Browsing by Author "LePera, Stephen D."

Now showing 1 - 4 of 4
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    Conversion of a Gas Turbine Engine to Operate on Lean-Premixed Hydrogen-Air: Design and Characterization
    Farina, Jordan Thomas (Virginia Tech, 2010-01-18)
    The continued use of fossil fuels along with a rise in energy demand has led to increasing levels of carbon emissions over the past years. The purpose of this research was to design a lean premixed hydrogen fuel system that could be readily retrofit into an existing gas turbine engine to provide a clean renewable energy solution to this growing problem. There were major hurdles that had to be overcome to develop a hydrogen fuel system that would be practical, stable, and would fit into the existing space. High flame temperatures coupled with high flame speeds are major concerns when switching from jet fuel or natural gas to hydrogen. High temperatures lead to formations of pollutants such as oxides of nitrogen (NOx) and can potentially cause damage to critical engine components. High flame speeds can lead to dangerous flashbacks in the fuel premixers. Past researches have developed various hydrogen premixers to combat these problems. This research designed and developed new hydrogen premixers using information gathered from these designs and utilized new ideas to address their shortcomings. A gas turbine engine was modified using 14 premixers and a matching combustor liner to provide lean operation with the existing turbomachinery. The engine was successfully operated using hydrogen while maintaining normal internal temperatures and practically eliminating the NOx emissions when compared to normal Jet-A operation. Even though full power operation was never achieved due to flashbacks in two premixers, this research demonstrated the feasibility of using lean-premixed hydrogen in gas turbine engines.
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    Development of a Novel Planar Mie Scattering Method for Measurement of Spray Characteristics
    LePera, Stephen D. (Virginia Tech, 2012-02-03)
    The work herein details an optical droplet measurement system based on planar multi-angle Mie scattering. Sizing information consists of a mean droplet diameter and droplet distribution estimates for every individual point within a planar (2D) area of interest. The planar method makes possible the fast acquisition of data within a large field of interest, and uses relatively inexpensive instrumentation. As presented, the method demonstrated the ability to measure water droplets from a typical simplex spray nozzle, across the range of 5-50 micrometers within +/-10% of known values, and in addition return an estimate of the shape and width of the size distribution at each location within the planar region of interest. Measurements demonstrating the agreement between results from this current method and known PDA data were successfully completed for a 1-gallon-per-hour spray nozzle, and repeatability was demonstrated in 2.5-gallon-per-hour and 4.5-gallon-per-hour nozzles. Additionally the limits of the technique are explored with simulated data. Conclusions from these exercises show that the multi-angle planar Mie scattering method is capable of measuring droplet distribution characteristics and means within a nominal range of 0.3 micrometers up to 150 micrometers.
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    An Investigation of Lean Premixed Hydrogen Combustion in a Gas Turbine Engine
    Perry, Matthew Vincent (Virginia Tech, 2009-06-22)
    As a result of growing concerns about the carbon emissions associated with the combustion of conventional hydrocarbon fuels, hydrogen is gaining more attention as a clean alternative. The combustion of hydrogen in air produces no carbon emissions. However, hydrogen-air combustion does have the potential to produce oxides of nitrogen (NOx), which are harmful pollutants. The production of NOx can be significantly curbed using lean premixed combustion, wherein hydrogen and air are mixed at an equivalence ratio (the ratio of stoichiometric to actual air in the combustion process) significantly less than 1.0 prior to combustion. Hydrogen is a good candidate for use in lean premixed systems due to its very wide flammability range. The potential for the stable combustion of hydrogen at a wide range of equivalence ratios makes it particularly well-suited to application in gas turbines, where the equivalence ratio is likely to vary significantly over the operating range of the machine. The strong lean combustion stability of hydrogen-air flames is due primarily to high reaction rates and the associated high turbulent burning velocities. While this is advantageous at low equivalence ratios, it presents a significant danger of flashback — the upstream propagation of the flame into the premixing device — at higher equivalence ratios. An investigation has been conducted into the operation of a specific hydrogen-air premixer design in a gas turbine engine. Laboratory tests were first conducted to determine the upper stability limits of a single premixer. Tests were then carried out in which eighteen premixers and a custom-fabricated combustor liner were installed in a modified Pratt and Whitney Canada PT6A-20 turboprop engine. The tests examined the premixer and engine operability as a result of the modifications. A computer cycle analysis model was created to help analyze and predict the behavior of the modified engine and premixers. The model, which uses scaled component maps to predict off-design engine performance, was integral in the analysis of premixer flashback which limited the operation of the modified engine.
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    Premixing injector for gas turbine engines
    (United States Patent and Trademark Office, 2011-01-18)
    A premixing injector for use in gas turbine engines assists in the lean premixed injection of a gaseous fuel/air mixture into the combustor of a gas turbine. The premixing injector is designed to mix fuel and air at high velocities to eliminate the occurrence of flashback of the combustion flame from the reaction zone into the premixing injector. The premixing injector includes choked gas ports, which allow the fuel supply to be decoupled from any type of combustion instability which may arise in the combustor of the gas turbine and internal passages to provide regenerative cooling to the device.