| 1. |
- Larsson, Tara, 1993-
(författare)
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The Effects of Oxygenated Fuels on DISI Engine Particle Emissions and Efficiency : Experimental investigation of the effects of oxygenated biofuels on particle emissions and engine performance
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The transport sector is one of the main sources of greenhouse gas emissions.Replacing fossil fuels with renewable fuels can help reduce the impact oftransportation on the climate. Liquid, oxygenated biofuels show great potentialas a replacement in spark-ignited engines, as they exhibit similarcombustion behavior to gasoline, and are compatible with existing infrastructure.This thesis aims to expand the knowledge on how oxygenated fuelsaffect emissions and performance in direct-injected spark-ignited (DISI) engines.Experiments on a gasoline optimised DISI engine at low and mid loadconditions, were conducted to establish how these fuels affect engine efficiency,combustion propagation, and emissions. A thorough investigationon how the particle emissions change with different fuels was also performed.The research evaluated five different oxygenated fuels in comparison to gasoline:ethanol, methanol, n-butanol, iso-butanol, and methyl tert-butyl ether.The oxygenated fuels all increased engine efficiency, even at low loads wherethe engine was not knock limited. The most significant increase in efficiencywas observed for methanol, with up to 12% improvement in indicated thermalefficiency compared to gasoline. At low loads all oxygenated fuels decreasedthe emissions of unburned hydrocarbons, carbon monixde and nitrogenoxides. The results at mid load conditions show that fuels with lowvolatility will increase these emissions. The findings also indicate that fuelvolatility will have a more significant impact on the particle emissions levelsthan fuel oxygen content. This effect is more pronounced at lower enginespeeds and higher engine loads.This thesis work reveals great potential to use liquid, oxygenated biofuelsin DISI engines to decrease transport-associated carbon dioxide emissions.Even without engine modifications, oxygenated fuels yield improved engineefficiency compared to gasoline. Optimized injection for fuels with decreasedvolatility is needed to reduce emissions at higher engine loads.
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| 2. |
- Strömbergsson, Daniel
(författare)
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Improving detection and diagnosis of bearing failures in wind turbine drivetrains
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wind power has in the last 20 years grown into one of the main sources of renewable energy in the world, with both the amount and size of the turbines increasing substantially. One of the major challenges for the wind power industry is the premature failures of especially the drivetrain components. These failures cause a lot of turbine downtime, which increases the operation and maintenance costs of the turbines. Failures in the gearbox have been shown to lead to the highest downtime and the multitude of bearings within that subsystem is overrepresented in the total amount of component failures. Vibrationbased condition monitoring is considered the best method to find these types of defects early and avoid prolonged turbine downtime. Previous research has therefore been focused on the different aspects of condition monitoring; i.e. measurement technologies, signal analysis of vibration measurements to improve detection and diagnosis as well as the implementation of machine learning solutions. However, the majority of research work has yet to evaluate the performance of new developments using wind turbine field data, and still no fundamentally new developments have seen a large-scale implementation in the industry. Further, it is known that the positioning of the accelerometer, used to measure the vibrations, affects the ability to detect and diagnose defects. However, it is not known how to optimally position the accelerometers to monitor the individual drivetrain sub-systems. Also, previous research does not show how the influence of the measurement properties of the field data affect the ability to detect and diagnose component failures.Therefore, this thesis provides a comprehensive evaluation of how to improve the detection and diagnosis of bearing failures specifically in wind turbine drivetrains. In this thesis, a simulation model was developed to study how the accelerometer positioning affects the measurement quality. Vibration simulations of a similar sized bearing to ones found in the wind turbine drivetrain show an optimal accelerometer position as close to the primary loaded zone of the bearings as possible. The current placement of the accelerometers in the wind turbine drivetrain are often diametrically opposed to the loaded zone, and the performance of the vibration monitoring with respect to the commonly used signal analysis tools could thereby be increased. Further, wavelet-based signal analysis has been evaluated using historical wind turbine drivetrain field data. A new implementation of the wavelet packet transform to analyse enveloped vibration measurements in the frequency domain was developed, where the measurements were decomposed into packets matching the frequency resolution of the fast Fourier transform, and analysing the packet energy spectra. Finally, an anomaly detection solution utilizing an artificial neural network has been implemented to separate the condition indicator values, used for detection and diagnosis, from their inherent variance due to the dynamic turbine operation seen in the drivetrain rotational speed. The results in this thesis show the inadequacy of the commonly stored vibration measurements to the condition monitoring databases when used in post failure investigations and application of research developments on available field data. Measurements both taken over a long period of time and covering wide frequency range should be stored, instead of the either/or of today. Otherwise, the real-time monitoring of wind turbine drivetrain bearing failures cannot be replicated and monitoring improvements not fully evaluated. By implementing the wavelet packet transform, the detection and diagnosis performance was increased 250% compared to the fast Fourier transform, in an example of gearbox output shaft bearing failure. By implementing the anomaly detection by the artificial neural network, the performance increased further and was able to provide indications in a planet bearing failure case, which was not possible before. For turbine owners, these results provide both practical actions to take and provide an example of an easily implementable signal analysis tool to improve the detection and diagnosis of drivetrain bearing failures. The anomaly detection, which utilizes available historic data from healthy turbines and does not require any amount of labelled data for all considered types of bearing failures, also shows promise to detect failures in the drivetrain components which has been historically problematic. For the research community, the results mainly provides guidance into using historic field data when evaluating new developments. Also, they highlight potential pitfalls one can face using field data and what data properties to look for to successfully show the potential of your work.
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| 3. |
- Bergstedt, Edwin, 1986-
(författare)
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A Comparative Investigation of Gear Performance BetweenWrought and Sintered Powder Metallurgical Steel : Utilizing In-situ Surface Profile Measurements to Investigate theInitiation and Evolution of Micropitting and Pitting Damage
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vehicle electrification is a strong trend that introduces new challenges, such as increased input speed of the transmission and increased power density. Alsothe noise emittance of the gearbox is of increasing importance, as the sound of the gearbox is no longer masked by the internal combustion engine. Pressed and sintered powder metallurgical steel could be an interesting alternative towrought steel; the internal porosity has a dampening effect on the noise, and gears can be made in a fast and efficient process. However, current manufacturing of powder metallurgical steel has significant performance limitations. The Nanotechnology Enhanced Sintered Steel Processing project aims to reduce the gap in performance between conventional steel and powder metallurgical steel. One of the potential benefits is that with the inclusion of nano-powder the density can be increased. To validate the new material, its performance needs to be compared to the performance of current generation powder metallurgical materials and also to wrought steel. It is therefor crucial to be able to test and evaluate different materials and gears. This thesis has developed methods for testing, comparing, and evaluating the performance of gears. Powder metallurgical steel has been tested and compared to wrought steel; the efficiency as well as pitting life have been investigated in an FZG test rig. Also the effects of different surface finishing operations have been evaluated. The gear flanks were measured in-situ in the gearbox using a stylus instrument; an optimisation routine was created to fit the measurements to the theoretical involute profile. This enabled an in-depth analysis of surface wear and presented an opportunity to investigate micropitting initiation. It was found that the damage mechanisms of wrought steel and powder metallurgical steel are similar and related to the surface finishing method. However, the powder metallurgical steel was also susceptible to sub-surface cracks. Superfinished gears can be negatively influenced by the lack of tip relief as cracks initiate in the surface layer of the root, rapidly destroying the tooth.
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| 4. |
- Lius, Andreas, 1990-, et al.
(författare)
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Experimental and chemical-kinetic evaluation of a heavy-duty methanol PFI engine with direct water injection
- 2024
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Ingår i: Fuel. - : Elsevier Ltd. - 0016-2361 .- 1873-7153. ; 359
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Tidskriftsartikel (refereegranskat)abstract
- Internal combustion engines are still widely used for propulsion in modern vehicles. Upcoming emission legislation imposes stricter limits on exhaust emissions. One method to achieve emission compliance is by using a three-way catalyst (TWC), which offers excellent emission reduction if the mixture is stoichiometric. However, stoichiometric mixtures in spark-ignited engines have the drawback of increased knock propensity. Knock can be mitigated by using water injection, which serves as both a diluent and utilizes latent heat to reduce the temperature, thereby reducing the reactivity of the unburned mixture. Methanol as a fuel has received more attention thanks to its high research octane number (RON) and its potential to contribute to decarbonization when produced as e- or bio-methanol. In the current study, Direct Water Injection (DWI) was evaluated on a Heavy-Duty (HD) single-cylinder research engine fueled by methanol. This work aims to fill a research gap on methanol-fueled engines with water injection. A direct injection system of water was chosen as it offers the freedom to inject during the closed cycle. Furthermore, a chemical kinetic study on the oxidation of stoichiometric methanol–water mixtures was conducted based on findings in the literature suggesting that, under certain conditions, water mixed with alcohol (in this case, ethanol) can reduce the ignition delay. The experimental results demonstrate that DWI effectively suppresses knock and reduced Nitrogen Oxides (NOx), albeit with deteriorated combustion efficiency. The chemical kinetic study suggested that at lower to intermediate temperatures, water acts as an efficient third-body collider, which lowers the ignition delay. However, this effect is not significant for the typical timescales encountered in HD engines.
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| 5. |
- Perricone, Guido, 1973-
(författare)
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Laboratory measurements of airborne emissions from car brakes for clean air
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Brake systems are used to safely stop vehicles. The brake pads are pressed against the brake disc, transforming the kinetic energy of the vehicle into heat to be dissipated. In this process a tribological contact causing wear takes place at the interface of the pads and disc: particles are generated, a fraction of which is airborne and therefore creates an aerosol. To meet demands on air quality and sustainable transport, significant challenges are to find means to measure particles, and provide solutions able to decrease such source of emissions.Paper A proposes a test cycle executed in an inertia brake dynamometer during which a measurement of the airborne particles is carried out: the sampling point is close to the source of emissions. The experimental results are then analysed to determine how many particles are generated per test section.Paper B presents a redesign of an inertial disc brake dynamometer with the aim to have clean air while measuring particles, and isokinetic sampling. A comparison in terms of number and size distributions of the brake emissions with and without control of the cleanness of the intake air is studied.Paper C is the ranking, from the non-exhaust brake emissions point of view, of five different current brake pair materials using the novel redesigned inertia disc brake dynamometer. Particles are both counted, collect on filters and weighed.Paper D investigates the evolution of the friction performance in terms of friction coefficient and emissions, over five repetitions of the same test procedure – so considering the running-in effect. The friction performance is discussed as a consequence of the dominating wear mechanisms.Paper E conducts a study on real driving data that are transformed into a brake dynamometer testing procedure by an energy–temperature approach. The consequent emissions study allows the calculation of brake emission factors.Paper F presents a comparison of the brake particle emissions measurement when volatile and semi-volatile organic compounds (if any), as for exhaust emissions, are thermal treated before being measured.Paper G illustrates a holistic approach, developed within the REBRAKE EU-financed project, for reducing airborne emissions for car brakes by 50% integrating different perspectives: the tribological testing of the friction pair at different scale levels, the analysis of the relevant wear products and correlated wear mechanisms, the development of specific contact mechanics simulation approaches, and the optimisation of the friction pair materials.
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| 6. |
- Tu, Minghui, 1992-
(författare)
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Measuring and Modelling PM Levels on Underground Platforms
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Urban railways have become an essential part of the transportation network of cities due to their convenience and high capacity. To make full use of urban space, many urban railway platforms are built underground. However, according to local surveys and studies, the concentration of airborne particles on underground platforms is significantly higher than that of particle concentrations aboveground. These platform particulates are often rich in heavy metal elements such as iron, copper and manganese, which may adversely affect the health of commuters riding urban railways. Therefore, the primary purpose of this research is to explore various factors that affect the airborne particle concentrations on urban underground railway platforms and then provide some suggestions for improving the air quality of the urban railway commuting environment.The papers appended are all based on the analysis of field measurements on the Stockholm urban railway platforms in Sweden between 2016 and2020 (Paper A to E). According to different research purposes, diverse statistical models have been established. By exploring the model parameter factors, it is possible to quantify the airborne particle concentrations on underground platforms. The thesis started with the qualitative trend between train movement and platform particle concentration and found that train operation and braking are closely related to the increase in platform particle concentration (Paper A). Then, by comparing linear and non-linear train frequency and particle concentration relationship models, the critical direction for studying the train frequency factor using the linear model was determined (Paper B). After that, the train frequency factor was deconstructed into two approaches. Namely, train brake effect factor, train accumulative effect factor (Paper C) and equivalent train frequency factor, train-type factor (Paper D and E). Finally,non-train-related elements were added to the train-related model as an extension (Paper E). A preliminary quantitative study of non-train-related factors was conducted.Based on the above research results, this thesis proposes three possible methods to improve the air quality of underground platforms. These consist of: replacing train types that emit higher particles with those that emit lower ones; deploying the intelligent control ventilation system; and adding night cleaning in the underground system.
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