Experimental Study on Primary Soot Particle Inception in Laminar Premixed and Diffusion Flames

摘要

Measurements of flame and soot structure for a variety of round laminar jet premixed and nonpremixed flames fueled with hydrocarbons have been analyzed to study the properties of primary soot particle nucleation. The following properties were measured along the axes of the flames as a function of distance from the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multilane emission in the visible, soot structure by thermophoretic sampling and analysis by transmission electron microscopy (TEM), concentrations of major stable gas species (N_2, Ar, H_2O, H_2, O_2, CO, CO_2, CK_4, C_2H_2, C_2H_4, C_2H_6, C_3H_6,C_3H_8 and C_6H_6) by isokinetic sampling and analysis using gas chromatography, concentrations of some radical species (H, OH and O) by deconvoluted Li/LiOH atomic absorption in the visible wavelength, and flow velocities by laser velocimetry. These measurements were analyzed to yield local primary soot particle nucleation rates. Based on the assumptions that poly-aromatic-hydrocarbon (PAH) species grow via hydrogen-abstraction/carbon addition (HACA) mechanism, soot particle surface grows via HACA mechanism, and soot precursor particles form via coagulation of large PAH species, it was found that soot particle nucleation rates can be correlated well with the hydrogen atom concentrations. Such correlation was found to be relatively independent of flame type, original hydrocarbon-fuel type, gas temperature (1400-2350 K) and pressure (0.1-8.0 atm). The results using a general approach to predict soot volume fraction evolutions along the axes by applying the correlations found in this study are compared with the experimental values.