Browsing by Author "Woolard, Chris"
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- 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 AccessThe effect of hydrocarbon exposure and temperature on the behaviour of elastomeric seals(2013) Scully, Christopher; Woolard, ChrisSynthetic jet fuels have been proposed as alternatives to petroleum Jet A-1. Compatibility issues, however, are of concern; specifically the interaction of synthetic fuels with polymeric materials which are commonly used to seal fuel systems. This is because of differences between the composition of synthetic fuels and petroleum-derived fuels. Synthetic fuel streams contain no or very low aromatics, unlike petroleum-derived fuels. This investigation was consequently initiated to gain a greater understanding of the factors affecting seal swell in the aviation industry. The study focussed interactions between fuel components from various fuel classes and nitrile rubber (NBR) as well as a restricted set of investigations on fluorocarbon (FKM) rubber. No comprehensive study of the temperature sensitivity of fuel composition on swelling has been attempted prior to this study. NBR and FKM were swollen in petroleum Jet A-1, synthesised paraffinic kerosene (SPK) and a variety of blends of pure components with SPK. These components were selected from aromatic species (monoaromatic, diaromatic and heterocyclic), cycloparaffins, aromatic oxygenates and other oxygenates. Aromatic species were blended at 8% (v/v) while all other species were blended at 15% (v/v). Within the class of aromatic hydrocarbon components, it was found that decreasing molecular size, increasing the number of ring structures (particular aromatic rings) as well as increasing all Hansen solubility parameters increased swelling. Of the Hansen solubility parameters, the greatest correlation was found with the hydrogen-bonding (electron exchange) parameter. Nonetheless the dispersion parameter which is strongly affected by the number of aromatic rings and length of any aliphatic side-chain was also important. A very good correlation was found between swelling and the density of the aromatic species. It was found furthermore that introducing oxygen atoms increased swelling. The introduction of cycloparaffins also increase swelling although to a much lesser extent than aromatics. Cyclisation together with a polar moiety was observed to increase swell significantly. With FKM elastomers, fuel composition had less influence. Temperature sensitivity was explored by performing swelling at 20oC, 35 oC and 50 oC. Van't Hoff plots were used to obtain enthalpies of mixing. It was found that all hydrocarbons swelled more as temperature rose. This is indicative of endothermic interactions between these species and polar NBR. However, it was observed that species with high polar and hydrogenbonding Hansen solubility parameters had lower sensitivity to temperature. It is postulated that in these species, less aromatic concentration in the NBR occurs at elevated temperatures, contributing to lower sensitivities. Aromatic oxygenates were observed to decrease in swelling with temperature. This is ascribed to a strong exothermic interaction. This behaviour was in contrast to non-aromatic oxygenates. It is possible that blends of these non-aromatic oxygenates with SPK are less stable at elevated temperatures leading to component separation into the NBR and thus more swelling. Similar trends were observed with fluorocarbon elastomers (FKM). Physical property measurements were made on swollen NBR O-rings. A distinct relationship between decreased glass transition temperature and the extent of swelling was observed. Fuel which had adsorbed into the elastomer was observed to act as an effective plasticiser. Not only did increased swelling lower the glass transition temperature but it reduced the modulus of NBR O-rings in a predictable fashion. A significant decrease in storage modulus was associated with increased swelling. Increased swelling was found to be associated with increased compression set although the mechanism by which this manifests itself is unclear.
- ItemOpen AccessModelling spherical flame propagation in a closed volume(2014) Scott, Ian Stefanes; Möller, Klaus; Woolard, ChrisThe highly exothermic reaction of fuel combustion is the most common source of usable energy in the world. The fuel itself originates almost entirely from fossil fuels, such as crude oil and natural gas. The use of these fuels for energy production is under pressure in recent times due to environmental and availability concerns. This then sets the stage for combustion research aimed at providing more efficient combustion processes and characterising the combustion behaviour of alternative fuels. The laminar flame speed of a combustible mixture is a well defined combustion characteristic that influences the efficiency and performance of many combustion processes. An example of where flame speed has a strong impact on the performance of a combustion process, is the blow-out and relight ability in flight applications of gas turbine engines. A very common experimental setup to obtain laminar flame speed data is the constant volume combustion bomb, where the laminar flame speed is calculated from the measured flame speed of a spherical flame, propagating outwards inside a usually spherical combustion chamber.
- ItemOpen AccessA novel method to evaluate synthetic fuel options for gas turbines in terms of O-ring swelling(2009) Visram, Shehzaad; Yates, Yates, Andrew; Woolard, ChrisBefore 1999, all commercial aviation fuel had been produced from petroleum feedstock. With the growth in demand, it has put significant strain on the availability of jet fuel at Oliver Tambo International Airport (ORTIA). In 2008, Sasol was granted an approval to use fully synthetic jet fuel upon the publication of Defence Standard 91-91, Issue 6 [1]. Sasol's fully synthetic jet fuel is the only fuel in the world which had obtained the necessary approval for commercial use. The DEF STAN had an 8 minimum aromatic limit in the final blend. Sasol produces fully synthetic jet fuel from its Fischer-Tropsch process and the latter is the source of synthesised paraffinic kerosene (SPK). SPK typically contain iso paraffins and small quantities of normal paraffins. However, they do not contain heteroatomic species or aromatic compounds. Advantages of the use of F-T fuels over petroleum-derived fuels include outstanding thermal-oxidative stability characteristics with relatively lower particulate matter (PM) combustion emissions. The lack of aromatics causes a decrease in the tendency of the fuel to swell nitrile O-rings. This is of particular concern as the transition of synthetic fuels to conventional fuels can result in fuel leakage and elastomer shrinkage in fuel distribution systems.
- ItemOpen AccessThe effect of different chemical classes on the swelling of NBR O-rings in blends with synthetic paraffinic kerosene(2012) Burnham, Ross; Woolard, Chris; Van Steen, EricSynthetic jet fuels provide a number of benefits over petroleum-derived fuels. They have thus been considered as alternative fuels. Compatibility issues, however, are of concern; specifically the interaction of synthetic fuels with polymeric materials which are commonly used to seal fuel systems. This is because of differences between the composition of synthetic fuels and petroleum-derived fuels. Synthetic fuel streams contain no or very low aromatics, unlike petroleum-derived fuels. This investigation was consequently initiated to gain a greater understanding of the factors affecting seal swell in the aviation industry. The study focussed interactions between fuel components from various fuel classes and nitrile rubber (NBR). Currently fully and semi-synthetic jet fuels are required to contain a minimum of 8% aromatic components by volume in order to minimise any changes in polymeric swell when switching between synthetic jet fuels and petroleum-derived jet fuels. In this study procedures were refined to allow seal swell to be assessed. ASTM 01414 and 0471 were used as base methods together with the use of an elastomer compression rig that had been designed and built at the Sasol Advanced Fuel Laboratory (SAFL). A method was developed to remove plasticiser for the O-ring seals to provide samples that are more representative of O-rings in service. Experiments were conducted on both new and conditioned (deplasticised) NBR O-ring samples. Materials tested in this investigation included petroleum-derived Jet A-1, Fischer Tropsch-derived synthetic paraffinic kerosene (SPK) and pure compounds including isomers of n-, iso- and cyclic paraffins, aromatics and oxygenates. The paraffins were tested as neat components. With the aromatics and oxygenates, 8% (v/v) blends with coal-to-liquid (CTL) SPK were prepared to simulate fully synthetic jet fuels that meet the minimum 8% aromatic specification. The data which were collected were primarily changes in mass and volume of the O-rings which underwent fuel exposure. An assessment was made of both the kinetics of fuel uptake and the extent of swell achieved at equilibrium. Initial experiments focussed on method refinement. This included the measurement techniques (gravimetric, volumetric and seal swell rig), O-rlng conditioning (i.e. plasticiser removal), the effects of temperature and the solvent to polymer ratio used. The greatest level of repeatability was achieved with gravimetric measurements. Similar swelling trends were observed with volumetric measurements, although with lower repeatability. Solubility parameters and molar volume were shown to be key determinants of seal swell. It was demonstrated that the extent of swell was not significantly different between n- and iso- isomers of octane and dodecane. What was different was that n-paraffins initially swell faster than their iso-equivalents. A significant difference was observed with cycloalkane isomers which swell to a much greater extent. It is suggested that this difference is the result of a combination of molar volume and solubility parameter differences. A study on a series of n-alkanes showed that although solubility parameters increase with increasing carbon number, seal swell decreases. Molar volume, by contrast, decreases. Thus for n-alkanes molar volume is the key determinant. A statistically significant correlation between the density of n-alkanes and the extent of swell was observed. Investigations into blends of coal-to-liquid (CTL) SPK showed that the seal swell was highly dependent on the hydrocarbon aromatic used. Some blends swelled more than petroleum-derived Jet A-1 and some less than Jet A-1. Again molar volume was demonstrated to be important but also the ability of aromatics to form hydrogen-bond like interactions with NBR. Lower molar volumes and higher Bh values produced more favourable swelling. The importance of the presence of multiple rings was also demonstrated by the increased swelling of the C10, tetralin, over other C10 aromatics such as n-butylbenzene. Aromatic ethers caused significantly more swell than hydrocarbon aromatics. Some of these aromatic oxygenates swelled even more than petroleum-derived Jet A-1 even when used at the minimum 8% aromatic level. This was explained in terms of their even stronger polar and hydrogen bond interactions. The effects of temperature were an increase in the rate of swelling, as expected, and a slight decrease in the extent of swelling at elevated temperatures. However, the influence of temperature on the aromatic oxygenate, benzyl alcohol, which has previously been reported as producing large swell even when added at concentrations as low as 0.5%, was significant. It is suggested that this is because of the very strong hydrogen bond between benzyl alcohol and NBR. Because of the exothermic nature of hydrogen bonding, the equilibrium constant for this interaction decreases at elevated temperatures leading to less swell. The results from this study suggest that lighter (lower carbon number) SPKs and SPKs containing cycloparaffins would promote swelling. The addition of lighter, higher Sh and/or multi-ring aromatics to SPK would produce the most swell of the aromatic species added. This could be even more enhanced by the presence of aromatic oxygenates. Such compounds could be targeted for blending with synthetic paraffins to produce fully synthetic jet fuels but their impact on other properties such as flash point and distillation behaviour cannot be ignored.
- ItemOpen AccessThermal and chemical analysis of carbonaceous materials: diesel soot and diesel fuel reactor deposits(2013) Kaminuza, Irénée; Woolard, ChrisMethods for the characterisation of fuel-derived carbonaceous materials were assessed. These methods were applied to two such materials, viz. diesel soot and diesel fuel deposits. Diesel soot: Diesel soot, sampled from a commuter bus, was characterised using an array of analytical techniques. Physical and chemical characterisation of diesel soot was conducted with particular interest in the component of soot known as the soluble organic fraction (SOF). The SOF represents adsorbed chemical species and is traditionally obtained via Soxhlet extraction of soot using an organic solvent. Chemical speciation of the SOF was performed using GC-MS analysis. Five solvents (hexane, cyclohexane, toluene, methanol and acetone) were compared with dichloromethane, the most extensively used solvent for the extraction of soot with respect to their ability to extract a variety of species, including polyaromatic hydrocarbons (PAHs) and potential endocrine disrupting molecules, e.g. phthalates. Extraction results suggest that the SOF quantity depends significantly on the extraction solvent. For the soots analysed, SOF ranged between 1.0 and 4. 8 wt %, depending on the solvent used. Moreover, it was shown that polar solvents extracted a greater SOF than non- polar solvents. For PAH extraction the order of efficiency was acetone > methanol > > toluene > hexane > cyclohexane while for esters, including endocrine disrupting phthalates, the order in efficiency was methanol > dichloromethane >acetone > toluene > > hexane > cyclohexane > n-hexane. A suggestion is made that to maximise SOF, sequential extraction should be made. Thermogravimetric analysis revealed a discrepancy between VOF and SOF which was ascribed to the presence of sulfurous and sulfuric acid which were not extracted by the organic solvents investigated Fuel deposits: Fuel was degraded in three reaction vessels, viz. a continuous flow reactor, open glass flask s and closed metal reactors (bombs) in an attempt to synthesise carbonaceous deposits, analogous to those found in diesel injectors. The degradation of four diesel fuels, viz. an EN590 reference diesel, a commercial diesel and two B20 biodiesel blends (rapeseed and soybean methyl esters blended with EN590 diesel), was investigated in the thermo-oxidative temperature regime, i.e. below 300° C.
- ItemOpen AccessThe use of model compounds to investigate the influence of fuel composition on the thermo-oxidative stability of fame/diesel blends(2015) Vukeya, Hundzukani; Woolard, ChrisBiodiesel can be used in diesel engines without significant modification of the engine prior to use because it has properties similar to those of petroleum diesel. Biodiesel, however, exhibits lower stability compared to petroleum diesel. Small differences in fuel properties such as component concentration or total acidity can lead to the formation of deposits which can reduce engine performance and increase maintenance requirements and costs. Thermo-oxidative stressing was performed in two reactor systems in this study. For comparative purposes both sets of experiments were performed at 140° C. The systems used were a quartz crystal microbalance (QCM) in which oxygen was limited and open glass flasks under flowing air (unlimited oxygen). To simplify analysis, diesel model compound systems were used in which full boiling range diesel was replaced with single compounds representing the classes of compounds found in petroleum diesel. The model compounds were n-hexadecane, tetralin and decalin. Fuel analysis was performed using gas chromatography (GC) with mass spectrometric (MS) and flame ionisation (FID) detection. Further analytical methods included Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy as well as electrospray ionisation-mass spectrometry (ESI-MS).