scholarly journals Investigation of Dilution Effect on CH4/Air Premixed Turbulent Flame Using OH and CH2O Planar Laser-Induced Fluorescence

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 325
Author(s):  
Li Yang ◽  
Wubin Weng ◽  
Yanqun Zhu ◽  
Yong He ◽  
Zhihua Wang ◽  
...  
Keyword(s):  
Reaction Zone ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Dilution Effect ◽  
Dilution Ratio ◽  
Lean Combustion ◽  
Mild Combustion ◽  
Planar Laser ◽  
Premixed Turbulent Flame ◽  
The Given

Diluting the combustion mixtures is one of the advanced approaches to reduce the NOx emission of methane/air premixed turbulent flame, especially with high diluents to create a distributed reaction zone and mild combustion, which can lower the temperature of reaction zone and reduce the formation of NOx. The effect of N2/CO2 dilution on the combustion characteristics of methane/air premixed turbulent flame with different dilution ratio and different exit Reynolds number was conducted by OH-PLIF and CH2O-PLIF. Results show that the increase of dilution ratio can sharply reduce the concentration of OH and CH2O, and postpone the burning of fuel. Compared with the ultra-lean combustion, the dilution weakens the combustion more obviously. For different dilution gases, the concentration of OH in the combustion zone varies greatly, while the concentration of CH2O in the unburned zone is less affected by different dilution gas. The CO2 dilution has a more significant effect on OH concentration than N2 with the given dilution ratio, but a similar effect on the concentration of CH2O in the preheat zone of flame. However, dilution does not have much influence on the flame structure with the given turbulent intensity.

CO and OH Imaging in Flames Using a Single Broadband Femtosecond Laser Pulse

2020 ◽  
Author(s):  
Pradeep Parajuli ◽  
Ayush Jain ◽  
Waruna D. Kulatilaka
Keyword(s):  
Laser Pulse ◽  
Reaction Zone ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Chemical Species ◽  
Oxidation Reactions ◽  
Simultaneous Excitation ◽  
Spatiotemporal Information ◽  
Flame Burner ◽  
Fs Laser

Abstract Carbon monoxide (CO) and hydroxyl (OH) are the two key intermediate species formed during chemical reactions inside gas turbine combustors. Spatiotemporal information and a detailed understanding of CO formation in the reaction zone are important during the combustion processes as a major part of the heat release is obtained from the oxidation of CO to CO2. Turbulent flame structures and reaction zone in different flame conditions can also be visualized through the spatial distribution profiles of OH. In the current study, both these species are excited simultaneously using a single ultrashort, broad spectral bandwidth of approximately 100-femtosecond (fs) duration laser pulse at λ = 283.8 nm. Subsequent fluorescence signals are separated through spectral filters of appropriate bandwidth and imaged using two cameras. This present study was performed in a McKenna flat-flame burner with ethylene/air as a pilot flame and non-premixed turbulent ethylene jet at the center. The partial spectral overlap of CO–X (4,0) and OH A–X (1,0) transitions are utilized for simultaneous excitation, thereby characterize the overall flame structure (via OH) and regions of oxidation reactions (via CO) in a range of flame conditions. Besides, CO and OH profiles follow the trends obtained from model predictions for a range of equivalence ratios in ethylene/air flames stabilized over the Hencken calibration burner. These results are used for obtaining quantitative calibrations of CO and OH signals. Overall, the present study extends the applicability of a single, broadband fs laser pulse for simultaneous imaging of multiple chemical species in flame.

Combustion Structures in Lifted Ethanol Spray Flames

2004 ◽  
Vol 126 (2) ◽  
pp. 254-257 ◽  
Author(s):  
Stephen K. Marley ◽  
Eric J. Welle ◽  
Kevin M. Lyons
Keyword(s):  
Reaction Zone ◽  
Flame Structure ◽  
Leading Edge ◽  
Laser Induced Fluorescence ◽  
Premixed Combustion ◽  
Diffusion Mode ◽  
Spray Flames ◽  
Partially Premixed Combustion ◽  
Planar Laser ◽  
Single Reaction

The development of a double flame structure in lifted ethanol spray flames is visualized using OH planar laser-induced fluorescence (PLIF). While the OH images indicate a single reaction zone exists without co-flow, the addition of low-speed co-flow facilitates the formation of a double flame structure that consists of two diverging flame fronts originating at the leading edge of the reaction zone. The outer reaction zone burns steadily in a diffusion mode, and the strained inner flame structure is characterized by both diffusion and partially premixed combustion exhibiting local extinction and re-ignition events.

Further development of the three-region model of a premixed turbulent flame II. Instability dominated region 1

1979 ◽  
Vol 368 (1733) ◽  
pp. 283-293 ◽  
Keyword(s):  
Energy Balance ◽  
Viscous Dissipation ◽  
Balance Equation ◽  
Large Scale ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Small Scale ◽  
Laminar Burning Velocity ◽  
Premixed Turbulent Flame

An analysis of the balance equation for turbulent kinetic energy of an instability dominated region 1 is presented for a turbulent, premixed propane-air flame. The effects of intensity, scale and laminar burning velocity on the energy balance are also examined. Specifically, the nature of instability in a turbulent flame and its influence on the flame structure are highlighted. These results show that either increase in scale or reduction in intensity of approach turbulence increases the magnitude of all the terms in the balance equation. The core region of the flame is unaffected by a small scale instability, whereas, for a large scale instability, the ratio of turbulence production/viscous dissipation remains independent of scale. The dominant terms in the energy balance are found to be those of convection and advection when the structure of the flame turbulence consists mainly of a large scale fluctuating motion. Finally, increase in laminar burning velocity restores stability and causes transition to region 2, in which production and viscous dissipation predominate over convection and advection terms, respectively.

OH PLIF and Soot Volume Fraction Imaging in the Reaction Zone of a Liquid-Fueled Model Gas-Turbine Combustor

2004 ◽  
Author(s):  
Terrence R. Meyer ◽  
Sukesh Roy ◽  
Sivaram P. Gogineni ◽  
Vincent M. Belovich ◽  
Edwin Corporan ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Reaction Zone ◽  
Large Scale ◽  
Volume Fraction ◽  
Soot Formation ◽  
Flame Structure ◽  
Soot Volume Fraction ◽  
Gas Turbine Combustor ◽  
Planar Laser ◽  
Model Gas Turbine Combustor

Simultaneous measurements of OH planar laser-induced fluorescence (PLIF) and laser-induced incandescence (LII) are used to characterize the flame structure and soot formation process in the reaction zone of a swirl-stabilized, JP-8-fueled model gas-turbine combustor. Studies are performed at atmospheric pressure with heated inlet air and primary-zone equivalence ratios from 0.55 to 1.3. At low equivalence ratios (φ < 0.9), large-scale structures entrain rich pockets of fuel and air deep into the flame layer; at higher equivalence ratios, these pockets grow in size and prominence, escape the OH-oxidation zone, and serve as sites for soot inception. Data are used to visualize soot development as well as to qualitatively track changes in overall soot volume fraction as a function of fuel-air ratio and fuel composition. The utility of the OH-PLIF and LII measurement system for test rig diagnostics is further demonstrated for the study of soot-mitigating additives.

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