Experimental study of the effect of outlet boundary on combustion instabilities in premixed swirling flames

Abstract The present work investigates effects of the corner recirculation zone (CRZ) on flame macrostructures and combustion instabilities in the Beihang Axial Swirler Independently Stratified (BASIS) burner, a double-swirled full-scale burner characterized by separated stratified swirling flames at atmospheric pressure supplied with methane/air mixture. Three different macrostructures are observed, i.e. a lifted L-flame, a double-conical S-flame and a single conical V-flame as the stratification ratio (SR, the ratio of the inner stream equivalence ratio to the outer stream equivalence ratio) varies from 0.25 to 2.50 at a fixed total equivalence ratio of 0.6. It is found that the penetration of the flame into the corner recirculation zone leads to a sudden increase of acoustic oscillation. Rayleigh index maps confirm the driving effect of the CRZ region on combustion instabilities for the 0.25 ≤ SR ≤ 1.75 cases. When the corner recirculation zone is removed by the use of segmented confinements, similar flame macrostructures arise in the same SR range. More interestingly, the combustion instability is suppressed under all stratification ratios. A parametric experiment is also performed to confirm the generality of above findings, including three types of the segmented confinement, two premixednesses of the outer flame and a wider range of operating conditions. The suppressive effect is outstanding in all segmented confinements. The present study reveals the effect of the corner recirculation zone on combustion instabilities and demonstrates a potential method for passive control.

Download Full-text

Combustion Instabilities of Separated Stratified Swirling Flames With Different Degrees of Premixedness

Volume 4A: Combustion, Fuels, and Emissions ◽

10.1115/gt2019-90852 ◽

2019 ◽

Author(s):

Xinyao Wang ◽

Xiao Han ◽

Xin Hui ◽

Chi Zhang ◽

Heng Song ◽

...

Keyword(s):

Large Scale ◽

Convective Motion ◽

Dominant Frequency ◽

Oscillation Period ◽

Premixed Flame ◽

Combustion Instabilities ◽

Swirling Flames ◽

Partially Premixed ◽

Partially Premixed Flame ◽

Point Fast Fourier Transform

Abstract The effects of premixedness degrees on combustion instabilities of separated stratified swirling flames have been investigated experimentally in the Beihang Axial Swirler Independently-Stratified (BASIS) burner. The degree of premixedness is modulated by the fuel split between two injection positions in the outer stream. In the spectra of pressure oscillations, both the dominant frequency and amplitude of partially premixed flames are positively correlated with fuel split ratios. The partially premixed flame is found to feature a large-scale periodic convective motion based on CH* chemiluminescence images, which have been analyzed under different fuel split ratios by a point-to-point Fast Fourier Transform (FFT) method. The development of above convective motion is explained by combining the variation of pressure and heat release in the oscillation period. Local Rayleigh index maps show that the driving factor of combustion instability for the partially premixed flame mainly comes from the upstream of the combustor. Finally, thermoacoustic network analysis is applied to predict observed frequencies under both perfectly and partially premixed conditions. The supposed additional convective time due to equivalence ratio fluctuations and the elongated flame region for the partially premixed flame is validated by its longer time delay in the sensitivity analysis of the n-τ flame model.

Download Full-text

An experimental study into the effect of injector pressure loss on self-sustained combustion instabilities in a swirled spray burner

Proceedings of the Combustion Institute ◽

10.1016/j.proci.2018.06.125 ◽

2019 ◽

Vol 37 (4) ◽

pp. 5205-5213 ◽

Cited By ~ 6

Author(s):

Guillaume Vignat ◽

Daniel Durox ◽

Kevin Prieur ◽

Sébastien Candel

Keyword(s):

Experimental Study ◽

Pressure Loss ◽

Combustion Instabilities

Download Full-text

Experimental Study on Instability Characteristics of Low-Swirl Flames in a Multi-Nozzle Combustor With Different Swirling Arrays

Volume 4A: Combustion, Fuels and Emissions ◽

10.1115/gt2016-56714 ◽

2016 ◽

Cited By ~ 2

Author(s):

Weijie Liu ◽

Bing Ge ◽

Yinshen Tian ◽

Shusheng Zang ◽

Shilie Weng ◽

...

Keyword(s):

Experimental Study ◽

Combustion Instabilities ◽

Longitudinal Modes ◽

Stable Operating ◽

Wide Range ◽

Planar Laser ◽

Combustion Region ◽

Unstable Combustion ◽

Fluctuation Amplitude ◽

Operating Window

This paper presents experimental study on self-excited combustion instability characteristics of premixed low-swirl flames in a multi-nozzle can combustor with counter-swirl and co-swirl arrays. Experiments were carried out over a wide range of inlet velocity from 4 m/s to 15.5 m/s and equivalence ratio from 0.5 to 0.85. Phase-locked OH planar laser-induced fluorescence was employed to measure flame shape and identify heat release rate. Four operation regions: stable combustion region, unstable combustion region, flashback region and extinguish region are observed for both array burners. The stable operating window for counter-swirl array is wider compared to the co-swirl array. Pressure fluctuation amplitude for co-swirl burner is larger than the counter-swirl arrangement at the same operating condition. In the unstable combustion region, the counter-swirl flames trigger the 2L mode of the combustion system while co-swirl flames incite three longitudinal modes with the highest amplitude near 3L. Rayleigh index distribution reveals neighboring flame interaction results in thermoacoustic coupling for multi-nozzle flames. Additionally, for counter-swirl array, thermoacoustic couplings in flame base region and shear region are also the main reasons for inducing self-excited combustion instabilities. For co-swirl array, the instability driving zones also locate at the lip region and the tail of center flame.

Download Full-text

Experimental Study of Combustion Instabilities in a Single-Element Coaxial Swirl Injector

41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit ◽

10.2514/6.2005-4298 ◽

2005 ◽

Cited By ~ 12

Author(s):

Kevin Miller ◽

James Sisco ◽

Nicholas Nugent ◽

William Anderson

Keyword(s):

Experimental Study ◽

Single Element ◽

Combustion Instabilities ◽

Swirl Injector

Download Full-text

Experimental study on the restoration from a tilt-azimuth series for improvement in resolution

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010013955x ◽

1995 ◽

Vol 53 ◽

pp. 636-637

Author(s):

Norio Baba ◽

Norihiko Ichise ◽

Syunya Watanabe

Keyword(s):

Experimental Study ◽

Spherical Aberration ◽

Incident Beam ◽

Optical Parameters ◽

Beam Tilting ◽

Illumination Method ◽

Restoration Method ◽

Illumination Mode

The tilted beam illumination method is used to improve the resolution comparing with the axial illumination mode. Using this advantage, a restoration method of several tilted beam images covering the full azimuthal range was proposed by Saxton, and experimentally examined. To make this technique more reliable it seems that some practical problems still remain. In this report the restoration was attempted and the problems were considered. In our study, four problems were pointed out for the experiment of the restoration. (1) Accurate beam tilt adjustment to fit the incident beam to the coma-free axis for the symmetrical beam tilting over the full azimuthal range. (2) Accurate measurements of the optical parameters which are necessary to design the restoration filter. Even if the spherical aberration coefficient Cs is known with accuracy and the axial astigmatism is sufficiently compensated, at least the defocus value must be measured. (3) Accurate alignment of the tilt-azimuth series images.

Download Full-text