Oxidation of model soot by NO2 and O2 in the presence of water vapor

The combustion of model soot (i.e. Printex U) by NO 2 and O 2 in the presence of water was investigated in a fixed bed micro reactor under isothermal conditions. A wide range of experimental conditions (e.g. 250–350 °C, 0–5 vol% O 2 , 0–500 ppmv NO 2 , 0–5 vol% H 2 O) were considered in order to investigate the role of NO 2 , O 2 and H 2 O in the combustion process. It was found that the oxidation of soot is initiated by NO 2 at temperatures where oxygen is unreactive. In addition, a synergistic effect between NO 2 and O 2 on soot combustion was observed in the presence of the NO 2 -O 2 mixture. Both the direct reaction between soot and NO 2 and also the contribution of gaseous oxygen on the combustion process appeared to rise with the increasing temperature and in the presence of water. Finally, the kinetic analysis of the experimental results showed a non-negligible dependence of the kinetic parameters on carbon conversion and in particular the poor accuracy of the shrinking-core model at low conversion degree.