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This combined numerical simulation and experimental study focuses on the effect of nitrogen dioxide (NO2) in strong diluted oxygen-rich NOx/NH3/O2/H2O gas mixtures representative at exhaust gas aftertreatment in diesel engines. Conversion of nitrogen oxides (NOx) and ammonia (NH3) and the change of the NO/NO2 and NH3/NOx ratios were analyzed by means of comparison between experimental measurements and kinetic simulations. Homogeneous gas-phase experiments have been carried out in a special countercurrent continuous flow reactor at intermediate temperature (473-923 K) and elevated pressure up to 5 bar. In the simulation with an ideal plug-flow model, the occurring reactions in the gas mixture were calculated. To explain the observations, a reactions flow analysis was also performed. The experimental and modeling results revealed that despite a high NH3 conversion, the NOx concentration stays nearly constant in the presence of NO2.

The selective catalytic reduction (SCR) based on urea-water-solution is an effective technique to reduce nitrogen oxides (NOx) emitted from diesel engines. A 3D numerical computer model of the injection of urea-water-solution and their interaction with the exhaust gas flow and exhaust tubing is developed to evaluate different configurations during the development process of such a DeNOx-system. The model accounts for all relevant processes appearing from the injection point to the entrance of the SCR-catalyst: momentum interaction between gas phase and droplets evaporation and thermolysis of droplets hydrolysis of isocyanic acid in gas phase heat transfer between wall and droplets spray/wall-interaction two-component wall film including interaction with gas phase and exhaust tube The single modeling steps are verified with visualizations, patternator measurements, phase-doppler-anemometer results and temperature measurements.

The ultimate goal in the numerical simulation of automotive catalytic converters is the prediction of exhaust gas emissions as function of time for varying inlet conditions, i.e. the simulation of a driving cycle. Such a simulation must include the calculation of the transient three-dimensional temperature-field of the monolithic solid structure of the converter, which results from a complex interaction between a variety of physical and chemical processes such as the gaseous flow field through the monolith channels, the catalytic reactions, gaseous and solid heat transport, and heat transfer to the ambience. This paper will discuss the application of the newly developed CFD-code DETCHEMMONOLITH for the numerical simulation of the transient behavior of three-way catalytic converters that have a monolithic structure.