Soot oxidation kinetics: Pressure and fuel comparisons

Thermo-Gravimetric Analysis (TGA) studies were performed with soot obtained from a mixture of mxylene and n-dodecane as well as with the pure compounds. Soot samples were produced in a flatflame, premixed burner under heavily-sooting conditions and the soot was oxidized using a Cahn TherMax 500 high pressure TGA. The TGA conditions were optimized to reduce mass transfer effects; 10 mg of sample and a volumetric flow rate of 1.5 l/min was used. Two total pressures of the system were evaluated (1 and 10 atm) and the O₂ concentrations varied between 10 and 21%. An inert material was used in all the tests to minimize thermal and mass transfer effects by decreasing the stagnant region between the top surface of the soot and the entrance of the crucible. Mass transfer corrections had to be considered for the higher pressures. The estimated activation energies ranged from 140 to 170 kJ/mol. There was not a significant difference in the activation energies obtained for different soot samples at the pressures evaluated in this study. The activation energy of the soot was found to be on the same order of magnitude as published values.