Browsing by Author "Stouffer, Scott David"

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    The development and operating characteristics of an improved plasma torch for supersonic combustion applications
    Stouffer, Scott David (Virginia Polytechnic Institute and State University, 1989)
    The design of the VPI plasma torch, which has been used as an ignitor and flameholder in supersonic combustion studies, has been modified in order to decrease the electrode wear and to increase stability. The plasma torch can be used as a source of hydrogen or nitrogen radicals which initiate and stabilize combustion. During previous testing of the unmodified torch, electrode erosion limited operation of the torch to about two hours. The improved torch features a flow swirler in the gas inlet, which adds vortex stabilization to the arc. The vortex stabilization causes the anode attachment point of the arc to be anchored in the low pressure region, downstream of the constrictor. This lowers the heat flux to the anode, so that erosion is decreased. The torch body was redesigned with an emphasis on the alignment of the electrodes. Also, the electrode gap in the improved torch was made continuously adjustable, allowing fine adjustment of the electrode gap during operation of the torch. The operational characteristics of the improved torch were monitored by a microcomputer-based data acquisition system. Stable operation of the improved torch with pure nitrogen was demonstrated, thus eliminating the requirement for argon to stabilize the arc. Operational characteristics of the improved torch running on argon, nitrogen, argon/hydrogen and argon/nitrogen mixtures as feedstocks, are reported. The electrode wear was studied between tests by observation with a microscope, and by measuring the mass change of the electrodes. The electrode erosion of the improved torch was reduced significantly. Anode lifetimes of greater than 20 hours have been demonstrated with operation on mixtures of nitrogen and argon.
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    The effect of flow structure on the combustion and heat transfer in a scramjet combustor
    Stouffer, Scott David (Virginia Tech, 1995)
    A combined experimental and computational study of two different swept-ramp injector configurations was conducted in a scramjet combustor. The object of the study was to determine the effect of mixing augmentation, resulting from the streamwise vortices generated by injector ramps, on scramjet engine operation characteristics, combustion, and heat transfer. Hydrogen was injected from the base of swept compression and expansion ramps in direct-connect tests that simulated flight at Mach 6.6. The experimental effort included combustor wall pressure and heat flux measurements with Gardon gages and surface thermocouples for the two injector configurations. A novel, side-view laser light sheet technique was developed to obtain images of the combustion product distribution at selected planes in the closed combustor duct downstream of the swept-compression ramp. injectors. In addition, a miniature refractory probe was developed to determine the pitot pressure at the exit of the combustor. Three-dimensional computations were made for mixing and reacting cases of the swept-compression ramp injector using the SPARK computer code. The flow field calculations were compared to the experimental measurements. The experimental tests demonstrated combustor performance with parallel injection comparable to that reported using normal injection. This unusually rapid parallel jet mixing and combustion was obtained using swept ramp injectors with near-parallel injection. The experiments and calculations showed that the injectors were effective in promoting lateral spreading of the fuel jets. The incomplete penetration of the fuel jets in the direction normal to the walls was a major limiting factor in the amount of mixing that could occur for both configurations. In addition, the proximity of the burning shear layer to the injector wall led to increased heat transfer on the injector wall. The effect of the flow structure on the heat flux was not principally through a large increase in the film coefficient caused by the vortical flow. Instead, it was due to the proximity of the reacting fuel jet to the wall, which led to high adiabatic wall temperatures near the wall.