Browsing by Author "Schaberg, Paul"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Open Access
    Development of a constant-volume combustion apparatus for fuels research
    (2007) Miller, Geoff; Schaberg, Paul; Yates, Andy
    This project, initiated by the Sasol Advanced Fuels Laboratory at UCT, was to develop a piece of apparatus in which single compression ignition events could be viewed and studied. The pressure and temperature at injection were to be independently variable. Following a literature survey into previous fuels research work and the associated equipment used, such as rapid compression machines and continuous flow combustion chambers, the decision was made to develop a constant volume combustion chamber (CVCC). This option provided the greatest potential for optical access. The development of the high pressure and temperature environment was to be achieved using a pre-charge combustion event as opposed to electrical heating. The combustion of a lean mixture of flammable gas resulted in the desired conditions being developed rapidly, avoiding the material strength limitations of sustained electrical heating. The CVCC has a cylindrically shaped chamber, 100mm in diameter and 50mm deep, which is formed by a martensitic tool steel vessel of 230mm nominal diameter. The chamber is optically accessible by means of sapphire windows on both ends as well as from a maximum of three 38mm diameter (medium-sized) circumferential ports. Flexibility of the experimental setup was ensured by the use of common porting, whereby the two ends, the four medium-sized ports and the four small circumferential ports were interchangeable with one another. All ports were sealed with Viton 0-rings that permitted a maximum operating temperature of 200°C. The CVCC could be electrically heated to 150°C to prevent condensation on the windows. The exhaust valve, which also served as a safety relief valve, was pneumatically powered and automatically controlled by a solenoid valve. The high pressure and temperature environment required for compression ignition combustion events were achieved by the introduction of predetermined amounts of Hydrogen and/or Acetylene, Nitrogen and Oxygen into the chamber. The gases were metered into the CVCC by means of a pressure transmitter feedback loop and a solenoid valve, both of which were controlled by the main computer that made use of a data acquisition card. The mixture was ignited by a spark plug, resulting in complete pre-charge combustion and a rapid pressure and temperature increase. Following pre-charge combustion, the temperature and pressure dropped relatively gradually due to heat lost to the walls of the vessel. At a pre-selected pressure, the fuel being tested was injected into the chamber by an electronically controlled high pressure injector via a common rail or accumulator system. The predetermined component of residual oxygen in the chamber, being dependent on the original constituents, could yield either an inert environment (for non-combustive fuel spray studies) or a range of environments supporting compression ignition (i.e. a range of oxygen concentrations including an equivalent atmospheric fresh charge). In this way, visual observations could be made of controlled compression-ignition combustion events. These events were also recorded in a high-speed pressure trace from the quartz pressure transducer within the chamber. A thermodynamic model was set up to determine the required fill pressure of each gas to be metered into the vessel. Testing up to 180bar was achieved and results showed that peak pressures were repeatable to within 4%. Up to 60 highquality image experiments were achieved in one day without significant fouling of the windows or degradation of the seals. A discrepancy of approximately 15% existed between predicted peak pressures and measured pressures (being lower). Several losses were known to cause this pressure shortfall, such as slight gas leakage from the exhaust valve, radiation losses through the windows and heat lost to, and reaction quenching at, the walls of the chamber. Recommendations for improvements to the CVCC included reducing the causes and rates of leakage and quantifying the impact of surface-area to volume ratio on losses at the internal surfaces.
  • Thumbnail Image
    Item
    Open Access
    An investigation into the effects of diesel fuel properties on the injection characteristics of a common rail injection system
    (2012) Cross, Brenainn A; Schaberg, Paul
    This study set out to investigate the effects of diesel fuel properties on the behaviour of a common rail fuel injection system, with particular emphasis on the injection rate shape characteristics. The investigation included the design and commissioning of experimental equipment for the measurement of fuel properties at typical common rail pressures, as well as the measurement of instantaneous fuel flow rate by a modified Bosch Indicator method. Data was then collected for two different diesel fuels, operating in two different fuel injector designs. The two fuels were EN590 (a European reference fuel) and GTL (a fuel derived from natural gas). The two injectors were a Bosch solenoid type injector, and a Bosch piezo type injector.
  • Thumbnail Image
    Item
    Open Access
    Investigation of combustion image analysis by the two-colour method as a technique for comparing diesal fuels
    (2006) Velaers, Adrian; Schaberg, Paul; Yates, Andrew; Swarts, André
    This 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.
  • Thumbnail Image
    Item
    Open Access
    Modification of an ignition quality tester and its use in characterizing middle distillate fuels
    (2015) Ehrenreich, Aidan Lloyd; Floweday, Gareth; Schaberg, Paul
    The Ignition Quality Tester ( IQTTM ) is a constant volume combustion chamber based device which is used to determine the derived cetane number of diesel fuel oils when used in conjunction with ASTM D6890. During a test, the fuel sample is injected into heated, pressurised gas where it combusts. Suitable measurements are made during the combustion event to determine the ignition delay of the fuel and the latter is used with a correlation to determine the derived cetane number of the sample. The IQT offers improved repeatability and reproducibility when compared with the conventional method of determining cetane number, namely ASTM D613. Despite these advantages, the device features a fuel injection system not indicative of the state of the art, in terms of direct injection diesel components and associated fuel spray behavior. Therefore this project sought to make suitable mechanical, electrical and control modifications to incorporate a more technologically appropriate injector. It is believed that by improving the spray characteristics of the IQT along with the incorporation of a flexible control system, that it can be leveraged to a greater extent in a fuels research context. The modifications made to the system included the incorporation of a single hole common rail diesel injector along with a custom control system. The control system allowed flexible control of all variables considered to be significant to the study of auto-ignition delays. Additionally, an optical sensor was added to detect luminous emissions from the reacting fuels. The modified system was used to rate diesel fuels with varied composition including solvents, diesel primary reference fuels, crude derived as well as Low Temperature Fischer Tropsch (LTFT) products. These tests were performed at two temperatures and oxygen concentrations and the resulting data was used to redevelop correlations between the cetane number of the respective samples and their ignition delays in order to surmise the optimal operating conditions of the modified IQT.
  • Thumbnail Image
    Item
    Open Access
    Optimised combustion control for different diesel fuels
    (2007) Wattrus, Mark; Schaberg, Paul
    Includes bibliographical references (leaves 51-53).