Detailed analysis of kinetic reactions in soot oxidation by simulated diesel exhaust emissions

Abstract Development of an advanced diesel particulate filter system requires efficient regeneration strategies, which, in turn, require a comprehensive understanding of soot oxidation kinetics. A goal of this study is first to define the effect of inert balance gases and heating rates used for thermogravimetric analyses on soot oxidation, with applying different analytic methodologies to the calculation of kinetic parameters. We identified an inert gas-independent activation energy value of surrogate soot to be 155 kJ/mole, evaluated at a heating rate of 1 °C/min, and proposed the differential method for evaluating kinetic parameters. Using the results, we conducted subsequent non-isothermal soot oxidation experiments to characterize the effects of reactant gases (NO, NO 2 , CO 2 , and O 2 ) in the various compositions of gas mixtures simulating diesel exhaust emissions. Notable results include the following. With no O 2 in the mixtures, NO gases rarely affected soot oxidation, while CO 2 effects also appeared to be minor. In the presence of a constant NO 2 concentration, the increased O 2 concentration (particularly up to 4%) significantly enhanced soot oxidation. In the case of a constant O 2 concentration, increasing the NO 2 concentration promoted soot oxidation in a fairly low temperature range of 200–580 °C. These O 2 and NO 2 effects turned out to be quite significant and temperature dependent. Overall, a higher degree of oxidation was observed with the mixture composition simulated for the higher engine load. The Arrhenius plots exhibited two distinct linear regression lines as NO 2 was present in the mixture, where the low temperature linearity range was extended with increasing NO 2 concentration. The activation energy quite significantly decreased from 153 to 39 kJ/mole in the low temperature range, as NO 2 concentration increased from 0 to 1250 ppm. In the high temperature range, however, the activation energy changed only slightly between 153 and 159 kJ/mole, indicating negligible dependence on mixture compositions.