| 21. |
- Binder, Christian, 1988-, et al.
(författare)
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Phosphor Thermometry for In-Cylinder Surface Temperature Measurements in Diesel Engines
- 2019
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Ingår i: Measurement science and technology. - 0957-0233 .- 1361-6501.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Surface temperature measurements in technically relevant applications can be very hallenging and yet of great importance. Phosphor thermometry is a temperature measurement technique that has previously been employed in technically relevant applications to obtain surface temperature. The technique is based on temperature-dependent changes in a phosphor’s luminescence. To improve the accuracy and precision of temperature measurements with this technique, the present study considers, by way of example, the impact of conditions inside the cylinder of a diesel engine on decay time based phosphor thermometry. After an initial, general assessment of the effect of prevailing measurement conditions, this research investigates errors caused by soot luminosity, extinction, signal trapping and changes of phosphors’ luminescence properties due to exposure to the harsh environment. Furthermore, preferable properties of phosphors which are suitable for in-cylinder temperature measurements are discussed. 16 phosphors are evaluated, including four which – to the authors’ knowledge –have previously not been used in thermometry. Results indicate that errors due to photocathode bleaching, extinction, signal trapping and changes of luminescence properties may cause an erroneous temperature evaluation with temperature errors in the order of serval tens of Kelvin.
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| 22. |
- Johansson, Anders, 1985, et al.
(författare)
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Experimental Investigation of Soot in a Spray-Guided Single Cylinder GDI Engine Operating in a Stratified Mode
- 2013
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Forthcoming reductions in legal limits for emissions of particle matter (PM) from direct injection engines have increased the need for understanding particle distributions in the engines and the factors affecting them. Therefore, in the presented study the influence on PM-emissions of potentially important factors (fuel injection pressure, load, speed and 50% mass fraction burned phasing) on particle mass, number and size distributions were experimentally investigated. The experimental system was a spray-guided, direct injection, single-cylinder research engine operated in stratified charge mode (using gasoline with 10% ethanol as fuel), under five load and speed settings that are appropriate for stratified combustion. The particle distributions obtained from operating the engine in homogeneous combustion and stratified combustion modes were also compared. The particle distributions were measured using a Cambustion DMS500 fast particle analyzer in combination with a Dekati FPS4000 fine particle sampler and a thermodenuder in all tests except the comparison of distributions under stratified and homogeneous combustion conditions. The sampling system was designed to remove as much of the volatile unburned hydrocarbons as possible in order to sample mostly solid particles. Under all of the stratified operating conditions studied, the results indicate that the particle distribution has a characteristic shape with a tail and one large peak. The operating speed significantly affected the size of the largest particles and the quantity of the particles represented by the tail. An almost linear, positive relationship was found between the load and particle number. Increasing the fuel injection pressure reduced particle numbers whereas combustion phasing had no significant observed effects. More particles were generated in stratified combustion mode than in homogeneous mode.
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| 23. |
- Brahma, Arindam, 1987, et al.
(författare)
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A study on the mechanisms of change propagation in mechanical design
- 2021
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Ingår i: Journal of Mechanical Design - Transactions of the ASME. - : ASME International. - 1050-0472. ; 143:12
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Tidskriftsartikel (refereegranskat)abstract
- Design changes and change propagation have been recognized as ubiquitous in the engineering design process. But why are some design changes propagated while others are absorbed? This paper reports on a study to investigate the specific properties of a mechanical design that influence whether a change is either propagated or absorbed. Student participants in the study were asked to complete a well-defined mechanical design task and then to introduce several design changes. Analysis of the recorded design processes reveals new insight into the mechanisms of change propagation in terms of properties of the design. The insights suggest avenues for future research to make designs more tolerant to potential future change and to develop improved methods to predict change propagation.
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| 24. |
- Högman, Ulf, 1961, et al.
(författare)
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Requirements on New Technology and the Technology Implementation Process
- 2010
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Ingår i: 8th International NordDesign Conference, NordDesign 2010; Goteborg; Sweden; 25 August 2010 through 27 August 2010. ; 2, s. 289-300
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Konferensbidrag (refereegranskat)abstract
- In literature, many authors have pointed to the importance of technology and technology development for company competitiveness. In this study we aim to study the technology in more detail and attempt to develop an understanding on the requirements and needs on “technology” from the perspective of product development. The research question which we aim to answer in this study is:“What are the requirements on maturity of technology when this technology is about to enter into the product development process?“A qualitative research strategy, based on three study cases involving 17 interviewees, has been chosen. All three cases come from one single company, Volvo Aero Corporation (VAC) in Sweden, in the context of the aero engine industry. The study contributes with a broad mapping of requirements and how they relate to different categories of technologies, showing big differences both regarding content and timing. It is concluded that attention should be payed both to how the organization builds new capabilities and to the capabilities of the technology itself. A surprisingly complicated picture on the requirements relating to the implementation of new technologies has emerged in the study. This contributes to the understanding regarding the difficulties of developing new technology and integrating it into an application.
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| 25. |
- Caprioli, Sara, 1978
(författare)
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Thermal impact on rolling contact fatigue of railway wheels
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rolling contact fatigue (RCF) is a very common and costly damage mechanism for rails and wheels. This thesis investigates the influence of combined thermal and mechanical loading on RCF of railway wheels on the basis of numerical predictions. The established computational framework includes heat flux analyses, (two- and three-dimensional) elastoplastic finite element simulations and subsequent RCF life analyses. The computational framework is employed to quantify the influence of various operational parameters and modelling presumptions such as applied heat and tangential stress characteristics, load application schemes, mesh densities etc. Examples of results include quantifications of how partial slip conditions result in higher plastic strain magnitudes in a thin layer at the wheel tread surface, and differences in material responses between accelerating and braking wheels.The numerical model was extended to incorporate surface initiated cracks. With the extended model it is shown that 1 mm deep cracks have a substantial influence on the state of stress and strain in the bulk material between surface cracks. Further, comparisons between radial (thermal) and inclined (RCF) surface cracks show that the deformation of significantly inclined cracks (30 degrees) is more severe than that of radial cracks. Further, acceleration is found to give larger crack face displacements. However braking tends to induce tensile residual stresses that open the crack mouth, thus allowing fluid penetration that can promote crack growth. Also thermal loading is found to cause a significant crack mouth opening that is decreased by subsequent rolling contact.In a final study numerical RCF predictions are compared to full-scale experimental studies carried out at the Railway Technical Research Institute in Japan. Thermal loading tuned towards measurements by thermocameras and thermocouples are introduced in a truncated loading scheme corresponding to the test configuration. Estimated crack initiation life is found to be in good agreement with test results. The investigation also shows the significant influence of the employed material model. In addition to thermomechanical fatigue analyses, the case of purely thermal fracture has been investigated. This study quantified how the risk of fracture and resulting crack sizes depend on braking conditions and initial surface cracks. The results of this thesis are believed to be of importance in defining and enforcing sustainable operational conditions and maintenance actions. Further, this thesis provides tools to establish root causes and pertinent mitigating actions when thermomechanical wheel cracking nevertheless occurs.
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| 26. |
- Li, Xiaojian, 1991, et al.
(författare)
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A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:19
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Tidskriftsartikel (refereegranskat)abstract
- Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.
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| 27. |
- Gantasala, Sudhakar, et al.
(författare)
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Numerical Investigation of the Aeroelastic Behavior of a Wind Turbine with Iced Blades
- 2019
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 12:12
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Tidskriftsartikel (refereegranskat)abstract
- Wind turbines installed in cold-climate regions are prone to the risks of ice accumulation which affects their aeroelastic behavior. The studies carried out on this topic so far considered icing in a few sections of the blade, mostly located in the outer part of the blade, and their influence on the loads and power production of the turbine are only analyzed. The knowledge about the influence of icing in different locations of the blade and asymmetrical icing of the blades on loads, power, and vibration behavior of the turbine is still not matured. To improve this knowledge, multiple simulation cases are needed to run with different ice accumulations on the blade considering structural and aerodynamic property changes due to ice. Such simulations can be easily run by automating the ice shape creation on aerofoil sections and two-dimensional (2-D) Computational Fluid Dynamics (CFD) analysis of those sections. The current work proposes such methodology and it is illustrated on the National Renewable Energy Laboratory (NREL) 5 MW baseline wind turbine model. The influence of symmetrical icing in different locations of the blade and asymmetrical icing of the blade assembly is analyzed on the turbine’s dynamic behavior using the aeroelastic computer-aided engineering tool FAST. The outer third of the blade produces about 50% of the turbine’s total power and severe icing in this part of the blade reduces power output and aeroelastic damping of the blade’s flapwise vibration modes. The increase in blade mass due to ice reduces its natural frequencies which can be extracted from the vibration responses of the turbine operating under turbulent wind conditions. Symmetrical icing of the blades reduces loads acting on the turbine components, whereas asymmetrical icing of the blades induces loads and vibrations in the tower, hub, and nacelle assembly at a frequency synchronous to rotational speed of the turbine.
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| 28. |
- Wadekar, Sandip, 1989
(författare)
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Large-eddy simulation on the effects of fuel injection pressure on gasoline spray characteristics
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing the injection pressure in gasoline direct injection engines has a substantial potential to reduce emissions while maintaining high efficiency in spark ignition engines. Present gasoline injectors operate at pressures of 20 to 30 MPa. However, the use of higher-pressure fuel injection (40 to 60 MPa or more) could potentially reduce emissions and increase fuel efficiency. To fully exploit the capabilities of high-pressure fuel injection technology, a fundamental understanding of gasoline spray characteristics and behavior at such high injection pressures is vital. Such an understanding could also be used to further model development and facilitate the integration of advanced injection systems into future gasoline engines. This work presents numerical simulation studies on gasoline sprays formed at fuel injection pressures between 40 and 150 MPa. Three nozzle hole shapes (divergent, convergent, and straight) with different configurations (6 or 10 holes) were considered in the simulation to determine how a nozzle geometry affects spray formation. The numerical calculations were performed in a constant volume spray chamber under non-vaporizing conditions to best match the experimental setup. The gas flow was modeled using a large-eddy simulation (LES) approach, while a standard Lagrangian model was utilized to describe the liquid fuel spray. Spray atomization was modeled using the Kelvin Helmholtz –Rayleigh Taylor (KH-RT) atomization model, with the droplet size distribution being assumed to follow a Rosin-Rammler distribution function. Simulation results for the spray liquid penetration length are validated with experimental findings under different fuel injection pressures. Afterwards, an arithmetic mean droplet diameter (D10) and a Sauter mean droplet diameter (D32) as a function of pressure are compared against the measured droplet diameters. Simulated drop size distributions are presented and compared with measured droplet sizes. The results indicate that high fuel injection pressures increase the liquid penetration length and significantly reduce droplet sizes, and that nozzle shape significantly affects spray characteristics and spray formation. In addition, raising the injection pressure from 40 to 150 MPa with a divergent nozzle was predicted to reduce the SMD from 13.4 to 7.5 μm while increasing the probability of observing droplet diameters of 5-10 μm from 40% to 72%. Similar results were obtained for the other nozzle shapes.
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| 29. |
- Bayani, Mohsen, 1981
(författare)
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Squeak and Rattle Prediction for Robust Product Development in the automotive industry
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Squeak and rattle are nonstationary, irregular, and impulsive sounds that are audible inside the car cabin. For decades, customer complaints about squeak and rattle have been, and still are, among the top quality issues in the automotive industry. These annoying sounds are perceived as quality defect indications and burden warranty costs to the car manufacturers. Today, the quality improvements regarding the persistent type of sounds in the car, as well as the increasing popularity of electric engines, as green and quiet propulsion solutions, stress the necessity for attenuating annoying sounds like squeak and rattle more than in the past. The economical and robust solutions to this problem are to be sought in the pre-design-freeze phases of the product development and by employing design-concept-related practices. To achieve this goal, prediction and evaluation tools and methods are required to deal with the squeak and rattle quality issues upfront in the product development process. The available tools and methods for the prediction of squeak and rattle sounds in the pre-design-freeze phases of a car development process are not yet sufficiently mature. The complexity of the squeak and rattle events, the existing knowledge gap about the mechanisms behind the squeak and rattle sounds, the lack of accurate simulation and post-processing methods, as well as the computational cost of complex simulations are some of the significant hurdles in this immaturity. This research addresses this problem by identifying a framework for the prediction of squeak and rattle sounds based on a cause-and-effect diagram. The main domains and the elements and the sub-contributors to the problem in each domain within this framework are determined through literature studies, field explorations and descriptive studies conducted on the subject. Further, improvement suggestions for the squeak and rattle evaluation and prediction methods are proposed through prescriptive studies. The applications of some of the proposed methods in the automotive industry are demonstrated and examined in industrial problems. The outcome of this study enhances the understanding of some of the parameters engaged in the squeak and rattle generation. Simulation methods are proposed to actively involve the contributing factors studied in this work for squeak and rattle risk evaluation. To enhance the efficiency and accuracy of the risk evaluation process, methods were investigated and proposed for the system excitation efficiency, modelling accuracy and efficiency and quantification of the response in the time and frequency domains. The demonstrated simulation methods besides the improved understanding of the mechanisms behind the phenomenon can facilitate a more accurate and robust prediction of squeak and rattle risk during the pre-design-freeze stages of the car development.
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| 30. |
- Johansson, Anders, 1985, et al.
(författare)
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Experimental Investigation of the Influence of Boost on Combustion and Particulate Emissions in Optical and Metal SGDI-Engines Operated in Stratified Mode
- 2016
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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 9:2, s. 807-818
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Tidskriftsartikel (refereegranskat)abstract
- Boosting and stratified operation can be used to increase the fuel efficiency of modern gasoline direct-injected (GDI) engines. In modern downsized GDI engines, boosting is standard to achieve a high power output. However, boosted GDI-engines have mostly been operated in homogenous mode and little is known about the effects of operating a boosted GDI-engine in stratified mode.This study employed optical and metal engines to examine how boosting influences combustion and particulate emission formation in a spray-guided GDI (SGDI), single cylinder research engine. The setup of the optical and metal engines was identical except the optical engine allowed optical access through the piston and cylinder liner.The engines were operated in steady state mode at five different engine operating points representing various loads and speeds. The engines were boosted with compressed air and operated at three levels of boost, as well as atmospheric pressure for comparison. The fuel used was market gasoline (95 RON) blended with 10% ethanol. The spark plug and injector were mounted in parallel with the intake valves. The gas motion induced by the engine head was primarily tumble motion with a small amount of swirl.Results on particulate emissions indicated that nucleation mode particulates increased with increasing boost. In contrast, agglomeration mode particulates decreased with increasing boost pressure. The combustion was found to consist of a yellow flame in the center of the combustion chamber and a pre-mixed blue flame in the perimeter. The optical studies indicated that the flame area decreased with increasing boost.
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