A Phenomenological Description of Particulate Formation during Constant Volume Combustion

Abstract

Experiments to characterize soot particulate formation processes during the combustion of rich homogeneous mixtures have been conducted in a constant volume combustion bomb. Soot formation is observed to occur very rapidly in the flame front, and the particles are dispersed over the burned gas region as these gases are continually compressed. Particles sampled and analyzed by transmission electron microscopy exhibit three-dimensional chain-like structures. In the present premixed experiments, any parameter change that increases the flame zone temperature, such as reducing the diluent concentration, decreasing the diluent heat capacity, increasing the initial reactant temperature, or changing the fuel type, reduces the quantity of soot formed. Thus, temperature is shown to be a key parameter in determining the tendency of a mixture to soot. In many of these tests, burned gas temperature is nearly constant with time, suggesting that particulate blackbody radiation may be a stabilizing influence on the burned gas temperature. Coupling this radiation back into the chamber influences the particulate oxidation process and actually reduces the quantity of soot formed.