Influence of water vapor addition on soot oxidation at high temperature

An experimental study was carried out into the influence of water vapor on the oxidation of Printex-U at high temperature. Printex-U is a commercial carbon black considered as a surrogate for diesel soot. Two types of experiments were carried out at a given temperature of 1273 K: experiments with different concentrations of water vapor from 3 to 10% vol., called soot-H2O system, and Printex-U oxidation experiments using 500 ppm of O2 with the addition of different concentrations of water vapor from 0 to 10% vol., called soot-O2–H2O system. The particular case of 500 ppm of O2 and 0% of water vapor was denominated the soot-O2 system. From the soot-H2O experiments, it was observed that the gasification reaction is the dominant mechanism in this interaction. From the experiments with O2 and water vapor, it was noticed that in general the greater the water vapor concentration, the greater the concentration of gas products (CO, CO2 and H2) obtained. From these soot-O2–H2O system experiments it was concluded that lower concentrations of CO and higher values of CO2 were reached with respect to single reactions systems. Moreover, similar (CO + CO2) concentration values were obtained from soot-O2–H2O system if compared to (CO + CO2) concentration values obtained from the sum of the single reactions (soot-H2O and soot-O2). Also, similar H2 concentration values were found for the soot-O2–H2O system and for the sum of the individual reactions. The lower concentrations of CO and higher values of CO2 obtained may be due to the fact that the CO produced turned into CO2, as well as the fact that water vapor influences the stability of surface oxygen complexes in such a way that the production of CO2 is favored over CO in the soot-O2–H2O system.