Influence of Fuel-Air Mixing on Flame Dynamics of Premixed Swirl Burners

Abstract

The influence of fuel-air mixing on the flame dynamics of premixed swirl flames is investigated comparing flame transfer functions determined for perfectly premixed (PP) and technically premixed (TP) operation. In PP operation fuel and air are mixed far upstream of the burner so no equivalence ratio fluctuations appear during thermo-acoustic oscillation. In TP operation the fuel is injected in the swirler slots so equivalence ratio fluctuations occur. The employed swirl burner is a modular system that consists of a swirler and a mixing tube with three different lengths. It was investigated in an atmospheric single burner test rig equipped for flame transfer matrix measurements. Flame transfer function data are presented for both the PP and the TP operation for a variation of power at fixed equivalence ratio and a variation of equivalence ratio for constant power. The unforced flame shapes corresponding to these operation points were acquired and analyzed for scaling parameters of the flame response. It was found that a basic frequency scaling can be achieved for both operation modes using the nominal burner velocity and the flame stand-off distance. A detailed comparison of the PP and TP flame transfer functions is performed for the three different mixing tubes at one operation point. Finally the difference between the PP and the TP flame transfer function is presented and discussed. It is shown that the influence of equivalence ratio fluctuations exhibits a generalized delay time behavior.

Comparison of the flame dynamics of a premixed dual fuel burner for kerosene and natural gas

“…While the FTF for the gas burner is in very good agreement with data from previous work, 13 the FTF for the dual fuel burner has an increased amplitude between Str = 0.1 and Str = 0.3 with a local maximum at Str = 0.2. This is very similar to the curves observed for leaner cases with an equivalence ratio of ϕ = 0.625.…”

“…For low amplitudes, the different contributions are linearly superposed. 12 This motivates an experimental decomposition approach which has already been followed by Bade et al 13 for natural gas flames and is now extended to liquid fuel combustion in this study. Flame transfer functions (FTFs) are measured in order to characterize the flame dynamics.…”

“…This is very similar to the curves observed for leaner cases with an equivalence ratio of ϕ = 0.625. 13 A possible explanation for this behaviour is that due to the atomizing air injection, the flame exhibits regions that are leaner than the global equivalence ratio at the central axis.…”

Experimental analysis of thermo-acoustic instabilities in a generic gas turbine combustor by phase-correlated PIV, chemiluminescence, and laser Raman scattering measurements

“…Frequently, minor geometrical modifications of the combustor or small changes in the operating or boundary conditions lead to drastic changes in the stability of the system, such as transition from attached to detached flames or flames with and without precessing vortex cores [Allison 2012, Arndt 2010, Biagioli 2008, Fritsche 2007, Hermeth 2014. In addition, understanding and predicting combustor thermo-acoustic behavior is complicated by significant effects of turbulence-chemistry interaction , Gicqel 2012, Lückerath 2011, Rebosio 2010, and spatially and temporally varying degrees of premixing [Bade 2014, Masri 2015, Stopper 2013. The occurrence of hydrodynamic instabilities like precessing vortex cores, vortex shedding, or other shear layer instabilities [Candel 2014, Caux-Brisebois 2014, Kim 2014, Moeck 2012, Stöhr 2013b further complicates the situation.…”

Numerical analysis of the dynamic flame response of a spray flame for aero-engine applications

“…The increased flame length and volume should lead to lower power density, a decrease of heat release fluctuations amplitude and therefore a reduced FTF gain. 44,45 The distance between the injector outlet plane and the PFR peak location is unchanged. Therefore, no significant differences are observed for the FTF phase.…”