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‘Fuel-flexible’ gas turbines will be required over the next 20 years at least. However, this contrasts with recent experiences of\ud global operators who report increasing emissions and difficult combustion dynamics with even moderate variations in the fuel\ud supply. Swirl stabilized combustion, being the most widely spread technology to control combustion in gas turbines, will be a\ud technology needed for dynamic stabilization of the flow field. However, the features of the recirculation zone are highly complex,\ud three dimensional and time dependent, depending on a variety of parameters. A high momentum flow region inherent to swirling\ud flows has attracted the attention of several groups interested in blowoff and stretch flame phenomena. Therefore, this study\ud focuses on experimental results obtained to characterise the relation between the central recirculation zone and the high momentum\ud flow region under moderate swirl levels using a well-studied tangential swirl burner for power generation applications. As\ud to be expected the recirculation zone and the high momentum flow region rotate together about the central axis. Moreover, the\ud interaction between them produces high, intense local velocities. This region of High Momentum (shearing flow) also presents a\ud complex geometry that seems to be based on the geometrical features of the burner, different to previous findings on the burner\ud where the system was thought to have a unique shearing flow region. The high three dimensional interaction of these structure is\ud confirmed at the point where the precessing vortex core losses its strength.

Lean premixed combustion using swirling flows is widely used in gas tur\ud -\ud bines and combustion. Although flashback is not generally a problem with\ud natural gas combustion, there are some reports of flashback damage with\ud existing gas turbines, whilst hydrogen enriched fuel blends cause concerns\ud in this area. Thus, this paper describes a practical approach to study and\ud avoid flashback in a pilot scale 100\ud kW tangential swirl burner. The flash\ud -\ud back phenomenon is studied experimentally via the derivation of flashback\ud limits for a variety of different geometrical conditions. A high speed camera\ud is used to visualize the process and distinguish new patterns of avoidance.\ud The use of a central fuel injector is shown to give substantial benefits in terms\ud of flashback resistance. Conclusions are drawn as to mitigation technologie

This paper presents a series of experiments and numerical simulations using commercial software (ANSYS) to determine the behaviour and impact on the blowoff process with various geometries and simulated syngas compositions at fixed power outputs. Experiments were performed using a generic premixed swirl burner. The Central Recirculation Zone and the associated turbulent structure contained within it were obtained through CFD analyses providing details of the structures and the Damkolher Number (Da) close to blowoff limits. The results show how the strength and size of the recirculation zone are highly influenced by the blend, with a shift of Da and turbulence based on carbon-hydrogen ratio, shearing flows and Reynolds number. Instabilities such as thermoacoustics, flashback, autoignition and blowoff are highly affected by the flow structures and chemical reactions/diffusivity. Moreover, it has been observed that turbulence close to the boundaries of the central recirculation zone, a region of high stability for swirling flows, is highly altered by the chemical characteristics of the fuel blends. In terms of blowoff, the phenomenon is still not entirely understood. As the process occurs, its theoretical limits do not match its real behaviour. Therefore, one possibility could be the difference in turbulence and Da numbers across the flame, being critical at the base of the flame where the system is stabilized.