| 1. |
- Berg, Victor, 1990, et al.
(författare)
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Characterization of Gaseous and Particle Emissions of a Direct Injection Hydrogen Engine at Various Operating Conditions
- 2023
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Ingår i: SAE Technical Papers. - 0148-7191 .- 2688-3627.
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the gaseous and particulate emissions of a hydrogen powered direct injection spark ignition engine. Experiments were performed over different engine speeds and loads and with varying air- fuel ratio, start of injection and intake manifold pressure. An IAG FTIR system was used to detect and measure a variety of gaseous emissions, which include standard emissions such as NOX and unburned hydrocarbons as well as some non-standard emissions such as formaldehyde, formic acid, and ammonia. The particle number concentration and size distribution were measured using a DMS 500 fast particle analyzer from Cambustion. Particle composition was investigated using ICP analysis as well as a Sunset OC/EC analyzer to determine the soot content and the presence of any unburned engine oil. The results show that NOX emissions range between 0.1 g/kWh for a λ of 2.5 and 10 g/kWh λ of 1.5. The highest particle concentration was found for low loads and low intake pressures, with peaks values as high as 5*108 n/cc. ICP analysis confirmed that the particles contained traces of engine oil, while the OC/EC analysis showed that 99% of particle matter collected on filters was organic carbon, and <1% soot. The emissions of N2O as well as several other species measured with FTIR was found to be in the single ppm range, and thus not significant.
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| 2. |
- Sjöblom, Jonas, 1968, et al.
(författare)
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Modelling of non uniform washcoat in catalytic monolith reactors
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- For advances in the design of exhaust aftertreatment systems, modelling can be a valuable tool. There have been various efforts in modelling the diesel oxidation catalyst (DOC) with varying degree of complexity. The simplest 1D models discretize the monolithic channel axially and use an effectiveness factor to account for different washcoat geometries. The more complex 1+1D models also resolve the catalyst washcoat which makes them able to better predict efficiency of e.g. layered catalysts. However, the vast majority of these 1+1D models assume the washcoat to be a uniform slab with homogeneous properties. Thus, they cannot identify tangential washcoat variations which have been found to have substantial effects on washcoat diffusivity (1). In this work a new parallel 1+1D reactor model has been developed. Similar to the sectionalizing method presented by Papadias et al (2), the washcoat is sliced into multiple tangential sections based on an evenly distributed angle. The model then solves each section of the washcoat independently – assuming that no mass is transferred between each section. Preliminary results (see figure 1) compare NO light-off simulations using the original 1+1D model and the parallel model using 3 sections. If the washcoat properties for each section are kept constant, then the conversion efficiency of the parallel model is slightly decreased because of the increased diffusive resistance of the thicker corners. However, if including the local porosity of each section (where the corners show a 13% increase in local porosity based on SEM images), the conversion efficiency of the parallel model is significantly higher because of the increased pore diffusivity in the corners. The proposed methodology enables analysis of local washcoat properties. The results are important for high performance modelling towards zero emission vehicles.
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| 3. |
- Sjöblom, Jonas, 1968, et al.
(författare)
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Robust parameter estimation methodology for heterogeneous catalytic reactors
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modeling of Exhaust-Gas Aftertreatment Systems is an important tool for improved understanding and thus improved performance and durability. The challenges for accurate modeling of the multi-scale reactor are many and one important challenge is the interplay between mass transfer and kinetics. Although intrinsic kinetics (without effects from mass transfer) are possible to obtain by analysis of the washcoat separately, many challenges (e.g. washcoat distribution, ageing effects) are best studied using the monolith reactor structure. In this study, a 1+1D diesel oxidation catalyst model was tuned to synthetic catalyst activity test (SCAT) bench data using a robust parameter estimation algorithm based on response surface methodology (RSM). The final residuals (SSE) were compared with experimental uncertainties to enable a statistical F-test to assess the model fit. Two different design of experiment (DoE) design matrices were compared to evaluate potential interaction effects between parameters. While the choice of DoE had different benefits, problems with each design could easily be circumvented. Several parameter estimation cases were compared to investigate the importance of some key algorithm choices: (a) the choice of a weight function for the residual calculation. A weight function sensitive to the experimental observation distribution obtained different fits with different parameter sets. (b) The importance of carefully designed experimental observations. Simulations with catalysts containing an inert washcoat layer proved invaluable for tuning of internal mass transfer coefficients. (c) The importance of experimentally measured constants as initial guesses. The use of intelligent gravimetric analysis (IGA) showed to give a much more suitable initial guess for tortuosity compared to literature data. For all cases, the model fit gave insignificant F-test values (experimental uncertainties were larger than the model residuals), rendering that none of the parameter sets could be rejected. To demonstrate the significance of the different cases, the final parameter set for each case were compared through comparison of ratios of classical timescales, showing the experimental conditions for the various controlling regions of mass transfer and kinetics.
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| 4. |
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| 5. |
- Walander, Magnus, 1991, et al.
(författare)
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Use of 3D-printed mixers in laboratory reactor design for modelling of heterogeneous catalytic converters
- 2021
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Ingår i: Chemical Engineering and Processing. - : Elsevier B.V.. - 0255-2701 .- 1873-3204. ; 164
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Tidskriftsartikel (refereegranskat)abstract
- A method for identifying radial concentration maldistribution in synthetic catalyst activity test (SCAT) benches, is presented, where spatially resolved concentration measurements are not available. The developed methodology was successfully tested for an injection-based SCAT. To resolve the radial concentration maldistribution a static mixer was designed, 3D-printed and inserted upstream the test sample. The methodology could also prove the effectiveness of the mixer, which did not only resolve the concentration maldistribution but also avoided causing reaction disturbances. The resulting increased axial dispersion from the turbulence created by the static mixer was evaluated using a 3D CFD model in Ansys Fluent 19. The axial dispersion of the injection-based SCAT bench was compared to a premixed SCAT bench through classical Aris-Taylor calculations. The results from the axial dispersion calculations show that the injection-based design with the use of a static mixer is far superior to the premixed design – both with regards to pulse broadening but also time delay. This is highly desirable for modelling studies towards zero emission exhaust aftertreatment. © 2021 The Authors
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| 6. |
- Andonova, Stanislava, 1977, et al.
(författare)
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Chemical deactivation by phosphorous under lean hydrothermal conditions over Cu/BEA NH3-SCR catalysts
- 2014
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 147, s. 251-263
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Tidskriftsartikel (refereegranskat)abstract
- To obtain a better understanding of the deactivation of SCR catalysts that may be encountered due to the presence of P-containing impurities in diesel exhausts, the effects induced by P over Cu/BEA NH3-SCR catalysts were studied as functions of the temperature of poisoning and P concentration in the feed. Cu/BEA catalysts with different Cu loadings (4 and 1.3 wt% Cu) were exposed to P by controlled evaporation of H3PO4 in the presence of 8% O2 and 5% H2O at 573 and 773 K. The reaction studies were performed by NH3-storage/TPD, NH3/NO oxidation and standard NH3-SCR. In addition, a combination of several characterisation techniques (ICP–AES, BET surface area, pore size distribution, H2-TPR and XPS) was applied to provide useful information regarding the mechanism of P deactivation. Pore condensation of H3PO4 in combination with pore blocking was observed. However, the measured overall deactivation was found to occur mostly by chemical deactivation reducing the number of the active Cu species and hence deteriorating the redox properties of the Cu/BEA catalysts. The process of P accumulation on the surface preferentially occurs on the “over exchanged” Cu active sites with the formation of phosphate species. This is likely the reason for the more severe deactivation of the 4% Cu/BEA compared to 1.3% Cu/BEA. Further, the higher NOx reduction performance at 773 K of the P-poisoned Cu/BEA catalysts was found to originate from the lower selectivity towards NH3 oxidation, which occurs predominately on the “over-exchanged” sites.
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| 7. |
- Andric, Jelena, 1979, et al.
(författare)
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Development and Calibration of One Dimensional Engine Model for Hardware-in-the-Loop Applications
- 2018
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2018-April
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Tidskriftsartikel (refereegranskat)abstract
- The present paper aims at developing an innovative procedure to create a one-dimensional (1D) real-time capable simulation model for a heavy-duty diesel engine. The novelty of this approach is the use of the top-level engine configuration, test cell measurement data, and manufacturer maps as opposite to common practice of utilizing a detailed 1D engine model. The objective is to facilitate effective model adjustments and hence further increase the application of Hardware-in-the-Loop (HiL) simulations in powertrain development. This work describes the development of Fast Running Model (FRM) in GT-SUITE simulation software. The cylinder and gas-path modeling and calibration are described in detail. The results for engine performance and exhaust emissions produced satisfactory agreement with both steady-state and transient experimental data. Therefore, the presented methodology shows a great potential for testing and validation of new control strategies in Engine Management System (EMS) and for optimizing engine performance using HiL systems. The model has been successfully used in powertrain testing and calibration in the VIRtual TEst Cell (VIRTEC) system at Volvo Penta.
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| 8. |
- Bergman, Becky, 1970, et al.
(författare)
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An inclusive, international learning environment?
- 2020
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- One of the Chalmers’ prioritized strategies for 2019-2021 is to reflect the diversity of society in an inclusive international learning environment. This should include developing activities that contribute to greater inclusion between international and national students and enabling global perspectives by drawing up learning objectives and activities for intercultural standards, attitudes and values. These strategies connect to national requirements for the engineering programs where students should demonstrate the capacity for teamwork and collaboration with various constellations. However, results from the International Student Barometer (2019) that show that although international students rank Chalmers highest in Europe when it comes to teaching and learning, they also rank Chalmers near the bottom when it comes to integration between home and international students. At Master’s level, approximately 35% of the students are labelled international i.e. from outside Sweden though this percentage varies quite dramatically from program to program. The main groups represented are India and China but we have students from at least 80 countries. According to the Chalmers mission statement, we should raise our level of internationalization in education to secure intellectual exchange and new stimuli. But how can this exchange take place if home and international students are not integrating with each other? This session will consist of three 10-minute presentations from three different Master programs at Chalmers. Each program has different challenges, for example in terms of the ratio between home and international students and pre knowledge required to follow courses. The presenters will provide a brief description of their individual situation in terms of their student groups. They will then describe how they have worked proactively to encourage greater inclusion, including work with both the formal and the informal curriculum (Leask, 2015). The formal curriculum is defined as the syllabus in terms of the program goals and the courses within the program. The informal curriculum covers any additional unassessed activities, for example, social activities. Finally, they will provide a future vision to work with these questions, in terms of future priorities and actions. The presentations will be followed by a panel discussion led by the session chair where questions will be taken from the audience. This session will be of particular interest to anyone who is working in an international learning environment, particularly those involved at Master program level. An inclusive environment will not only benefit all students, but has been shown to have a positive effect on results as well (De Vita, 2010). References De Vita, G. (2002). Does assessed multicultural group work really pull UK students' average down?. Assessment & Evaluation in Higher Education, 27(2), 153-161. Leask, B. (2015). Internationalizing the curriculum. Routledge.
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| 9. |
- Chanda Nagarajan, Pratheeba, 1978, et al.
(författare)
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Numerical Assessment of Flow Pulsation Effects on Reactant Conversion in Automotive Monolithic Reactors
- 2022
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- Highly transient engine-out emissions imply significant challenges for the optimization and control of automotive aftertreatment systems, motivating studies of the effects of flow pulsations on the system behavior. In this work, an axisymmetric aftertreatment system with a first-order reaction in the monolith section is chosen to demonstrate the role of pulsations on the time-averaged conversion at the exit. Reactive computational fluid dynamics simulations under transient conditions are performed by applying the SST k-ω turbulence model along with a reactant species balance equation and a porous medium description of the catalyst. Four different types of temporal velocity variations (constant, step-like, sawtooth and sinusoidal) are applied at the inlet. Additionally, the corresponding fluctuations driven by a prescribed inlet pressure are also investigated. It was found that the fluctuations in the incoming flow affect the transient response of the monolith, the time-averaged conversion, the evolution of the flow uniformity index and the dispersion downstream of the catalyst. It is also shown that the retention time distribution is modulated by the pulsations and that the mixed-cup conversion span is different for geometrically identical systems having the same velocity span if the fluctuation characteristics are different. In conclusion, simulations of phenomena that depend on time-resolved boundary conditions from experiments require proper characterization of fluctuations present in the real-world systems; otherwise, the method of recreating the signal at the boundary may influence the obtained results.
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| 10. |
- Chanda Nagarajan, Pratheeba, 1978, et al.
(författare)
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Transient Flow Uniformity Evolution in Realistic Exhaust Gas Aftertreatment Systems using 3D-CFD
- 2022
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Ingår i: Emission Control Science and Technology. - : Springer Science and Business Media LLC. - 2199-3629 .- 2199-3637. ; 8:3-4, s. 154-170
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Tidskriftsartikel (refereegranskat)abstract
- To precisely control a vehicle powertrain to minimize emissions, accurate and detailed models are needed to capture the spatio-temporal variability of the variables of interest. The aim of this work is to analyze flow and temperature fields in a geometrically realistic — and thus complex — exhaust gas aftertreatment system under transient conditions. The spatio-temporal response of these fields to upstream step changes is predicted using three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) κ- ω simulations where the catalytic converter is described as a porous medium. A catalytic converter geometry with a 90∘-bend and a partially dead volume is used to demonstrate the effects of time-resolved flow maldistribution on the profiles of velocity and temperature. Two sets of transient simulations in terms of step changes in velocity and temperature are performed. Uniformity indices are used to characterize the distribution and variability of the different catalyst channels under transient conditions. The evolution of the uniformity indices as functions of time and axial distance into the catalyst are calculated at different cross-sectional planes. The results show that the evolution of the temperature uniformity is rate controlling, continuously modulating the otherwise much faster flow uniformity response via the fluid properties. The temperature uniformity time scale is determined by the balance of flow, thermal inertia, and the heat losses from the system. The interplay between pressure drop and heat losses governs the transition to the new steady state in uniformity. These types of transient simulations and analyses can contribute essential information when developing reduced-order engineering models to represent the spatio-temporal variability in exhaust aftertreatment systems, in particular during rapid events such as cold start.
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