A non-conventional method based on forced-flow combustion oscillations is investigated regarding the improvement of combustion conditions at suboptimal operating conditions.
In the field of gas turbines, uncontrolled combustion oscillations are called combustion instabilities and they have been extensively studied over the last two decades. Low NOx systems that operate in the lean combustion domain are prone to enable combustion instabilities. A common way to investigate combustion instabilities is to reproduce these with help of an acoustic driver, e.g. using a loudspeaker or a fast valve in order to drive forced-flow combustion oscillations. When the oscillations match with one of the natural resonant frequencies of the combustor cavities or of the feeding pipes, the thermoacoustic coupling can occur in a well-controlled way.
Some positive effects of this type of forcing can be found in the literature. In a similar context, it was shown in a previous work (GT2015-42377) under which conditions and by how far a forced-flow thermoacoustic drive can further push the lean-blow-out limits in the lean region. Following to this work, it is described that driving a resonant flame can also be beneficial regarding combustion quality. Better combustion performances were observed with the help of pulsating the burner air feed at part-load conditions on a premixed swirling flame, where combustion quality is known to be impaired at steady-state.
The presented technology can then be seen as a flexible On-Off thermoacoustic drive, based on forced pulse combustion and using a siren tunable in frequency and amplitude in a refined way. The benefits and the challenges about its hypothetic implementation in the field of turbomachinery conclude this paper.