Turbulent Lifted Flames in the Hysteresis Regime and the Effects of Coflow

2006 ◽  
Vol 128 (4) ◽  
pp. 319-324 ◽  
Author(s):  
S. D. Terry ◽  
K. M. Lyons
Keyword(s):  
Flow Regime ◽  
Laminar Flames ◽  
Stability Criteria ◽  
Jet Flames ◽  
Lifted Flame ◽  
Fuel Flow ◽  
Lifted Flames

A study of the characteristics of turbulent lifted-jet flames in the hysteresis regime was performed using methane and ethylene fuels in laminar and turbulent air coflows. Reattachment velocities and lifted flame heights just prior to reattachment vary linearly as for laminar flames in coflow. The flow regime of the coflow (i.e., laminar or turbulent) did not appear to affect the behavior of these flames. These observations are of utility in designing maximum turndown burners in air coflow, especially for determining stability criteria in low fuel-flow applications.

Lifted flame structure of coannular jet flames in a triple port burner

2011 ◽  
Vol 33 (1) ◽  
pp. 1195-1201 ◽  
Author(s):  
Kazuhiro Yamamoto ◽  
Shinya Kato ◽  
Yusuke Isobe ◽  
Naoki Hayashi ◽  
Hiroshi Yamashita
Keyword(s):  
Flame Structure ◽  
Jet Flames ◽  
Lifted Flame

Assessment of Stabilization Mechanisms of Confined, Turbulent, Lifted Jet Flames: Effects of Ambient Coflow

2013 ◽  
Author(s):  
Andrew R. Hutchins ◽  
James D. Kribs ◽  
Richard D. Muncey ◽  
Kevin M. Lyons
Keyword(s):  
Turbulent Mixing ◽  
Leading Edge ◽  
Ambient Air ◽  
Turbulent Jet ◽  
Fuel Flow Rate ◽  
Jet Flames ◽  
Combustion Chemistry ◽  
Intermittent Behavior ◽  
Fuel Flow ◽  
Fuel Jet

The aim of this investigation is to determine the effects of confinement on the stabilization of turbulent, lifted methane (CH4) jet flames. A confinement cylinder (stainless steel) separates the coflow from the ambient air and restricts excess room air from being entrained into the combustion chamber, and thus produces varying stabilization patterns. The experiments were executed using fully confined, semi-confined, and unconfined conditions, as well as by varying fuel flow rate and coflow velocity (ambient air flowing in the same direction as the fuel jet). Methane flames experience liftoff and blowout at well-known conditions for unconfined jets, however, it was determined that with semi-confined conditions the flame does not experience blowout. Instead of the conventional unconfined stabilization patterns, an intense, intermittent behavior of the flame was observed. This sporadic behavior of the flame, while under semi-confinement, was determined to be a result from the restricted oxidizer access as well as the asymmetrical boundary layer that forms due to the viewing window. While under full confinement the flame behaved in a similar method as while under no confinement (full ambient air access). The stable nature of the flame while fully confined lacked the expected change in leading edge fluctuations that normally occur in turbulent jet flames. These behaviors address the combustion chemistry (lack of oxygen), turbulent mixing, and heat release that combine to produce the observed phenomena.

scholarly journals Characterization of Periodic, Quasiperiodic, and Chaotic States in Nonpremixed Biodiesel/Air Jet Flames

2011 ◽  
Vol 2011 ◽  
pp. 1-14 ◽  
Author(s):  
Jianxin Xu ◽  
Hua Wang ◽  
Hui Fang
Keyword(s):  
Image Analysis ◽  
Maximum Lyapunov Exponent ◽  
Recurrence Plots ◽  
Jet Flames ◽  
Fuel Flow ◽  
Air Jet ◽  
Analysis Technique ◽  
Tip Position ◽  
Relative Change

Characterization for nonpremixed biodiesel/air jet flames instability is investigated by the 0-1 test for chaos and recurrence plots. Test conditions involve biodiesel from Jatropha curcas. L-fueled flames have inlet oil pressure of 0.2–0.6 MPa, fuel flow rates (Q1) of 15–30 kg/h, and combustion air flow rate (Q2) of 150–750 m3/h. This method is based on image analysis and nonlinear dynamics. Structures of flame are analyzed using an image analysis technique to extract position series which are representative of the relative change in temperature of combustion chamber. Compared with the method of maximum Lyapunov exponent, the 0-1 test succeeds in detecting the presence of regular and chaotic components in flame position series. Periodic and quasiperiodic characteristics are obtained by the Poincaré sections. A common characteristic of regular nonpremixed flame tip position series is detected by recurrence plots. Experimental results show that these flame oscillations follow a route to chaos via periodic and quasiperiodic states.

Nitrogen-Diluted Methane Flames in the Near-and Far-Field

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
James Kribs ◽  
Nancy Moore ◽  
Tamir Hasan ◽  
Kevin Lyons
Keyword(s):  
Reynolds Number ◽  
Natural Gas ◽  
Low Reynolds Number ◽  
Industrial Applications ◽  
Flame Height ◽  
Far Field ◽  
Jet Flames ◽  
Jet Flame ◽  
Lifted Flame ◽  
Nitrogen Dilution

With the increased utilization of multicomponent fuels, such as natural gas and biogas, in industrial applications, there is a need to be able to effectively model and predict the properties of jet flames for mixed fuels. In addition, the interaction of these diluted fuels with outside influences (such as differing levels of coflow air) is a primary consideration. Experiments were performed on methane jet flames under the influence of varying levels of nitrogen dilution, from low Reynolds number lifted regimes to blowout, observing the influence of the nitrogen on lifted flame height and flame chemiluminesence images. These findings were analyzed and compared with existing lifted jet flame relations, such as the flammable region approximation proposed by Tieszen et al., as well as to undiluted flames. The influence of nitrogen dilution was seen to have an effect on the liftoff height of the flame, as well as the blowout velocity of the flame, but was seen to have a less pronounced effect compared with flames with coflowing air.

Prediction of Boundary Layer Flashback Limits of Laminar Premixed Jet Flames

2018 ◽  
Author(s):  
Vera Hoferichter ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Burning Velocity ◽  
Laminar Flames ◽  
Good Prediction ◽  
Jet Flames ◽  
Low Velocity ◽  
Local Flow ◽  
Wall Distance ◽  
Good Prediction Accuracy ◽  
Flame Stretch

Preventing flame flashback into the premixing section is one of the major challenges in premixed combustion systems. For jet flames, the flame typically propagates upstream inside the low velocity region close to the burner wall, referred to as boundary layer flashback. The physical mechanism of boundary layer flashback of laminar flames is mainly influenced by flame-wall interaction and flame quenching. Flashback is initiated if the burning velocity at some wall distance is higher than the local flow velocity. Since the burning velocity drops towards the wall due to heat losses, the wall distance of flashback can be defined at the location closest to the wall where the burning velocity still is sufficiently high. The well-established critical gradient concept of Lewis and von Elbe to predict flashback limits of laminar flames represents these assumptions but neglects the important influence of flame stretch on the burning velocity close to the wall. For that reason, a modified prediction model is developed in this work based on similar assumptions as in the critical gradient concept, but including the effect of flame stretch. A validation for hydrogen-air and methane-air flames highlights its advantages compared to the critical gradient concept and shows good prediction accuracy.

scholarly journals Numerical Modeling of Gaseous Partially Premixed Low-Swirl Lifted Flame at Elevated Pressure

2020 ◽  
Author(s):  
Leonardo Langone ◽  
Julia Sedlmaier ◽  
Pier Carlo Nassini ◽  
Lorenzo Mazzei ◽  
Stefan Harth ◽  
...  
Keyword(s):  
Experimental Data ◽  
Flame Front ◽  
Gas Turbine ◽  
Nozzle Exit ◽  
Numerical Results ◽  
Pollutant Emissions ◽  
Lifted Flame ◽  
Lifted Flames ◽  
Partially Premixed ◽  
Lift Off

Abstract Lifted flames have been investigated in the past years for their benefits in terms of NOx emissions reduction for gas turbine applications. In a lifted flame, the flame front stabilized on a position that is significantly detached from the nozzle exit, improving the premixing process before the reaction zone. The distance between the flame front and the nozzle exit is called lift-off height and it represents the main parameter that characterize this type of flame. In the present work, a partially premixed lifted flame employing air-methane mixture is investigated through numerical simulation. Indeed, even if lifted jet flames have been widely studied in the literature, there are only a few examples of lifted partially premixed flames. Nevertheless, this kind of flames assumes an important role considering the current gas turbine applications, since their benefits in terms of stability and low pollutant emissions. This study has been performed with LES calculations using a commercial software suite and the numerical results are compared with experimental data coming from a dedicated campaign held at Karlsruher Institute für Technologie (KIT) on a novel low-swirl injector nozzle. Quenching effects due to strain, curvature and heat loss have been introduced into the combustion model thanks to a correction of the source term in the progress variable equation within the FGM model. The comparison between numerical results and experimental data have been performed in terms of lift-off height and OH* chemiluminescence maps, showing the capability to properly predict the overall flow and to catch flame lift-off even if with an underpredicted height. This points out promising capability of the numerical model in the representation of lifted flames, allowing further investigations of the flame structure otherwise not available from experimental techniques.

Influences of Nitrogen Dilution in the Near Flow Field of Transition Regime Lifted Natural Gas Jet Flames

2011 ◽  
Author(s):  
Tamir S. Hasan ◽  
James S. Kribs ◽  
Kevin M. Lyons
Keyword(s):  
Natural Gas ◽  
Mass Fraction ◽  
Reynolds Numbers ◽  
Transition Regime ◽  
Jet Flames ◽  
Gas Combustion ◽  
Low Reynolds Numbers ◽  
Lifted Flames ◽  
Methane Flames ◽  
Low Reynolds

Flame liftoff height data were obtained on lifted methane jet flames diluted with nitrogen at transition regime Reynolds numbers. The data were analyzed to better understand and model natural gas combustion phenomena, in particular the effects of dilution in the near transition regime of methane jet flames. Images of the stable lifted flames were obtained at low Reynolds numbers from 2000 to 3800. This regime of Reynolds numbers was chosen due to the instability of laminar, lifted methane flames at these lower Reynolds numbers. Amongst other applications, lifted flames are often utilized in boilers and industrial burners to reduce thermal stresses, and are thus of importance in natural gas and low calorific fuel gas combustion. Radial and axial locations of the lowest flammable regions were observed. Since definitive models depicting lifted flames in the transition regime between laminar and turbulent flows have not yet been developed, the data was compared to the approximations of a turbulent flame model. The mass fraction model proposed by Tieszen et al (1996), which approximates the flammable regions based on mass fraction of fuel, was utilized in the analysis. For the conditions examined, turbulent lifted methane flames exist between mass fractions of 0.05 and 0.15. Applying this model showed that experimental results occurred outside of the leanest combustion zone predicted. At low Reynolds numbers, the model’s limit for radial location was the most pronounced factor which distinguished the predicted and observed values. These findings could be a result of the instabilities in the transition regime that result from lower stream velocities, such as unsteady vortical structures or small radial variance. It may also be a result of the data occurring at the lower limit of the model’s applicable regime. Some examination of the data also shows a correlation between mass flow rate of the diluent and the deviation of the experimental data from the theoretical data. Further investigations will continue to observe the effects of dilution into higher Reynolds number jet flames under dilution and co-flow, since they are important in understanding fundamental behavior seen in syngas and low calorific gas combustion.

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