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Pressure Dependence of the Stability Limits and the NOX Exhaust Gas Concentrations in Case of Swirl-Stabilized, Diffusion Flames Burning in a Lift-Off Regime

[+] Author Affiliations
Plamen Kasabov, Nikolaos Zarzalis

University of Karlsruhe (TH), Karlsruhe, Germany

Paper No. GT2009-59801, pp. 613-622; 10 pages
doi:10.1115/GT2009-59801
From:
  • ASME Turbo Expo 2009: Power for Land, Sea, and Air
  • Volume 2: Combustion, Fuels and Emissions
  • Orlando, Florida, USA, June 8–12, 2009
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4883-8 | eISBN: 978-0-7918-3849-5
  • Copyright © 2009 by ASME

abstract

The present study deals with confined, swirl-stabilized, diffusion flames burning in a lift-off regime and is meant to be a meaningful extension of our previous work [1]. The unique features of these hybrid flames originate from the presence of the so called lift-off zone located between the burner exit and the reaction zone. In the lift-off zone, surrounded by hot recirculating exhaust gases, the liquid fuel heats up and will reach a certain degree of prevaporation and premixing before entering the reaction zone. For that reason lifted flames posses some of the advantages of the premixed flames, for example in respect of emissions, but lack their major drawbacks, such as susceptibility to flashback and combustion noise. The investigations were motivated by the high NOX reduction potential of the lifted flames and the scarce information about their emission characteristics, flame behaviour and stability limits for gas turbine typical conditions especially when operated with liquid fuels. In order to gain a deeper understanding of the stabilization mechanism of lifted flames, several process parameters were varied within this study. The impact of the pressure (up to 18bar), of the air preheating and of the stoichiometry on the NOX emissions and on the lean blowout limits was investigated and discussed. The lift-off burning mode was achieved by utilizing a modified airblast nozzle and kerosene serving as a fuel. To acquire measurement data for a set of Reynolds numbers and residence times, four nozzles with similar geometries, but different scaling factors were employed. All main components of the exhaust gas were detected by means of conventional gas analysis. The NOX concentrations for the whole measured pressure range and for adiabatic flame temperatures up to 1800K does not exceed 20ppm normalized for 15% O2 . The carbon monoxide concentration served as indicator for the presence of flame instabilities. The evaluation of the gathered data revealed some interesting phenomena. For example a sudden change in the nitrogen oxides concentration plotted over the equivalence ratio allows to distinguish between two burning modes: lift-off and detached flame. Another interesting finding is a maximum in the profile of the LBO limits as a function of the operational pressure, signifying a change in the predominant stabilization mechanism.

Copyright © 2009 by ASME

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