scholarly journals Flame Stabilization and Blow-off of Ultra-Lean errortypeceH2-Air Premixed Flames

Energies ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1977
Author(s):  
Faizan Habib Vance ◽  
Yuriy Shoshin ◽  
Philip de Goey ◽  
Jeroen van Oijen
Keyword(s):  
Bluff Body ◽  
Flame Stabilization ◽  
Cfd Simulations ◽  
Preferential Diffusion ◽  
Previous Hypothesis ◽  
Hydrogen Flame ◽  
Efficient Combustion ◽  
Lean Limit ◽  
Displacement Speed

The manner in which an ultra-lean hydrogen flame stabilizes and blows off is crucial for the understanding and design of safe and efficient combustion devices. In this study, we use experiments and numerical simulations for pure errortypeceH2-air flames stabilized behind a cylindrical bluff body to reveal the underlying physics that make such flames stable and eventually blow-off. Results from CFD simulations are used to investigate the role of stretch and preferential diffusion after a qualitative validation with experiments. It is found that the flame displacement speed of flames stabilized beyond the lean flammability limit of a flat stretchless flame (ϕ=0.3) can be scaled with a relevant tubular flame displacement speed. This result is crucial as no scaling reference is available for such flames. We also confirm our previous hypothesis regarding lean limit blow-off for flames with a neck formation that such flames are quenched due to excessive local stretching. After extinction at the flame neck, flames with closed flame fronts are found to be stabilized inside a recirculation zone.

Experimental Investigation Into the Role of Mean Flame Stabilization On the Combustion Dynamics of High-Hydrogen Fuels in a Turbulent Combustor

2021 ◽  
Author(s):  
Nikhil Ashokbhai Baraiya ◽  
Vikram Ramanan ◽  
Baladandayuthapani Nagarajan ◽  
Chetankumar S Vegad ◽  
S. R. Chakravarthy
Keyword(s):  
Bluff Body ◽  
Flame Structure ◽  
High Amplitude ◽  
Acoustic Mode ◽  
Flame Stabilization ◽  
Pure Hydrogen ◽  
Airflow Rate ◽  
High Hydrogen ◽  
Combustion Dynamics

Abstract A bluff-body turbulent combustor is mapped for its thermo-acoustic stability across variation in airflow rate, non-dimensionalized as the Reynolds number (Re) and fuel composition. The combustor stability is evaluated for three fuels, namely, pure hydrogen (PH), synthesis natural gas (SNG), and syngas (SG). The combustion dynamics display markedly different behavior across the fuels, in the extent of the unstable region, as well as the observed dominant Eigenvalues. At low Re, SNG displays stable combustion, while SG exhibits high amplitude oscillations at the fundamental duct acoustic mode. As the Re is increased, SNG displays very high amplitude oscillations at the duct acoustic mode, while SG exhibit relatively low amplitude oscillations at the third harmonic. In the case of PH, high amplitude oscillations observed at higher Re at the first harmonic. These peculiarities are investigated in light of the role of mean flame stabilization. The combustion dynamics of fuels is influenced by the global equivalence ratio, as well as the jet momentum ratio. These effects significantly demarcates the dynamics of SNG and SG combustion. This is seen manifested in mean flame structure of flame at high amplitude oscillations, whereby result in SNG flame to be present in the wake, while the SG flame resides in the shear layer. The driving by the flame because of their mean stabilization quantified by a spatial Rayleigh index. It confirms the presence of large driving regions for SNG compared to that of SG, results in the observed differences in amplitude of the oscillations.

Role of atomic hydrogen diffusion in a hydrogen flame

2007 ◽  
Vol 43 (2) ◽  
pp. 125-131 ◽  
Author(s):  
V. A. Bunev ◽  
V. N. Panfilov ◽  
V. S. Babkin
Keyword(s):  
Atomic Hydrogen ◽  
Hydrogen Diffusion ◽  
Hydrogen Flame

Review and Analysis of Bluff Body Flame Stabilization Data

2008 ◽  
Author(s):  
Sajjad A. Husain ◽  
Ganesh Nair ◽  
Santosh Shanbhogue ◽  
Tim C. Lieuwen
Keyword(s):  
Activation Energy ◽  
Kinetic Modeling ◽  
First Principles ◽  
Bluff Body ◽  
Large Range ◽  
Flame Stabilization ◽  
Local Extinction ◽  
Data Set ◽  
Flame Sheet ◽  
Semi Empirical

This paper compiles and analyzes bluff body stabilized flame blowoff data from the literature. Many of these studies contain semi-empirical blowoff correlations that are, in essence, Damko¨hler number correlations of their data. This paper re-analyzes these data, utilizing various Damko¨hler number correlations based upon detailed kinetic modeling for determining chemical time scales. While the results from this compilation are similar to that deduced from many earlier studies, it demonstrates that a rather comprehensive data set taken over a large range of conditions can be correlated from “first-principles” based calculations that do not rely on empirical fits or adjustable constants (e.g., global activation energy or pressure exponents). The paper then discusses the implications of these results on understanding of blowoff. Near blowoff flames experience local extinction of the flame sheet, manifested as “holes” that form and convect downstream. However, local extinction is distinct from blowoff — in fact, under certain conditions the flame can apparently persist indefinitely with certain levels of local extinction. We hypothesize that simple Damko¨hler number correlations contain the essential physics describing this first stage of blowoff; i.e., they are correlations for the conditions where local extinction on the flame begins, but do not fundamentally describe the ultimate blowoff condition itself. However, such correlations are reasonably successful in correlating blowoff limits because the ultimate blowoff event appears to be correlated to some extent to the onset of this first stage.

Simulation of Two-Dimensional Turbulent Recirculating Flow Field Behind a V-Shaped Bluff Body

1994 ◽  
Author(s):  
Z. Gu ◽  
M. A. R. Sharif
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Flame Stabilization ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Combustion Chambers ◽  
Recirculating Flow ◽  
Conservative Form ◽  
Curvilinear Grid ◽  
Predictor Corrector

Abstract The two-dimensional turbulent recirculating flow fields behind a V-shaped bluff body have been investigated numerically. Similar bluff bodies are used in combustion chambers for flame stabilization. The governing transport equations in conservative form are solved by a pressure based predictor-corrector method. The standard k-ϵ turbulence closure model and a boundary fitted multi-block curvilinear grid system are used in the computation. The code is validated against turbulent flow over a backward facing step problem. The predicted flow field behind the bluff body is also compared with experiment. It is found that while the qualitative features of the flow are well predicted, there is quantitative disagreement between the measurement and prediction. This disagreement can be partially attributed to the k-ϵ turbulence model which is known to be inadequate for recirculating flows. Parametric investigation of the flow field by varying the shape and size of the bluff body is also performed and the results are reported.

scholarly journals Dynamics of lean premixed flames stabilized on a meso-scale bluff-body in an unconfined flow field

2018 ◽  
Vol 13 (6) ◽  
pp. 48 ◽  
Author(s):  
Yu Jeong Kim ◽  
Bok Jik Lee ◽  
Hong G. Im
Keyword(s):  
Bluff Body ◽  
Proper Time ◽  
Premixed Flames ◽  
Narrow Channel ◽  
Flame Stabilization ◽  
Inflow Velocity ◽  
Lean Premixed Flames ◽  
Lean Premixed ◽  
The Mean ◽  
Meso Scale

Two-dimensional direct numerical simulations were conducted to investigate the dynamics of lean premixed flames stabilized on a meso-scale bluff-body in hydrogen-air and syngas-air mixtures. To eliminate the flow confinement effect due to the narrow channel, a larger domain size at twenty times the bluff-body dimension was used in the new simulations. Flame/flow dynamics were examined as the mean inflow velocity is incrementally raised until blow-off occurs. As the mean inflow velocity is increased, several distinct modes in the flame shape and fluctuation patterns were observed. In contrast to our previous study with a narrow channel, the onset of local extinction was observed during the asymmetric vortex shedding mode. Consequently, the flame stabilization and blow-off behavior was found to be dictated by the combined effects of the hot product gas pocket entrained into the extinction zone and the ability to auto-ignite the mixture within the given residence time corresponding to the lateral flame fluctuations. A proper time scale analysis is attempted to characterize the flame blow-off mechanism, which turns out to be consistent with the classic theory of Zukoski and Marble.

Lean Blowout Phenomena and Prior Detection of Lean Blowout in a Premixed Model Annular Combustor

2019 ◽  
Author(s):  
Arijit Bhattacharya ◽  
Bikash Gupta ◽  
Satyajit Hansda ◽  
Zohadul Haque ◽  
Ashish Kumar ◽  
...  
Keyword(s):  
Bluff Body ◽  
Nox Reduction ◽  
Marked Change ◽  
Nox Emission ◽  
Thermoacoustic Instability ◽  
Lean Blowout ◽  
Lean Combustion ◽  
Annular Combustor ◽  
Lean Limit ◽  
Lift Off

Abstract Strict emission norms in the last few decades have paved the path for adaptation of new low NoX emission alternatives to power generation and aircraft propulsion. Lean combustion is a very promising and practicable technology for reducing NOX reduction and also have very high fuel efficiency. However, lean combustion technology suffers from inherent combustion instabilities that are manifested under different conditions, most importantly, thermoacoustic instability and lean blowout. Lean blowout occurs when a gas turbine combustor operating close to lean limit, for lowest NoX emission, faces abrupt changes in fuel homogeneity, quality or flow rate. While many work have been done in thermo-acoustic instability and flame propagation in annular combustors, studies in lean blowout in annular combustors are very limited. The lean limit of combustors are not fixed and is dependent on fuel characteristics and operating condition including environmental effects. So accurate online prediction of lean limit is very important to keep the combustors operating safely near lean limit. Recent works have demonstrated that single burner combustors leave out a significant amounts of physics including interaction of flames from different burners prior to blowout. In this work, a stepped down swirl and bluff body stabilized annular combustor in CB configuration (having chamber and burner), is used as experimental test rig having 4 number of identical burners. Video and heat release data are taken at different conditions as lean blowout is approached. Frequent attachment and reattachment of the flames prior to lift off was seen. As lean blowout is approached, inherent subtle differences in the different burners get amplified when flame becomes sufficiently weak and flame symmetry is broken. As air fuel mixture is made gradually leaner, one by one the flames from different burners elongates although remains partially attached to burner. Further lowering the equivalence ratio results in lift off and merging of the flame fronts of different burners. Three pixel averaged color ratios are extracted from still camera RGB images as flame stability indicators which are, red by blue, red by green and blue by green. The parameters show marked change at the point of lift off as well as at the lean blowout point.

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