The Oxidation of Soot Deposits from Diesel Engines

Combustion and gasification characteristics of deposits from diesel exhaust were investigated. Properties which may influence soot reactivity, such as morphology, specific surface area, organic adsorbate, and occlusions of inorganic origin were characterized. Effects of temperature, oxygen pressure, and stepwise combustion on the reactivity were determined. Ignition and combustion kinetics of various soot deposits were measured gravimetrically, and requirements for fast soot oxidation in the presence of an exhaust gas were assessed. Reliable completion of soot combustion after ignition depends strongly on oxygen pressure and bulk density of the soot. The ignition temperature can be lowered by suitable catalysts. Organic molecules, adsorbed on the soot surface, may also have a significant influence on the ignition of soot deposits. The results confirm that soot particles suspended in exhaust gas are not oxidized significantly under the conditions prevailing in diesel exhaust.