| 1. |
- Lundberg, Björn, 1982, et al.
(författare)
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DOC modeling combining kinetics and mass transfer using inert washcoat layers
- 2016
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 191, s. 116-129
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to develop a kinetic and transport model for diesel oxidation catalysts (DOC) with a satisfactory compromise between accuracy and computational demands for robust simulation of transient full-scale operation. Specifically the model accounts for surface concentrations of key species needed to capture transient features for typical lean exhaust conditions. In addition, the model accounts for transport limitations and distinguish them from reaction kinetics as well as apparent NO oxidation inhibition effects due to reactions. To achieve this, lab scale experiments were performed with DOCs with different platinum loadings and three different washcoat configurations of which two had an inert top layer. Both kinetic parameters for a detailed kinetic model and effective diffusivities were optimized for the experimental data using a single channel catalyst model. The experiments showed a clear effect of increased transport resistance for propene and CO and also that NO2 plays an important role as an oxidizing agent for preferentially CO at low temperature (
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| 2. |
- Lundberg, Björn, 1982, et al.
(författare)
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Model-based experimental screening for DOC parameter estimation
- 2015
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Ingår i: Computers and Chemical Engineering. - : Elsevier BV. - 0098-1354. ; 74, s. 144-157
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Tidskriftsartikel (refereegranskat)abstract
- In the current study a parameter estimation method based on data screening by sensitivity analysis is presented. The method applied Multivariate Data Analysis (MVDA) on a large transient data set to select different subsets on which parameters estimation was performed. The subset was continuously updated as the parameter values developed using Principal Component Analysis (PCA) and D-optimal onion design. The measurement data was taken from a Diesel Oxidation Catalyst (DOC) connected to a full scale engine rig and both kinetic and mass transport parameters were estimated. The methodology was compared to a conventional parameter estimation method and it was concluded that the proposed method achieved a 32% lower residual sum of squares but also that it displayed less tendencies to converge to a local minima. The computational time was however significantly longer for the evaluated method.
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| 3. |
- Lundberg, Björn, 1982, et al.
(författare)
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New Methodology for Transient Engine Rig Experiments for Efficient Parameter Estimation
- 2013
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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 6:4, s. 1995-2003
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Tidskriftsartikel (refereegranskat)abstract
- Introduction The diesel oxidation catalyst (DOC) is a well established technology to reduce CO and hydrocarbon (HC) emissions from diesel engines. Strengthened emission standards have made the importance of the DOC even greater in recent years since it plays an indispensible role in enhancing the performance of diesel particulate filters (DPF) and selective catalytic reduction (SCR) by utilization of NO oxidation to NO2. Therefore correct prediction of the DOC performance is very important for simulations of the entire aftertreatment system. When performing kinetic parameter estimation, laboratory scale experimental data is generally used. In laboratory scale it is possible to use essentially any combination of exhaust gas composition and temperature which makes it possible to estimate parameters over a wide range of conditions. However the applicability of these parameters in full scale models is often limited. Parameter estimation on full scale engine rig experiments on the other hand is limited by the exhaust compositions that are possible for the engine to produce. As a result, the fraction of CO is closely linked to the fraction of hydrocarbons and the fraction of NO is closely linked to the fraction of NO2. When switching between two engine operation points it generally takes several minutes before the properties of the emissions have stabilized. This does not only make the experiments time consuming, but it also complicates the transient modeling of the DOC since the changes in inlet properties are far from ideal step functions. In this study an experimental set-up is presented that makes it possible to change the inlet properties of the DOC without changing engine load point which results in much faster transients. The method also makes it possible to change the fraction of NO2 independently of the NO fraction. Method To achieve more controlled and faster changes in the inlet to the catalyst an extra DOC (DOC1) with the possibility for bypass flow and an SCR with urea injection are mounted before the catalyst. The fraction of exhaust gas flow through DOC1 allows variation in the conversion of HC and CO to CO2 and the conversion of NO to NO2. By injecting different amounts of urea the conversion of NO2 and NO to N2 is controlled. The SCR also makes it possible to obtain an inlet composition to the DOC that contains NO2 but is free of NO. Fast changes in inlet conditions are in other words possible and it is also possible to achieve compositions not achievable by only controlling the operation of the engine. Experiments have been performed at several engine conditions and using catalysts with different noble metal loading, lengths and washcoat thicknesses. To achieve high HC and CO concentrations the engine was tuned to run with late fuel injection. Significance A method to carry out engine rig experiments with a wider range of emission conditions makes it possible to more efficiently retune model parameters for a full-scale catalyst from literature data. This should result in faster model development which is of great importance in exhaust gas aftertreatment.
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| 4. |
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| 5. |
- Lundberg, Björn, 1982, et al.
(författare)
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Parameter Estimation of a DOC from Engine Rig Experiments with a Discretized Catalyst Washcoat Model
- 2014
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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 7:2, s. 1093-1112
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Tidskriftsartikel (refereegranskat)abstract
- Parameter tuning was performed against data from a full scale engine rig with a Diesel Oxidation Catalysts (DOC). Several different catalyst configurations were used with varying Pt loading, washcoat thickness and volume. To illustrate the interplay between kinetics and mass transport, engine operating points were chosen with a wide variation in variables (inlet conditions) and both transient and stationary operation was used. A catalyst model was developed where the catalyst washcoat was discretized as tanks in series both radially and axially. Three different model configurations were used for parameter tuning, evaluating three different approaches to modeling of internal transport resistance. It was concluded that for a catalyst model with internal transport resistance the best fit could be achieved if some parameters affecting the internal mass transport were tuned in addition to the kinetic parameters. However it was also shown that a model with negligible internal transport resistance still could obtain a good fit since kinetic parameters could compensate for transport limitations. This highlighted the inherent difficulties using kinetic models with high parameter correlation and also showed the importance of using a kinetic model with a structure that is capable of describing exclusively intrinsic kinetics.
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| 6. |
- Lundström, Andreas, 1980, et al.
(författare)
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Modelling of urea gas phase thermolysis and theoretical details on urea evaporation
- 2011
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 225:10, s. 1392-1398
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Tidskriftsartikel (refereegranskat)abstract
- A model study of droplet decomposition of a urea–water solution (UWS) for selective catalytic reduction applications (SCR) has been undertaken. A new vapour pressure equation for urea has been adopted to predict the rate of urea evaporation. The vapour pressure above liquid urea is obtained by extrapolating the vapour pressure above solid urea. Gas phase decomposition of urea into ammonia and isocyanic acid is further assumed to be fast, dictating the boundary conditions for the evaporation process. The rate of UWS evaporation is compared to recently published data and shows good agreement. A set of Antoine parameters was fitted to the derived vapour pressure to facilitate future simulations.
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| 7. |
- Acke, Filip, 1968, et al.
(författare)
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Influence of the platinum-support interaction on the direct reduction of NOx under lean conditions
- 1998
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 116, s. 285-294
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Tidskriftsartikel (refereegranskat)abstract
- Catalysts containing Pt supported on SiC, Al2O3 and ZSM-5 were prepared and studied for NOx reduction by C3H6 in Oz excess under transient (temperature ramps) and steady-state conditions. The maximum NOx reduction activity in the heating ramp experiments was similar for Pt/SiC and Pt/ZSM-5, while Pt/Al2O3 showed higher maximum activity. Both N-2 and N2O formation was observed for all catalysts, although the respective amounts varied with the investigated system. Highest Nz selectivity was observed for Pt/Al2O3. When the NOx reduction activity was studied under steady-state conditions the activity of Pt/Al2O3 decreased substantially (mainly due to a loss in N-2 production). Pt/ZSM-5 became somewhat more selective towards Na production whereas the activity and selectivity of Pt/SiC remained at about the same values as far the heating ramp experiments. Adsorbed species on the surface of the different catalysts were investigated using in-situ FTIR in order to obtain information about the reaction mechanisms. The adsorption of species on Pt/SiC was negligible, while a number of absorption bands were observed for Pt/Al2O3 (N and C containing species, and -NCO) and Pt/ZSM-5 (HC).
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| 8. |
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| 9. |
- Acke, Filip, 1968, et al.
(författare)
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Selective reduction of NO by HNCO over Pt promoted Al2O3
- 1998
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 179:2, s. 528-536
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Tidskriftsartikel (refereegranskat)abstract
- The activity of Pt supported on gamma-Al2O3 towards HNCO oxidation and reduction of NO by HNCO under oxygen excess is examined under transient conditions (temperature ramps between 100 and 500 degrees C). Formation of N-2, N2O, NO, and NO2 is observed. Isotope labelled (NO)-N-15 is used to show the scrambling of nitrogens in N-2 ((NN)-N-14-N-15) and N2O ((NNO)-N-14-N-15). Adsorbed species on the surface are characterised by in-situ FTIR spectroscopy in order to obtain information on reaction intermediates. Adsorbed NNx species are discussed as important intermediates in the N-2 and N2O formation. The absence of Pt results in a delay in HNCO ignition and only a small N2O formation is observed.
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| 10. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Sulphur dioxide deactivation of NOx storage catalysts
- 1999
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 126, s. 317-324
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Tidskriftsartikel (refereegranskat)abstract
- The influence of sulphur dioxide on the NOx storage performance of a Pt-Rh/BaO/Al2O3 model catalyst has been investigated. Addition of 2.5-25 vol.-ppm SO2 to a synthetic lean-burn exhaust, containing NO, C3H6, O2 and Ar, caused deactivation of the NOx storage function of the catalyst. The rate of deactivation was found to be proportional to the exposure of SO2. This effect is seen for temperatures between 250 and 450 degrees C. Together with in situ FTIR measurements, this leads to the conclusion that sulphur accumulates in the NOx storage component of the catalyst during the exposure. Furthermore, SO2 also inhibits the oxidation capacity of the catalyst during lean periods as is observed by a decreased NO oxidation activity. The presence of SO2 also reduces the reduction capacity of the catalyst under rich periods, which leads to an increased N2O formation and a decreased NO conversion.
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