A heuristic model of turbulent mixing applied to blowout of turbulent jet diffusion flames

Tieszen, Sheldon R.

doi:10.1016/0010-2180(96)00008-9

Cited by 56 publications

(38 citation statements)

References 26 publications

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“…Tieszen et al which explored blowout mechanisms [6]. Their results confirmed the theory proposed by Vanquickenbourne and van Tiggelen: blowout occurs when the local flow velocity exceeds the turbulent burning speed of the flame.…”

Section: Introductionsupporting

confidence: 60%

Flame Propagation and Blowout in Hydrocarbon Jets: Experiments to Understand the Stability and Structure

Lyons¹

2012

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The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. This research supported by the U.S. Army Research Office examines a myriad of facets of lifted hydrocarbon jet flames in the presence of air co-flow. At a certain jet exit velocity, a flame will lift from the fuel nozzle and stabilize at some downstream position. The partially-premixed flame front of the lifted flame oscillates, with the oscillations becoming greater in flames stabilized further downstream. These Inventions (DD882) Scientific ProgressThe main advances in jet flame flow interaction in oblique jet/air flows, as well as flame blowout, are detailed in the attachment. blowout were compared against two parameters: nozzle angle and coflow velocity. The resulting correlations indicated that flames at more oblique angles have a greater upper stability limit and were more resistant to changes in coflow velocity. This behavior occurs due to a lower effective coflow velocity at angles more oblique to the coflow direction.Additionally, stability limits were determined for flames in crossflow and mild counterflow configurations, and a relationship between the liftoff and blowout velocities was observed.For flames in crossflow and counterflow, the stability limits are higher. Further studies may include more angle and coflow combinations, as well as the effect of diluents or different fuel types. IntroductionA multitude of studies have been performed on lifted jet flames and their behavior in various air flow configurations. In such partially-premixed flames, the characteristics of the surrounding air flow (velocity, temperature) can strongly impact the overall combustion process and the stability parameters. As fuel flows from a nozzle and mixes with the air, the fuel and oxidizer concentrations vary throughout space and time. The extent of mixing due to turbulence also changes depending on the surrounding flow. The perpetually varying concentrations help to determine the overall behavior of a flame: its shape, velocity, size, color, temperature, and composition. In parallel, the heat release serves to laminarize regions, and serves to limit reducing mixing.In particular, two important behavioral parameters are liftoff and blowout velocity.Initially, a jet flame will remain attached to the nozzle at low fuel velocities. However, at a critical jet velocity, the flame will lift off from the nozzle and stabilize at a position While jet behavior in coflow has been extensively studied, less attention has been devoted to jets in crossflow. In a review, Bandaru and Turns included a comprehensive list of all major crossflow research to date [9]. Many of the works relevant to this study were observation-based experiments performed by Kalghatgi, whosecrossflow flame experiments were conducted in a wind tunnel and involved propane, ...

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Section: Introductionsupporting

confidence: 60%

Flame Propagation and Blowout in Hydrocarbon Jets: Experiments to Understand the Stability and Structure

Lyons¹

2012

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“…Hence choosing the correct timescale for micromixing will be critical when attempting to accurately model mean particle sizes. (Tieszen et al, 1996). Predictions using plain non-stochastic solution and Stochastic Fields.…”

Section: Discussionmentioning

confidence: 99%

“…1. Also shown is the velocity predicted by using an empirical expression from Tieszen et al (1996) for axial velocity of a free jet with different density to the background:…”

Section: Methodsmentioning

confidence: 99%

Aerosol nucleation and growth in a turbulent jet using the Stochastic Fields method

Garmory

Mastorakos

2008

Chemical Engineering Science

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The Stochastic Fields transported PDF method for turbulent reacting flows has been used to model the nucleation and growth of Dibutyl Phthalate particles in a hot, turbulent jet in a colder background for which experimental data is available.The aerosol population is modelled using an assumed log-normal size distribution.It has been found that neglecting the effect of turbulent fluctuations leads to the peak particle concentration being predicted too close to the jet and the concentration downstream underpredicted. However, this effect was small compared to that of adjusting modelled surface tension. Only by adjusting this was it possible to reproduce correctly the downstream evolution of particle number found in experiment.Particle mass mean diameter was significantly underpredicted at the centre of the jet, which may be due to the inability of log-normal size distribution to capture the distribution in detail. Taking account of turbulent fluctuations leads to increased mean particle size at the edge of the plume. The extent of this increase is strongly dependent on the choice of micromixing timescale.

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“…Broadwell et al [13] Large-scale structures move hot product to flame leading edge Mixing between hot products and unburned fuel allows insufficient time for combustion to occur Dahm and Dibble [15] Molecular mixing rate Reduction in the fuel velocity with increased coflow velocity corresponds to a consistent blowout parameter Tieszen et al [22] Local flow velocity exceeds turbulent flame speed Turbulent flame propagation towards the outer edge of the reaction zone stabilizes flames near blowout…”

Section: Blowout Concepts Supported Proposed Blowout Mechanismmentioning

confidence: 99%

“…Sequences of digital images of the lifted reaction zone are provided along with details of the flame movement for different combinations of fuel and coflow velocities. Interpretations of the data are discussed, utilizing a relation for the stoichiometry from Tieszen et al [22]. This allows for the assessment of past theories and the development of a physically-based concept of flame blowout in turbulent jets, along with proposing a new signature which indicates the imminence of flame blowout.…”

Section: Introductionmentioning

confidence: 99%

Observations on Jet-Flame Blowout

Moore

McCraw

Lyons

2008

International Journal of Reacting Systems

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The mechanisms that cause jet-flame blowout, particularly in the presence of air coflow, are not completely understood. This work examines the role of fuel velocity and air coflow in the blowout phenomenon by examining the transient behavior of the reaction zone at blowout. The results of video imaging of a lifted methane-air diffusion flame at near blowout conditions are presented. Two types of experiments are described. In the first investigation, a flame is established and stabilized at a known, predetermined downstream location with a constant coflow velocity, and then the fuel velocity is subsequently increased to cause blowout. In the other , an ignition source is used to maintain flame burning near blowout and the subsequent transient behavior to blowout upon removal of the ignition source is characterized. Data from both types of experiments are collected at various coflow and jet velocities. Images are used to ascertain the changes in the leading edge of the reaction zone prior to flame extinction that help to develop a physically-based model to describe jet-flame blowout. The data report that a consistent predictor of blowout is the prior disappearance of the axially oriented flame branch. This is witnessed despite a turbulent flames' inherent variable behavior. Interpretations are also made in the light of analytical mixture fraction expressions from the literature that support the notion that flame blowout occurs when the leading edge reaches the vicinity of the lean-limit contour, which coincides approximately with the conditions for loss of the axially oriented flame structure.

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A heuristic model of turbulent mixing applied to blowout of turbulent jet diffusion flames

Cited by 56 publications

References 26 publications

Flame Propagation and Blowout in Hydrocarbon Jets: Experiments to Understand the Stability and Structure

Flame Propagation and Blowout in Hydrocarbon Jets: Experiments to Understand the Stability and Structure

Aerosol nucleation and growth in a turbulent jet using the Stochastic Fields method

Observations on Jet-Flame Blowout

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