Experimental Determination of the Kinetics of Diesel Soot Oxidation by O2 - Modeling Consequences

Several complementary experimental techniques were applied to investigate kinetics of diesel soot oxidation by O₂ in an attempt to provide accurate data for modeling of the Diesel Particulate Filters regeneration process. For two diesel soot samples with measurably different properties, it was shown that the complexity of their overall kinetic behavior was due to an initial period of rapidly changing reactivity. This initial high reactivity was understood not to be related to the SOF, and was quantitatively correlated to the extent of soot pre-oxidation. This initial reactivity can affect the averaged apparent kinetic parameters, for example resulting in the lower apparent activation energy values.

After the initial soot pre-oxidation, which consumed ∼10-25% of carbon, the remaining soot was behaving very uniformly, producing linear Arrhenius plots in a remarkably broad range of temperatures (330-610°C) and integral conversions (up to 90%). The two samples of diesel soot were found to behave differently even after the SOF desorption and pre-oxidation, with the measurable difference in the light-off characteristics (∼20-30°C) and activation energies (126±3 and 143±3 kJ/mol).

Good mathematical description of the results was obtained using the hypothesis that reaction order with respect to soot mass is close to unity. Implications of the first order are discussed, including its effect on the model structure.