Azimuthal Instabilities of an Annular Combustor With Different Swirling Injectors

Abstract Experiments are carried out on the laboratory-scale MICCA-Spray annular combustor to examine effects of swirlers combustion instabilities. This system comprises 16 spray-swirl injectors and gives rise instabilities coupled by azimuthal modes. Five types producing clockwise rotation varying in swirl numbers pressure drops considered. These can be broadly categorized into two groups: lower-swirl higher-swirl groups, based their numbers. An arrangement where counterclockwise alternate is also studied. performed systematically with liquid heptane at five levels thermal power six equivalence ratios. Results reveal that none category exhibit instability operating region considered, whereas units feature strong trace an overall limit cycle envelope a few short random bursts. Among group, higher drop swirler associated broader map. shows transition mainly depends number through its effect flame structure adds further variations amplitude frequency oscillation. The spin ratio time series indicate modes mixed type distribution condition. On specifically comparing between full set rotating (CR) configuration (CCR) alternatively placed, it found there no definite statistical preference for linked bulk swirl. In some cases, however, CCR promotes ratios centered around standing mode (sr = 0) while CR setup favors spinning direction. attempt made interpret occurrence making use describing functions (FDFs) measured single-injector combustor. It FDFs corresponding categories (lower-swirl higher-swirl) relatively distinct. observed behavior tentatively interpreted using analysis which injector upstream plenum represented impedance shifts band instability. unstable then relative position FDF phase respect range expected frequency. gain notably depend number, possible distinguish, present configuration, low inducing stable operation another high leading oscillations.