Chair Concept

The CHAIRLIFT combustor concept comprises two novel features: The first is to adopt “low swirl” lean lifted spray flames which feature a high degree of premixing and consequently significantly reduced NOx emissions. Inherent characteristics of such flames are the strongly reduced risk of flashback and a reduced susceptibility to thermo-acoustics instabilities compared to conventional swirl stabilized flames. As second novelty of the CHAIRLIFT concept an alternative approach to standard flame piloting is proposed, enabling a further reduction of NOx emissions. Stable and safe operations of the combustor are ensured by the interaction of adjacent flames in circumferential direction within the annular combustion chamber. This requires tilting of the axis of the flames relative to the axis of the machine. The rationale of this concept is to extend the operability of ultra-low NOx emissions capabilities of low-swirl lean lifted spray flames by the inherent piloting effect provided by the onset of mutual tangential interaction of flames in the annular chamber. The use of low-swirl flames is also found to prevent large flow instabilities observed by Ariatabar et al in preliminary studies on the so-called Short Helical Combustor operated with standard swirl-stabilized flames with high swirl number burners. Additional benefits are the reduced length of the combustor, a smaller number of NGVs and hence reduced cooling air requirements. Recent investigation carried out by CHAIRLIFT partners have supported the general validity of the concept in terms of combustion aerodynamics with an improvement of LBO margins and a confirmation of ultra-low NOx emissions. Even if not directly measured, almost negligible PM emissions are associated to the concept as confirmed by non-sooty blue lean flames observed during tests on multi-burner rig installed at KIT. A preliminary investigation of the use of nano-pulsated plasma discharges to further improve lifted flames stability has also been investigated pointing out further promising capabilities in terms of widening the combustor LBO margins.