The temporal and spatial distribution of fuel in cylinders is a key factor affecting the combustion characteristics and emission generation of a DI diesel engine. The airfuel mixing quality is critical for controlling ignition timing and combustion duration. Avoiding fuel-rich areas within the cylinder can significantly reduce soot formation as well as high local temperatures resulting in low NOx formation. The present investigation is focused on the effects of advanced fuel injections and air path strategies as well as the effects of piston geometry and fuel spray angle on air-fuel homogeneity, combustion process and their impacts on the performance and emission of the engine. A Ricardo Hydra single-cylinder engine in combination with AVL Fire CFD software was used in this investigation. An experimental analysis was conducted to assess the combustion characteristics and emissions formation of the engine under various injection strategies such as different injection timing, quantity, ratio, dwell angles between injections with various exhaust valve opening times and exhaust back pressures. A quan- titative factor named Homogeneity Factor (HF) was employed in the CFD code in order to quantify the air-fuel mixing and understand how the air-fuel homogeneity within the cylinder can influence the combustion and emissions of the engine. The investigation concludes that multiple injection strategies have the potential to reduce diesel emissions while maintaining meaningful fuel economy. Split injection can be used to improve the air-fuel mixture locally and control temperature generation during the start of combustion. Increased air-fuel homogeneity results in fewer fuel-rich areas within the cylinder and contributes to the reduction of soot emission. Extending the pre-mixed combustion phase has a direct effect on the reduction of soot formation while NOx generation is highly dependent on the scale of the primary fuel injection event.

In this study, the Partially Premixed Compression Ignition (PPCI) combustion strategy in the high-speed, direct-injection diesel engine was investigated numerically by KIVA-3V code coupled with detailed chemistry, aiming to find the solution to meet the increasingly stringent emission regulations. Using split-injection, the parameters including injection timing, split-proportion, spray angle and injection pressures have been studied for their effects on combustion performance and emissions. The effects of swirl ratio, EGR rate and boost pressure are evaluated for improving the mixing and combustion of PPCI. The Homogeneity Factor (HF) was proposed for evaluating the quality of mixing and for quantitatively investigating the effects of injection parameters and in-cylinder air motion on mixture formation. Relationships between the quality of mixing and combustion performance and emissions were discussed using this factor. The results showed that HF had well revealed overall quality of mixture and the effects of operating parameters explicitly. Different EGR compositions with varied fractions of CO2 or H2O were applied in PPCI combustion in order to evaluate the effects of EGR constituents on the combustion performance and emissions. Moreover, the parametric study was conducted under a sweep of the 2nd injection timing and EGR rate, for the understanding of the effects of CO2 and water vapour in EGR at different operating modes. The speed range and load range for the PPCI diesel combustion using split injection was investigated. The results showed that the high level of EGR rate limited the implementation of PPCI combustion at high engine load, while the engine speed was limited by increased CO emissions. The application of high level cooled EGR had the potential for extending operating limits. The proposed Premixed Rate (PR) has revealed the correlations between the degree of premixed combustion and ignition delay, together with overall equivalence ratio. Good responses in fuel consumption have been shown with increase PR. And the significant reduce in PR indicated low degree of premixed at high engine load.

Knowledge of the pressure inside the combustion chamber of a gasoline engine would provide very useful information regarding the quality and consistency of combustion and allow significant improvements in its control, leading to improved efficiency and refinement. While measurement using incylinder pressure transducers is common in laboratory tests, their use in production engines is very limited due to cost and durability constraints. This thesis seeks to exploit the time series prediction capabilities of recurrent neural networks in order to build an inverse model accepting crankshaft kinematics or cylinder block vibrations as inputs for the reconstruction of in-cylinder pressures. Success in this endeavour would provide information to drive a real time combustion control strategy using only sensors already commonly installed on production engines. A reference data set was acquired from a prototype Ford in-line 3 cylinder direct injected, spark ignited gasoline engine of 1.125 litre swept volume. Data acquired concentrated on low speed (1000-2000 rev/min), low load (10-30 Nm brake torque) test conditions. The experimental work undertaken is described in detail, along with the signal processing requirements to treat the data prior to presentation to a neural network. The primary problem then addressed is the reliable, efficient training of a recurrent neural network to result in an inverse model capable of predicting cylinder pressures from data not seen during the training phase, this unseen data includes examples from speed and load ranges other than those in the training case. The specific recurrent network architecture investigated is the non-linear autoregressive with exogenous inputs (NARX) structure. Teacher forced training is investigated using the reference engine data set before a state of the art recurrent training method (Robust Adaptive Gradient Descent – RAGD) is implemented and the influence of the various parameters surrounding input vectors, network structure and training algorithm are investigated. Optimum parameters for data, structure and training algorithm are identified.

The Theory of Constraints (TOC) is a holistic management philosophy put forward by Eliyahu Goldratt in 1984. The thinking process and improvement tools discussed in this theory are mainly geared to manufacturing environments, however their applicability to service environments has also been shown for private professional service organizations. This study demonstrates that the steps and principles of the TOC can also be applied to non-profit services, such as the elective course registration process described in this thesis. In the case of non-profit organizations, the challenge is to define the performance measures of the TOC, which are Throughput, Inventory, and Operating Expense. This study offers a novel definition for these measurements, and using the principles of the TOC, it identifies the bottleneck and constraints of the elective course registration process. Using this analysis, the study then redesigns the system in order to improve the performance measures of the system.

South Africa is currently building MeerKAT, a 64 dish radio telescope array, as a pre-cursor for the proposed Square Kilometre Array (SKA). Both telescopes will be located at a remote site in the Karoo with a low level of Radio Frequency Interference (RFI). It is important to maintain a low level of RFI to ensure that MeerKAT has an unobstructed view of the universe across its bandwidth. The only way to effectively manage the environment is with a record of RFI around the telescope. The RFI management team on the MeerKAT site has multiple tools for monitoring RFI. There is a 7 dish radio telescope array called KAT7 which is used for bi-weekly RFI scans on the horizon. The team has two RFI trailers which provide a mobile spectrum and transient measurement system. They also have commercial handheld spectrum analysers. Most of these tools are only used sporadically during RFI measurement campaigns. None of the tools provided a continuous record of the environment and none of them perform automatic RFI detection. Here we design and implement an automatic, continuous RFI monitoring solution for MeerKAT. The monitor consists of an auxiliary antenna on site which continuously captures and stores radio spectra. The statistics of the spectra describe the radio frequency environment and identify potential RFI sources. All of the stored RFI data is accessible over the web. Users can view the data using interactive visualisations or download the raw data. The monitor thus provides a continuous record of the RF environment, automatically detects RFI and makes this information easily accessible. This RFI monitor functioned successfully for over a year with minimal human intervention. The monitor assisted RFI management on site during RFI campaigns. The data has proved to be accurate, the RFI detection algorithm shown to be effective and the web visualisations have been tested by MeerKAT engineers and astronomers and proven to be useful. The monitor represents a clear improvement over previous monitoring solutions used by MeerKAT and is an effective site management tool.

We demonstrate a path to hitherto unachievable differential photometric precisions from the ground, both in the optical and near-infrared (NIR), using custom-fabricated beam-shaping diffusers produced using specialized nanofabrication techniques. Such diffusers mold the focal plane image of a star into a broad and stable top-hat shape, minimizing photometric errors due to non-uniform pixel response, atmospheric seeing effects, imperfect guiding, and telescope-induced variable aberrations seen in defocusing. This PSF reshaping significantly increases the achievable dynamic range of our observations, increasing our observing efficiency and thus better averages over scintillation. Diffusers work in both collimated and converging beams. We present diffuser-assisted optical observations demonstrating 62(-16)(+26) ppm precision in 30 minute bins on a nearby bright star 16 Cygni A (V = 5.95) using the ARC 3.5 m telescope-within a factor of similar to 2 of Kepler's photometric precision on the same star. We also show a transit of WASP-85-Ab (V = 11.2) and TRES-3b (V = 12.4), where the residuals bin down to 180(-41)(+66) ppm in 30 minute bins for WASP-85-Ab-a factor of similar to 4 of the precision achieved by the K2 mission on this target-and to 101 ppm for TRES-3b. In the NIR, where diffusers may provide even more significant improvements over the current state of the art, our preliminary tests demonstrated 137(-36)(+64) ppm precision for a K-S = 10.8 star on the 200 inch. Hale Telescope. These photometric precisions match or surpass the expected photometric precisions of TESS for the same magnitude range. This technology is inexpensive, scalable, easily adaptable, and can have an important and immediate impact on the observations of transits and secondary eclipses of exoplanets.

No description available.

This study was motivated by a need to better understand the sprays that can develop when oil leaks occur in gas turbine engines. Current gas turbine engines incorporate an extensive network of oil distribution pipes which deliver lubrication oil to bearings and seals at various locations across the engine. Parts of the oil pipe network are situated in hot, high pressure engine cavities where an oil leak, from a fractured pipe or leaking seal, could ignite and lead to an engine fire. Oil leaks in gas turbine engines create liquid injection in cross-airstream situations, a subject which has been widely studied for combustion systems. However, previous studies are almost exclusively based on circular nozzle geometries. For a fractured oil pipe, the geometry through which the oil leaks approximates to a slot shape rather than a circular nozzle. Sprays which develop in cross-airstreams are most sensitive to the parameters of Weber number (Weg eq) and momentum flux ratio (q). A wide range for these parameters are considered to be possible in engine oil leak scenarios because of the variety of crack dimensions possible and range of airflow conditions across the different sections of the engine; from zero to in excess of We g eq = 4000 and q = 300 could be possible in extreme cases. The aim of this study was to generate and then characterise sprays in representative conditions. The main focus was the characterisation of the droplets which formed in the sprays, with the key objective of providing validation data for CFD codes. Droplet characterisation was performed using a phase Doppler particle analysis system. High speed video as well as pulsed laser sheet digital imaging were also used in the study to provide insight into upstream features of the spray field. A 0.5 x 5.38 mm slot shaped nozzle geometry was used in two orientations; perpendicular alignment ↓↓⦶ and parallel alignment ↓↓⦶ . Water was injected into a cross-airstream over a twelve point test matrix with momentum flux ratios (q) values within the range of 4 ≳ q ≳ 32 and Weber number (We g eq) values within the range of 300 ≳ We g eq ≳ 1600. The position of the spray was highly dependent on slot nozzle orientation. The spray was considerably further offset from the nozzle injection wall in parallel alignment ↓↓⦶ , compared to the perpendicular alignment ↓↓⦶. However, the centre-line distribution of Arithmetic Mean Diameter (AMD) was similar for both orientations, albeit offset further from the injection wall for the parallel slot nozzle. The underlying structure of droplet size distribution was consistent with results for sprays from circular nozzles. At low liquid injection pressures the sprays produced by the perpendicular aligned slot ↓↓⦶ exhibited impingement, producing large droplets in the near wall region. Where impingement was not present, the data showed that AMD was not significantly influenced by the orientation of the slot nozzle; with all tests generating results in the range of 16 μm ≳ AMD ≳ 80 μm.

Current gas turbine technology for power generation is generally optimised for natural gas. On the basis of current instabilities in natural gas price and supply, the use of alternative fuels, such as syngas, has recently gained high interest. Due to the different thermodynamic properties of syngas compared to natural gas the behaviour of existing gas turbine components may significantly change. From practical and economic points of view, it is generally considered that in order to meet the new fuel properties, the main effort should be put on the adaptation of conventional gas turbines in integrated gasification combined cycle (IGCC) plants rather than producing a new generation of gas turbine designs from scratch. In addition to the requirement of new combustion technologies, main critical issues are represented by the reduction of compressor surge margin and turbine blade overheating. Solutions might include thermodynamic cycle as well as turbine geometry modifications. The latter would be preferred in terms of power plant performance. The main aim of this thesis is to explore suitable solutions to be applied to gas turbine compressors in order to accommodate syngas combustion. Among others, the use of variable stator vanes (VSVs) and blade radial stacking line modifications are considered. These are investigated on reference geometries available in the public domain. A baseline compressor geometry representative of a conventional heavy-duty gas turbine fueled with natural gas is generated and modified according to the understating gained during this study. The re-designed machine is a result of the application of stator vanes re-staggering in the front stages and blade sweep in the rear stages in order to cope with compressor air supply control and critical flow separation regions respectively. The obtained results show that efficient and stable operation during power modulation can be achieved, while reducing the need of other modifications to the combined cycle plant. It was therefore concluded that the proposed option can be considered a viable option to satisfy some important technical and economic constraints imposed by the integration of an existing gas turbine within an IGCC plant.

Information and Communication Technologies (ICTs) in general, and mobile phones in particular, have demonstrated positive outcomes in the various social transformation and human development dimensions. As a result, many researchers have focused on ICTs innovations targeting the poor. Among the poor are the low-skilled day-labourers who belong to the Day-labour Market (DLM), which is also made up of employers, job-brokers and intermediary organisations. The DLMs’ main activities involve a great deal of travelling in search of jobs by workers and a search for workers by employers. These travels place heavy economic pressure on the day-labourers, hence reducing their net earnings while they struggle with extreme poverty. The first objective of our study was to find out how and which ICT interventions can be used to alleviate the challenges faced by the DLM stakeholders. The nature of our problem resembled studies that use ICTs to reduce travel distance. Such studies fall under subjects such as teleactivities and teleworking/telecommuting, and advocate for prospects of working anywhere anytime. These studies have not received much research attention in the developing world. They have mainly been done in the developed world, and mostly on white-collar workers and organisations. This brought about our second objective: to find out whether the ICT interventions for the DLM could be studied under teleworking/telecommuting and whether the telecommuting benefits can be realised for the blue-collar workers. Our research methodology was Action Research applying three case studies. We used participant observation and both structured and unstructured interviews for qualitative data collection and questionnaires to collect quantitative data. Contextual inquiry, prototyping and technology probe was applied as our design technique. The prototypes were evaluated in-situ to assess usability and uncover user experience. We mainly employed qualitative data analysis, but where appropriate, triangulated with quantitative data analysis. The research outcomes were divided into three categories: (1) the knowledge on the DLM characteristics which depicted different forms of the DLM and shaped our design process, (2) the DLM software designs tested as prototype applications and software artefacts deployed for use by the DLM and (3) the meaning and the state of telecommuting/teleworking before and after our experiments in the DLM. In the first category, appreciating the challenges faced by our primary target users, the day-labourers, helped shape our designs and our inquiry to include intermediation. With regard to the prototype applications, they included the remote mobile applications and the web-based server side software systems. Although most of these applications where meant for proof of concept, some of them ended up being implemented as fully functional systems. Finally, in the third finding, travel reduction using ICTs (mainly the mobile phones) had been practised by some of the DLM stakeholders even before the commencement of our study. After our intervention, we discovered that implementing telecommuting/teleworking within the DLM may be possible, but with a raft of redefinitions and changes in technology innovations. We therefore identified factors to consider when thinking of implementing telecommuting among blue-collar employees, organisations and employers.