On Using a CFD Based Global Kinetic Reaction Model to Simulate Catalyst Exotherm with Exhaust Fuel Dosing Device (Fuel Vaporizer) 2012-01-1290

Under the current emissions legislation, most of the diesel-powered vehicles have to use Diesel Particulate Filters (DPF) to remove soot particles from the exhaust gas and the accumulated soot particles have to be removed in regular intervals. To initialize the exhaust gas temperature for soot regeneration, diesel fuel is either injected into the combustion chamber in late engine cycle (e.g. post injection) or vaporized and then discharged into the exhaust gas via a dosing device (e.g. fuel vaporizer). Both approaches though require the exothermic catalyst to convert the fuel into thermal energy. For practical reasons, this paper is concentrated on describing how CFD could be used to model the fuel distribution in an aftertreatment system equipped with fuel vaporizer and the exothermic reactions in the catalysts. The authors have already demonstrated in other publications that in order to capture the correct mixing behavior of the exhaust gas and vaporized fuel, one has to use an advanced turbulence model which does not rely on a wall function assumption. On the other hand, it is also critical to have a reliable chemical reaction model to determine the HC conversion because this will affect the temperature distribution at the entry of the DPF. This paper describes the development of a simplified chemical reaction model which takes the heat and mass transfer between gas and surface into consideration. Based on engine dynamometer tests conducted on a typical aftertreatment system with two design variants, comparisons between the measured and predicted data confirm that the new reaction model is capable to predicate the post catalyst gas temperature and HC concentration accurately at various test conditions. The correlation also confirms that an aftertreatment system with good gas flow and HC distribution behavior could result in good soot regeneration performance.