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Measurement of Air-Fuel Ratio Fluctuations Caused by Combustor Driven Oscillations FREE

[+] Author Affiliations
Rajiv Mongia, Robert Dibble

University of California at Berkeley, Berkeley, CA

Jeff Lovett

Pratt & Whitney, West Palm Beach, FL

Paper No. 98-GT-304, pp. V003T06A026; 7 pages
doi:10.1115/98-GT-304
From:
  • ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition
  • Volume 3: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations
  • Stockholm, Sweden, June 2–5, 1998
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7864-4
  • Copyright © 1998 by ASME

abstract

Lean premixed combustion has emerged as a method of achieving low pollutant emissions from gas turbines. A common problem of lean premixed combustion is combustion instability. As conditions inside lean premixed combustors approach the lean flammability limit, large pressure variations are encountered. As a consequence, certain desirable gas turbine operating regimes are not approachable. In minimizing these regimes, combustor designers must rely upon trial and error because combustion instabilities are not well understood (and thus difficult to model). When they occur, pressure oscillations in the combustor can induce fluctuations in fuel mole fraction that can augment the pressure oscillations (undesirable) or dampen the pressure oscillations (desirable). In this paper, we demonstrate a method for measuring the fuel mole fraction oscillations which occur in the premixing section during combustion instabilities produced in the combustor that is downstream of the premixer.

The fuel mole fraction in the premixer is measured with kHz resolution by the absorption of light from a 3.39 μm He-Ne laser. A sudden expansion combustor is constructed to demonstrate this fuel mole fraction measurement technique. Under several operating conditions, we measure significant fuel mole fraction fluctuations that are caused by pressure oscillations in the combustion chamber. Since the fuel mole fraction is sampled continuously, a power spectrum is easily generated. The fuel mole fraction power spectrum clearly indicates fuel mole fraction fluctuation frequencies are the same as the pressure fluctuation frequencies under some operating conditions.

Copyright © 1998 by ASME
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