Flame-flame interaction in gas-turbine combustors

For industrial gas turbines and aeroengines the trend is towards optimum use of fuels and reduced emissions. To achieve this goal different combustion chamber concepts are under investigation. Unfortunately, combustors operating near the lean flammability limit have a strong tendency towards combustion instabilities. Oscillations of the static pressure amplitude caused by these instabilities might result in severe mechanical damage of the machine and therefore must be controlled. The Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology, supports this research on novel concepts for combustion chambers by participating in relevant EU projects and by the operation of large experimental facilities, including a 3 MW compressor station supplying compressed air to several test rigs, and a 2 MW air heater, which can be used together with the compressor station. This system can produce air at a temperature up to 550C with a mass flow of 5kg/s at 10 bar. The objective of the proposed project is the investigation of flame-flame interaction in a gas-turbine model combustion chamber with forced flow instabilities by a laser interferometric technique (Laser Vibrometer) and the development of a feedback control by a GaPO4 sensor. The most innovative aspect lies in the novel application of the laser optical metrology, especially in the correlation of signals obtained by a Laser Vibrometer, directly detecting density fluctuations, and correlate them to the pressure signals recorded by a GaPO4 sensor in a complex multi-flame configuration. Additional information from the oscillating flame will be obtained by Particle Image Velocimetry and Laser Induced Fluorescence. This research will result in the possibility to control these instabilities by a feedback control from novel type high- temperature pressure sensors in the combustion chamber. Within active international cooperation the novel measurement techniques developed within this project will be presented and discussed.

For modern industrial gas turbines and aeroengines the trend is towards optimum use of fuel and reduced emissions. Since modern combustors operate near the lean flammability limit they have strong tendency towards combustion instabilities. Unwanted effects like self-sustained pulsed heat release and oscillations of the static pressure caused by these instabilities might result in severe mechanical damage of the machine. Within this project single- and multi-flame gas-turbine model combustors were investigated with and without forced flow instabilities, as well as, self-excited thermoacoustic oscillations. The most innovative aspect of this work lies in the novel application of laser optical metrology, especially in the correlation of signals obtained by multiple laser vibrometers, directly detecting local density fluctuations and their spectrum of frequencies. To validate this novel technique additional data from the flames were recorded by laser- Doppler-velocimetry, Raman spectroscopy and interferometric technique (shearography). With this novel laser-based measurement technique international cooperations in the field of combustion research were triggered.