Investigation of the Oxidation Behavior of Soot in Diesel Particle Filter structures 2015-24-2516
Particulate matter in diesel exhaust is captured in diesel particulate filters (DPFs). Since increased load in the filter and thus increased pressure drop deteriorates the engine performance, the filter load of the DPF has to be removed during a process referred to as regeneration. Measures for successful regeneration aim at accelerating soot oxidation and increase fuel consumption. Regeneration lay-out and thus fuel consumption increase is strongly depending on the oxidation behavior of soot.
The aim of the present study is the investigation of soot oxidation characteristics. Therefore particle filters have been loaded with soot using the exhaust gas of small heavy duty vehicle operated under defined conditions on an engine dynamometer. The particle filters have been then dismantled and fragmented on their constituting segments. Each filter segment has been regenerated individually in a specifically designed test bench. Heated gas of constant temperature has been induced through the segments. Based on the species balances measured, soot oxidation rates have been computed. In parallel, a scale with milligram resolution recorded the time evolution of the segment weight.
Based on the soot oxidation rates characteristic kinetic parameters have been computed. Regeneration progress has been approached by a simple Arrhenius, a shrinking core and a random pore size distribution growth model. The influence of two different oxygen levels in the feed gas has been investigated. Soot regeneration characteristics in segments from the filter core have been similar exhibiting rather low activation energies of around 50kJ/mol. Soot in filter segments located in the periphery had substantially higher activation energies, 80kJ/mol. This different behavior is attributed to the lower temperatures of the filter periphery during the loading procedure and differences in the soot structure and composition.