| 31. |
- Johansson, Anders, 1985, et al.
(författare)
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Measurements of particulate size distribution from a GDI engine using a nafion dryer and a DMS500 without sample dilution
- 2014
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Ingår i: FISITA 2014 World Automotive Congress - Proceedings.
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Konferensbidrag (refereegranskat)abstract
- Several types of engine exhaust contain moisture that must be maintained in gaseous state when sampling particulates to prevent potential destruction of the particles or damage to the measurement apparatus. This is normally achieved by diluting the sample in order to reduce the partial pressure, thus avoiding condensation. When measuring size distributions of particulates emitted from a gasoline engine, a dilution ratio of at least 5:1 is recommended. However, in some operating modes (e.g. lean homogenous modes) or measurement locations (e.g. downstream of a particulate filter) this ratio can be too high for high-resolution measurements due to the low levels of particulates. The presented study investigates the potential for using a nafion dryer to remove water from the exhaust instead of diluting the sample. An electrical mobility measurement device, a Cambustion DMS500 mk II, was operated without diluting the exhaust gases but with a nafion dryer to remove water from the exhaust. These dryers are commonly used for measuring particulates in airborne aerosols, but no information has been found in the open literature on their application in engine research. The sampling system was connected to a four cylinder SGDI-engine operating in modes that generate small amount of particulates. Samples were taken in four operating conditions, downstream of the catalyst. Overall losses in the complete system and components of the system were determined by tests with an artificially generated aerosol. Factors such as particulate losses, system performance and sample manipulation are discussed. Particulate size distributions were successfully recorded in operating regimes in which they are difficult to measure with conventional sampling systems using the required dilution. Particulate losses were found to be small in the nafion dryer but large in the heated hose prior to the nafion dryer.
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| 32. |
- Lundberg, Oskar, 1980-
(författare)
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On the influence of surface roughness on rolling contact forces
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.
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| 33. |
- Torstensson, Peter, 1981, et al.
(författare)
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Hybrid model for prediction of impact noise generated at railway crossings
- 2016
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Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16 (2016). ; , s. 539 - 545
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Konferensbidrag (refereegranskat)abstract
- A hybrid model for the prediction of impact noise at railway crossings is presented. The hybrid model combines the simulation of vertical wheel‒rail contact force in the time domain and the prediction of sound pressure level using a linear frequency-domain model. The time-domain model uses moving Green’s functions for the vehicle and track models (accounting for wheel flexibility and a discretely supported rail with space-variant beam properties) and a non-Hertzian wheel‒rail contact model. The time-domain and frequency-domain models are coupled based on the concept of an equivalent roughness spectrum. The model is demonstrated by investigating the influence of axle load, vehicle speed and wheel profile on generated impact noise levels. A negligible influence on impact noise is observed for axle loads in the interval 15 – 25 tonnes. On the other hand, increasing vehicle speed from 80 km/h to 150 km/h, or comparing a nominal S1002 wheel profile with a severely hollow worn profile, result in substantially higher levels of impact noise; for the given wheel and track conditions the differences are in the order of 10 dB(A).
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| 34. |
- Winroth, Julia, 1981, et al.
(författare)
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Contact stiffness considerations when simulating tyre/road noise
- 2017
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 409, s. 274-286
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Tidskriftsartikel (refereegranskat)abstract
- Tyre/road simulation tools that can capture tyre vibrations, rolling resistance and noise generation are useful for understanding the complex processes that are involved and thereby promoting further development and optimisation. The most detailed tyre/road contact models use a spatial discretisation of the contact and assume an interfacial stiffness to account for the small-scale roughness within the elements. This interfacial stiffness has been found to have a significant impact on the simulated noise emissions but no thorough investigations of this sensitivity have been conducted. Three mechanisms are thought to be involved: The horn effect, the modal composition of the vibrational field of the tyre and the contact forces exciting the tyre vibrations. This study used a numerical tyre/road noise simulation tool based on physical relations to investigate these aspects. The model includes a detailed time-domain contact model with linear or non-linear contact springs that accounts for the effect of local tread deformation on smaller length scales. Results confirm that an increase in contact spring stiffness causes a significant increase of the simulated tyre/road noise. This is primarily caused by a corresponding increase in the contact forces, resulting in larger vibrational amplitudes. The horn effect and the modal composition are relatively unaffected and have minor effects on the radiated noise. A more detailed non-linear contact spring formulation with lower stiffness at small indentations results in a reduced high-frequency content in the contact forces and the simulated noise.
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| 35. |
- Yang, Shun-Han, 1987, et al.
(författare)
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Parametric study of the dynamic motions and mechanical characteristics of power cables for wave energy converters
- 2018
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Ingår i: Journal of Marine Science and Technology. - : Springer Science and Business Media LLC. - 0948-4280 .- 1437-8213. ; 23:1, s. 10-29
-
Tidskriftsartikel (refereegranskat)abstract
- A case study of a point-absorber wave energy converter (WEC) system is presented. The WEC system forms an array, with several WECs located around a central hub to which they are each connected by a short, free-hanging power cable. The objective of the study is to analyse the dynamic characteristics and estimate the fatigue life of the power cable which is not yet in use or available on the commercial market. Hence, a novel approach is adopted in the study considering that the power cable’s length is restricted by several factors (e.g., the clearances between the service vessel and seabed and the cable), and the cable is subject to motion and loading from the WEC and to environmental loads from waves and currents (i.e., dynamic cable). The power cable’s characteristics are assessed using a numerical model subjected to a parametric analysis, in which the environmental parameters and the cable’s design parameters are varied. The results of the numerical simulations are compared and discussed regarding the responses of the power cables, including dynamic motion, curvature, cross-sectional forces, and accumulated fatigue damage. The effects of environmental conditions on the long-term mechanical life spans of the power cables are also investigated. Important cable design parameters that result in a long power cable (fatigue) service life are identified, and the cable service life is predicted. This study contributes a methodology for the first-principle design of WEC cables that enables the prediction of cable fatigue life by considering environmental conditions and variations in cable design parameters.
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| 36. |
- Bergseth, Ellen, 1979-
(författare)
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On tribological design in gear tooth contacts
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The correct tribological design will have a considerable effect on a gear’s service life and efficiency. The purpose of this thesis is to clarify the impact of variation in the gear tooth flank tribological system on the gear contact load capacity – to increase the understanding of how surface topography and lubricant interact.In this thesis the variation in surface topography inherent in the manufacturing method has been shown, by experimental work and computer simulations, to be an important factor for the contact condition in the early life of gears. Surface analysis revealed that the formation and composition of surface boundary layers depends strongly on the chemical composition of the lubricant, but also on pre-existing surface boundary layers. Additionally, surface boundary layers play a major role in frictional behaviour, wear and in allowing the lubricant to react properly with the surfaces.Paper A presents the current ISO 6336 calculation of surface durability. A robust design approach was used to investigate the extent to which the current standard for calculation of surface durability allows for manufacturing variations and the choice of lubricant.Paper B investigates the extent to which a logarithmical profile modification can increase gear contact pressure robustness compared to traditional lead profiles for gears.Paper C compares different gear manufacturing methods and their as-manufactured (fresh unworn) surface topographies, using measured surface topographies as input to a contact simulation program.Paper D examines surface boundary layer formation and the corresponding wear in relation to different anti-wear additives in an environmentally adapted base oil.Papers E and F make use of specimens with surface topographies imitating two gear manufacturing methods (grinding and superfinishing) to be used in a twin-disc and barrel-on-disc machine respectively. The contacts are analysed by friction measurements and simulations combined with methods for surface analysis.
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| 37. |
- Berntsson, Andreas, 1978, et al.
(författare)
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A LIF-study of OH in the Negative Valve Overlap of a Spark-assisted HCCI Combustion Engine
- 2008
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Tidskriftsartikel (refereegranskat)abstract
- Future requirements for emission reduction from combustionengines in ground vehicles might be met byusing the HCCI combustion concept. In this study,negative valve overlap (NVO) and low lift, short duration,camshaft profiles, were used to initiate HCCIcombustion by increasing the internal exhaust gas recirculation(EGR) and thus retaining sufficient thermalenergy for chemical reactions to occur when a pilot injectionwas introduced prior to TDC, during the NVO.One of the crucial parameters to control in HCCI combustionis the combustion phasing and one way of doingthis is to vary the relative ratio of fuel injected inpilot and main injections. The combustion phasing isalso influenced by the total amount of fuel supplied tothe engine, the combustion phasing is thus affectedwhen the load is changed. This study focuses on thereactions that occur in the highly diluted environmentduring the NVO when load and pilot to main ratio arechanged.To monitor these reactions, planar laser-induced fluorescence(PLIF) from OH radicals was analyzed ina series of experiments with an optical single-cylinderengine, since these radicals are known to be associatedwith high temperature reactions. A series of experimentswas also performed using a multi-cylinderengine with varied NVO timings, which showed thatthe combustion phasing was influenced by both theratio between the pilot and main injection amountsand the total amount of fuel. Data acquired from correspondingoptical analysis showed the occurrenceof OH radicals (and thus high temperature reactions)during the NVO in all tested operating conditions. Theresults also indicate that the extent of the high temperaturereactions was influenced by both varied parameters,since decreasing the relative amount of the pilotinjection and/or increasing the total amount of fuel ledto larger amounts of OH radicals.
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| 38. |
- Dahlén, Leon, et al.
(författare)
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Vegetable and synthetic hydraulic fluids to improve the overall efficiency of a hydrostatic transmission
- 2001
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Ingår i: Journal of Synthetic Lubrication. - : Wiley. - 0265-6582 .- 1557-6841. ; 17:4, s. 263-276
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the investigation reported here was to determine whether or not a hydrostatic transmission can act as an alternative to a conventional one, and, if so, to ascertain to what extent the fluid type contributes to an improvement in the efficiency of the hydrostatic transmission. The results presented in this paper are derived from an experimental field test of the hydrostatic transmission of a belt conveyor. This belt conveyor is one part in an ore-transport line at LKAB mining company in Kiruna. The hydrostatic transmission replaced a conventional transmission consisting of an electric motor, a belt drive and a gearbox. The hydrostatic transmission was operated using three different hydraulic fluids: Shell Tellus TX 68, a conventional mineral oil; Mobil SHC 526, a synthetic fluid; and Binol Hydrap II, a vegetable fluid. All fluids have the same ISO viscosity grade, VG 68. The measurements on the transmission show a 3% overall efficiency improvement when using vegetable and synthetic hydraulic fluids compared with the mineral oil. The current at the start of the transmission was reduced by a factor of 6, compared to that of the conventional transmission. The installed 110 kW electric motor was replaced with one of 55 kW. The test also showed that a closer study of all operating conditions, and a selection of components suited to the size of the load, can improve the overall efficiency of the hydrostatic transmission.
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| 39. |
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| 40. |
- Persson, Urban, 1961-
(författare)
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Realise the Potential! : Cost Effective and Energy Efficient District Heating in European Urban Areas
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Member States of EU27 need to accelerate the integration of energy efficient technology solutions to reach the 20% energy efficiency target set for 2020. At current pace, projections indicate that only half of expected primary energy reductions will be reached. To meet the energy demands of growing populations and a vibrant economy, while simultaneously reducing primary energy supplies, the European continent faces a new kind of challenge never previously encountered. The identification and application of feasible, competitive, and comprehensive solutions to this problem are of highest priority if the remaining gap is to be closed in time. How is this multi-dimensional and complex dilemma to be dissolved? In this work, expanded use of district heating technology is conceived as a possible solution to substantially reduce future primary energy demands in Europe. By extended recovery and utilisation of vast volumes of currently disregarded excess heat from energy and industry sector fuel transformation processes, district heating systems and combined generation of heat and power can improve the general efficiency of the European energy balance. To investigate the possible range of this solution, this thesis introduces a set of methodologies, theoretical concepts, and model tools, by which a plausible future excess heat utilisation potential, by means of district heat deliveries to residential and service sectors, is estimated. At current conditions and compared to current levels, this potential correspond to a threefold expansion possibility for directly feasible district heating systems in European urban areas and a fourfold increase of European excess heat utilisation.
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