Design and Analysis of a Staged Combustor Featuring a Premixed Transverse Reacting Fuel Jet Injected into a Vitiated Confined Crossflow
Abstract
In this work the images from a novel designed high subsonic Mach number combustor were analyzed using complementary techniques of OH-PLIF and OH* chemiluminescence. The analysis of internal combustion in High subsonic Mach number environments is applicable to multiple flows including the combustor discharge flow supplying the inlet guide vanes of modern stationary gas turbines. For this experimental analysis, a High subsonic combustion test rig was designed. It comprised of a head end vitiator, supplying high pressure vitiated air through a high temperature nozzle to the test section after which reaction quenching in a long mixing section provided uniform flow for emissions sampling. The High temperature nozzle design featured a regeneratively cooled and film cooled converging nozzle with vitoshinski flow profile. The survivability exceeded expectations and was the major milestone for this experimental effort. The nozzle design allowed high subsonic Mach number combustion in the test section at the high heat fluxes typical of nozzle flows. This combustor ran continuously for an average of 5 hours every test. The test section design allows secondary injection of fuel and oxidizer in a transverse fashion into the combustor. The emissions characteristics of this combustor revealed improved NOx emissions over the low subsonic Mach number behavior documented in literature. The emissions results from the high subsonic Mach number combustion identified operating conditions for NOx abatement. To further identify why these transverse jet flames burned differently from their low subsonic counterparts motivated imaging of the spatio-tempporal behavior of the flames. Advanced imaging techniques such as kHz OH* chemiluminescence and OH-PLIF were used on these flames. Using OH-PLIF, the measurement of the transverse jet flames revealed that at the high subsonic Mach numbers for the test matrix, the fuel jet was unable to ignite in the upstream shear layer, and stabilized only in the near wake as a leeward stabilized flame, which was dependent on the subsonic boundary layer for flame attachment near the injector. Significant jet flapping in the near field was also identified. A far wake transverse jet flame was also observed, broken into flamelets that do not connect with the bottom wall of the combustor, revealing more distributed burning in the shear flow. The OH* chemiluminescence obtained at a higher repetition rate, revealed that the dynamics of the flames in the subsonic boundary layer is largely in response to the increased strain rate field in the jet wake. In order to attach the flame at the injector, hydrogen was added to increase the reactivity of the flame. Increasing the reactivity of the fuel jet to comparatively similar chemical timescales as the flow timescales allowed the leading point of the flame to consume fuel at the injector before convection pulled the hot gasses into the jet wake for further heat release. This result also showed that any flames attached at the injector behaved similarly irrespective of the crossflow Mach number so that the flames were governed more by reactivity, with similar features in the mean field. The unattached flames were shown to be capable of attachment given sufficiently high reactivity at the same crossflow Mach number.
Degree
Ph.D.
Advisors
Lucht, Purdue University.
Subject Area
Optics|Energy|Mathematics|Thermodynamics
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