Abstract
Small scale experimentation using particle image velocimetry investigated the effect of the diffusive injection of methane, air, and carbon dioxide on the coherent structures in a swirling flame. The interaction between the high momentum flow region (HMFR) and central recirculation zone (CRZ) of the flame is a potential cause of combustion induced vortex breakdown (CIVB) and occurs when the HMFR squeezes the CRZ, resulting in upstream propagation. The diffusive introduction of methane or carbon dioxide through a central injector increased the size and velocity of the CRZ relative to the HMFR whilst maintaining flame stability, reducing the likelihood of CIVB occurring. The diffusive injection of air had an opposing effect, reducing the size and velocity of the CRZ prior to eradicating it completely. This would also prevent combustion induced vortex breakdown CIVB occurring as a CRZ is fundamental to the process; however, without recirculation it would create an inherently unstable flame.
Highlights
The depletion of fossil fuels and concern about the climate change have led to the development of new technologies to meet power generation demand, whilst maintaining security of supply and decreasing the environmental impact
In order to reduce the emission of nitrogen oxides (NOx), gas turbines operate using lean premixed combustion, utilising swirl stabilisation and resulting in the central recirculation zone (CRZ) of the flame becoming crucial
(i) methane which is often used as a pilot fuel in gas turbines and will increase the global equivalence ratio of the flame, global equivalence ratio being that of the premixed air and methane, and the (ii) carbon dioxide which does not affect oxidant-to-fuel ratio but has been shown in previous studies to alter flame conditions [27,28,29,30,31], Table 1: Details of AGSB test points 1–26
Summary
The depletion of fossil fuels and concern about the climate change have led to the development of new technologies to meet power generation demand, whilst maintaining security of supply and decreasing the environmental impact. The use of gas turbines, a well-developed technology, fired on nontraditional fuels, is an increasingly viable method for producing energy in the short to medium term. Gas turbine technologies are evolving to cope with the use of these new fuels. Operators are still finding problems with fuels that vary in composition, posing a new challenge to manufacturers to produce equipment with less stringent fuel requirements [5]. In order to reduce the emission of nitrogen oxides (NOx), gas turbines operate using lean premixed combustion, utilising swirl stabilisation and resulting in the central recirculation zone (CRZ) of the flame becoming crucial. The CRZ can for instance readily extend back into the burner surrounding the fuel injector and facilitating early flashback (low stability limit) [6,7,8]. Flashback can be caused by (i) boundary layer flame propagation, (ii) turbulent flame propagation in the core flow, (iii) thermoacoustics, and (iv) upstream flame propagation of coherent vortical structures [7, 9,10,11]
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