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1
LI, GUOQIANG. "EMISSIONS, COMBUSTION DYNAMICS, AND CONTROL OF A MULTIPLE SWIRL COMBUSTOR." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1092767684.
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Yellugari, Kranthi. "Effects of Swirl Number and Central Rod on Flow in Lean Premixed Swirl Combustor." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563872979440851.
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Okon, Aniekan. "Combustion dynamics in a lean premixed combustor with swirl forcing and fuel conditions." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/108265/.
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Fossil fuels still account for a large percentage of global energy demand according to available statistics. Natural gas is increasingly gaining the share of these fuels due to the retired coal and nuclear plants. The more stringent emission standards have also put natural gas ahead of other fuels as a result of its efficiency, cost, environmental attributes as well as the operational efficiency of the gas turbine, an engine that uses this fuel. A standard low emission combustion technique in gas turbines is the dry low NOx combustion, with lean fuel and fuel-air premixed upstream of the flame holder. However, this condition is highly susceptible to combustion instabilities characterised by large amplitude oscillations of the combustor’s acoustic modes excited by unsteady combustion processes. These pressure oscillations are detrimental both to the efficiency of performance as well as the hardware of the system. Although the processes and mechanisms that result in instabilities are well known, however, the current challenges facing gas turbine operators are the precise understanding of the operational conditions that cause combustion instabilities, accurate prediction of the instability modes and the control of the disturbances. In a bid to expand this knowledge frontier, this study uses a 100kW swirl premixed combustor to examine the evolution of the flow structures, its influence on the flame dynamics, in terms of heat release fluctuation and the overall effects on the pressure field, under different, swirl, fuel and external excitation conditions. The aim is to determine the operational conditions whose pressure oscillation is reduced to the barest minimum to keep the system in an excellent running condition. The results of this study are expected to contribute towards the design of a new control system to damp instabilities in gas turbines.
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Abdulsada, Mohammed. "Flashback and blowoff characteristics of gas turbine swirl combustor." Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/24193/.
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Gas turbines are extensively used in combined cycle power systems. These form about 20% of global power generating capacity, normally being fired on natural gas, but this is expected in the future to move towards hydrogen enriched gaseous fuels to reduce CO2 emissions. Gas turbine combined cycles can give electrical power generation efficiencies of up to 60%, with the aim of increasing this to 70% in the next 10 to 15 years, whilst at the same time substantially reducing emissions of contaminants such as NOx. The gas turbine combustor is an essential and critical component here. These are universally stabilized with swirl flows, which give very wide blowoff limits, and with appropriate modification can be adjusted to give very low NOx and other emission. Lean premixed combustion is commonly used at pressures between 15 to 30 bar, these even out hot spots and minimise formation of thermal NOx. Problems arise because improving materials technology/improved cooling techniques allow higher turbine inlet temperatures, hence higher efficiencies, but with the drawback of potentially higher emissions and stability problems. This PhD study has widely investigated and analysed two different kinds of gas turbine swirl burners. The research has included experimental investigation and computational simulation. Mainly, the flashback and blowoff limits have been comprehensively analysed to investigate their effect upon swirl burner operation. The study was extended by using different gas mixtures, including either pure gas or a combination of more than one gas like natural gas, methane, hydrogen and carbon dioxide. The first combustor is a 100 kW tangential swirl combustor made of stainless steel that has been experimentally and theoretically analysed to study and mitigate the effect of flashback phenomena. The use of a central fuel injector, cylindrical confinement and exhaust sleeve are shown to give large benefits in terms of flashback resistance and acts to reduce and sometimes eliminate any coherent structures which may be located along the axis of symmetry. The Critical Boundary Velocity Gradient is used for characterisation of flashback, both via the original Lewis and von Elbe formula and via new analysis using CFD and investigation of boundary layer conditions just in front of the flame front. Conclusions are drawn as to mitigation technologies. It is recognized how isothermal conditions produce strong Precessing Vortex Cores that are fundamental in producing the ii final flow field, whilst the Central Recirculation Zones are dependent on pressure decay ratio inside the combustion chamber. Combustion conditions showed the high similarity between experiments and simulation. Flashback was demonstrated to be a factor highly related to the strength of the Central Recirculation Zone for those cases where a Combustion Induced Vortex Breakdown was allowed to enter the swirl chamber, whilst cases where a bluff body impeded its passage showed a considerable improvement to the resistance of the phenomenon. The use of nozzle constrictions also reduced flashback at high Reynolds number (Re). All these results were intended to contribute to better designs of future combustors. The second piece of work of this PhD research included comprehensive experimental work using a generic swirl burner (with three different blade inserts to give different swirl numbers) and has been used to examine the phenomena of flashback and blowoff in the swirl burner in the context of lean premixed combustion. Cylindrical and conical confinements have been set up and assembled with the original design of the generic swirl combustor. In addition to that, multi-fuel blends used during the experimental work include pure methane, pure hydrogen, hydrogen / methane mixture, carbon dioxide/ methane mixture and coke oven gas. The above investigational analysis has proved the flashback limits decrease when swirl numbers decrease for the fuel blends that contain 30% or less hydrogen. Confinements would improve the flashback limit as well. Blowoff limits improve with a lower swirl number and it is easier to recognise the gradual extinction of the flame under blowoff conditions. The use of exhaust confinement has created a considerable improvement in blowoff. Hydrogen enriched fuels can improve the blowoff limit in terms of increasing heat release, which is higher than heat release with natural gas. However, the confinements complicate the flashback, especially when the fuel contains a high percentage of hydrogen. The flashback propensity of the hydrogen/methane blends becomes quite strong. The most important features in gas turbines is the possibility of using different kinds of fuel. This matter has been discussed extensively in this project. By matching flashback/blowoff limits, it has been found that for fuels containing up to 30% of hydrogen, the designer would be able to switch the same gas turbine combustor to multifuels whilst producing the same power output.
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Colby, Jonathan A. "Flow Field Measurements in a Counter-Swirl Stabilized Liquid Combustor." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10470.
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To adhere to the current requirements for NOx and CO emissions in combustion systems, modern land and air based gas turbine engines often operate in the fuel lean regime. While operating near the lean blow out (LBO) limit does reduce some harmful emissions, combustor stability is sacrificed and extinction becomes a major concern. To fully understand the characteristics of lean operation, an experimental study was conducted to map the time averaged flow field in a typical industrial, counter-swirling, liquid fuel combustor. This study examined two steady-state operating conditions, both near the lean extinction limit for this swirl burner. Using an LDV/PDPA system, 2-D mean and fluctuating velocities, as well as Reynolds stresses, were measured throughout the combustor. These measurements were taken for both the non-reacting and reacting flow fields, enabling a direct analysis of the result of heat addition and increased load on a turbulent swirling flow field. To further understand the overall flow field, liquid droplet diameter measurements were taken to determine the fuel spray characteristics as a function of operating pressure and rated spray angle. Chemical composition at the combustor exit was also measured, with an emphasis on the concentrations of both CO and NOx emissions. This large database of aerodynamic and droplet measurements improves understanding of the swirling, reacting flow field and aids in the accurate prediction of lean blow-out events. With this understanding of the lean blow-out limit, increased fuel efficiency and decreased pollutant emissions can be achieved in industrial combustors, especially those used for thrust in the airline industry.
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Sheen, Dong-Hyon. "Swirl-stabilised turbulent spray flames in an axisymmetric model combustor." Thesis, Imperial College London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445249.
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Thiruchengode, Muruganandam. "Sensing and Dynamics of Lean Blowout in a Swirl Dump Combustor." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10538.
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This thesis describes an investigation on the blowout phenomenon in gas turbine combustors. The combustor primarily used for this study was a swirl- and dump-stabilized, atmospheric pressure device, which did not exhibit dynamic combustion instabilities. The first part of the thesis work concentrated on finding a sensing methodology to be able to predict the onset of approach of combustor blowout using optical methods. Temporary extinction-reignition events that occurred prior to blowout were found to be precursor events to blowout. A threshold based method was developed to identify these events in the time-resolved sensor output. The number and the average length of each event were found to increase as the LBO limit (fuel-air ratio) is approached. This behavior is used to predict the proximity to lean blowout.
In the second part of this study, the blowout sensor was incorporated into a control system that monitored the approach of blowout and then actuated an alternate mechanism to stabilize the combustor near blowout. Enhanced stabilization was achieved by redirecting a part of the main fuel to a central preinjection pilot injection. The sensing methodology, without modification, was effective for the combustor with pilot stabilization. An event based control algorithm for controlling the combustor from blowing out was also developed in this study. The control system was proven to stabilize the combustor even when the combustor loading was rapidly changed.
The final part of this study focused on understanding the physical mechanisms behind the precursor events. High speed movies of flame chemiluminescence and laser sheet scattering from oil droplets seeded into the reactants were analyzed to explain the physical processes that cause the extinction and the reignition of the combustor during a precursor event. A physical model for coupling of the fluid dynamics of vortex breakdown and combustion during precursor and blowout events is proposed.
This model of blowout phenomenon, along with the sensing and control strategies developed in this study could enable the gas turbine combustor designers to design combustors with wider operability regimes. This could have significant payoffs in terms of reduction in NOx emissions from the combustor.
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Linck, Martin Brendan. "Spray flame and exhaust jet characteristics of a pressurized swirl combustor." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3627.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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WANG, DEXIN. "STRONGLY SWIRLING FLOW STUDY ON PRESSURE-SWIRL ATOMIZER AND CYCLONE COMBUSTOR." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1032210020.
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Ayache, Simon Victor. "Simulations of turbulent swirl combustors." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/243609.
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This thesis aims at improving our knowledge on swirl combustors. The work presented here is based on Large Eddy Simulations (LES) coupled to an advanced combustion model: the Conditional Moment Closure (CMC). Numerical predictions have been systematically compared and validated with detailed experimental datasets. In order to analyze further the physics underlying the large numerical datasets, Proper Orthogonal Decomposition (POD) has also been used throughout the thesis. Various aspects of the aerodynamics of swirling flames are investigated, such as precession or vortex formation caused by flow oscillations, as well as various combustion aspects such as localized extinctions and flame lift-off. All the above affect flame stabilization in different ways and are explored through focused simulations. The first study investigates isothermal air flows behind an enclosed bluff body, with the incoming flow being pulsated. These flows have strong similarities to flows found in combustors experiencing self-excited oscillations and can therefore be considered as canonical problems. At high enough forcing frequencies, double ring vortices are shed from the air pipe exit. Various harmonics of the pulsating frequency are observed in the spectra and their relation with the vortex shedding is investigated through POD. The second study explores the structure of the Delft III piloted turbulent non-premixed flame. The simple configuration allows to analyze further key combustion aspects of combustors, with further insights provided on the dynamics of localized extinctions and re-ignition, as well as the pollutants emissions. The third study presents a comprehensive analysis of the aerodynamics of swirl flows based on the TECFLAM confined non-premixed S09c configuration. A periodic component inside the air inlet pipe and around the central bluff body is observed, for both the inert and reactive flows. POD shows that these flow oscillations are due to single and double helical vortices, similar to Precessing Vortex Cores (PVC), that develop inside the air inlet pipe and whose axes rotate around the burner. The combustion process is found to affect the swirl flow aerodynamics. Finally, the fourth study investigates the TECFLAM configuration again, but here attention is given to the flame lift-off evident in experiments and reproduced by the LES-CMC formulation. The stabilization process and the pollutants emission of the flame are investigated in detail.
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TOKEKAR, DEVKINANDAN MADHUKAR. "MODELING AND SIMULATION OF REACTING FLOWS IN LEAN-PREMIXED SWIRL-STABLIZED GAS TURBINE COMBUSTOR." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1141412599.
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LaBry, Zachary Alexander. "Suppression of thermoacoustic instabilities in a swirl combustor through microjet air injection." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/60212.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 85-87).
Thermoacoustic or combustion instability, a positive feedback loop coupling heat release rate and acoustic oscillations in a combustor, is one of the greatest challenges currently facing the development of new gas turbine systems for propulsion and power generation. Traditional gas turbine designs have bypassed the problem of combustion instability by designing non-premixed combustors around a fixed operating point. Increasing trends toward lower emissions and greater fuel flexibility have placed more emphasis on developing lean-premixed combustors that are stable over a range of operating conditions. This thesis explores two aspects of combustion instability in the context of a swirl-stabilized, lean-premixed combustor: the role of the major coherent flow structures, and the potential for using secondary air injection to passively suppress combustion instability. Microjets inject air into the combustion chamber in the flame anchoring zone. These microjet injectors attempt to modify the flow field so as to break the feedback mechanism between the chamber acoustics and the heat release rate. Eight microjet injector configurations are studied. Flow is injected axially into the outer recirculation zone or radially into the inner recirculation zone. The injectors inject air with either no swirl, the same swirl direction as the main air flow, or the opposite swirl direction as the main air flow. Chamber acoustics are measured using sensitive microphones. The flame and flow field are interrogated using high-speed imaging and stereoscopic particle image velocimetry. The bulk of this work was conducted for lean propane/air flames, slightly above the lean blowoff limit. Two modes of instability were examined: the 1/4 wave mode at 40 Hz, and the 3/4 wave mode at 105 Hz. Without microjet injection, the combustor transitions directly from the 1/4 wave mode instability to the 3/4 wave mode instability as the equivalence ratio is increased above 0.58. Counter-swirling radial microjets injecting air into the inner recirculation zone increased the lower limit of the 3/4 wave mode to an equivalence ratio of 0.62 and reduced the amplitude of the 1/4 wave mode, effectively creating a stable operating regime for equivalence ratios between the two modes. Microjet injector tests indicate that the inner recirculation zone has a dominant role in the dynamic stabilization of the flame. This observation is confirmed by stereoscopic PIV measurements that reveal periodic formation and collapse of the vortex breakdown bubble in the 3/4 wave mode and vortex shedding in the inner recirculation zone in the 1/4 wave mode.
by Zachary Alexander LaBry.
S.M.
13
Sharma, Anshu. "Numerical Investigation of a Swirl Induced Flameless Combustor for Gas Turbine Applications." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613731788158991.
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Kedukodi, Sandeep. "Numerical Analysis of Flow and Heat Transfer through a Lean Premixed Swirl Stabilized Combustor Nozzle." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/77393.
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While the gas turbine research community is continuously pursuing development of higher cyclic efficiency designs by increasing the combustor firing temperatures and thermally resistant turbine vane / blade materials, a simultaneous effort to reduce the emission levels of high temperature driven thermal NOX also needs to be addressed. Lean premixed combustion has been found as one of the solutions to these objectives. However, since less amount of air is available for backside cooling of liner walls, it becomes very important to characterize the convective heat transfer that occurs on the inside wall of the combustor liners. These studies were explored using laboratory scale experiments as well as numerical approaches for several inlet flow conditions under both non-reacting and reacting flows. These studies may be expected to provide valuable insights for the industrial design communities towards identifying thermal hot spot locations as well as in quantifying the heat transfer magnitude, thus aiding in effective designs of the liner walls.
Lean premixed gas turbine combustor flows involve strongly coupled interactions between several aspects of physics such as the degree of swirl imparted by the inlet fuel nozzle, premixing of the fuel and incoming air, lean premixed combustion within the combustor domain, the interaction of swirling flow with combustion driven heat release resulting in flow dilation, the resulting pressure fluctuations leading to thermo-acoustic instabilities there by creating a feedback loop with incoming reactants resulting in flow instabilities leading to flame lift off, flame extinction etc. Hence understanding combustion driven swirling flow in combustors continues to be a topic of intense research.
In the present study, numerical predictions of swirl driven combustor flows were analyzed for a specific swirl number of an industrial fuel nozzle (swirler) using a commercial computational fluid dynamics tool and compared against in-house experimental data. The latter data was obtained from a newly developed test rig at Applied Propulsion and Power Laboratory (APPL) at Virginia Tech. The simulations were performed and investigated for several flow Reynolds numbers under non-reacting condition using various two equation turbulence models as well as a scale resolving model. The work was also extended to reacting flow modeling (using a partially premixed model) for a specific Reynolds number. These efforts were carried out in order investigate the flow behavior and also characterize convective heat transfer along the combustor wall (liner). Additionally, several parametric studies were performed towards investigating the effect of combustor geometry on swirling flow and liner hear transfer; and also to investigate the effect of inlet swirl on the jet impingement location along the liner wall under both non-reacting as well as reacting conditions.
The numerical results show detailed comparison against experiments for swirling flow profiles within the combustor under reacting conditions indicating a good reliability of steady state modeling approaches for reacting conditions; however, the limitations of steady state RANS turbulence models were observed for non-reacting swirling flow conditions, where the flow profiles deviate from experimental observations in the central recirculation region. Also, the numerical comparison of liner wall heat transfer characteristics against experiments showed a sensitivity to Reynolds numbers. These studies offer to provide preliminary insights of RANS predictions based on commercial CFD tools in predicting swirling, non-reacting and reacting flow and heat transfer. They can be extended to reacting flow heat transfer studies in future and also may be upgraded to unsteady LES predictions to complement future experimental observations conducted at the in-house test facility.Ph. D.
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Tokekar, Devkinandan Madhukar. "Modeling and simulation of reacting flows in lean-premixed swirl-stabilized gas turbine combustor." Cincinnati, Ohio : University of Cincinnati, 2005. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1141412599.
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Thesis (M.S.)--University of Cincinnati, 2005.Title from electronic thesis title page (viewed Apr. 18, 2006). Includes abstract. Keywords: Large Eddy Simulation; LES; Lean Pre-mixed; LPM; Gas Turbine Combustor; Combustion; Reacting Flows. Includes bibliographical references.
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Endicott, Derick S. "Experimental Development of a Lean Direct Injection Combustor Utilizing High-Low Swirl Intensity Combinations." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1416231599.
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Dsouza, Jason Brian. "Numerical Analysis of a Flameless Swirl Stabilized Cavity Combustor for Gas Turbine Engine Applications." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627663015527799.
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Periagaram, Karthik Balasubramanian. "Determination of flame characteristics in a low swirl burner at gas turbine conditions through reaction zone imaging." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45828.
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This thesis explores the effects of operating parameters on the location and shape of lifted
flames in a Low Swirl Burner (LSB). In addition, it details the development and analysis of
a CH PLIF imaging system for visualizing flames in lean combustion systems. The LSB is
studied at atmospheric pressure using LDV and CH PLIF. CH* chemiluminescence is used
for high pressure flame imaging.
A four-level model of the fluorescing CH system is developed to predict the signal intensity
in hydrocarbon flames. Results from imaging an atmospheric pressure laminar flame are used
to validate the behavior of the signal intensity as predicted by the model. The results show
that the fluorescence signal is greatly reduced at high pressure due to the decreased number
of CH molecules and the increased collisional quenching rate. This restricts the use of this
technique to increasingly narrow equivalence ratio ranges at high pressures. The limitation
is somewhat alleviated by increasing the preheat temperature of the reactant mixture. The
signal levels from high hydrogen-content syngas mixtures doped with methane are found to
be high enough to make CH PLIF a feasible diagnostic to study such flames. Finally, the
model predicts that signal levels are unlikely to be significantly affected by the presence of
strain in the flow field, as long as the flames are not close to extinction.
The results from the LSB flame investigation reveal that combustor provides reasonably
robust flame stabilization at low and moderate values of combustor pressure and reference
velocities. However, at very high velocities and pressures, the balance between the reactant
velocity and the turbulent flame speed shifts in favor of the former resulting in the flame
moving downstream. The extent of this movement is small, but indicates a tendency towards
blow off at higher pressures and velocities that may be encountered in real world gas turbine
applications. There is an increased tendency of relatively fuel-rich flames to behave like
attached flames at high pressure. These results raise interesting questions about turbulent
combustion at high pressure as well as provide usable data to gas turbine combustor designers
by highlighting potential problems.
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Park, Suhyeon. "Experimental Investigation of Flow and Wall Heat Transfer in an Optical Combustor for Reacting Swirl Flows." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/82349.
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The study of flow fields and heat transfer characteristics inside a gas turbine combustor provides one of the most serious challenges for gas turbine researchers because of the harsh environment at high temperatures. Design improvements of gas turbine combustors for higher efficiency, reduced pollutant emissions, safety and durability require better understanding of combustion in swirl flows and thermal energy transfer from the turbulent reacting flows to solid surfaces. Therefore, accurate measurement and prediction of the flows and heat loads are indispensable.
This dissertation presents flow details and wall heat flux measurements for reacting flow conditions in a model gas turbine combustor. The objective is to experimentally investigate the effects of combustor operating conditions on the reacting swirl flows and heat transfer on the liner wall. The results shows the behavior of swirling flows inside a combustor generated by an industrial lean pre-mixed, axial swirl fuel nozzle and associated heat loads.
Planar particle image velocimetry (PIV) data were analyzed to understand the characteristics of the flow field. Experiments were conducted with various air flow rates, equivalence ratios, pilot fuel split ratios, and inlet air temperatures. Methane and propane were used as fuel. Characterizing the impingement location on the liner, and the turbulent kinetic energy (TKE) distribution were a main part of the investigation. Proper orthogonal decomposition (POD) further analyzed the data to compare coherent structures in the reacting and non-reacting flows. Comparison between reacting and non-reacting flows yielded very striking differences. Self-similarity of the flow were observed at different operating conditions.
Flow temperature measurements with a thermocouple scanning probe setup revealed the temperature distribution and flow structure. Features of premixed swirl flame were observed in the measurement. Non-uniformity of flow temperature near liner wall was observed ranging from 1000 K to 1400 K. The results provide insights on the driving mechanism of convection heat transfer.
As a novel non-intrusive measurement technique for reacting flows, flame infrared radiation was measured with a thermographic camera. Features of the flame and swirl flow were observed from reconstructed map of measured IR radiation projection using Abel transformation. Flow structures in the infrared measurement agreed with observations of flame luminosity images and the temperature map. The effect of equivalence ratio on the IR radiation was observed.
Liner wall temperature and heat transfer were measured with infrared thermographic camera. The combustor was operated under reacting condition to test realistic heat load inside the industrial combustors. Using quartz glass liner and KG2 filter glass, the IR camera could measure inner wall surface temperature through the glass at high temperature. Time resolved axial distributions of inner/outer wall temperature were obtained, and hot side heat flux distribution was also calculated from time accurate solution of finite difference method.
The information about flows and wall heat transfer found in this work are beneficial for numerical simulations for optimized combustor cooling design. Measurement data of flow temperature, velocity field, infrared radiation, and heat transfer can be used as validation purpose or for direct inputs as boundary conditions. Time-independent location of peak location of liner wall temperature was found from time resolved wall temperature measurements and PIV flow measurements. This indicates the location where the cooling design should be able to compensate for the temperature increase in lean premixed swirl combustors.
The characteristics on the swirl flows found in this study points out that the reacting changes the flow structure significantly, while the operating conditions has minor effect on the structure. The limitation of non-reacting testing must be well considered for experimental combustor studies. However, reacting testing can be performed cost-effectively for reduced number of conditions, utilizing self-similar characteristics of the flows found in this study.Ph. D.
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Giri, Ritangshu. "Numerical Analysis of Non-Reacting Flow in a Multi-nozzle Swirl Stabilized Lean Direct Injection Combustor." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1447690568.
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Lapeyre, Corentin. "Numerical study of flame stability, stabilization and noise in a swirl-stabilized combustor under choked conditions." Phd thesis, Toulouse, INPT, 2015. http://oatao.univ-toulouse.fr/14493/1/Lapeyre.pdf.
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Air transportation is an essential part of modern business and leisure needs, and the number of passengers carried per year is rapidly increasing worldwide. The International Civil Aviation Organization estimates that this number went from 2.2 billion in 2009 to 3.0 billion in 2013, due in part to rapid growth in emerging countries such as China. Many challenges for aircraft designers arise from this increase in air traffic, such as meeting pollutant and noise emission regulations. The engines play a major part in these emissions, and combustor technology has evolved towards high-pressure Lean Prevaporized Premixed (LPP) combustion to increase efficiency and decrease pollutant emissions. Unfortunately, this technology tends to reduce engine robustness, with a decrease in flame stability and stabilization margins. Recent studies suggest that combustion noise could also be increased in these systems. New methods are needed to describe and understand the mechanisms at hand for future design and optimization in order to operate these engines safely while still achieving emission targets. Large Eddy Simulation (LES) is a numerical approach to these problems which has shown excellent results in the past and is very promising for future design. The description of unsteady phenomena in these power-dense, confined and unsteady systems is essential to describe flame-turbulence interactions, acoustics and multiphysic couplings. As computing power grows, so does the amount of physics which can be modeled. Computational domains can be increased, and have gone from including only the reacting zone, to adding the fuel-air mixing areas, the heat liners and secondary flows, and the upstream and downstream elements. In this Ph.D., a compressible LES solver named AVBP is used to describe an academic test rig operated at the EM2C laboratory named CESAM-HP, a pressurized combustion chamber containing a swirl-stabilized partially-premixed flame and ended by a choked nozzle with high-speed flow. This leads to an accurate description of the chamber outlet acoustic behavior, and offers the possibility to investigate the dynamic behavior of the full system, and the occurrence of flame-acoustic coupling leading to combustion instabilities. It also gives insight into the combustion noise mechanisms, which are known to occur both in the reacting zone and in the nozzle. As shown in this study, this behavior also has an impact on flame stabilization in this system. This manuscript is organized as follows. In a first part, the context for chemistry, motion and acoustics of reacting multi-species flow is given. State of the art theories on reacting multi-species flow thermodynamics, thermoacoustics, combustion noise and flame stabilization in swirled burners are presented. Basic toy models and test cases are derived to validate the understanding of direct and indirect combustion noise, and numerical validations are performed. In a second part, the practical details about numerical investigation of such systems are reported. Finally, the third part describes the application of these tools and methods to the CESAM-HP4 test rig. The inclusion of the compressible nozzle in the LES computation yields results concerning three major issues for the burner: (1) flame stability, related to thermoacoustic instabilities; (2) flame stabilization, and the occurrence of flame flashback into the system’s injection duct; (3) combustion noise produced by the system, and identification of its separate contributions.
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Kumar, Vivek Mohan. "3D Numerical Simulation to Determine Liner Wall Heat Transfer and Flow through a Radial Swirler of an Annular Turbine Combustor." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/51949.
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RANS models in CFD are used to predict the liner wall heat transfer characteristics of a gas turbine annular combustor with radial swirlers, over a Reynolds number range from 50,000 to 840,000. A three dimensional hybrid mesh of around twenty five million cells is created for a periodic section of an annular combustor with a single radial swirler. Different turbulence models are tested and it is found that the RNG k-e model with swirl correction gives the best comparisons with experiments. The Swirl number is shown to be an important factor in the behavior of the resulting flow field. The swirl flow entering the combustor expands and impinges on the combustor walls, resulting in a peak in heat transfer coefficient. The peak Nusselt number is found to be quite insensitive to the Reynolds number only increasing from 1850 at Re=50,000 to 2200 at Re=840,000, indicating a strong dependence on the Swirl number which remains constant at 0.8 on entry to the combustor. Thus the peak augmentation ratio calculated with respect to a turbulent pipe flow decreases with Reynolds number. As the Reynolds number increases from 50,000 to 840,000, not only does the peak augmentation ratio decrease but it also diffuses out, such that at Re=840,000, the augmentation profiles at the combustor walls are quite uniform once the swirl flow impinges on the walls. It is surmised with some evidence that as the Reynolds number increases, a high tangential velocity persists in the vicinity of the combustor walls downstream of impingement, maintaining a near constant value of the heat transfer coefficient. The computed and experimental heat transfer augmentation ratios at low Reynolds numbers are within 30-40% of each other.Master of Science
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Lacarelle, Arnaud [Verfasser], and C. O. [Akademischer Betreuer] Paschereit. "Modeling, control, and optimization of fuel/air mixing in a lean premixed swirl combustor using fuel staging to reduce pressure pulsations and NOx emissions / Arnaud Lacarelle. Betreuer: C. O. Paschereit." Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2011. http://d-nb.info/1017839778/34.
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Ahmad, N. T. "Swirl stabilised gas turbine combustion." Thesis, University of Leeds, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356423.
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Shelil, Nasser. "Flashback studies with premixed swirl combustion." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/55494/.
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The important conclusion was reached that when combusting H2/CH 4 fuel mixes flashback behaviour approaches that of pure methane for equivalence ratios less than about 0.65, all pressures investigated up to 7 bara and air inlet temperatures of 300 and 473K. Significant deleterious changes in flashback behaviour for H2/CH4 fuel mixes occurred for air inlet temperatures of 673K, although operation at weak equivalence ratios less than 0.65 was still beneficial.
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Anapolski, José Luis Potrich. "Modelagem numérica do escoamento reativo com rotação em uma fornalha cilíndrica." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/134559.
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O desenvolvimento de queimadores de baixo NOx é baseado na compreensão da interação entre a cinética química da combustão e o campo do escoamento. Escoamentos rotacionais (swirling flows) são caracterizados pela presença de gradientes de pressão radiais e axiais, e tem sido aplicados como técnica de combustão para a minimização desses poluentes. Neste trabalho é apresentada a modelagem numérica de uma câmara de combustão cilíndrica com queimador dotado com swirler de blocos móveis. O modelo, composto pela equação de continuidade, balanços da quantidade de movimento em três dimensões, o transporte da energia cinética turbulenta e da vorticidade, transporte de espécies químicas e energia, foi implementado numericamente sob a plataforma computacional Fluent. A câmara foi simulada considerando propano combustível e os resultados comparados a dados experimentais de uma câmara cilíndrica operada com GLP. Como principal resultado foi possível identificar a ocorrência da ZCR no escoamento e a influência do número de swirl sobre as características da combustão.The development of low NOx burners is based on the comprehension of the interaction between combustion kinetics and flow field. Swirling flows are characterized by radial and axial pressure gradients, which improve the recirculation of the hot products into the flame region, and then enhance the combustion efficiency have being proposed as a mean to reduce NOx emissions from these equipment’s. This work presents the numerical modeling of cylindrical combustion chamber equipped with movable blocks burner. The model includes the continuity equation along with the 3D momentum balance equations, the k-ω shear stress transport turbulence model equations, the energy balance and the equations for transport chemical species. Results of the simulation of the swirling reactive flow in the combustion chamber, performed using Fluent CFD package, are validated by comparison with experimental data obtained elsewhere. As a main result, it was possible to identify the occurrence of a CRZ in the flow and to discuss the influence of the swirl number on the combustion characteristics.
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Prassas, Ilias. "Combustion of pulverised coal in swirl burners." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286343.
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Sinha, Amit. "Study of Hydrocarbon and Carbonyl Compound Emissions from Combustion of Biodiesel Blends using Plasma and Swirl Stabilized Combustors." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470672537.
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Bompelly, Ravi K. "Lean blowout and its robust sensing in swirl combustors." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47529.
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Lean combustion is increasingly employed in both ground-based gas turbines and aircraft engines for minimizing NOx emissions. Operating under lean conditions increases the risk of Lean Blowout (LBO). Thus LBO proximity sensors, combined with appropriate blowout prevention systems, have the potential to improve the performance of engines. In previous studies, atmospheric pressure, swirl flames near LBO have been observed to exhibit partial extinction and re-ignition events called LBO precursors. Detecting these precursor events in optical and acoustic signals with simple non-intrusive sensors provided a measure of LBO proximity.
This thesis examines robust LBO margin sensing approaches, by exploring LBO precursors in the presence of combustion dynamics and for combustor operating conditions that are more representative of practical combustors, i.e., elevated pressure and preheat temperature operation. To this end, two combustors were used: a gas-fueled, atmospheric pressure combustor that exhibits pronounced combustion dynamics under a wide range of lean conditions, and a low NOx emission liquid-fueled lean direct injection (LDI) combustor, operating at elevated pressure and preheat temperature. In the gas-fueled combustor, flame extinction and re-ignition LBO precursor events were observed in the presence of strong combustion dynamics, and were similar to those observed in dynamically stable conditions. However, the signature of the events in the raw optical signals have different characteristics under various operating conditions. Low-pass filtering and a single threshold-based event detection algorithm provided robust precursor sensing, regardless of the type or level of dynamic instability. The same algorithm provides robust event detection in the LDI combustor, which also exhibits low level dynamic oscillations. Compared to the gas-fueled combustor, the LDI events have weaker signatures, much shorter durations, but considerably higher occurrence rates. The disparity in precursor durations is due to a flame mode switch that occurs during precursors in the gas-fueled combustor, which is absent in the LDI combustor.
Acoustic sensing was also investigated in both the combustors. Low-pass filtering is required to reveal a precursor signature under dynamically unstable conditions in the gas-fueled combustor. On the other hand in the LDI combustor, neither the raw signals nor the low-pass filtered signals reveal precursor events. The failure of acoustic sensing is attributed in part to the lower heat release variations, and the similarity in time scales for the precursors and dynamic oscillations in the LDI combustor. In addition, the impact of acoustic reflections from combustor boundaries and transducer placement was addressed by modeling reflections in a one-dimensional combustor geometry with an impedance jump caused by the flame.
Implementing LBO margin sensors in gas turbine engines can potentially improve time response during deceleration transients by allowing lower operating margins. Occurrence of precursor events under transient operating conditions was examined with a statistical approach. For example, the rate at which the fuel-air ratio can be safely reduced might be limited by the requirement that at least one precursor occurs before blowout. The statistics governing the probability of a precursor event occurring during some time interval was shown to be reasonably modeled by Poisson statistics. A method has been developed to select a lower operating margin when LBO proximity sensors are employed, such that the lowered margin case provides a similar reliability in preventing LBO as the standard approach utilizing a more restrictive operating margin. Illustrative improvements in transient response and reliabilities in preventing LBO are presented for a model turbofan engine. In addition, an event-based, active LBO control approach for deceleration transients is also demonstrated in the engine simulation.
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Yuan, Ruoyang. "Measurements in swirl-stabilised spray flames at blow-off." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709345.
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Mirat, Clément. "Analyse des instabilités de combustion dans des foyers de centrale thermique fonctionnant au fioul lourd." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2015. http://www.theses.fr/2015ECAP0037/document.
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Des crises vibratoires ont été constatées dans plusieurs centrales thermiques d’EDF opérant avec du fioul lourd, certaines ayant entraîné l’arrêt du foyer. Ce travail traite des instabilités de combustion pouvant se déclencher dans ce type de système où le combustible liquide est injecté avec de la vapeur d’eau et où l’écoulement d’air est mis en rotation. Ces phénomènes vibratoires résultent d’un couplage résonant entre la dynamique de la combustion et l’acoustique du foyer. La réponse acoustique des flammes diphasiques non-prémélangées swirlées reste largement méconnue et est difficilement analysable sur le foyer réel. L’objectif de ce travail est donc d’étudier la stabilité des chaudières EDF à partir de l’analyse de la réponse d’une flamme diphasique non-prémélangée swirlée issue d’un injecteur générique et soumise à des perturbations de la vitesse acoustique. Cette réponse est déterminée sur un dispositif original (DIFAV) équipé d’un swirler et d’un injecteur bi-fluides fonctionnant à la vapeur d’eau et au dodécane. Ce système est constitué des principaux éléments des brûleurs utilisés sur les centrales thermiques EDF à une échelle 1/7000. Le dispositif est conçu pour facilement modifier la géométrie de la tête d’injection, les conditions d’injection de combustible et de vapeur et ainsi contrôler le spray généré. Des visualisations à la sortie d’une buse d’injection montrent l’influence de la topologie de l’écoulement diphasique dans l’injecteur sur la taille des gouttes mesurées dans le spray. Des mesures de taille et de vitesse des gouttes lorsque le rapport des débits de vapeur et de combustible (GLR) est modifié sont réalisées. Ces données comparées à des modèles ont permis d’estimer l’évolution de la taille des gouttes générées par l’injecteur qui équipe les centrales thermiques lorsque le GLR varie. Une analyse modale du foyer DIFAV et d’un modèle simplifié de la chaudière réelle est ensuite menée. Les fréquences propres et les taux d’amortissement du foyer DIFAV sont déterminés expérimentalement en soumettant le système à une modulation acoustique externe. Un modèle acoustique simplifié composé de trois cavités couplées représentatif du brûleur DIFAV est également développé. Des simulations acoustiques réalisées avec COMSOL Multiphysics sur une coupe transverse d’une chaudière générique représentative de la chaudière industrielle permettent d’identifier trois modes à basses fréquences établis entre les plenums et la chambre de combustion qui sont susceptibles d’être instables. La sensibilité de ces modes à la géométrie du foyer et aux conditions limites est étudiée. La réponse de la flamme générique lorsqu’elle est soumise à des modulations acoustiques de l’écoulement d’air en amont du brûleur est ensuite mesurée sur le banc DIFAV pour différents niveaux d’excitation et deux topologies de flamme lorsque les conditions d’injection sont modifiées. Les mécanismes qui pilotent l’évolution du gain de l’une des fonctions de transfert généralisées (FDF) de la flamme sont étudiés à l’aide de visualisations en moyenne de phase de l’écoulement et de mesures des vitesses axiale et azimutale de l’écoulement d’air au cours d’un cycle de modulation. Une forte sensibilité de la phase de la FDF à l’amplitude des perturbations acoustiques est observée. Un adimensionnement par le nombre de Strouhal basé sur la vitesse débitante et la longueur efficace de la flamme est proposé pour transposer ces FDFs sur le brûleur réel. Une analyse de stabilité du foyer DIFAV est réalisée en intégrant les FDF au modèle acoustique afin de déterminer les cycles limites des oscillations lorsque la longueur de la chambre de combustion varie. Ces calculs sont comparés aux fréquences des instabilités auto-entretenues mesurées aux cycles limites dans le foyer DIFAV. [...]Vibratory crises have been observed in EDF thermal power plants operating with heavy fuel oil. Such instabilities may lead to shutdown and damage the boiler. This work deals with combustion instabilities that can take place in boilers equipped with steam-assisted atomizers and where the airflow is swirled. These vibratory phenomena result from a resonant coupling between the combustion dynamics and the boiler acoustics. Analyses of combustion dynamics of non-premixed swirling spray flames remain rare and are difficult to realize on the real system. The objective of this work is to analyze the stability of EDF boilers using the response of generic non-premixed swirling spray flames submitted to acoustic velocity disturbances. This response is determined on an original device (DIFAV) equipped with a swirling vane and a twin-fluid atomizer operated with steam and dodecane. This burner is equipped with the main elements of those used in the thermal power plant, but has a reduced scale of 1/7000. The influence of the injector geometry and of the operating conditions on the spray generated by the injector can be studied. Spray visualizations at the outlet of the injector reveal the relationship between the topology of the two-phase flow in the injector and the measured droplet size. Measurements of the droplet diameter and velocity as a function of the gas-to-liquid ratio (GLR) have been performed at the outlet of the injector. These data have been compared to models and were used to estimate the evolution of the droplets diameter as a function of the GLR generated by the industrial injector. A modal analysis of the DIFAV combustor is then carried out and a simplified acoustic model made of three coupled cavities is developed. The natural frequencies and damping rates of the DIFAV combustor are determined experimentally when it is submitted to acoustic modulation. Acoustic simulations are performed with COMSOL Multiphysics on a simplified geometrical model of the industrial boiler. Three low frequency modes established between the plenums and the combustion chamber have been identified and may be unstable. Their sensitivity to modifications of the boiler geometry and boundary conditions are studied. Flame responses subjected to acoustic modulations of the airflow rate are then measured on the DIFAV combustor for several amplitudes and two flames topologies obtained at globally lean condition. Phase-conditioned flame visualizations and measurements of swirl number fluctuations during an acoustic forcing cycle are conducted to explain the mechanisms that control the evolution of gain of the Flame Describing Function (FDF). A high sensitivity of the phase of the FDF to the amplitude of the acoustic disturbance is observed. The Strouhal number based on the airflow velocity and the effective length of the flame is used to transpose these FDF on the industrial burner. FDF are integrated in the acoustic model of the DIFAV setup to carry out a stability analysis and predict the limit cycle oscillations as a function of the combustion chamber length. These calculations are compared to frequencies of self-sustained instability measured at the limit cycles in the DIFAV combustor. A reasonable agreement is obtained showing the validity of the stability analysis for the non-premixed two-phase flames investigated based on the knowledge of their FDF. Finally, a stability analysis of the EDF boiler is conducted with the COMSOL Multiphysics model by including the acoustic flame response of the industrial burner in the simulation. This FDF is deducted from the dimensionless FDF measured on the generic burner. The Rayleigh criterion is used to analyze the stability of the combustor as a function of the flame length for different boundary conditions. Indications are given to improve the stability of the EDF boiler
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Prakash, Shashvat. "Lean Blowout Mitigation in Swirl Stabilized Premixed Flames." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16159.
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Lean, premixed combustion offers a practical approach for reducing nitrogen oxide (NOx) emissions, but increases the risk of lean blowout (LBO) in gas turbines. Active control techniques are therefore sought which can stabilize a lean flame and prevent LBO. The present work has resulted in the development of flame detection, dynamic modeling, blowout margin estimation, and actuation and control techniques. The flame s acoustic emissions were bandpass filtered at select frequencies to detect localized extinction events, which were found to increase in number near LBO. The lean flame was also found to intermittently burst into a transient tornado configuration in which the flame s inner recirculation zone would collapse. The localized extinctions were dynamically linked to the tornado bursts using a linear, first order model. The model was subsequently applied to predict tornado bursts based on optically detected localized extinction events. It was found that both localized extinctions and tornado bursts are by themselves Poisson processes; the exponential distribution of their spacing times could be used to determine blowout probability. Blowout mitigation was achieved by redistributing the fuel flow between the annular swirlers and central preinjection pilot, both of which were premixed. Rule-based and lead-lag control architectures were developed and validated.
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Valera-Medina, Agustin. "Coherent structures and their effects on processes occurring in swirl combustors." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/54815/.
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Access to energy is fundamental to civilisation, both as economic and social yTL development. This is fuelling a growing demand for reliable, affordable and clean energies. The current problems related to climate change have made imperative the search of technologies that can produce higher amounts of energy at lower emission rates. Therefore, technologies such as swirling flows with premixed lean injection have been characterized as one of the most reliable to achieve this objective. However, the use of this technology implicates the appearance of phenomena that have been barely studied such as the manifestation of coherent structures that are crucial for the stability and high efficiency of the combustion process, and which have been assumed from indirect measurements. Moreover, these structures have been recognised as major players in the generation of instabilities such as pressure and heat transfer variations, internal vibrations and flashback into the mixing chambers. Therefore, a better understanding of these structures will allow the design of better burners and a greater control over the former, permitting a more efficient process. This project is intended to reveal some of the characteristics of these structures, showing their high 3 dimensionality and high dependence on geometrical parameters, equivalence ratio, Swirl and Reynolds numbers, amongst other factors. It is recognised how under isothermal conditions the system produces strong Precessing Vortices that are fundamental in the final shape of the flow field, while the Central Recirculation Zones are dependent on the pressure decay ratio inside of the combustion chamber. Combustion conditions showed the high dependence on the method of fuel injection used, with the appearance of stronger structures at lower equivalence ratios when high amounts of premixed gas were pumped into the system and the change in shape of the recirculation zones by using different injectors. Flashback demonstrated to be a factor highly related to the strength of the Central Recirculation Zone for those cases where a Combustion Induced Vortex Breakdown was allowed to enter the swirl chamber, whilst cases where a bluff body impeded its passage showed a considerable improvement to the resistance of the phenomenon. The use of nozzle constrictions also reduced flashback at high Re. All these results were aimed to contribute to better designs of future combustors.
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O'Connor, Jacqueline. "Response of a swirl-stabilized flame to transverse acoustic excitation." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43756.
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This work addresses the issue of transverse combustion instabilities in annular gas turbine combustor geometries. While modern low-emissions combustion strategies have made great strides in reducing the production of toxic emissions in aircraft engines and power generation gas turbines, combustion instability remains one of the foremost technical challenges in the development of next generation combustor technology. To that end, this work investigates the response of a swirling flow and swirl-stabilized flame to a transverse acoustic field is using a variety of high-speed laser techniques, especially high-speed particle image velocimetry (PIV) for detailed velocity measurements of this highly unsteady flow phenomenon. A description of the velocity-coupled transverse instability mechanism is explained with companion measurements describing each of the velocity disturbance pathways. Dependence on acoustic frequency, amplitude, and field symmetry is discussed. Significant emphasis is placed on the response of a swirling flow field to a transverse acoustic field. Details of the dynamics of the vortex breakdown bubble and the shear layers are explained using a wide variety of measurements for both non-reacting and reacting flow cases. This thesis concludes with an overview of the impact of this work and suggestions for future research in this area.
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Salcedo, Saulo Alfredo Gómez. "CFD analysis in spray combustion using a pressure swirl injector." Instituto Tecnológico de Aeronáutica, 2015. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=3292.
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The object of this work is to apply CFD simulation in the description of the spray burning. As a case study, a pressure swirl injector, characterized and tested by NIST, has been chosen, which atomize liquid kerosene in an atmosphere of gaseous oxygen. The chamber dimensions allow a complete evaporation, avoiding the impact of drops on the circular wall. Swirl-axisymmetric domain and steady state permit to include combustion, a complex process, without requiring of high computational resources. Continuous phase is treated with an Eulerian reference, while fuel drops are tracked following the Lagrangian formulation. Chemical kinetics is reduced to the concept of mixture fraction. This assumption avoids the solution of too many transport equations for all involved species. In the first simulation, the inlet boundary of the continuous phase is obtained from the numerical solution of a fully developed flow transporting the oxidant gas. Then, four cases are proposed and solved, changing the turbulence intensity and swirl velocity on the inlet boundary, each parameter with two different values. Finally, results for the axial velocity, streamlines, drops trajectories, temperature, distribution and total production of selected species are analyzed and compared with other related studies.
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Mohamed, Jainulabdeen Mohammed Abdul Kadher. "Combustion Noise and Instabilities from Confined Non-premixed Swirl Flames." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1560867354695989.
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Wang, Xionghui. "Experimental Investigation of Self-Excited Instabilities in Liquid-Fueled Swirl Combustion." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1516361245616083.
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Palies, Paul. "Dynamique et instabilités de combustion des flammes swirlées." Phd thesis, Ecole Centrale Paris, 2010. http://tel.archives-ouvertes.fr/tel-00545421.
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Ce travail traite de la dynamique des flammes turbulentes prémélangées confinées et swirlées soumises à des perturbations de vitesses acoustiques. L'objectif général est d'acquérir une compréhension des mécanismes régissant la réponse de ces flammes et d'en tirer des méthodes de prévision des instabilités de combustion. Les écoulements swirlés sont d'abord examinés en termes de nombre de swirl et de nouvelles expressions sont données pour cette quantité. On traite notamment des effets de perturbations de vitesse et une expression est proposée qui tient compte des fluctuations de vitesses dans l'écoulement. Le système utilisé pour l'étude expérimentale comprend une cavité amont, un injecteur équipé d'un swirler et un tube à flamme transparent permettant la visualisation directe du mouvement de la flamme. Deux points de fonctionnement sont étudiés correspondant à des vitesses débitantes différentes. La cavité amont et le tube à flamme du brûleur peuvent être facilement changés pour étudier plusieurs configurations différentes. L'acoustique du brûleur est également analysée au moyen d'une approche de cavités couplées pour déterminer les fréquences de résonance du système en configuration non-réactive. Des expériences sont menées pour mesurer les fréquences propres du système et l'estimation du coefficient d'amortissement est réalisée à partir de la réponse du système à une modulation externe. Un critère de découplage des mode acoustiques est proposé. La dynamique de l'écoulement est examinée en termes de conversion de modes au niveau de la vrille (swirler) ou dans une grille d'aubes. Cette partie du travail, effectuée au moyen de simulations numériques montre que lorsqu'une grille ou une vrille sont soumis à une onde acoustique, le swirler donne naissance à une onde azimutale convective en plus de l'onde acoustique axiale transmise. Les deux types de swirlers, axial et radial, donnent lieu à ce mécanisme, un fait confirmé par des expériences. Il est montré que ce processus de conversion de mode a un impact important sur la dynamique de la flamme swirlée. La dynamique de la combustion est ensuite analysée en mesurant la fonction de transfert généralisée ainsi que les distributions de taux de dégagement de chaleur au cours du cycle d'oscillation. La fonction de transfert est utilisée pour déterminer la réponse de la flamme à des perturbations acoustiques se propageant dans l'écoulement en amont de la flamme. Il est aussi montré que le nombre de Strouhal est un groupe sans dimensions qui permet de caractériser la réponse de la flamme. La dynamique est également analysée au moyen d'un ensemble de diagnostics comprenant des sondes de pression, un photomultiplicateur et un vélocimètre laser Doppler. Un modèle pour la fonction de transfert linéaire de la flamme est dérivé théoriquement à partir d'une description de la flamme au moyen de l'équation pour une variable de champ G. Les mécanismes physiques de la réponse de la flamme sont identifiés : enroulement tourbillonnaire et fluctuations du nombre de swirl. L'enroulement tourbillonnaire est associé à l'onde acoustique transmise en aval du swirler et qui pénètre dans la chambre de combustion. Tandis que les fluctuations du nombre de swirl sont directement liées aux mécanismes de conversion de mode au swirler qui induit différentes vitesses pour les perturbations axiales et azimutales. L'enroulement tourbillonnaire enroule l'extrémité de la flamme tandis que les fluctuations du nombre de swirl agissent sur l'angle de la flamme. Ces deux mécanismes en compétition se combinent de manière constructive ou destructive conduisant à des gains faibles ou élevés dans la réponse de la flamme en fonction de la fréquence. Ces mécanismes sont retrouvés par simulation aux grandes échelles (LES). Enfin, une analyse d'instabilité est réalisée en combinant la fonction de transfert généralisée expérimentale et un modèle acoustique du brûleur afin de déterminer la fréquence et l'amplitude des perturbations de vitesse au cycle limite.
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Caillat, Sébastien. "Combustion en atmosphère humide : étude d'une flamme méthane/air confinée non prémélangée à Swirl." Rouen, 1999. http://www.theses.fr/1999ROUES049.
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Ce travail est destiné à une meilleure compréhension des phénomènes physiques et chimiques à l'origine de la réduction des oxydes d'azote lors de la combustion en air humide. Une synthèse bibliographique sur des sujets connexes fait apparaître un manque de données expérimentales locales nécessaires à une analyse fine du rôle de l'eau dans la combustion du gaz naturel. Nous avons donc développé un brûleur de laboratoire produisant une flamme méthane / air non prémélangée à Swirl, confinée, dans laquelle différents débits de vapeur d'eau sont injectés (jusqu'a 1,7 mole / mole de combustible). Les techniques de mesures utilisées sur cette flamme sont l'anémométrie Doppler laser, la mesure de température par microthermocouples, et l'analyse locale des gaz (CO, CO2, O2, C NH M, NOx). Des visualisations de la flamme par fluorescence (spontanée et induite par laser) du radical OH sont aussi effectuées. L'analyse des mesures locales montre que l'injection d'eau ne modifie la structure aérodynamique de la flamme que dans les proportions des débits volumiques de diluants injectés, les températures maximales au niveau de la zone de recirculation centrale diminuent de 200 à 300° K. Une simulation numérique du brûleur a été effectuée au moyen du logiciel Fluent, la turbulence étant modélisée par le modèle K- et la combustion par un modèle simplifié à cinq réactions. Elle permet de retrouver les tendances du comportement du brûleur. L'aspect chimique de l'eau est étudié par comparaison avec une dilution à l'argon. La similitude des comportements locaux, y compris de la réduction des NOx, indique une forte prédominance de l'effet physique, plutôt que chimique, de l'eau sur la production des NOx. Cet effet est confirmé par une simulation effectuée à l'aide du code Chemkin II, en utilisant le schéma cinétique GRI 2. 11. Toutefois les images de fluorescence du radical OH, corrigées du quenching, mettent en évidence une concentration de OH plus élevée dans le cas de la dilution par l'eau.
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Idahosa, Uyi. "COMBUSTION DYNAMICS AND FLUID MECHANICS IN ACOUSTICALLY PERTURBED NON-PREMIXED SWIRL-STABILIZED FLAMES." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2721.
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The prevalence of gas turbines operating in primarily lean premixed modes is predicated on the need for lower emissions and increased efficiency. An enhancement in the mixing process through the introduction of swirl in the combustion reactants is also necessary for flame stabilization. The resulting lean swirling flames are often characterized by a susceptibility to feedback between velocity, pressure and heat release perturbations with a potential for unstable self-amplifying dynamics. The existing literature on combustion dynamics is predominantly dedicated to premixed flame configurations motivated by power generation and propulsive gas turbine applications. In the present research effort, an investigation into the response of atmospheric, non-premixed swirling flames to acoustic perturbations at various frequencies (fp = 0-315Hz) and swirl intensities (S=0.09 and S=0.34) is carried out. The primary objective of the research effort is to broaden the scope of fundamental understanding in flame dynamics in the literature to include non-premixed swirling flames. Applications of the research effort include control strategies to mitigate the occurrence of thermoacoustic instabilities in future power generation gas turbines. Flame heat release is quantitatively measured using a photomultiplier with a 430nm bandpass filter for observing CH* chemiluminescence which is simultaneously imaged with a phase-locked CCD camera. Acoustic perturbations are generated with a loudspeaker at the base of an atmospheric co-flow burner with resulting velocity oscillation amplitudes, u'/Uavg in the 0.03-0.30 range. The dependence of flame dynamics on the relative richness of the flame is investigated by studying various constant fuel flow rate flame configurations. The effect of varying fuel flow rates on the flame response is also examined using with dynamic time-dependent fuel supply rates over the data acquisition period. The Particle Image Velocimetry (PIV) method is used to study the isothermal flow field associated with acoustic pulsing. The acoustic impedance, wavelet analysis, Rayleigh criteria and phase conditioning methods are used to identify fundamental mechanisms common to highly responsive flame configurations.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering PhD
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Huang, Yun. "Combustion dynamics of swirl-stabilized lean premixed flames in an acoustically-driven environment." Diss., University of Iowa, 2008. https://ir.uiowa.edu/etd/203.
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Combustion instability is a process which involves unsteady chemical kinetic, fluid mechanic, and acoustic processes. It can lead to unstable behavior and be detrimental in ways ranging from faster part fatigue to catastrophic system failure. In terms of combustion methodology, combustion instability has been a key issue for lean premixed combustion. The primary objective of this work is to improve understanding of combustion dynamics through an experimental study of lean premixed combustion using a low swirl combustor. This special burner was developed at the Lawrence Berkeley National Laboratory and has recently received significant interest from the gas turbine industry.
In these experiments, acoustic perturbations (chamber modes) are imposed on a low swirl stabilized methane-air flame using loudspeakers. The flame response is examined and quantified with OH planar laser induced fluorescence. Rayleigh index maps of the flame are computed for each frequency and operating condition. Examining the structures in the Rayleigh maps, it is evident that, while the flame shows no significant response in some cases, acoustic forcing in the 70-150 Hz frequency range induces vortex shedding in the flame shear layer. These vortices distort the flame front and generate locally compact and sparse flame areas. This information about the flow field shows that, besides illuminating the combustion dynamics, the Rayleigh index is a useful way to reveal interesting aspects of the underlying flow.
The experiments also revealed other interesting aspects of this flame system. It was found that the flame becomes unstable when the perturbation amplitude reaches 0.7% of the mean pressure. Decreasing the swirl number makes the flame shape more jet-like, but does little to alter the shear-layer coupling. In a similar fashion, increasing the pressure was found to alter the flame shape and flame extent, but the thermo-acoustic coupling and induced large scale structure persisted to 0.34MPa, the highest pressure tested.
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White, Colin Laurence. "Experimental and analytical studies based on a high swirl combustion chamber representing the DI diesel engine combustion system." Thesis, University of Bath, 1986. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370455.
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Jourdaine, Paul. "Analyse des mécanismes de stabilisation d'oxy-flammes prémélangées swirlées." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLC046/document.
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Les travaux présentés dans cette thèse s'inscrivent dans le cadre de la chaire OXYTEC qui regroupe l'entreprise Air Liquide, CentraleSupélec et le CNRS. Ce travail bénéficie également de l'appui de l'ANR. Ce manuscrit fait état des premiers développements et résultats sur le plan expérimental. Un dispositif complet a été développé au laboratoire EM2C pour étudier l'oxy-combustion de flammes stabilisées sur un injecteur tourbillonneur jusqu'à des pressions de 30 bar. Les résultats présentés dans cette thèse ont traits à des prémélanges dont le combustible est du méthane lorsque le foyer opère à pression atmosphérique. Les techniques de LIF-OH, la PIV, la LDV complétées par des mesures de chimiluminescence et de température sont utilisées (1) pour accumuler des données sur la structure de trois flammes de référence CH4/air, CH4/O2/N2 et CH4/O2/CO2 qui sont utilisées pour valider des outils de simulation de la combustion et des transferts thermiques, (2) élucider les mécanismes de stabilisation des oxy-flammes swirlés pré-mélangées à partir d'études paramétriques sur le nombre de swirl, la vitesse débitante, la vitesse laminaire de flamme et l'angle de l'ouvreau de l'injecteur, et (3) comparer la structure des oxy-flammes diluées au CO2 avec des flammes CH4/air en examinant notamment la position de pied de flamme, la topologie générale de la flamme et les températures des parois du foyerThe work presented in this thesis falls within the framework of the OXYTEC chair, a partnership between Air Liquide, CentraleSupélec and the CNRS. This work also benefits from the support of the ANR. This manuscript reports the first developments and results on the experimental level. A test rig has been developed to study oxy-combustion of swirl-stabilized flames up to pressures of 30 bar. The results presented deal with premixed conditions where the fuel is methaneand the setup is operated at atmospheric pressure. Laser induced fluorescence on the hydroxyl radical, particle imaging velocimetry, Doppler laser velocimetry completed by chemiluminescence imaging and temperature measurements are used to (1) gather data on the structure of three reference flames CH4/air, CH4/O2/N2 and CH4/O2/CO2 which are used to validate simulations of the reacting flow and heat transfer and (2) elucidate the stabilization mechanisms of premixed swirling oxy-flames from parametric studies by varying the swirl number, the bulk injection velocity, the laminar burning velocity and the injector cup angle and (3) compare the structure of CO2 diluted oxy-flames with CH4/air flames by examining the position of the flame leading edge, the general topology of the flame and the temperatures of flow and the combustor walls
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Emadi, Majid. "Flame structure and thermo-acoustic coupling for the low swirl burner for elevated pressure and syngas conditions." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/4968.
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Reduction of the pollutant emissions is a challenge for the gas turbine industry. A solution to this problem is to employ the low swirl burner which can operate at lower equivalence ratios than a conventional swirl burner. However, flames in the lean regime of combustion are susceptible to flow perturbations and combustion instability. Combustion instability is the coupling between unsteady heat release and combustor acoustic modes where one amplifies the other in a feedback loop. The other method for significantly reducing NOx and CO2 is increasing fuel reactivity, typically done through the addition of hydrogen. This helps to improve the flammability limit and also reduces the pollutants in products by decreasing thermal NOx and reducing CO2 by displacing carbon.
In this work, the flammability limits of a low swirl burner at various operating conditions, is studied and the effect of pressure, bulk velocity, burner shape and percent of hydrogen (added to the fuel) is investigated. Also, the flame structure for these test conditions is measured using OH planar laser induced fluorescence and assessed.
Also, the OH PLIF data is used to calculate Rayleigh index maps and to construct averaged OH PLIF intensity fields at different acoustic excitation frequencies (45-155, and 195Hz). Based on the Rayleigh index maps, two different modes of coupling between the heat release and the pressure fluctuation were observed: the first mode, which occurs at 44Hz and 55Hz, shows coupling to the flame base (due to the bulk velocity) while the second mode shows coupling to the sides of the flame. In the first mode, the flame becomes wider and the flame base moves with the acoustic frequency. In the second mode, imposed pressure oscillations induce vortex shedding in the flame shear layer. These vortices distort the flame front and generate locally compact and sparse flame areas. The local flame structure resulting from these two distinct modes was markedly different.
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Seeley, Warren A. "A predictive study of barrel swirl flow in a spark ignition engine using computational fluid dynamics." Thesis, Coventry University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245343.
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Camata, Mauricio Bishop. "Análise da influência de diferentes geometrias de retificador de fluxo no desempenho de um sensor tipo \"impulse swirl meter\" utilizado para medição de cabeçotes." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3149/tde-03032017-114543/.
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O número de swirl de um cabeçote de motor de combustão interna pode ser medido pelo método de vazão em regime permanente. Nesse método o ar é forçado através do cabeçote para diferentes aberturas de válvula. O sensor comumente utilizado nas plataformas para a medição do swirl é o do tipo ISM (impulse swirl meter) que utiliza um retificador de fluxo como o componente principal para capturar o momento angular de rotação do fluxo de ar. Esse trabalho visa encontrar as dimensões geométricas para o retificador de fluxo utilizado em sensor tipo ISM, de tal forma que esse retificador possibilite a realização das medições com a menor interferência possível no resultado final. Dezesseis retificadores de diferentes dimensões foram construídos a partir do processo conhecido como prototipagem rápida. Vários ensaios foram realizados em uma plataforma que utiliza o método de vazão em regime permanente para a medição de swirl em cabeçotes. Para todos os ensaios foi utilizando um mesmo cabeçote de motor diesel como gerador de swirl. No capítulo conclusões são apresentadas as dimensões geométricas que resultaram em menor interferência no fluxo e uma maior eficiência do sensor, bem como sugestões para trabalhos futuros.The swirl number of a cylinder head can be measured by a steady state flow method in which air is forced through the cylinder head for different valve openings. The sensors commonly used on the swirl measurement platform are of the ISM type (impulse swirl meter) that use a flow straightener as the main component to capture the rotational angular momentum of the air flow. This study objective is to determine the geometric dimensions for the flow straightener used in the ISM sensor, which still allows the measurement but causes the least interference on the measurement result. Sixteen different flow straighteners were constructed by rapid prototyping process. Several tests were performed on a platform that uses the steady state flow method to measure the swirl number of cylinder heads. For all tests the same cylinder head was used as swirl generator. The conclusion chapter presents the geometric dimensions that caused the least interference in the flow and resulted in a greater sensor efficiency, as well as suggestions for future studies.
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Homitz, Joseph. "A Lean-Premixed Hydrogen Injector with Vane Driven Swirl for Application in Gas Turbines." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/36334.
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Hydrogen, as an alternative to conventional aviation fuels, has the potential to increase the efficiency of a gas turbine as well as reduce emissions of greenhouse gases. In addition to significantly reducing the number of pollutants due to the absence of carbon, burning hydrogen at low equivalence ratios can significantly reduce emissions of oxides of nitrogen (NOx). Because hydrogen has a wide range of flammability limits, fuel lean combustion can take place at lower equivalence ratios than those with typical hydrocarbon fuels.
Numerous efforts have been made to develop gas turbine fuel injectors that premix methane/natural gas and air in fuel lean proportions prior to the reaction zone. Application of this technique to hydrogen combustion has been limited due to hydrogen's high flame rate and the concern of the reaction zone propagating into the premixing injector, commonly referred to as flashback. In this investigation, a lean-premixing hydrogen injector has been developed for application in small gas turbines. The performance of this injector was characterized and predictions about the injector's performance operating under combustor inlet conditions of a PT6-20 Turboprop have been made.
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Le, Bris Thomas. "Etude de la combustion du charbon pulvérisé et de la biomasse sur un brûleur à swirl bas NOx." Valenciennes, 2010. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/7b27fd73-7593-4ba6-96e1-5afc95ca172a.
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Ce travail présente la combustion du charbon pulvérisé et la cocombustion charbon/biomasse (pellets de bois) en vue d’une utilisation dans des foyers de grande puissance dans le cadre d’un projet Européen Interreg IIIA Franco-Britannique nommé COSAMM. L’étude présente des résultats d’instruments expérimentaux et traditionnels ainsi que de la modélisation numérique sur une chaudière équipée d’un brûleur bas-NOx à swirl de 3 MWth. Trois instruments sont à valider. Le premier sert à la mesure des particules dans la veine d’alimentation avant le brûleur. Juste en aval, une mesure optique expérimentale de la granulométrie est faite. Le dernier instrument sert à la mesure de la température de flamme et à contrôler sa stabilité. Dans la flamme, des mesures de température par thermocouple et des mesures d’espèces sont faites en complément. La thèse présente la nature des combustibles utilisés, leur combustion et les bases de la théorie de la modélisation de leur combustion. Le système expérimental et les conditions d’entrée pour les modèles sont présentés. La première campagne d’essais permet la validation des instruments avec l’appui des mesures et de la modélisation. La seconde campagne d’essais se fait sur les paramétrages du brûleur. La troisième campagne se fait sur la cocombustion, différents mélanges de charbon/biomasse sont brûlés. La modification de la flamme est significative lors du passage de la combustion du charbon pur au mélange de charbon et de 5% massique de biomasse. On observe une diminution des imbrûlés avec l’augmentation de la quantité de biomasse. Cette amélioration de la combustion avec l’ajout de biomasse est contrebalancée par l'encrassement du foyerThis work concerns pulverised coal combustion and coal/biomass co-firing (wood pellets) for use in large power plants. The study presents results from classical instrumentation, new experimental devices and CFD computational fluid dynamics modeling on a 3 MWth boiler equipped with a swirl low-NOx burner. The work takes place in the framework of a Franco-British European project Interreg IIIA named COSAMM. Three new tools for industry are developed at the university of Kent, an instrument to measure particle speed in the feeding pipe before the burner. Just downstream on the feeding pipe, an optical particle size measurement by imaging is made, the last instrument used is measuring flame temperature and stability. In the flame, thermocouple and species measurements are made in complement. This measurement package coupled with modeling allows the validation of new the measurement instruments. The test on the semi-industrial boiler are used for anticipating problems for upgrading to the industrial stage. The thesis presents the used fuels nature, their combustion and the theoretical bases for the combustion modeling. Moreover, the experimental setup is described. The first test campaign allows testing the experimental instruments by the measures and the modeling. The second test campaign is done on burner parameters. The last campaign biomass is added with a mass fraction input going from 0 to 20%. There is a clear decrease in unburned carbon with the increasing biomass quantity. This combustion improvement with the biomass addition is offset by a strong slagging
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Degeneve, Arthur. "Stabilization, structure and thermal behavior of oxy-flames with a variable swirl level." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST025.
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Ce travail porte sur la stabilisation, la structure et le comportement thermique d’oxy-flammes turbulentes opérées avec du méthane comme combustible. L’étude recouvre des flammes fonctionnant dans des conditions prémélangées et non prémélangées, avec et sans swirl, et avec un oxydant dont la concentration d'oxygène est variable. Plus de 3000 flammes sont étudiées sous une large gamme de conditions de fonctionnement grâce à une chambre de combustion polyvalente, et à des diagnostics laser et des outils de calcul haute-fidélité. L'objectif de cette thèse est de répondre à la question suivante. Si un changement de composition du combustible ou de l'oxydant, de la puissance thermique ou une légère modification de l'injecteur est effectué, est-il possible d’ajuster le swirl conféré aux réactifs afin de retrouver la même structure de flamme et le même régime de stabilisation ? L'impact de l’angle d’ouverture d’un divergent placé en sortie d’injecteur sur l’écoulement est étudié sous un angle à la fois théorique et expérimental au moyen de diagnostics optiques. Un modèle est développé pour prédire la position de la zone de recirculation centrale lorsque cet angle varie. Les effets d'une modification de la composition de l'oxydant sur la structure de flamme sont ensuite étudiés lorsque la flamme passe d'une dilution en N2 à une dilution en CO2. Il est démontré que le swirl a un impact considérable sur la structure de la flamme. La température et la distribution du transfert thermique sont ensuite caractérisées expérimentalement le long des parois latérales de la chambre de combustion. Un modèle de premier ordre est développé pour expliquer les changements de transferts thermiques observés entre les flammes diluées en N2 et en CO2. Le comportement thermique de la chambre de combustion Oxytec est ensuite étudié à l’aide de la simulation numérique aux grandes échelles couplée à un solveur de rayonnement Monte Carlo. La prise en compte détaillée du rayonnement thermique modifie faiblement la position de la flamme et la structure de l’écoulement, mais a un impact considérable sur la température des gaz brûlés et sur la distribution du flux thermique à l'intérieur de la chambre de combustion. Un modèle permettant de prédire la température moyenne du gaz et la distribution du transfert thermique des parois lors du passage d'une simulation non couplée à une simulation couplée est finalement proposé.La suite de l’étude est consacrée à la caractérisation expérimentale des effets du swirl sur la structure et les modes de stabilisation des oxy-flammes en condition non prémélangées et opérées avec un injecteur coaxial dans lequel les deux jets peuvent être swirlés. Une analyse paramétrique est menée en couvrant une large gamme de rapports de flux de moments axiaux et de fractions massiques d'O2, et aboutit sur un modèle qui prédit la longueur d’oxy-flammes coaxiales avec et sans swirl. Il est ensuite montré qu’une augmentation du swirl interne peut détacher la flamme des lèvres de l’injecteur. L'origine des différentes structures de flamme et d'écoulement qui en résultent est étudiée plus en détail à l'aide de mesures couplées OH-PLIF / PIV. Il apparaît que le phénomène de détachement de la flamme hors de l’injecteur central est provoqué par un blocage partiel du jet de méthane central lorsque le swirl interne augmente. De plus, la température mesurée à la surface de l’injecteur lorsque la flamme est détachée est considérablement plus faible que lorsque la flamme est accrochée. Enfin, la structure des oxy-flammes coaxiales non prémélangées est étudiée lorsque les swirls centraux et annulaires sont injectés de manière co- et contra-rotatives. Il est prouvé qu’un swirl contra-rotatif diminue la recirculation du gaz tandis qu’un swirl co-rotatif l'améliore. Cette analyse aboutit à un modèle prédisant l’évolution de la position du pied d’une flamme lorsqu’elle est décrochée de l’injecteurThe thesis deals with the stabilization, structure, and thermal behavior of turbulent oxy-flames burning methane. It covers flames operated in premixed and non-premixed conditions, with and without swirl conferred to the flow, and with a variable concentration of oxygen in the oxidizer stream. These flames are investigated over a broad range of operating conditions on a versatile lab-scale combustor with laser diagnostics and high-fidelity computational tools. The objective is to answer the following question. If a change of fuel or oxidizer composition, thermal power, or a slight modification of the injector nozzle is made, can the swirl motion conferred to the reactants be adjusted to retrieve the same flame structure and stabilization regime before the modification? The work relies both on parametrical analysis conducted on a large set of 3000 operating conditions and a thorough investigation of selected flames. Swirled premixed flames are investigated first. The impact on the flow pattern of a diverging cup at the nozzle outlet is investigated both theoretically and experimentally with optical diagnostics. Expressions for the evolution of the swirl level through this diffuser are derived. A model is then developed to predict the position of the central recirculation zone as the quarl angle varies. The study proceeds by assessing effects of a change in the oxidizer composition when switching from N2- to CO2-dilution on the structure of swirled flames. It is found that the swirl has a considerable impact on the flame structure, and two flame wrinkling processes are identified depending on the swirl level. An experimental characterization of the temperature and heat flux distribution along the combustor sidewalls is then conducted. A low-order model is derived to explain changes of the heat flux distributions for the N2- and CO2-diluted flames. The thermal behavior of the Oxytec combustor is then investigated with large-eddy simulations coupled with a Monte Carlo radiative heat transfer solver. It is found that a detailed description of the thermal radiation barely alters the flame and flow position, but has a tremendous impact on the burned gas temperature and the heat flux distribution inside the combustor. A model which enables to predict the global gas temperature and wall heat flux distribution when switching from a non-coupled simulation to a coupled-simulation is finally proposed.An experimental characterization of the effects of swirl on the structure and stabilization modes of non-premixed oxygen-enriched flames above a coaxial injector in which the two streams are eventually swirled is carried out. A model is derived to predict the length of coaxial oxy-flames with and without swirl. It is found that increasing the inner swirl level detaches the flame from the nozzle rim and lowers the flame liftoff distance. Varying the quarl opening angle or the oxygen concentration in the annular oxidizer stream also enables to control the flame liftoff height. The origin of the different flame and flow patterns is further investigated with the help of coupled OH-PLIF/PIV experiments. It is shown that flame detachment from the internal nozzle is caused by a partial blockage of the inner fuel stream by an intense central recirculation zone when the inner swirl increases. The temperature measured at the nozzle rim of the injector is in this case drastically reduced compared to attached flames. The structure of non-premixed co-axial oxy-flames is finally investigated for co- and counter-rotating operations. It is found that counter-swirl cancels gas recirculation along the burner axis while co-swirl enhances it. This allows to separate effects occurring at the outlet of the injector from swirl dissipation taking place further downstream after the coaxial jets have merged. This analysis has resulted in a model for the evolution of the flame root position and validated for about 200 lifted flames
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Ramalingam, Ammaiyappan Arul Kumaran. "Design and Development of a High Swirl Burner with Gaseous Fuel Injection through Porous Tubes." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511795499271833.
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