The formation, growth and oxidation of soot has been studied in a
laminar counterflow configuration. Soot inception occurs in a fuel rich burner sta-bilized premixed acetylene-air flame at the bottom of the system. Oxidation of soot takes place downstream in a diffusion flame, generated by unburnt hydrocar-bons, carbonmonoxid and hydrogen in the burnt gas of the premixed flame and a counterflow of pure oxygen. In the region between the two flames soot particles grow due to surface reactions and coagulation. The residence time of the particles in this region is long, because the counterflow flame is placed near the stagnation point of the system. Mean particle diameter up to 100 nm are observed.
Concentration profiles of various stable species up to benzene were measured by gas chromatography. Thermocouples were used for temperature measurements. The soot volume fraction was determined by laser light extinction and Abel's inversion. Particle sizes measured with the combined scattering/extinction mea-surement technique, with the dispersion quotient method and with dynamic light scattering technique are compared.
Numerical calculations including a chemical model for soot formation have been performed for this system. The calculated profiles for temperature, concentrations, soot volume fraction and particle size were compared with the experimental data. The predicted profiles of soot volume fractions and particle sizes are found to be of the same accuracy as the predicted profiles of temperature and gas phase concentrations.