Browsing by Author "Yates, Andrew"
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- 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 AccessAssessment of disparate strategies for octane prediction(2009) Viljoen, Carl; Möller, Klaus; Yates, AndrewOctane quality is a key factor in determining the profitability in a modern refinery. The final commercial product is defined by the combined blend of various gasoline component streams which are produced from different units within the refinery. The accurate prediction of the octane numbers of these blends enables the economic optimization of the production process. Currently, empirical octane models are used exclusively for this purpose. Octane is a measure of the spontaneous autoignition propensity of a fuel-air mixture and it is quantified using a specific engine-based test method. This research project was founded on the premise that an improved octane prediction model could be harvested from building blocks that included a fundamental understanding of autoignition, appropriate choices of autoignition models and an engine model. This objective was pursued in this work by investigating detailed and reduced kinetic mechanisms for the oxidation of selected fuel molecules using various modeling techniques. Empirical octane models and semi-chemical models of autoignition were also investigated. All of these methodologies were assessed as possible strategies towards octane prediction. In this study it was observed that both detailed and highly reduced kinetic models could describe the oxidation behaviour of pure fuel components and predict their subsequent ignition delays.
- ItemOpen AccessA CFD investigation of cavitation and associated deposit formation in modern diesel fuel injectors(2007) Pelteret, Jean-Paul; Yates, AndrewReducing the pollution of new vehicles has become a priority to vehicle manufacturers, particularly given the fact that emissions requirements that must be achieved by diesel vehicles are becoming more stringent. Modem fuel injectors on common-rail diesel vehicles use very high rail pressures to aid atomisation and increase combustion efficiency. However, associated with the high injections pressures is the issue of nozzle cavitation. Cavitation leads to pockets of diesel vapour forming in the nozzle and it is hypothesised that this causes the formation of deposits in the nozzle. It is also suggested that the collapse of the cavitation vapour space results in extremely high temperatures within the nozzle, resulting in thermal cracking of the fuel and eventually the formation of carbon deposits. A two-dimensional axisymmetric CFD model with dimensions representative of an injector nozzle was constructed using a fully structured grid.
- ItemOpen AccessCharacterisation of the autoignition delay behaviour of n-heptane in the IQT combustion bomb using CFD modelling(2007) Metcalf, Owen J; Swarts, André; Yates, Andrew; Meyer, ChrisWhen n-heptane was tested in the IQT device over a range of temperatures and pressures, the measured autoignition delay did not correlate with the chemical autoignition delay associated with a stoichiometric, homogenous mixture as predicted by detailed chemical kinetic models. ... This project involved an investigation to study and reconcile this discrepancy, using computational fluid dynamic (CFD) techniques to explore the physical conditions prevailing in the IQT device. Specifically, CFD was used to model fuel injection into the IQT, this allowed a more accurate description of the fuel/air ratio and temperature history of the fuel inside the IQT combustion chamber than an assumption of global values. An empirical description of autoignition delay, developed by Yates et al. (2004), was then coupled to the CFD code: enabling the model to determine the progress of the fuel/air mixture to autoignition.
- ItemOpen AccessCombustion characteristics of synthetic gasoline in modern charge boosted GDI Engines(2015) Rockstroh, Manuel Tobias; Yates, Andrew; Floweday, GarethSasols synthetically derived gasoline blending components have traditionally been combined predominantly according to process economics to formulate commercial fuel blends that meet in-house fit-for-purpose requirements and the legislated fuel specifications in South Africa. In this study the potential for optimisation of a fuel blend using full boiling range synthetic blending components to enhance its performance in a modern charge boosted gasoline direct injection engine was investigated. An evaluation of detailed analytical fuel chemistry data was conducted followed by laminar ame speed experiments in a constant-volume combustion bomb apparatus in order to characterise the combustion behaviour of the blending components according to their characteristic chemical properties. A matrix of test fuels was established by splash blending the synthetic components with a commercial synthetic reference fuel. The performance of the fuels was subsequently evaluated using a modern, charge boosted, single cylinder GDI research engine. While the engine operation was verified to be in the negative-K region using model fuel components, anomalies in de fining the K-value using the synthetic blends were discovered. A fuel blending model was composed to allow prediction of linear and non-linear fuel properties of user de fined synthetic blend ratios. By integrating an engine performance test fuel scoring system, the model could be used to de fine optimal fuel blends through selection of a desired performance criterion while constraining the optimisation process to adhere to the national legislated gasoline specifications. Four final fuel blends were optimised according to best power output, gravimetric specific fuel consumption, volumetric specific fuel consumption and specific legislated emissions. A fifth blend was optimised for highest power output with no regard for fuel property specifications other than Reid vapour pressure. The performance of the optimised blends was evaluated on the test engine and the results indicated the potential to positively affect the performance characteristics of a synthetic fuel blend for use in a modern spark ignition engine. This study demonstrates a methodology for optimisation of a synthetic fuel to user-selected performance criteria and it is believed that this work represents a novel and valuable contribution to this field.
- ItemOpen AccessThe design of a combustion test facility for synthetic jet fuel research(2009) Burger, Victor; Yates, AndrewWith the relatively recent emergence of non-petroleum-derived aviation gas turbine fuels, it was appropriate to review the complete list of jet-fuel specifications to assess whether they were sufficiently robust to ensure fit-forpurpose within the new paradigm. Although this has been an industry-wide endeavour, there were some particular research areas that were identified for special in-house attention by Sasol, as the world’s first commercial producer of approved and certified semi-synthetic and fully synthetic jet fuel. The project described in this report formed part of one of these research areas, which pertained to ignition and combustion stability in gas turbines and the role played by various fuel attributes and properties. The project was conducted at the Sasol Advance Fuels Laboratory based at the University of Cape Town. The project entailed the design and construction of a combustion test facility for conducting synthetic jet fuel research. The primary intended focus of the facility was the investigation of ignition and combustion stability behaviour of various test fuels, ranging from commercial jet fuel to single component model fuels. The scope of the project also included the design of both a basic homogeneous and a heterogeneous combustor which served to verify the facility’s suitability for investigating the influence of fuel chemistry and combustor inlet conditions on ignition and combustion stability limits.
- ItemOpen AccessThe design of a mechanical driver(1988) Pryor, Paul John; Yates, AndrewThis report describes the design of a mechanical driver for use in the testing of vehicles on a rolling road dynomometer by the Energy Research Institute (ERI) at the University of Cape Town. Many vehicle tests involve using driving cycles which tend to be long and repetitive. Consequently, the driver finds it boring and difficult to repeat a specific dr1ving pattern within the required tolerance. One solution to this is the use of a mechanical driver, where the vehicle being tested is "driven" mechanically and controlled by a computer. The main objective of this project was to design a system that would return accurate and repeatable results when testing vehicles for fuel consumption, emissions, speeds etc.
- ItemOpen AccessThe design of a prototype Otto-Atkinson engine and evaluation of the part load fuel efficiency(1992) Van Binsbergen, Peter J; Yates, AndrewThis thesis is an investigation into the application of the hybrid Otto-Atkinson cycle, as a means of improving the part load fuel efficiency of spark-ignition engines. The primary objective of this thesis was to investigate the technical feasibility of the modified Atkinson cycle as a spark-ignition engine concept and thus to quantify the associated potential for greater fuel efficiency. The modified Atkinson cycle is a hybrid cycle which approximates the Otto cycle at full load but tends to emulate the Atkinson cycle at part load, and therefore it is referred to as the Otto-Atkinson cycle. In order to fulfil this objective, a single cylinder engine which operated on the Otto-Atkinson cycle, was designed and constructed. This unusual cycle was achieved by a crank linkage which allowed the power output to be controlled by varying the inlet and compression strokes rather than by the more conventional method of throttling the induced fuel-air mixture. Thus the pumping losses associated with throttled part-load operation are eliminated. Furthermore, the expansion stroke is always greater than the compression stroke, the difference being greatest at part loads. This results in a cycle which approximates the Atkinson cycle for part-load operation. A simplified thermodynamic simulation of the cycle was formulated. Theoretical predictions were made based on this simulation.
- ItemOpen AccessDesign, build and commission a shock tube apparatus for autoignition research(2009) Downey, Michael; Yates, Andrew; Cloete, TrevorIncludes abstract. Includes bibliographical references (p. 65-67).
- ItemOpen AccessDetermination of the effectiveness of a Hot Tube igniter for initiating HCCI combustion(2006) Rabe, Tiaan; Swarts, André; Yates, AndrewHomogeneous Charge Compression Ignition (HCCI) is a new internal combustion system that promises high efficiency and dramatically reduced nitrous oxide (NOJ and particulate matter (PM) emissions when compared to current spark ignition (SI) and compression ignition (CI) engine technologies. In its simplest form, HCCI can be described as lean autoignition of a homogeneous fuel/air mixture that occurs without a flame front. HCCI can in theory be achieved using almost any fuel, provided that it evaporates readily and has a short enough ignition delay that it can be made to autoignite under the conditions typically found in an IC engine. Basically HCCI incorporates the best features of a SI (petrol) and CI (diesel) engine. Like in a SI engine, the fuel and air in the cylinder is allowed to be well mixed before the onset of combustion which promotes cleaner burnng (Low PM) and like in a CI engine the engine is operated overall fuel-lean and therefore has no throttling losses and near zero NOx emissions. The mixture is also compression ignited in the same way as in a CI engine. This causes combustion to occur simultaneously throughout the combustion chamber and thus no flame front is present.
- ItemOpen AccessDevelopment of a biomass gasification pre-treatment system(2013) Randall, Warren; Yates, AndrewThis project was focussed on drying and feeding timber-yard waste for a gasifier and the assessment of the feedstock drying on the gasifier performance. This required a thermodynamic model to be developed in order to assess the effect of drying as was highlighted in the literature survey. A heat exchanger model was also developed which formed the basis for the design of the drier. The project aim was to develop a reliable feed process for a lab-scale gasifier that was able to dry the proposed feedstock to below 10%. The plant was to be as far as possible, automated, with minimal maintenance requirements.
- ItemOpen AccessThe development of a prototype external heat engine based on the Ericsson cycle(2000) Hussey, Joseph; Yates, AndrewThe aim of this thesis was to develop a prototype external heat engine based on the Ericsson cycle, as an alternative to the internal combustion engine, to be used as a small-scale power source for rural Africa. Subsequently test and evaluate its viability and potential to fulfil the requirements of such an application. Despite the wide range of possible prime movers, it appears there is still a need for a simple, low-tech, low-output power plant for developing countries. This created an opportunity to revisit the origins of basic engine design in order to seek an alternative solution to the modern internal combustion engine. The hot air or external heat engine developed in the l800's provides an attractive alternative as it has a number of advantages over the modem internal combustion engine. A hot air engine is a cyclical heat engine that uses an external heat source, heat exchangers, pistons and a gaseous working fluid contained within the engine to convert heat to mechanical work by volumetric expansion. The project looked at old and new engines in an attempt to capture the best of both. Two experimental engines were constructed during the course of this project, the first engine was built to provide insight into the functioning of an unconventional external heat engine and to test the validity of theoretical predictions made using a thermodynamic computer model. This engine was designed to function off a cycle consisting of a polytropic compression, a polytropic expansion with heat addition and a constant volume heat rejection process, achieved using a two-stroke principal to exchange the hot exhaust gas with cold recharge gas. Based on experience gained from this model, the second generation engine was designed to circumvent the problems experienced with the first engine. It functioned off a near Ericsson cycle, with the compression and expansion truncated for practical purposes and valve control being achieved with solenoid valves controlled by a computer. A thermodynamic computer model similar to the one used for the first engine was employed to optimise the design of this engine. Experimental investigations were carried out with the Ericsson engine to examine how closely the actual cycle resembled that predicted by the thermodynamic model and to determine engine performance. The power and mean effective pressure produced by the engine were determined and compared with friction data. Hence the potential of this engine to meet the criteria necessary to function as a small-scale rural power source was judged and resultant conclusions as to the engines feasibility were drawn. The actual pressure-volume diagrams obtained closely conformed to the theoretical expectations for the cycle and the truncated Ericsson cycle functioned sufficiently well. However, the friction in the system was too high a percentage of the total engine output and therefore the engine was unable to operate unaided. Although the hot air engine has the potential to provide cheap power efficiently, in practice these engines need to be highly pressurised and run at temperatures close to their material limit in order to obtain useful work from them. Therefore, although with the use of low friction seals and high pressurisation the engine could potentially produce the 5kW design target, due to the complexity these efforts would add to the engine it is recommended that other options be explored for rural power generation in Africa.
- ItemOpen AccessDevelopment of an electronic control unit for the T63 gas turbine(2014) Robertson, Leanne; Yates, Andrew; Burger, VictorFundamental research has been undertaken at the SASOL Advanced Fuels Laboratory to investigate the effects of the chemistry and physical properties of both conventional and synthetic jet fuels on threshold combustion. This research was undertaken using a purpose built low pressure continuous combustion test facility. Researchers at the laboratory now wish to examine these effects on an aviation gas turbine in service for which “off-map” scheduling of fuel to the engine would be required. A two phase project was thus proposed to develop this capability; the work of this thesis embodies Phase I of that project.
- ItemOpen AccessThe development of an enhanced autoignition sub-model for use in CFD combustion simulations(2006) Cox, Ryan; Yates, Andrew; Meyer, ChrisWith the ever increasing pressure to manufacture more efficient engines that produce lowerexhaust emissions, there is a corresponding need for a greater understanding of the combustion processes within these engines. Specifically, it is the interaction between the fuel and the engine that represents one of the greatest research challenges. As the systemsbecome increasingly sophisticated, the fuel companies are experiencing an increased demand for high specification fuels with tighter tolerances. Now, more than ever, the fueldesign and engine design need to work as one integrated system to meet these expectations. In this project, an attempt was made to produce a computationally efficient mathematical model of the fuel ignition characteristics that could be used in a CFD simulation of an internal combustion engine or any other generic combustion system. The validation of the model provided useful insight into the need for good quality experimental data for the fuels of interest, highlighting the need for pure ignition delay curves without engine effects, which is a limitation of many of the current models. When modelling a single fuel droplet, the importance of the temperature profile in the vicinity of the evaporating particle was clearly illustrated, as well as the variation in the local air/fuel ratio. These effects were shown to playoff against each other - the centre of the droplet being coldest and hence yielding a longer ignition delay while, at the same time, the high equivalence ratio near the centre had the effect of shortening the ignition delay. Using a simple, two dimensional model and using n-Heptane as the fuel, a realistic prediction of the overall ignition delay was obtained. More importantly, the critical zone of the initial auto ignition was identified. These simulations show how this model can be used in an environment that exhibits both gradients of temperature and equivalence ratio. It also shows the importance of including such in-homogeneities when creating engine models that include fuel injection. This approach can easily be extended into any type of combustion simulation involving fuel droplets where local temperature and equivalence ratios have a controlling effect on the ignition. Some recommendations for future work include the modelling of the IQT™ with the possibility of reconciling the ignition delay of the IQT™ and the cetane test.
- ItemOpen AccessThe effects of fuel evaporation on engine knock(1993) Moran, Derek Paul; Yates, AndrewIt has been known for a long time that alcohol-gasoline blended fuels exhibit an unexplained tendency to knock at high engine speeds; a characteristic that is not generally experienced with conventional gasoline. Early studies showed that the problem could be linked to an unusually high temperature sensitivity exhibited by the blended fuels, but the exact cause of this temperature sensitivity was not readily identified, and research efforts became diversified in attempts to make headway. Initial studies in the field of high-speed knock were based on the assumption that a chemical reaction sensitivity to temperature was the root cause. It is now suspected that the effect may be due to a thermal manifestation of the variation in evaporative cooling characteristics of different fuels at different engine speeds. Research findings leading up to the present project have indicated that the high-speed knock phenomenon could be explained by the influence on the overall mixture temperature of the thermal-evaporative behaviour of a fuel during the inlet process. The thermal-evaporative behaviour is very complex, however, and has been characterized only tentatively, as yet. The present project was initiated to study the effect of engine speed on the fuel evaporation behaviour and on the complex heat transfer processes that occur within the intake manifold of a spark-ignition engine. The primary aim of the project was to establish the temperature of the air/fuel mixture after the inlet process has been completed, and to identify how this temperature responds to changes in engine speed and fuel composition. The fuels investigated included conventional gasoline and gasoline-alcohol blends. It was anticipated that the findings of the project would enable the fundamental hypothesis concerning the basic cause of high-speed knock to be evaluated.
- ItemOpen AccessAn evaluation of the use of thermocouples for gas temperature determination in an I.C. engine environment(2007) Kundhlande, Ngonidzashe G; Yates, AndrewThe magnitude and transient nature of the gas temperature in the cylinder of an internal combustion engine makes the measurement quite difficult. Several techniques have been employed to try and determine the actual gas temperatures in internal combustion engines, and most of these have either shown inconsistency or turned out to be extremely expensive. In this thesis, the use of a thermocouple to determine the gas temperature was explored.
- ItemOpen AccessThe influence of fuel properties on threshold combustion in aviation gas turbine engines(2017) Burger, Victor; Yates, AndrewThis body of work investigated the influence of alternative jet fuel properties on aviation gas turbine performance at threshold combustor operating conditions. It focused on altitude blowout performance and was in part motivated by results that were encountered during an aviation industry evaluation of synthetic kerosene that complied with the Jet A-1 specification, but differed from the fuel that was used as a reference in terms of some significant properties. As a consequence the relative impact of physical properties and reaction chemistry properties were of primary interest in this study. The thesis considered the potential to blend a range of different alternative jet fuel formulations which exhibited independent variations in properties relating to evaporation and reaction behaviour whilst still conforming to legislated physical fuel specifications. It further explored the potential for said variations having a detectable and significant influence on the simulated high altitude extinction behaviour in a representative aviation gas turbine combustor. Based on the findings, appropriate metrics were suggested for scientifically quantifying the appropriate properties and conclusions were drawn about the potential impact of alternative jet fuel properties on blowout performance. These subjects were addressed primarily through the theoretical analyses of targeted experimental programmes. The experimental design adopted a novel approach of formulating eight test fuels to reflect real-world alternative fuel compositions while still enabling a targeted evaluation of the influences of both physical and chemical reaction properties. A detailed characterisation was performed of the test fuels' physical and reaction properties. The extinction and spray behaviours of the fuels were then evaluated in a laboratory scale combustor featuring dual-swirl geometry and a single prefilming airblast atomiser. The various experimental data sets were interpreted within the context of a theoretical model analysis. In doing so the relative performance of alternative jet fuel formulations under laboratory burner conditions were translated to predict relative real world altitude performance. This approach was validated against aforementioned industry evaluation results and demonstrated to be consistent. A technically defensible explanation was provided for the previously unexplored anomalous altitude extinction results that were observed during the industry evaluation of synthetic jet fuel. A conclusive case was made for the extinction limit differences having been caused by the relative differences in chemical ignition delays of the fuels. The probability of volatility (distillation profile) and fuel physical properties playing a significant role in the impaired altitude performance was discredited. Evaporation-controlled combustion efficiency was, however, shown to become a significant factor at low air mass flow rates or when the fuel evaporation is compromised. The influence of flame speed and chemical ignition delays were investigated. Laminar flame speed was shown not to correlate with LBO, discrediting its use as a proxy for reaction rate. The study showed a correlation between the lean blowout behaviour of jet fuels and the ignition delays associated with their derived cetane numbers. Additionally, there was substantive support indicating that an even stronger correlation could be obtained by operating the IQT™ device that is used to measure these delays at an elevated temperature. The thesis makes a contribution towards the development of both technical understanding and practical tools for evaluating the potential operating limits of alternative jet fuel formulations.
- ItemOpen AccessInsights relating to octane rating and the underlying role of autoignition(2006) Swarts, André; Yates, AndrewThe methods prescribed by the ASTM for Research and Motor octane number ratings are generally accepted as indicative of the anti-knock properties of gasoline when applied in spark ignition engines. However, it has been shown by the author that the manifestation of autoignition in the CFR engine that is used for octane rating differs significantly from that which is typically experienced in a modern production engine under knocking conditions (SAE paper 2005-01-2081). The present research examines the knock measurement system prescribed by the ASTM method and demonstrates how knock intensity is defined by the pressure rise associated with bulk autoignition heat release and that it is insensitive to the high frequency pressure fluctuations.
- ItemOpen AccessInvestigating the feasibility of characterising gasoline autoignition using a motored engine apparatus(2007) Demnitz, Simon; Yates, AndrewDevelopment of a predictive octane model is a potentially useful tool for designing fuel blends for meeting octane specifications. One of the approaches adopted is through chemical kinetic modelling of the autoignition properties of constituent compounds. The results obtained from models, however, are dependent on experimental data for validation. It was the intention of this thesis to provide empirical data that could be used confirm a recently proposed autoignition model based upon the results obtained from chemical kinetics modelling. Motored engines have been used extensively for the investigation of autoignition properties of fuels. They are useful in interpreting results from conventional ignition delay measuring systems as well as giving practical insight into the process of autoignition in spark ignition engines. The conditions required for autoignition reactions to take place are easily produced in a motored engine with a suitable compression ratio. A single cylinder engine was modified so that the inlet conditions could be adjusted and n-heptane was tested in the device. Fuelling was controlled with an injection system which was calibrated for n-heptane use in the engine. A range of inlet conditions were determined that would enable peak conditions in the engine to result in autoignition of the fuel. The autoignition data was then used in describing the ignition delay characteristics of the fuel and the range of interest, the so called negative temperature coefficient region. Autoignition experiments were performed in the engine and the data was analysed by the comparison of measured autoignition reactions with predicted reaction times; the predictions were calculated using the new empirical autoignition model. Direct analysis of the model resulted in good correlation of measured and predicted overall autoignition reaction times, with improved correlation of cool flame reaction times with initial temperature adjustment. Modification of initial temperature values in the indirect model application (whereby traces were generated using an engine model with autoignition prediction capabilities) resulted in similar observances. These initial results led to the conclusion that the temperature and Arrhenius parameter adjustments necessary to obtain a perfect fit in the autoignition model were indicative of errors involved in the temperature measurement or in the fuel metering. Recommendations for further work on the engine would be the investigation of a dynamometer system that would be free from noise transmission during operation and that would enable experimentation with lower engine speeds. Further work on the inlet system would be the installation of shielded thermocouples and a quicker acting heater controller. A fundamental change in fuel metering calibration is required. Further recommendation is that a variable compression ratio engine should be used to enable the attainment of a wider range of readings for fuel characterisation and possibly eradicate the problems experienced with fuelling.
- ItemOpen AccessInvestigation of combustion image analysis by the two-colour method as a technique for comparing diesal fuels(2006) Velaers, Adrian; Schaberg, Paul; Yates, Andrew; Swarts, AndréThis project involves an investigation of combustion image analysis by the two-colour method as a technique for comparing diesel fuels. The purpose is to master the technique of combustion imaging in both an engine and a Combustion Bomb, with a view to determine the suitability of the two-colour method for fuel comparisons. To evaluate the abilities of the method, an intensive range of testing was conducted on two diesel fuels with slightly different fuel properties.