Thermal control of a lab-scale in-situ reator for soot oxidation
Examensarbete för masterexamen
Innovative and sustainable chemical engineering (MPISC), MSc
CFD simulations were coupled with lab-scale experiments to study steep temperature increases (thermal fronts) during thermal regeneration of a diesel particulate filter (DPF) via soot oxidation. The study investigated the conditions under which these fronts appear. A more well-defined open-flow system in contrast to a wall-flow system as in DPFs was used for practicality reasons. An open-flow reactor was developed and soot oxidation experiments were carried out, using Printex-U and a synthetic gas mixture. Different operating conditions were used to provoke thermal fronts in the reactor. A peak of high temperature was observed, which is dependent on the conditions used. Input data from the experiments was used to develop a 2D CFD model and verification was done via comparison with a numerical study. The validity of the model was assessed via the ability of the model to predict the temperature profile obtained from the experiments. Kinetic expressions for non-catalytic oxidation for both diesel soot and Printex-U were evaluated. The soot reaction rate in the simulations is found to be very sensitive to kinetic parameters. The obtained CFD model is able to predict soot oxidation at low reaction rates. However, at high reaction rates numerical instabilities occur due to large gradients in the domain. Reasons for this can be oversimplification of the soot layer, but also the use of a very large time step. A thermal front that moves across the substrate during soot oxidation as reported by other studies (numerical and experimental) could not be obtained. It is found that oxygen depletion or soot depletion is needed in order to observe a moving thermal front which was not achieved under the experimental conditions used in this work. Mass transfer simulations suggest that mass transfer limitations are the main reason for this. Through coupling of the experimental and numerical results the placement of the thermocouples in the reactor is found to be very important to get a representative temperature measurement. It is finally concluded that the open-flow configuration cannot be used to predict the behavior of a DPF configuration.
Energi , Transport , Grundläggande vetenskaper , Hållbar utveckling , Maskinteknik , Strömningsmekanik , Kemiteknik , Energy , Transport , Basic Sciences , Sustainable Development , Mechanical Engineering , Fluid mechanics , Chemical Engineering