PhD Theses (FET)PhD theses approved by the Faculty of Engineering and Technologyhttp://hdl.handle.net/10311/14182024-03-29T06:47:30Z2024-03-29T06:47:30ZEffect of fruit maturity on yield and quality of seed oil and biodiesel of jatropha curcas found in BotswanaJonas, Mbakohttp://hdl.handle.net/10311/24502022-07-27T00:01:21Z2020-03-01T00:00:00ZEffect of fruit maturity on yield and quality of seed oil and biodiesel of jatropha curcas found in Botswana
Jonas, Mbako
This study was undertaken to investigate the influence of fruit maturity stage on yield and quality parameters of Jatropha curcas seed oil and derived biodiesel. The influence of fruit maturity on phorbol ester content (toxicity) in Jatropha curcas seed oil and seed cake was also investigated. Jatropha curcas (hereafter referred to as Jatropha) seeds used in this study were harvested from Jatropha plants adapted to Botswana climatic conditions. Biodiesel has received great attention as one of the renewable and clean burning fuels. This is so in an effort to reduce greenhouse gas emissions. Jatropha seed oil is considered as one of highly promising feedstock for biodiesel production. In order to meet the high demand of large scale biodiesel production, increment of seed oil output from Jatropha seeds is necessary. Harvesting Jatropha seeds/fruits when seed oil content is maximum is one of the factors than can help increase seed oil output from Jatropha seeds. Results from this investigation have shown that harvesting Jatropha fruits when they are yellow increases seed oil output by 6 to 9% as compared to harvesting the fruits on their final maturity stage (brown dry). Thus harvesting Jatropha seeds when they are yellow may increase feedstock (seed oil) availability in biodiesel production. The maximum oil content in Jatropha
seeds is attained at yellow maturity stage, and these are 30.1%, 30.6%, 26.2% and 27.9% for Jatropha seeds harvested from Thamaga, Mmadinare, Shashe and Maun areas, respectively. It is pertinent to mention that accumulation of seed oil in Jatropha seeds harvested from the aforementioned geographical locations follow a similar trend. Seed oil in Jatropha seeds increases continuously during fruit maturation and reaches peak level when the fruit turns yellow, thereafter it starts to decline until the final maturity stage (brown dry). The quality of both feedstock and biodiesel are of paramount importance, and Jatropha seed oil and derived biodiesel are no exception. Results from this investigation have revealed that fruit maturity have an impact on the quality of the seed oil hence the derived biodiesel. Fruit maturity influences some quality parameters of the seed oil. For instance, Free Fatty Acids (FFA) content in Jatropha seed oil varies with fruit maturity. Free fatty acid content in Jatropha seed oil increases continuously with seed maturity and this applies for all feedstock collected from all the geographical locations under investigation. These FFA content in Jatropha seed oil ranges from 0.2 to 0.7% for the four different fruit maturity stages, namely green yellow, yellow, yellow brown and brown dry. Seeds from
Mmadinare area (21.8811oS latitude, 27.7514oE longitude) recorded relatively highest FFA content from brown dry fruits (0.75%) whereas seeds from Thamaga area (24.72° S latitude, 25.53°
ii
E longitude) recorded relatively lowest FFA content (0.44%). Fatty acid composition of Jatropha seed oil also varies with fruit maturity. Fractional composition of unsaturated fatty acids, which makes up more than 70% of the total lipid, declines continuously with each consecutive maturity stage. As Jatropha fruits matures from green yellow to brown dry, the fractional composition of linoleic acid decrease by 8 to 9%. There is a logical relationship between the trend in fatty acid composition in Jatropha seed oil and seed oil content during fruit maturation. Based on this trend of unsaturated fatty acids in Jatropha seed oil, particularly linoleic and oleic acid, it can be concluded that reduction of seed oil content during seed desiccation stage (from yellow brown to brown dry) is a result of breakdown of some of the unsaturated fatty acids. The decline in fractional composition of unsaturated fatty acids in Jatropha seed oil during fruit maturation causes the cetane number of derived biodiesel to increase continuously with each successive maturity stage. The Peroxide Value (PV) of both Jatropha seed oil and derived biodiesel increase gradually and linearly with fruit maturity. The PV of seed oils from all the investigated geographical locations in Botswana (Mmadinare, Thamaga, Shashe and Maun) follow the same trend and in the same range. Effect of fruit maturity on other quality parameters such as cloud point, pour point, density, viscosity and calorific value (energy content) is minimal. Jatropha seeds from selected geographical locations in Botswana contain some levels of Phorbol Esters (PE) hence toxic. The PEs content vary with fruit maturity. Phorbol ester content in Jatropha seed oil ranges from 3.4 to 4.2mg/g whereas in seed cake ranges from 1.7 to 2.0mg/g during the four different fruit maturity stages. Jatropha seed oil and seed cake from yellow brown maturity stage are relatively the most toxic since they contain highest concentration of PEs.
A dissertation submitted to the Dept. of Industrial Design and Technology, Faculty of Engineering and Technology, University of Botswana in partial fulfillment of the requirement of the degree of Doctor of Philosophy in Engineering. Citation: Jonas, M. (2020) Effect of fruit maturity on yield and quality of seed oil and biodiesel of jatropha curcas found in Botswana, University of Botswana
2020-03-01T00:00:00ZCharacteristic influence of thermo-mechanical stresses leading to premature failure of compressor turbine blades of short-haul aircraft fleetNgoret, Joshua Kimtaihttp://hdl.handle.net/10311/23992022-04-22T00:05:00Z2019-02-26T00:00:00ZCharacteristic influence of thermo-mechanical stresses leading to premature failure of compressor turbine blades of short-haul aircraft fleet
Ngoret, Joshua Kimtai
Short-haul aircrafts play an integral role in air transport network, facilitating; passenger and cargo transport, security drills, ambulance services, disaster, wildlife and environment management, tourism amongst others. Unlike medium and long-hauls, these aircrafts are missioned to fly for under 3 hours and distances not exceeding 2000 km. As a result of short but, voluminous flight turnovers, changes in power settings, starts and stops; the compressor turbine (CT) blades of the engines are subjected to intense cyclic thermo-mechanical stresses.
Compressor turbine blades are specially profiled aerodynamic engine components specially designed to extract energy from high-temperature, high-pressure gases produced by the combustors. Due to severity of their operational environment, the CT blades degrade over time and often catastrophically fail without warning. In this regard, monitoring of CT blade life is crucial to ensure their proper health in service.
The current techniques employed to investigate the life of CT blades only inform of failure after exposure to service with scanty information on the numerous prematurely occurring failures. Consequently, accounting for CT blade life still poses a great challenge to air operators. This research therefore probed characteristic influence of thermo-mechanical stresses leading to premature failure of high pressure (HP), PT6A-114A engine CT blades from an assimilative approach. The prematurely retired HP, CT blades were collected from Vector Aerospace Kenya Limited after being in service for only 6378 creep-fatigue hours contrary to 10000 creep-fatigue hours preset by the manufacturer.
The CT blade was modeled for thermo-mechanical degradation in an environment that mimics the operational conditions to determine service life and resulting damage using commercial ANSYS tools version 15.0. A detailed microstructural and metallographic characterization was then performed using x-ray florescence (XRF), x-ray diffraction (XRD) and energy dispersive spectroscope-scanning electron microscopy (EDS-SEM) on the
protective coating and the substrate material. Mechanical testing was ultimately executed to ascertain the micro hardness and residual strength at time of retire from service.
The modeling results revealed that the tip of the CT blade had been rigorously attacked by exposure to heat as compared to the airfoil and the base. Notwithstanding this, it was noted that the CT blade could have served for another 1.44% more of the time it was in service, being exploited in the transient regime. The XRF results affirmed the existence of the bulk constituent elements that matched the manufacturers’ specification. The XRD analyses enabled positive identification of the resultant compounds which constituted the protective coating and the substrate material. The EDS-SEM results established that the protective coating of the tips was more attacked compared to the airfoils and the bases. As such, the substrate material degraded from evolution of creep and fatigue. The pores at the bases of the CT blades were found not influence distribution of uniform cuboidal phase at the bases in comparison the rafted tips and airfoils. This confirmed that degradation of the substrate material occurred as a result of creep and fatigue and not from manufacturing defects. Though micro hardness testing indicated that the material was still of high strength, continued safe service was not warrantied.
From this research, a robust assimilative approach was adopted for investigating life of CT blades enabling determination of instantaneous material status, magnitude of damage and remaining useful life (RUL). This work will assist air operators improve flight safety, enhance availability of aircrafts for operations while planning for maintenance will be made easier.
Premature failure of the CT blades can further be averted by; adhering to the engine’s operation limits, avoiding long and overexploitation of the engine and sticking to preset flight environments. In a move to improve heat, oxidation and corrosion resistance of the protective coating, inclusion of rare earth element such as yttrium, cesium and lanthanum would be noble. The substrate material could similarly be improved by addition of refractory elements such as ruthenium, iridium and rhenium in the composition of Inconel 713LC.
A dissertation submitted to the Dept. of Mechanical Engineering, Faculty of Engineering and Technology, University of Botswana in partial fulfillment of the requirement of the degree of Doctor of Philosophy in Engineering. Citation: Ngoret, J.K. (2019) Characteristic influence of thermo-mechanical stresses leading to premature failure of compressor turbine blades of short-haul aircraft fleet, University of Botswana.
2019-02-26T00:00:00ZAdvanced d-partitioning analysis and design of robust control systemsYanev, Kamenhttp://hdl.handle.net/10311/19792019-11-13T00:01:33Z2015-01-01T00:00:00ZAdvanced d-partitioning analysis and design of robust control systems
Yanev, Kamen
There is a need for control systems to be robust or insensitive to parameter variations, disturbances and noise. In the process of design and analysis of a robust control system, it is essential to determine the regions of stability, corresponding to the variation of one or more system parameters. Most of the research and development efforts on stability analysis of systems with variable parameters and robust control design have focused on very specific and limited cases. There is a shortage of a user friendly universal analysis tool or procedure that can show the variable parameters margins, their interaction and the robust assessment for different types of control systems. Also, there is a growing need for a comprehensive technique of a robust
controller design that can lead to system insensitivity for any of the parameters variations, disturbances and noise within specific limits.
A dissertation submitted to the Dept. of Electrical Engineering, Faculty of Engineering and Technology, University of Botswana in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Engineering. Yanev, K. (2015) Advanced d-partitioning analysis and design of robust control systems, University of Botswana.
2015-01-01T00:00:00ZClimatological droughts and their implications on water resources and agricultural production in semiarid regions: the case of BotswanaByakatonda, Jimmyhttp://hdl.handle.net/10311/18392018-12-05T00:03:04Z2018-09-01T00:00:00ZClimatological droughts and their implications on water resources and agricultural production in semiarid regions: the case of Botswana
Byakatonda, Jimmy
In recent years, the frequency of droughts have been increasing due to climate anomalies mostly attributed to climate variability and high water demand brought about by changing lifestyle and urban migration. Although several drought indices have been identified to characterise droughts in various literature and some even recommended by the World Meteorological Organisation (WMO), a more comprehensive index is the one known as Standardised Precipitation and Evapotranspiration Index (SPEI), as an extension of the well-known Standardised Precipitation Index (SPI) to include evapotranspiration in the water balance. Droughts have been described in this research using SPEI values to provide overall reasonable characteristics of different categories of drought at various timescales of 1-, 3-, 6-, 12-, 18- and 24-months. Further to make water resources management meaningful, it requires exploration of the association between SPEI and hydrological droughts represented by Standardised Flow Index (SFI). Climate anomalies leading to climate variability and frequent droughts have been associated with El Niño Southern Oscillation (ENSO) across southern Africa. These anomalies also are attributed to shifts in hydroclimatological factors. Hence it is necessary to carry out in-depth analysis of the onset and cessation of rainfall which otherwise impact agricultural production and food security of the region. These climate anomalies are being felt across the globe but vary to a large extent from one geographical location to another. For this reason, impacts from one location cannot be extrapolated to another. It is therefore necessary to develop location specific mitigation measures towards impacts of climate variability and change. It is on this premise that Botswana, located in the semiarid subtropics and relying mainly on surface water stored in reservoirs, is selected as a case study. Moreover 80% of Botswana’s population is engaged in rainfed agriculture as a source of livelihood. In order to arrive at futuristic status of rain onset and cessation dates, Standardised Flow Index (SFI) and cereal yields, an attempt has been made to use artificial intelligence framework in the form of Nonlinear Autoregressive with Exogenous input (NARX) Neural Network (NN) modelto make five (5) years ahead forecasts of the above climatic factors. This research therefore attempts to study the following using meteorological data from 14 synoptic stations for a period 1960-2016: (i) Climatic behavior under ENSO influence including trends in meteorological variables, (ii) determination of onset and cessation of rainfall including dry spell frequency analysis, (iii) determination of SPEI and SFI for climatic and hydrological drought characterisation respectively (iv) determination of the association between climatic indices and cereal yields and (v) providing predictions of stream flow drought in the form of SFI, cereal yields, onset and cessation of rain dates.
In order to achieve the above objectives, this research carried out homogeneity tests and trend analysis using four (4) absolute tests (Standard Normal Homogeneity test, Buishand test, Pettit test, Von Nuemann test) and Man-Kendall test. Results indicate that rainfall time series are fully homogeneous with minimum and maximum temperature showing some years of intervention (i.e. change points). These years of intervention closely followed patterns of ENSO events. Trends also indicate a regionalised decrease in rainfall by 14.7% coupled with 2% increase in temperature across Botswana. The influence of ENSO on local climate was also investigated by determining the degree of association between climatic variables and Sea Surface Temperatures (SSTs) on one hand and Southern Oscillation Index (SOI) on the other hand. Results show negative correlations between SST and rainfall while positive correlations were observed between rainfall and SOI following the ENSO phenomenon. To further understand the influence of summer rainfall on agriculture, seasonal characteristics in the form of dry spell frequency, number of rainy days, onset and cessation of rain were investigated. From these investigations, results show the earliest onset occurring on 30th/November in the northeast while the latest on 11th/January in the southwest. The cessation of rain dates took an opposite spatial trend with shorter rain season observed in the southwest. Shakawe, Pandamatenga and Kasane were found to have length of the rain season (LRS) of more than 100 days making them suitable for medium maturing cereals. Since droughts have been identified as a feature of climate variability, their spatiotemporal variability was explored. Botswana was found to be more vulnerable to moderate droughts which showed a high degree of association with ENSO during summer season. A common timescale of 15-months was identified to be suitable for drought monitoring across the study area. It was also observed that climatic droughts take 6 and 7 months to propagate into hydrological droughts in the Okavango and Limpopo river basins respectively. The implication of climate variability on agriculture was further investigated by determining the influence of climatic indices, LRS and ENSO on cereal yields of maize and sorghum. ENSO was found to have the greatest influence on cereal yield accounting for 85% and 78% in maize and sorghum yield variations respectively. Predictions from the three NARX-NN models reveal a likelihood of a shift in the rain season and higher variability in SFI in the near future. Cereal yield projections for the next 5 years reveal a possible yield decline in both maize and sorghum by 52 kg/ha and 126 kg/ha respectively. This research has demonstrated that Botswana’s climate is closely associated with ENSO leading to more uncertainty in rainfall and rainfed agriculture. It is envisaged that information generated from this research will enhance agriculture and water resources planning and management especially in semiarid regions where adaptation to climate variability and change is still a challenge.
A dissertation submitted to the Dept. of Civil Engineering, Faculty of Engineering and Technology, University of Botswana in partial fulfilment of the requirement of the Degree of Doctor of Philosophy of Engineering: Civil Engineering. Citation: Byakatonda, J. (2018) Climatological droughts and their implications on water resources and agricultural production in semiarid regions: the case of Botswana, University of Botswana.
2018-09-01T00:00:00Z