Detailed characterization of the dynamics of thermoacoustic pulsations in a lean premixed swirl flame

• Published in: Combustion and flame Vol. 150; no. 1; pp. 2 - 26
• Main Authors: Meier, W., Weigand, P., Duan, X.R., Giezendanner-Thoben, R.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01-07-2007; Elsevier Science
• Subjects: ABUNDANCE; ACCURACY; AIR; Applied sciences; ATMOSPHERIC PRESSURE; BOUNDARY CONDITIONS; COMBUSTION; COMBUSTION CHAMBERS; COMBUSTION KINETICS; Combustion oscillation; Dynamics; Energy; Energy. Thermal use of fuels; ENGINEERING; Engines and turbines; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; FEEDBACK; FLAMES; FLOW RATE; Gas turbine combustion; GAS TURBINES; HZ RANGE; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; INSTABILITY; Lasers; METHANE; MIXTURES; NOZZLES; OSCILLATIONS; PERIODICITY; POWER RANGE 10-100 KW; PROBABILITY DENSITY FUNCTIONS; Pulsation; PULSATIONS; Stability; Swirl flame; TEMPERATURE DISTRIBUTION; Thermoacoustics; Turbulence–chemistry interaction; VALIDATION; Validation measurements; VARIATIONS; VELOCITY; Turbulence–chemistry interaction; Combustion oscillation; Validation measurements; Gas turbine combustion; Swirl flame; Measurement; Methane; Laser Doppler velocimeters; Laser induced fluorescence; Premixed flame; Chemiluminescence; Operating conditions; Raman scattering; Laser; Probability density function; Flame structure; Instability; Numerical simulation; Turbulence-chemistry interaction; Gas turbine; Comparative study
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/j.combustflame.2007.04.002

A nozzle configuration for technically premixed gas turbine flames was operated with CH
4 and air at atmospheric pressure. The flames were confined by a combustion chamber with large quartz windows, allowing the application of optical and laser diagnostics. In a distinct range of operating conditions the flames exhibited strong self-excited thermoacoustic pulsations at a frequency around 290 Hz. A flame with
P
=
25
 kW
thermal power and an equivalence ratio of
Φ
=
0.7
was chosen as a target flame in order to analyze the dynamics and the feedback mechanism of the periodic instability in detail. The velocity field was measured by three-component laser Doppler velocimetry, the flame structures were measured by chemiluminescence imaging and planar laser-induced fluorescence of OH, and the joint probability density functions of major species concentrations, mixture fraction, and temperature were measured by laser Raman scattering. All measuring techniques were applied in a phase-locked mode with respect to the phase angle of the periodic pulsation. In addition to the pulsating flame, a nonpulsating flame with increased fuel flow rate (
P
=
30
 kW
,
Φ
=
0.83
) was studied for comparison. The measurements revealed significant differences between the structures of the pulsating and the nonpulsating (or “quiet”) flame. Effects of finite-rate chemistry and unmixedness were observed in both flames but were more pronounced in the pulsating flame. The phase-locked measurements revealed large variations of all measured quantities during an oscillation cycle. This yielded a clear picture of the sequence of events and allowed the feedback mechanism of the instability to be identified and described quantitatively. The data set presents a very good basis for the verification of numerical combustion simulations because the boundary conditions of the experiment were well-defined and the most important quantities were measured with a high accuracy.