Low-frequency combustion instability mechanisms in a side-dump combustor
- Ecole Centrale Paris, Malabry (France). E.M2.C Lab.
This article describes a study of a two-dimensional two-inlet side-dump combustor fed with a mixture of air and propane. The present results concern symmetric operating conditions with respect to the two inlets. Stable and unstable regimes which depend on the inlet velocity and the equivalence ratio have been identified. Schlieren visualization, radical imaging with an intensified CCD camera, and simultaneous pressure, inlet velocity and C[sub 2] emission light measurements, have been used to characterize the combustor behavior. Imaging of the flowfield has provided an insight on the flame structure and its interaction with the entering jets. Two low-frequency unstable modes (a fuel-rich regime and a fuel-lean regime with an instability frequency around 500 Hz) were studied using a conditional imaging technique. It was found that unsteady heat release occurs in two different ways: pulsating combustion in the dome region and convection of reaction zones downstream of the jet-impingement region. Flame oscillations were induced by a periodic impingement of the jets on the centerplane of the chamber. Pressure fluctuations in the test section were roughly in phase with the global C[sub 2] emission, indicating that the instabilities were sustained by energy addition to the acoustic field. A two-dimensional distribution of the Rayleigh index computed for each unstable mode indicated that the fuel-lean mode was driven by the unsteady heat release in the dome region whereas the fuel-rich mode was driven by the flame oscillations downstream of the jet-impingement region. The transition from the fuel-lean to the fuel-rich instability featured a shift of driving mechanism. This study shows that even in the idealized geometry the coupling mechanisms leading to low-frequency combustion instabilities are not unique and illustrates the difficulty of devising predictive models.
- OSTI ID:
- 6122453
- Journal Information:
- Combustion and Flame; (United States), Vol. 94:4; ISSN 0010-2180
- Country of Publication:
- United States
- Language:
- English
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33 ADVANCED PROPULSION SYSTEMS
PROPANE
COMBUSTION KINETICS
RAMJET ENGINES
COMBUSTION INSTABILITY
FLAMES
FLOW MODELS
FLOW VISUALIZATION
FORECASTING
FREQUENCY DEPENDENCE
FUEL-AIR RATIO
HEAT TRANSFER
JETS
MORPHOLOGY
OPERATION
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CHEMICAL REACTION KINETICS
ENERGY TRANSFER
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INSTABILITY
INTERNAL COMBUSTION ENGINES
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MATHEMATICAL MODELS
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034000* - Natural Gas- Combustion
330100 - Internal Combustion Engines