PUB - Publikationen an der Universität Bielefeld

The aim of the German federal government is to increase the share of renewable energy sources on the total energy production, like wind power or photovoltaic, from currently 12.6~\% to 35~\% in 2020. A consequence of the fluctuating energy production of wind and solar power plants is that conventional power plants, originally designed for continuous load, must perform rapid load changes. Gas power plants are the only conventional power plant type available that is able to perform the necessary load changes cost-effectively within a few minutes to a few hours. The main issue in development and operation of low-pollutant gas power plants is the occurrence of combustion instabilities. Combustion instabilities are a major problem under premixed and lean combustion conditions and are based on the coupling of a periodically fluctuating heat release with the acoustic field of the burner chamber. The occurrence of combustion instabilities is generally unfeasible as they degrade performance and increase the deterioration of hot burner parts, making combustion instabilities a very costly phenomenon. In order to tackle this problem the aim of this work is to increase the understanding of combustion instabilities with the ultimate goal of preventing or controlling these instabilities. To fulfill this goal, a burner chamber is designed and constructed, which shows combustion instabilities under specific operating conditionsd. The burner chamber features a square layout and stabilizes an inverted V-flame. This setup allows to regard the flame as two-dimensional in order to simplify the modelling of the combustion process. For the characterization of combustion instabilities, the acoustic field of the burner chamber and the heat release fluctuations of the flame have to be known. To allow the detection of the pressure oscillations, microphones are fitted inside the burner chamber. The heat release is monitored by a newly designed chemiluminescence detection system which is able to measure the chemiluminescence in real time with a robust and cost-effectively photomultiplier system. In addition, spatial- and phase-resolved 2D-measurements are performed. An analysis routine was developed to extract additional flame parameters, like the flame height, flame width, flame surface area and volume of the unburned fresh gas from these images. As the flame is influencing the pressure field of the burner, the pressure wave is likewise influencing the flame. In order to investigate the shape of the oscillating gas column, a flexible, lens based schlieren system is set up. With this newly constructed setup the visualization of refractive index gradients is possible. In addition to the classic black/white schlieren, a focus of this work was the use of quantitative color schlieren. Color schlieren images enable the reconstruction of the original refractive index field and derived parameters using a rainbow color filter instead of a classic knife edge. Acoustically forced and self-oscillating flames were investigated in order to achieve a detailed understanding of the instable flame behavior and associated changes of the flame morphology. Through the combination of chemiluminescence-, pressure-, and schlierenmeasurements the interaction of the flame heat release with the acoustic field of the burner chamber was characterized in great detail. Furthermore additional parameters influencing the instabilities, like the heat transfer from the flame to the burner chamber, are discussed. For an active control, a sufficiently fast actuator is needed. In this work, two different actuators, a loudspeaker and a high-voltage field, are used and their advantages and disadvantages for their use in industrial applications discussed. Whereas the loudspeaker is influencing the pressure field of the combustion chamber, the high voltage field has a direct effect on the combustion process on the molecular level. Thus the effect of the applied field on the flame morphology and the flame heat release is examined. Based on these results a novel control strategy, relying on the chemiluminescence as control variable, is developed and tested.