Browsing by Department "Sasol Advanced Fuels Laboratory"

Now showing 1 - 4 of 4
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    Combustion characteristics of synthetic gasoline in modern charge boosted GDI Engines
    (2015) Rockstroh, Manuel Tobias; Yates, Andrew; Floweday, Gareth
    Sasols 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.
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    Design, set up and commissioning of a test facility for smokeless rich diesel combustion research
    (2015) King, Timothy Cole; Floweday, Gareth
    Low Temperature Combustion (LTC) is a strategy that harnesses the properties of exhaust gas, through the use of large quantities of exhaust gas recirculation (EGR), to reduce the peak combustion temperatures below that favoured by the formation processes of oxides of nitrogen (Ox) and those of soot. There is interest within the fuels research community in investigating the effects of diesel fuel formulations on LTC, using a suitable engine test platform. The objective of this study was to design and set up a test apparatus capable of achieving LTC in a diesel research engine, that could subsequently be used to study LTC behaviour with different fuels. In addition, it was necessary to present test data demonstrating the engine's performance, in terms of engine-out emissions and indicated specific fuel consumption (ISFC), transitioning between conventional diesel combustion (CDC) and LTC. The mechanical, electrical and control requirements for attaining CDC and LTC conditions were investigated in the literature and through consultations with experts in the fuels research field. These requirements were distilled into a definitive System Requirement Specification.
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    The influence of fuel properties on threshold combustion in aviation gas turbine engines
    (2017) Burger, Victor; Yates, Andrew
    This 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.
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    Thermal and chemical analysis of carbonaceous materials: diesel soot and diesel fuel reactor deposits
    (2013) Kaminuza, Irénée; Woolard, Chris
    Methods 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.