Diesel soot oxidation by nitrogen dioxide, oxygen and water under engine exhaust conditions: Kinetics data related to the reaction mechanism

Experimental studies on diesel soot oxidation under a wide range of conditions relevant for modern diesel engine exhaust and continuously regenerating particle trap were performed. Hence, reactivity tests were carried out in a fixed bed reactor for various temperatures and different concentrations of oxygen, NO 2 and water (300–600 °C, 0–10% O 2 , 0–600 ppm NO 2 , 0–10% H 2 O). The soot oxidation rate was determined by measuring the concentration of CO and CO 2 product gases. The parametric study shows that the overall oxidation process can be described by three parallel reactions: a direct C–NO 2 reaction, a direct C–O 2 reaction and a cooperative C–NO 2 –O 2 reaction. C–NO 2 and C–NO 2 –O 2 are the main reactions for soot oxidation between 300 and 450 °C. Water vapour acts as a catalyst on the direct C–NO 2 reaction. This catalytic effect decreases with the increase of temperature until 450 °C. Above 450 °C, the direct C–O 2 reaction contributes to the global soot oxidation rate. Water vapour has also a catalytic effect on the direct C–O 2 reaction between 450 °C and 600 °C. Above 600 °C, the direct C–O 2 reaction is the only main reaction for soot oxidation. Taking into account the established reaction mechanism, a one-dimensional model of soot oxidation was proposed. The roles of NO 2 , O 2 and H 2 O were considered and the kinetic constants were obtained. The suggested kinetic model may be useful for simulating the behaviour of a diesel particulate filter system during the regeneration process.