THE NEW FRONTIERS FOR THE CONTROL OF COMBUSTION IN GAS TURBINES

Research and development in the control of combustion in gas turbines. Combustion processes play a key role in the efficiency of energy use and for the environmental impact of energy systems. The challenging topic of recent scientific and technological research in the field of combustion in gas turbine engines is the control of the fundamental physical and chemical processes, up to the molecular level, affecting the phenomena under investigation. The proposed speech will review the main research areas that actually focus on improvement of injection and vaporization of the fuel, new concepts of atomizers, control and optimization of air - fuel mixing. Moreover, control of oxidation processes with lean combustion, combustion instabilities, micro-scale combustion, control using active systems, development of new combustion concepts. Particularly significant are the results achieved in the investigation of the effects of air-assist atomization, at the combustor inlet of a modern gas turbine engine. The prefilming in airblast atomizer was investigated because the atomization of the fuel influences amongst others the amount of pollutant emissions. The research focused attention to other injection types, as the lean direct injection combustor, or the advanced multi-point fuel injector, analyzing the effects on the flow-field resulting from interactions between low and high-swirl counter-rotating air swirlers. Significant developments have been obtained for the technologies of microcombustion and micro gas turbines, as well as for new combustion concepts. For example, comprehensive experimental investigations were carried out on the flameless oxidation technology for small scale micro gas turbines, or on ultra-compact combustors. The new combustion concepts will offer various advantages in terms of flashback risk, lean blow-out limits and exhaust gas emissions. Particular attention will be payed to the characterization of the behavior of lean liquid fuel gas turbine near the lean blowout limit. The identification of the instability occurrence plays a key role for an efficient flame control. The behavior of high-speed images of the flame under stable and near blowout condition has been analyzed in conjunction with simultaneous optical data in order to better understand the phenomenology of the flame blowout process and the onset of instability. The data collected produce useful features for the development of an efficient tool for the flame control in industrial and aeronautical burners. The thermoacoustic behavior of gas turbine combustors is critical for the reliability and performance of the whole engine. With increasing demand of part load capability, the topic is as important as ever. The burners dynamics have been widely studied to prevent any undesirable behavior such as combustion instabilities, flashback and undesired blow-off. Although lean premixed combustion is very clean and basically soot-free, it has one serious drawback, as tendency to develop thermo-acoustic instabilities. These instabilities can be very violent, at the least causing unwanted noise and vibration, and in more serious cases, complete engine failure. Current research has shown methods to address such instabilities using passive and active control techniques. Finally, the research data can be used to extrapolate the implications on combustion and gas turbine performance and recommendations for the combustor design, considering the substantial impact on the delicate balance between combustor stability and gas turbine performance and emissions.