Different Flame Patterns Linked With Swirling Injector Interactions in an Annular Combustor

Abstract

Experiments in cold and reactive conditions carried out in linear arrays of injectors indicate that the flows established by neighboring injectors exhibit alternating patterns if the distance between two injectors is too small (see, for example, ASME-GT2013-94280, GT2014-25094, and GT2015-42509). This issue is investigated in this article by making use of a recently developed annular combustion chamber (ACC). This device designated as MICCA is equipped with multiple swirling injectors and its side walls are made of quartz providing full optical access to the flame region, thus allowing detailed studies of the combustion region structure and dynamics. Experiments reported in this article rely on direct observations of the flame region through light emission imaging using two standard cameras and an intensified high-speed CMOS camera. The data gathered indicate that interactions between successive injectors give rise to patterns of flames which exhibit an alternate geometry where one flame has a relatively low expansion angle while the next spreads sideways. This pattern is then repeated with a period which corresponds to twice the injector spacing. Such arrangements arise when the angle of the cup used as the end-piece of each injector exceeds a critical value. The effects of mass flow rate, equivalence ratio, and injector offset are also investigated. It is shown that the angle which defines the cup opening is the main control parameter. It is also found that when this angle exceeds a certain value and when the laminar burning velocity is fast enough, the flame pattern switches in an unsteady manner between two possible configurations. It is shown that these alternating flame patterns lead to alternating heat release rate distributions and inhomogeneous heat transfer to the chamber walls featuring a helicoidal pattern. Conditions leading to alternating flame patterns are finally discussed by making use of a recent flow regime diagram.

Combustion Dynamics of Annular Systems

“…The initial configuration was equipped with injectors fed by premixed reactants featuring a cylindrical exhaust section (Bourgouin et al 2013b). These injectors were later fitted with a conical cup and the corresponding configuration was designated as MICCA2 (Durox et al 2016). Swirling units were then replaced by matrix injectors comprising a periodic arrangement of small channels producing a multiplicity of small laminar flames.…”

Large Eddy Simulation and Acoustic Analysis of Combustion Instability in an Annular Combustor with Low-Swirl Flames

“…Experimental measurement is an effective way to directly characterize the modal structure and flame dynamics of the annular combustor. Experimental results from Worth and Dawson 9 , 10 and Durox et al 11 , 12 successfully captured the modal structures during the azimuthal instability. Recently, effects of hydrogen addition on the azimuthal instability in the annular combustor are reported by using experimental methods.…”

“…Experimental measurement is an effective way to directly characterize the modal structure and flame dynamics of the annular combustor. Experimental results from Worth and Dawson , and Durox et al , successfully captured the modal structures during the azimuthal instability. Recently, effects of hydrogen addition on the azimuthal instability in the annular combustor are reported by using experimental methods. , Results show that significant high-amplitude instabilities are excited with the hydrogen content reaching 25%, and the amplitudes decrease slightly when the H 2 content is further increased.…”

The Effects of Strong-Weak Swirling Interaction on Emissions in a Multi-Nozzle Combustor

“…However, the research on fuel staging mainly focuses on the combustion stability [12][13][14]. Variation of parameters such as the swirl direction and spacing of adjacent nozzles would affect the flow and flame interaction in the combustion chamber, and eventually had a greater impact on the flame structure and emission performance of the combustion chamber [15][16][17][18]. Worth and Dawson [19] studied the effect on the flame structure of the annular combustion chamber with 12, 15, and 18 nozzles by changing the spacing between the nozzles.…”