scholarly journals Flame and Spray Dynamics During the Light-Round Process in an Annular System Equipped With Multiple Swirl Spray Injectors

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Kevin Prieur ◽  
Guillaume Vignat ◽  
Daniel Durox ◽  
Thierry Schuller ◽  
Sébastien Candel
Keyword(s):  
Flame Front ◽  
Flame Structure ◽  
Axial Direction ◽  
Azimuthal Direction ◽  
Time Resolved ◽  
Fuel Droplets ◽  
Spray Flames ◽  
Annular Combustor ◽  
Swirling Flame ◽  
Injection Unit

A successful ignition in an annular multi-injector combustor follows a sequence of steps. The first injector is ignited; two arch-shaped flame branches nearly perpendicular to the combustor backplane form; they propagate, igniting each injection unit; they merge. In this paper, characterization of the propagation phase is performed in an annular combustor with spray flames fed with liquid n-hepane. The velocity and the direction of the arch-like flame branch are investigated. Near the backplane, the flame is moving in a purely azimuthal direction. Higher up in the chamber, it is also moving in the axial direction due to the volumetric expansion of the burnt gases. Time-resolved particle image velocimetry (PIV) measurements are used to investigate the evaporating fuel droplets dynamics. A new result is that, during the light-round, the incoming flame front pushes the fuel droplets in the azimuthal direction well before its leading point. This leads to a decrease in the local droplet concentration and local mixture composition over not yet lit injectors. For the first time, the behavior of an individual injector ignited by the passing flame front is examined. The swirling flame structure formed by each injection unit evolves in time. From the ignition of an individual injector to the stabilization of its flame in its final shape, approximately 50 ms elapse. After the passage of the traveling flame, the newly ignited flame flashbacks into the injector during a few milliseconds, for example, 5 ms for the conditions that are tested. This could be detrimental to the service life of the unit. Then, the flame exits from the injection unit, and its external branch detaches under the action of cooled burnt gases in the outer recirculation zone (ORZ).

scholarly journals Flame and Spray Dynamics During the Light-Round Process in an Annular System Equipped With Multiple Swirl Spray Injectors

2018 ◽  
Author(s):  
Kevin Prieur ◽  
Daniel Durox ◽  
Guillaume Vignat ◽  
Thierry Schuller ◽  
Sébastien Candel
Keyword(s):  
Flame Front ◽  
High Speed ◽  
Laser Sheet ◽  
Pressure Fluctuations ◽  
Flame Structure ◽  
Frame Rate ◽  
Ignition Process ◽  
Liquid Droplets ◽  
Spray Flames ◽  
Annular Combustor

The ignition process of an annular combustor can be divided in several steps that end with the light-round. This corresponds to the sequence from the ignition of the first injector to the merging of the two flame fronts spreading in the annular system. The present article focuses on this important step, where two arch-like flame branches propagate in the chamber. These two turbulent travelling flames, nearly perpendicular to the combustor backplane, successively ignite the injection units and finally collide head-on and merge. In the present study, light-round of spray flames fed by liquid n-heptane is investigated. A high-speed camera operating at a frame rate of 6000 Hz and equipped with a filter centered on CH* emission is positioned on the side of the annular combustor, at the chamber backplane level and records images of one half of the chamber annulus. Acoustic pressure fluctuations are recorded through waveguide microphones plugged on the chamber backplane and microphones flush mounted in the annular plenum. The behavior of one injector ignited by the passing flame front is examined. One finds that the swirling flame structure formed by each injection unit evolves in time and that the anchoring location changes just after the passage of the travelling flame and during a period of a few milliseconds. This behavior can eventually lead to a flashback of the flame in the injector with possible severe damages. This dynamical phenomenon is described in detail. The propagation of the arch-like flame branch is then investigated. Flame images are used to determine the direction and velocity of the flame front by making use of a PIV like processing. One may distinguish two regions for the flame propagation. One is near the backplane, moving in a purely azimuthal direction, while the other corresponds to the remaining flame motion in the azimuthal and axial directions due to the volumetric expansion of the burnt gases. Filtered light images give some indications on the complex flame structures and on the typical length scales characterizing the moving front. Information is also obtained on the dynamics of the spray by shining a continuous laser sheet passing through one injector central axis and recording the light scattered by the n-heptane spray of droplets. These images are used to determine the influence of the incoming flame front on the evaporating n-heptane liquid droplets. A major result is that the flame modifies the spray much before its leading point reaches the injector unit and that its passage through the spray drastically changes the local droplet concentration and thus the local mixture composition.

Spray Flame Study Using a Model Gas Turbine Swirl Burner

2013 ◽  
Vol 316-317 ◽  
pp. 17-22 ◽  
Author(s):  
Cheng Tung Chong ◽  
Simone Hochgreb
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Flame Structure ◽  
Fuel Droplets ◽  
Spray Flame ◽  
Spray Flames ◽  
Reaction Zones ◽  
Fixed Power ◽  
Particle Imaging ◽  
Gas Turbine Burner

A model gas turbine burner was employed to investigate spray flames established under globally lean, continuous, swirling conditions. Two types of fuel were used to generate liquid spray flames: palm biodiesel and Jet-A1. The main swirling air flow was preheated to 350 °C prior to mixing with airblast-atomized fuel droplets at atmospheric pressure. The global flame structure of flame and flow field were investigated at the fixed power output of 6 kW. Flame chemiluminescence imaging technique was employed to investigate the flame reaction zones, while particle imaging velocimetry (PIV) was utilized to measure the flow field within the combustor. The flow fields of both flames are almost identical despite some differences in the flame reaction zones.

scholarly journals Impedance modelling of acoustically treated circumferential grooves for over-tip-rotor fan noise suppression

2020 ◽  
Vol 19 (6-8) ◽  
pp. 277-293
Author(s):  
Sergi Palleja-Cabre ◽  
Brian J Tester ◽  
R Jeremy Astley ◽  
Hadrien Beriot
Keyword(s):  
Noise Suppression ◽  
Prediction Models ◽  
Axial Direction ◽  
Analytical Prediction ◽  
Azimuthal Direction ◽  
Fan Noise ◽  
Turbofan Engines ◽  
Circumferential Groove ◽  
Equivalent Impedance ◽  
Grooved Surface

Experimental investigation of Over-Tip-Rotor circumferential groove liners has shown potential for fan noise suppression in turbofan engines whilst providing minimal penalty in fan aerodynamic performance. The validation of Over-Tip-Rotor liner analytical prediction models against published experimental data requires the modelling of an equivalent impedance for such acoustic treatments. This paper describes the formulation of two analytical groove impedance models as semi-locally reacting liners, that is locally reacting in the axial direction and non-locally reacting in the azimuthal direction. The models are cross-verified by comparison with high-order FEM simulations, and applied to a simplified Over-Tip-Rotor configuration consisting of multiple grooves excited by a monopole point source located close to the grooved surface.

Effects of leading edge entrainment on the double flame structure in lifted ethanol spray flames

2004 ◽  
Vol 29 (1) ◽  
pp. 23-31 ◽  
Author(s):  
S.K. Marley ◽  
E.J. Welle ◽  
K.M. Lyons ◽  
W.L. Roberts
Keyword(s):  
Flame Structure ◽  
Leading Edge ◽  
Spray Flames

Characteristic of Low Calorific Fuel Gas Combustion in a Pressurized Porous Burner

2014 ◽  
Vol 1070-1072 ◽  
pp. 1713-1717
Author(s):  
Guan Qing Wang ◽  
Dan Luo ◽  
Ning Ding ◽  
Jiang Rong Xu
Keyword(s):  
Flame Front ◽  
Temperature Profile ◽  
Axial Direction ◽  
Normal Pressure ◽  
Maximum Temperature ◽  
Combustion Characteristic ◽  
Gas Combustion ◽  
Fuel Gas ◽  
Flame Propagation Velocity ◽  
Porous Burner

Combustion characteristic of low calorific fuel gas in a pressurized porous burner was numerically investigated. The two-dimensional temperature profile, flame front, and CO concentration distribution were analyzed under the pressure at the certain operating parameters, and compared with those of the normal pressure. The results shows that the pressured temperature profile is more clear than that of the normal pressure, and maximum temperature distribution region is larger. Compared with the normal pressure, the pressured flame front location is at the downstream, and the flame propagation velocity along with inclination increases with the pressure increasing. The CO distribution is corresponding to the temperature profile. Its maximum locates at the position of the flame front, and gradually decreasing along the axial direction. It decreases with the pressure increasing, which indicates that the pressure contributes to improve the combustion efficiency.

Analysis of the Flame Structure in a Trapped Vortex Combustor Using Low and High-Speed OH-PLIF

2014 ◽  
Author(s):  
Pradip Xavier ◽  
Alexis Vandel ◽  
Gilles Godard ◽  
Bruno Renou ◽  
Frederic Grisch ◽  
...  
Keyword(s):  
High Speed ◽  
Laser Diagnostics ◽  
Flame Structure ◽  
Combustion Process ◽  
Operating Conditions ◽  
Pollutant Emissions ◽  
Time Resolved ◽  
Lean Combustion ◽  
Stage Combustion ◽  
Trapped Vortex

Operating with lean combustion has led to more efficient “Low-NOx” burners but has also brought several technological issues. The burner design geometry is among the most important element as it controls, in a general way, the whole combustion process, the pollutant emissions and the flame stability. Investigation of new geometry concepts associating lean combustion is still under development, and new solutions have to meet the future pollutant regulations. This paper reports the experimental investigation of an innovative staged lean premixed burner. The retained annular geometry follows the Trapped Vortex Combustor concept (TVC) which operates with a two stage combustion chamber: a main lean flame (1) is stabilized by passing past a vortex shape rich-pilot flame (2) located within a cavity. This concept, presented in GT2012-68451 and GT2013-94704, seems to be promising but exhibits combustion instabilities in certain cases, then leading to undesirable level of pollutant emissions and could possibly conduct to serious material damages. No precise information have been reported in the literature about the chain of reasons leading to such an operation. The aim of this paper is to have insights about the main parameters controlling the combustion in this geometry. The flame structure dynamics is examined and compared for two specific operating conditions, producing an acoustically self-excited and a stable burner. Low and high-speed OH-PLIF laser diagnostics (up to 10 kHz) are used to have access to the flame curvature and to time-resolved events. Results show that the cavity jets location can lead to flow-field oscillations and a non-constant flame’s heat release. The associated flame structure, naturally influenced by turbulence is also affected by hot gases thermal expansion. Achieving a good and rapid mixing at the interface between the cavity and the main channel leads to a stable flame.

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