Effects of annular N2/O2 and CO2/O2 jets on combustion instabilities and NOx emissions in lean-premixed methane flames

2020

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Effects of combustion instability on flame macrostructures and NO x emissions were conducted experimentally in a model gas turbine combustor. Two variables of the CH 4 flame were investigated-the flow rate and the equivalence ratio. Results indicate that flame macrostructure changes when the equivalence ratio increases from 0.50 to 1.00, the average total length of flame front firstly decreases from 105 to 75 mm, and then increases to 110 mm. While the average length of flame root decreases from 25 to 5 mm. The appearance of the flame front evolves from a "M" shape to a reversed "V" shape, but the appearance of the flame root changes from elongated V shape to a flatted V shape. The envelop diagram of different combustion instability signifies that there are mode shifting of flame-acoustic interactions in the combustion chamber. Under instability conditions, the temperature and velocity distribution of the flame front or flame root affects the NO x emissions. Along the radial direction, the peak temperature in the inner recirculation region and the outer recirculation region drops. This article explored the dynamic characteristics of lean-premixed flames under combustion instability, which could be instructive to the designing of stable and clean combustors in industrial gas turbines.

Section: Geometric Structure Of the Combustormentioning

confidence: 99%

Section: Geometric Structure Of the Combustormentioning

confidence: 99%

Section: Geometric Structure Of the Combustormentioning

confidence: 99%

Section: Evolution Of Flame Macrostructuresmentioning

confidence: 99%

Section: Evolution Of Flame Macrostructuresmentioning

confidence: 99%

See 3 more Smart Citations

Macrostructure and NO_x emission evolution characteristics of lean‐premixed flames under combustion instability

2020

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Effect of carbon dioxide, argon, and helium jets on the synchronous control of combustion instability and NO_x emission

2020

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This article experimentally studies the synchronous control of combustion instability and NOx emission in a model gas turbine combustor. The application of tabular jet in cross flow was adopted to test the effectiveness of synchronous control. The flow rate, height, direction, and relative molecular masses were studied in this research. Results suggest that the ideal damping ratio of the sound pressure amplitude can be as high as 73.7% under the carbon dioxide jet in cross flow case. The carbon dioxide jet in cross flow case can lead to a better thermoacoustic instability suppression result than the instances of argon or helium. Besides, amplitude and frequency switching of the unsteady flame emerged during the experiment. Adding minimal inert gaseous can change the local oscillation of equivalence ratio. The suppression ratio of NOx emission can reach as high as 44% under the carbon dioxide cases, which performs better than the argon or helium cases. Moreover, the flame length declines as the tabular jet in cross flow rate increases. When the flow rate increases (or the height decreases), the size of the flame front or root will decrease. The average flame length dropped from 122 to 41 mm. The macrostructure of the flame changes significantly under different injecting heights or directions. This article can serve as a specific guideline for the passive control of thermoacoustic instability in gas turbine, rocket, and industrial burners.

Mitigating combustion instability and NO_x emissions with annular oxyfuel jets into the flame shear layer region

2021

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The shear layer is a region between the internal and external recirculating zone of the flame, which is critical for combustion stabilization and emission. This study experimentally studied the effects of oxyfuel (CO2/O2) shear layer injections on combustion dynamics and pollutant emissions of a model gas turbine combustor. To evaluate the damping performances of ‘Oxy’ CO2/O2 shear layer jets on unsteady combustion and pollutant formation processes, four variables of the CO2/O2 shear layer injection system are studied—the flow rate, the inner diameter, the injection angle and the oxygen ratio. Experimental results show that thermoacoustic instability and NOx emissions can be suppressed with the ‘Oxy’ CO2/O2 shear layer injection method. The minimum inner diameter cases could achieve better control effectiveness of 80%, with the sound pressure amplitude drops from 27 to 5.4 Pa. The maximum inner diameter case could achieve better control effectiveness of 59.2%, with the concentration of NOx emissions drops from 25 to 10.2 ppm. Flame oscillation modes experienced shifting and switching under different shear layer angles and oxygen ratios. There exist extreme points that can be selected for a better control effect. The CO2/O2 shear layer injection splits the inner and outer recirculation zones of the flame. As the oxygen ratio of CO2/O2 varied from 36% to 46%, a flame flapping phenomenon emerged. The ‘Oxy’ CO2/O2 shear layer injection method could eliminate combustion instability and NOx emissions at a relatively lower cost and complexity, which will promote the development of high‐performance burners.