Browsing by Subject "Mechanical Engineering"
Now showing 1 - 20 of 380
Results Per Page
Sort Options
- ItemOpen Access25cc HCCI engine fueled with Diethyl Ether(2009) Lemberger, Ian; Floweday, Gareth; Yates, AndrewThis research forms part of an ongoing HCCI study at the SASOL Advanced Fuels Laboratory to investigate and understand engine configuration and fuel chemistry effects on combustion in HCCI engines. This project continues from a previous project where a small Progress Aero Works (PAW) 6.5cc high speed model "diesel" aeroplane engine was found to operate in HCCI mode with surprising ease and flexibility. A 25cc, four-stroke, single cylinder Honda GX25 engine, possessing 2-valves with an overhead cam and separate oil sump lubrication system was used. This research aimed to provide insight with respect to which engine characteristics such as size, heat transfer, speed and fuel blending effects, play the primary role in operational differences between the Honda GX25, conventional HCCI engines and the remarkable operational flexibility of the PAW engine.
- ItemOpen AccessA CFD framework for aeroelastic gust load calculations(2018) Man, William Liw Tat; Malan, ArnaudA Computational Fluid Dynamics (CFD) framework for the simulation of the aeroelastic response of aircraft flying under gust loading was developed. The multiphysics, Finite Volume, VertexCentered code Elementaltextsuperscript{textregistered} was employed and calculations were performed for the transonic flow regime. In the structural domain, the fuselage was treated as rigid and the wing was considered for aeroelastic calculations. The latter was represented by a beam stick model using Timoshenko beam theory in Elementaltextsuperscript{textregistered}'s structural module. The case under consideration was the NASA Common Research Model (CRM) flying at Ma = 0.86 with a 30 ft gust applied over the aircraft. Key contributions of this work included implementation of a computationally efficient gust model as well as the development of a fluidstructure interface. The latter was to transfer forces from a deforming wing skin to the wing-beam in a conservative manner while reflecting the resulting displacements on the wing surface. An interface library was developed for this purpose and 3rd order accurate Bezier curves used to recover a smooth deformed wing. The various sub-components of the aeroelastic model were rigorously validated. Following this, the developed framework was applied to the CRM under gust load conditions.
- ItemOpen AccessA Higher-Order VOF Interface Reconstruction Scheme for Non-Orthogonal Structured Grids - with Application to Surface Tension Modelling(2021) Ilangakoon, Niran A; Malan, Arnaud GThe volume-of-fluid (VOF) method [24] is widely used to track the interface for the purpose of simulating liquid-gas interfacial flows numerically. The key strength of VOF is its mass conserving property. However, interface reconstruction is required when geometric properties such as curvature need to be accurately computed. For surface tension modelling in particular, computing the interface curvature accurately is crucial to avoiding so-called spurious or parasitic currents. Of the existing VOF-based schemes, the height-function (HF) method [10, 16, 18, 42, 46, 53] allows accurate interface representation on Cartesian grids. No work has hitherto been done to extend the HF philosophy to non-orthogonal structured grids. To this end, this work proposes a higher-order accurate VOF interface reconstruction method for non-orthogonal structured grids. Higher-order in the context of this work denotes up to 4 th-order. The scheme generalises the interface reconstruction component of the HF method. Columns of control volumes that straddle the interface are identified, and piecewise-linear interface constructions (PLIC) are computed in a volume-conservative manner in each column. To ensure efficiency, this procedure is executed by a novel sweep-plane algorithm based on the convex decomposition of the control volumes in each column. The PLIC representation of the interface is then smoothed by iteratively refining the PLIC facet normals. Rapid convergence of the latter is achieved via a novel spring-based acceleration procedure. The interface is then reconstructed by fitting higher-order polynomial curves/surfaces to local stencils of PLIC facets in a least squares manner [29]. Volume conservation is optimised for at the central column. The accuracy of the interface reconstruction procedure is evaluated via grid convergence studies in terms of volume conservation and curvature errors. The scheme is shown to achieve arbitrary-order accuracy on Cartesian grids and up to fourth-order accuracy on non-orthogonal structured grids. The curvature computation scheme is finally applied in a balanced-force continuum-surface-force (CSF) [4] surface tension scheme for variable-density flows on nonorthogonal structured grids in 2D. Up to fourth-order accuracy is demonstrated for the Laplace pressure jump in the simulation of a 2D stationary bubble with a high liquid-gas density ratio. A significant reduction in parasitic currents is demonstrated. Lastly, second-order accuracy is achieved when computing the frequency of a 2D inviscid oscillating droplet in zero gravity. The above tools were implemented and evaluated using the Elemental®multi-physics code and using a vertex-centred finite volume framework. For the purpose of VOF advection the algebraic CICSAM scheme (available in Elemental®) was employed.
- ItemOpen AccessA Precision Experiment for the Deformation and Fracture of Blast Loaded Plates(2022) Cloete, Trevor John; Nurick, Gerald NThe purpose of this thesis is to present a novel laboratory scale precision test [1] apparatus, developed specifically to study of the deformation and fracture of blast loaded plates. A review of published laboratory scale blast testing showed that classical ballistic pendulum techniques satisfy several precision testing criteria. However, specific aspects required improvement. Therefore, an instrumented ballistic pendulum has been developed, incorporating a central support, in the form of a Hopkinson bar, for use with a novel peripherally clamped centrally supported (PCCS) plate specimen, which allows the reaction force history at the inner boundary to be captured. Hence, in addition to the traditional impulse vs deflection data, this approach allows details such as the total deformation duration or the exact timing and magnitude of fracture processes to be captured. Furthermore, when used with a peripherally clamped annular (PCA) plate specimen, this approach allows the blast load pressure history to be captured. A literature review found several classical closed form solutions for the large deflection of impulsively loaded peripherally clamped solid (PCS) circular plates. However, several crucial aspects of the solutions were contradictory and/or incomplete. To address this a generalized energy method for modelling impulsively loaded axisymmetric plates was developed which subsumes previous solutions and facilitated novel analytical solutions that provide a theoretical framework for interpreting the experimental data. Extensive experimental results reported in this thesis provide a rich set of novel data for code validation. While the PCCS and PCA plate configurations require a refined definition of the observed failure modes, the transitions between the modes and the fracture behaviour are studied in great detail. The data is analysed using dimensionless impulse expressions obtained from the analytical solutions in this thesis. In addition to accurate deflection predictions, these solutions also provide improved deflection duration predictions using a novel two phase solutions that can also accommodate finite load duration. It is concluded that the instrumented ballistic pendulum, incorporating a central support in the form of a Hopkinson bar, in conjunction with the novel PCCS and PCA plate configurations and analytical solutions, satisfies all the requirement of a precision test.
- ItemOpen AccessA systems approach to the process dynamics of interpersonal selling in the financial services industry(1999) Van den Berg, J FThe Financial Services Industry (FSI) in South Africa is currently under severe criticism for the quality of service it provides to its customer base. Customer dissatisfaction expressed through individuals, (See Appendix A) consumer bodies and members of parliament has resulted in the draft and approval of three new bills in parliament, which will protect the rights of customers
- ItemOpen AccessA towed submersible(1973) Dunkley, William Rae; Boyle, W POne way to continuously scan the sea would be to tow a submarine vehicle that would cycle vertically in the water between set depths. Its period of vertical oscillation would be short compared with the changes in parameters to be measured, in this case long internal waves. It would carry continuously recording depth and temperature measuring instruments; if possible storing the results on a magnetic tape or paper drum or else transmitting the data to the towing vessel. It could be designed so that it was relatively independent of ship speed and self-contained so that it could operate unattended for long periods of the normal oceanographic surveys require regular stops for geological core samples to be taken or for sampling reversing bottles to be cast, and during these moments the vehicle could be hauled aboard and its recording sheets or power sources renewed as necessary. Accordingly a specification was determined in consultation with members of the Oceanography Department of the University for a suitable towed body (Table 1.1). Initially it was to carry temperature measuring devices, but it should have the possibility of extending this to carry instruments to measure pH, conductivity, etc.. The only published work at present concerning such a device is by Glover (2), who is developing an undulating plankton recorder for long distance towing with an oscillating wave length of 20 km. It is not very appropriate to make direct comparison with Glover's work since there local instabilities are damped out during the long, slow oscillations, whereas for a device with a much shorter wave period such local perturbations crucially affect the performance. A device with a relatively short undulation period for intense data collection would be a major advance in oceanographic recording techniques, and one that could have a wide variety of commercial applications.
- ItemOpen AccessA virtual element method for hyperelasticity(2021) van Huyssteen, Daniel; Reddy, DayaThis thesis studies the approximation of plane problems of hyperelasticity, using a loworder virtual element method (VEM). The VEM is an extension of the finite element method (FEM). It is characterised by considerable freedom with regard to element geometry, permitting arbitrary polygonal and polyhedral elements in two and three dimensions respectively. Furthermore, the local basis functions are not known explicitly on elements and take the simple form of piecewise-linear Lagrangian functions on element boundaries. All integrations are performed on element edges. The VEM formulation typically involves a consistency term, computed via a projection, and a stabilization term, which must be approximated. Problems concerning isotropic and transversely isotropic hyperelastic material models are considered. Examples of transversely isotropic materials, which are characterised by an axis of symmetry normal to a plane of isotropy, range from simple fibre-reinforced materials to biological tissues. To date, in the context of hyperelasticity, investigation of the performance of VEM has primarily focused on problems involving the isotropic neo-Hookean material model. Furthermore, there has been limited investigation into the behaviour of the VEM in the nearly incompressible and nearly inextensible limits. In this thesis a VEM formulation with a novel approach to the construction of the stabilization term is formulated and implemented for problems involving isotropic and transversely isotropic hyperelastic materials. The governing equations of hyperelasticity are derived and various isotropic and transversely isotropic constitutive models are presented. This is followed by presentation of the virtual element formulation of the hyperelastic problem and a possible approach to its practical implementation. Through a range of numerical examples, the VEM with the proposed stabilization term is found to exhibit robust and accurate behaviour for a variety of mesh types, including those comprising highly non-convex element geometries, and for problems involving severe deformations. Furthermore, the versatility of the proposed VEM formulation is demonstrated through its application to a range of popular isotropic and transversely isotropic material models for a wide variety of material parameters. Through this investigation the VEM is found to exhibit locking-free behaviour in the limiting cases of near-incompressibility and near-inextensibility, both separately and combined.
- ItemOpen AccessAbnormal combustion - methanol versus gasoline(1988) Yates, Andrew David Bennett; Bennett, KevinThe maximum efficiency of conventional gasoline engines is largely determined by the compression ratio, and this is limited by the onset of kno8k. The maximum cylinder size is similarly constrained. The relatively higher knock resistance of methanol opens up possibilities for increased efficiency or engine size. The auto-ignition of methanol and gasoline was characterised in terms of fundamental parameters and the results were compared. The research findings were used in the analysis of a particular combustion chamber design to assess the potential of using squish as a means of avoiding knock in a large, spark-ignition methanol engine.
- ItemOpen AccessAccurate characterisation of surface fatigue cracks (in steels) using the AC potential drop NDT technique(2002) Bright, Dominic; Tait, Robert BIn order to maintain the desired level of safety in an industrial environment, it is important that the structural integrity of all the components and equipment being utilised by the facilty is assured. To determine the structural integrity of an engineering system precisely, not only must the depth of the flaw be established, but the crack profile and orientation must also be obtained in order to assess the extent of the crack. The present work described in this thesis discusses the development of an AC potential drop (ACPD) system as a non-destructive testing (NDT) technique for flaw detection and sizing of variously shaped and oriented surface breaking fatigue cracks. The ACPD method was reviewed to establish its viability as an NDT technique, and to understand the response of the output to fatigue cracking. The proposed system using a mains power source with a frequency of 50Hz was investigated as a means of providing a sensitive and reliable measurement device that could be employed to analyse fatigue cracks in industrial components in situ.
- ItemOpen AccessActive control of passive safety in passenger motor vehicles : a feasibility study investigating dynamic denting of members using pyrotechnic devices(1995) Marshall, N S; Nurick, Gerald NThis report describes a feasibility study investigating dynamic denting of members using pyrotechnic devices to engineer favourable energy absorption characteristics into thin walled tubes. A tube of sufficiently low slenderness ratio and wall thickness, when loaded axially to failure, will collapse in the progressive buckling mode. After the ultimate buckling load has been exceeded, and as the tube continues to compress, the load oscillates between loads considerably lower than the ultimate buckling load. The object of introducing an advantageous deformation is to decrease the ultimate buckling load to a magnitude comparable with the subsequent peak loads, but at the same time avoiding a change in the buckling mode which is not advantageous. Testing was limited to thin walled square mild steel tubes. The test procedure began with a process to determine the limitations imposed on the geometric imperfections that could be achieved by the use of explosive. It was found that all the explosively induced deformations were rounded, i.e. the dents were hemi-spherical in shape. It was also found that a smooth edged round hole could be created in the centre of the dent with the use of a round, flat explosive charge. Geometric imperfections that could be induced explosively in the specimens (as well as other deformation shapes, tested for comparative purposes) were mechanically formed in the specimens. The tubes were then quasi - statically crushed to determine the energy absorption characteristics induced by the deformations. When spherical dents were induced, the deformation affected the tube beyond the immediate spherical dent and hence the distance between the plastic hinges was increased and instabilities in the crushing process were introduced. Holes (without any visible denting) decreased the distance between the plastic hinges and thus also induced instabilities. In both cases the tubes tended to skew over to one side and in extreme cases Euler buckling ensued.
- ItemOpen AccessAerodynamic analysis and optimisation of a servo-controlled aileron(2011) Day, Chris; Redelinghuys, ChristiaanThe pressure for the airline industry to reduce its consumption of fuel is mounting. It has been conjectured that smart materials could be employed to control the aileron deflections via the tab, using with an electrically-actuated system instead of the bulky hydraulics currently used. In a collaboration between a leading aircraft manufacturer and four South African universities, potentially more efficient technologies for aircraft roll control, which would reduce the weight, are being investigated. This dissertation involves the aerodynamic analysis component of the collaboration project.
- ItemOpen AccessAerodynamics drag reduction of commercial trucks(2000) Wang, Cheng; Sayers, AnthonyThis thesis deals with the airflow over a double trailer Gull Wing truck, with a view to reducing the drag of the truck. To investigate the flow over the truck, a 1:20 scale double trailer truck model was designed and constructed from chipboard for wind tunnel experiments. The overall size of the model is 1100 mm long, 130 mm wide and 215 mm high. A same scale numerical model was also built for computational simulations.
- ItemOpen AccessAn Algebraic Volume of Fluid Method for Strongly Coupled Spacecraft Fuel Slosh Modelling(2020) Jones, Bevan W S; Malan, Arnaud GThe increase in the number of commercial space missions has resulted in the increased need for efficient and effective spacecraft designs. A key contributor to the accuracy of space vehicle simulation is the prediction of fuel slosh loads during in-orbit manoeuvres, particularly due to the large fuel-to-solid mass ratios involved. To this end, this thesis details a high resolution mathematical model capable of predicting the dynamic interaction between fuel slosh and the rigid structure of a spacecraft. The Volume of Fluid (VoF) method provides a framework in which Computational Fluid Dynamics (CFD) can be used to model the fluid dynamics of two phase fuel slosh in a mass conservative manner. To be applicable to industrial geometries, an unstructured finite volume median dual cell methodology is employed for spatial discretisation. This gives rise to the first novel contribution of this work, namely the development of a new volume conservative VoF initialisation method for arbitrary interfaces on unstructured meshes. The scheme, called the Arbitrary Grid Initialiser (AGI), is rigorously validated and proven conservative to machine precision [1]. An algebraic, as opposed to geometric, VoF advection method is used due to being similarly well suited to unstructured grids. Improvements to the algebraic VoF method is therefore the next contribution of this thesis; where the CICSAM [2] and HiRAC [3] VoF methods are improved, and the first conservative HiRAC method presented. The improved CICSAM and HiRAC methods are shown to be competitive with their geometric counterparts on unstructured grids while being mass conservative. Both CICSAM and HiRAC are then coupled (HiRAC for the first time) to a well balanced Continuum Surface Force (CSF) surface tension discretisation. The surface tension implementation, for which standard height functions are used, is shown to be well-balanced with an accuracy that compares favourably to existing methods. In the final part of the thesis, the complete spacecraft model is constructed. A numerical rigid body code is developed for this purpose, which can additionally track its orientation. The rigid body and fluid schemes are finally coupled together in a strong, stable, and partitioned manner using the Aitken's ∆2 method [4]. The model is demonstrated to be numerically stable for large liquid-to-solid ratios via a benchmark test case.
- ItemOpen AccessAn economic and social review of the preferred bidders under the small projects IPP procurement programme: a cross-case synthesis(2019) Mew, Timothy; Marquard, Andrew; Kruger, WikusThe literature on the economic and social impacts of infrastructure projects, such as renewable energy projects, largely point towards these projects having positive direct and indirect benefits for the local economy, especially if the ownership, components, construction, and operation are sourced from local enterprises. The recipients of project expenditure, the location of their employees and to whom the profits accrue are essentially the factors that determine how much local economic benefit these renewable energy projects have. With this in mind, the Renewable Energy Independent Power Producers Procurement Programme (REIPPPP) was structured in such a way that gave additional weighting to socioeconomic criteria such as job creation, local content, local ownership, Socioeconomic Development (SED) funding, and Enterprise Development (ED) funding among others. The structuring of the REIPPPP in this way highlights the overarching policy objectives in the energy sector and how these renewable energy projects have been identified by the government as a means to achieve these socioeconomic objectives. The REIPPPP formed the foundation upon which the Small Projects Independent Power Producers Procurement Programme (SP-IPPPP) was based. The SP-IPPPP was created by the government to further localise the renewable energy industry in South Africa and give local developers and suppliers better access into this emerging sector. This research sought to compare Small Projects under the SP-IPPPP with projects of the same technology under the REIPPPP (in bid window 3 and 4) in a cross-case synthesis. Using an embedded, multiple-case study design the commitments made by Preferred Bidders in each programme were compiled and contrasted. Following this, the results for the Small Projects were scaled-up to identify how justified the additional costs associated with the Small Projects are, given their co-benefits to the South African economy. The findings suggest that the impact of the Small Projects on the overall price of renewable energy from the chosen cases would be negligible; and therefore, the co-benefits from these projects could justify this price premium. Even when scaled-up to the 400 MW allocated to Small Projects, the impact on the overall cost of renewables from BW3 and BW4 could be argued to have been justified by the co-benefits afforded by these Small Projects. The impact on the electricity price from projects in the scenario and BW3 and BW4 was not substantial; however, the job creation, local (national) expenditure, and community (within 50km of the project site) benefit were substantial, which may vi incentivise policy makers to go ahead with the procurement in order to meet these soci oeconomic objectives. In terms of the best technology option for the SP-IPPPP, the findings suggest that solar PV and biomass (in particular) are better suited to this capacity and offer improved socioeconomic benefits without a drastic price premium. Wind energy on the other hand, appeared to have a notable price premium over the Large Projects without proportionate socioeconomic benefits and would perhaps be better left to the REIPPPP.
- ItemOpen AccessAn exploration of mechanical engineering students' perceptions of the influence of their work placement experiences on their employability(2020) Ngonda, Tiyamike Nyozani; Shaw, Corrinne; Kloot, BruceMost researchers agree that work placement has a positive influence on students' employability. Despite this consensus, there has been conflicting research on the factors that contribute to this influence. Moreover, the social mechanisms through which this outcome is realised have not been well understood. To address these shortcomings, this study explores how mechanical engineering students' work placement experiences facilitate or hinder the growth of their occupational competency and self-efficacy, two commonly used indicators of student employability. It provides a clear explanation of the factors and social mechanisms that produce employability outcomes and it is hoped that this would enable the implementation of work placement programs in a manner that would promote rather than hinder students' employability. The study is informed by social cognitive theory's triadic reciprocal causation model, which suggests that student learning arises from interactions of environmental, personal, and behavioral factors. It is further informed by situated cognition, a sociocultural theory that focuses on learning through participation. The study collected qualitative data from a sample of 34 mechanical engineering students from a South African university of technology who were undergoing a year-long work placement. Data were collected using semi-structured interviews as well as document analysis of the students' logbooks and evidence portfolios. Thereafter, a two-phase qualitative analysis comprising thematic analysis and thematic synthesis was conducted. The thematic analysis produced seven themes: the learning environment, the industry mentor, student performance and participation as learning, quality of work affordances, student characteristics, student's agentic role and student learning trajectory. These themes represented elements of students' work placement experiences that they considered influential in the growth of their occupational competency and self-efficacy. The thematic synthesis uncovered work placement as a system with emergent outcomes arising from interactions of its variables. These interactions were represented by a qualitative systems dynamics model with negative and positive reinforcing loops. An enabling reinforcing feedback loop explained the growth of the students' occupational competency and self-efficacy, and a constraining reinforcing feedback loop explained how such growth was hindered. This qualitative systems dynamics model may resolve previous studies' explanatory shortcomings by illuminating the processes through which work placements' occupational outcomes are realised.
- ItemOpen AccessAnalysis of a car door subjected to side impact(2016) Long, Christopher Robert; Yuen, Steeve Chung Kim; Nurick, Gerald NThe study presented in this thesis focuses on the response of a side impact beam located in a car door to impact loading in close conformation to the Federal Motor Vehicle Safety Standard 214 (FMVSS 214) standard. The side impact beam is situated in both the front and rear side doors of a vehicle between the inner and outer shells to minimise intrusion into the passenger compartment whilst absorbing as much impact energy as possible in a collision. While some manufacturers use tubular side impact beams, others use corrugated structures. Different materials are also considered, depending on the class of vehicle, a nd market for which it is intended. In this study, a numerical model of a light -weight passenger car, developed by the National Crash Analysis Center (NCAC ) of The George Washington University under contract with the Federal Highway Administration (FHWA) and National Highway Traffic Safety Administration (NHTSA ) of the United States Department of Transportation (US DOT ), was used to simulate a side impact on the front side door using the LS -DYNA R7.1.1 explicit solver . The resulting deformation of the door from the full vehicle model was used to design an experiment for an impact test on a passenger door, which was used to validate an equivalent numerical simulation. In the experiments, the car door was modified and subjected to a drop mass of 385 kg from a height of 1.27 m. The drop mass and height were chosen such that the maximum deflection in the car door impact test would be of similar magnitude to the deflecti n of the door in full vehicle model when subjected to an impact load in accordance with the FMVSS 214 Standard - which requires that the vehicle be projected into a rigid vertical 10 inch diameter pole at 29 km/h in a direction 75° to the longitudinal axis of the vehicle . The results from the numerical simulation of the struck door test were in good agreement with the experiments in both shape and magnitude of deformation. The behaviour of the side impact beam located in the passenger door was isolated and further studied. Drop test experiments on beams with square and round cross -sections were carried out to validate the equivalent finite element model. The drop mass and height of the striker was varied such that the transient response of the isolated side impact beam matched the response of the beam in the simulation of the equivalent door model and full vehicle model. In the impact test experiments, the tubular structures were subjected to a 200 kg mass dropped from six incrementally varying heights of 250- 500 mm. Both square and round tubes were observed to buckle at approximately 835 mm from the free end with different magnitude s of maximum deformation (depending on the drop height). The results from the numerical simulations showed good correlation with the experiments for shape and magnitude of deformation. A quadratic curve fit to the experimental maximum transverse deflection resulted in an R -squared value of 0.92 and 0.96 for the square and round tubes respectively. A parametric study was carried out on the side impact beam to investigate the effect of: Thickness and material of a singular tube configuration, and: Inner tube length and outer tube thickness of a compound tube structure. The performance of the different configurations were assessed in terms of Crash Force Efficiency (CFE and Specific Energy Absorption (SEA). A parametric study on the effect of the tube thickness showed that thicker tubes of the same material exhibited deformation of lo wer magnitude and had lower SEA. Aluminium tubes absorbed two or more times the energy per unit mass than the equivalent steel tubes. A round aluminium tube with a thickness of 2.175 mm was found to give the best balance between SEA and maximum deflection with values of 1.5 kJ/kg and 350 mm respectively. The compound tube configuration with the inner tube extended beyond the buckling point performed better in terms of SEA and maximum deflection provided the length of the inner tube did not exceed 90% of the length of the outer tube. The optimised compound tube configuration performed better than the single tube configuration in the full vehicle model with a 1mm reduction in the overall intrusion of the rigid pole.
- ItemOpen AccessAnalysis of carbonaceous solid deposits from thermal stressing of FAMEs and FAME/diesel blends at different temperatures in a continuous flow reactor(2015) Mandavha, Uyuenendiwannyi; Woolard, ChrisFuel deposits are carbon-rich high molecular weight species that are formed from the degradation of fuel. Diesel deposits may form on vital parts of a vehicle's engine or fuel system such as the fuel injectors. Once these deposits have formed, they can block the spray holes of the injector and may also cause moving parts within the injector to stick. Diesel deposits can cause engine failure, engine malfunction and affect engine performance. This study aims to investigate early stage deposits, formed in laboratory reactors, in particular a flow reactor. This was performed in order to gain insight into the processes by which these deposits form and what factors influence their formation. A flow reactor and closed sand bath reactor were employed to produce carbonaceous deposits, with the aim being that these might be similar to those formed in diesel injectors. The solid deposits were analysed using a Temperature Programmed Oxidation (TPO), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). Soluble deposit precursors from the stressed fuels were assessed using ultraviolet visible spectroscopy (UV-Vis) and electrospray ionisation-mass spectroscopy (ESI-MS) in order to provide further insight into the chemical processes preceding deposit formation. The test fuels stressed in this study were an EN 590 reference diesel and two fatty acid methyl esters (FAMES), viz. rapeseed methyl ester (RME100) and soya methyl ester (SME100). Binary blends of 80 % EN 590 diesel and 20 %RME (RME20), 80 % EN 590 diesel and 20 % SME(SME20), 50 % EN 590 diesel and 50 % SME (SME50) and 93 % EN 590 diesel and 7 % SME (SME7) (v/v) were also investigated. Aerated fuels were thermally stressed at 300°C and 400°C for 5h in the presence of oxygen in a continuous flow reactor. This study represents the first application of the flow reactor methodology to systems that contain fatty acids methyl esters (FAMEs).
- ItemOpen AccessAnalysis of the dynamic behaviour of the hangingwall beam during a seismic event(1992) Daehnke, A; Martin, JBIn a deep-level gold mine planes of weakness oriented parallel to the reef allow the hangingwall to separate from adjacent rock strata. The hangingwall then acts as a separate beam supporting only its selfweight. Mining-induced near vertical shear fractures divide the hangingwall beam into distinct blocks of relatively intact material. The objective of this study is to investigate the response of the isolated hangingwall beam during a seismic event. The study is particularly concerned with the global, resonant behaviour of the hangingwall and local shear or crushing failure of the rock at the shear fractures is not considered. A finite element program is developed to compute the hangingwall response during seismicity. The response is normalised, thus permitting the response spectrum method to describe maximum hangingwall motions during a seismic event at various beam lengths. By comparing the response spectrum describing a single-degree-of-freedom (SDOF) system with the spectrum of the hangingwall, it is evident that, although the hangingwall response spectrum is shifted to a higher frequency and velocity domain, the shapes of the two spectra are essentially the same. The frequency and velocity shift is calculated for 15 seismic events and empirical rules are developed to quantify the spectral shift for a wide range of event magnitudes. Unlike the spectrum describing hangingwall motions, the construction of a SDOF response spectrum is computationally cheap and is standard practice in earthquake engineering. By applying the empirical rules the seismologist can extrapolate the SDOF spectrum to estimate maximum hangingwall motions due to a seismic event and critical beam lengths which are prone to resonance. The effect on the response of the hangingwall supported by backfill consisting of dewatered and cemented tailings is evaluated. It is shown that a fill-to-face lag of less than 5m reduces hangingwall motions considerably. Further, at small strains the stiffer cemented tailings provide superior support than that offered by comparatively soft dewatered tailings. A chart is presented which correlates event magnitudes to critical beam lengths prone to resonance.
- ItemOpen AccessAn analysis of the feasibility of using a solar water heating system in a hotel : a case study(2010) Fahy, Gary; Bennett, KevinThe use of solar energy to heat water will not only contribute to the mitigation of global climate change due to the reduced combustion of fossil fuels, but it will also reduce the demand on South Africa's strained electricity supply infrastructure. The hotel industry is particularly energy intensive and the production of hot water makes up a significant portion of its electricity consumption. Furthermore, South Africa boasts one of the world's most abundant solar radiation resources. Thus far, however, the use of large-scale solar water heating (SWH) systems in South African hotels is limited, with the lack of economic feasibility likely to be the core reason.
- ItemOpen AccessAnalyzing sustainable energy in developing countries: Selected South African case studies(2008) Howells, Mark IdwalThis thesis demonstrates the use of selected Energy-Environment-Economic (E3) modelling techniques to provide insight to developing country issues. The work focuses on analyzing combinations of technologies and energy use to satisfy potential requirements of consumers at the lowest cost to society. (Tools such as MARKAL- of the Energy International Energy Agency's (IEA) Technology Systems Analysis Program (ETSAP) - are used often). The thesis shows how these models may be adapted in novel ways to tackle different challenges in different contexts. The applications covered range from macro-economic problems to the micro-economic village level analysis of fuel and appliance use. The thesis demonstrates through a national (South African) analysis selected greenhouse gas (GHG) mitigation potentials. By examining markets in low-income areas dependent on biomass it shows relationships between institutional- and information-failure and traditional fuel use. Using the increased functionality available in the TIMES model (the successor to the afore-mentioned MARKAL), detailed dynamics of low income fuel use are simulated. By adopting simplifications, a robust, simple and critical analysis of an energy subsidy is made. Using a Multi-Criteria Decision Analysis (MCDA) approach a range of GHG mitigation options are compared in a developing country context. The thesis reports on environmentally friendly development paths derived from the application of the Goal Programming extension of MARKAL. Finally it questions the appropriateness of the Clean Development Mechanism's policy of supporting only 'additional' GHG mitigation in certain circumstances. In an appendix it develops an efficient industrial data collection process using an MCDA analysis. The main theme of this thesis is to show how suitable modelling can not only warn of inefficiency in development policies, but also indicate technical scenarios of how such inefficiencies are best remedied. Key words: South Africa, Energy-Environment-Economic Modelling, MARKAL, TIMES, Efficiency, MCDA, Greenhouse gas, Goal Programming, Clean Development Mechanism