Dissertations / Theses on the topic 'Stretched Flames'
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YAMAMOTO, Kazuhiro, and Satoru ISHIZUKA. "Temperatures of Positively and Negatively Stretched Flames." Japan Society of Mechanical Engineers, 2003. http://hdl.handle.net/2237/9370.
Full textLong, Scott R. "Experimental determination of strain rates in stretched laminar diffusion flames." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-08222009-040351/.
Full textDetomaso, Nicola. "Simulation aux grandes échelles de la combustion à volume constant : modélisation numérique des flammes turbulentes en expansion dans les mélanges non homogènes." Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSEP034.
Full textClassical gas turbine thermodynamic cycle has undergone no major changes over the last decades and the most important efficiency improvements have been obtained reducing thermal losses and raising the overall pressure ratio and peak temperature. Despite the efforts in research and development aiming at enhancing especially combustion chambers performances, current technologies may fall short of complying the increasingly stringent environmental constraints. Consequently, a technological breakthrough is essential to shape the future of thermal engines. Pressure Gain Combustion (PGC) emerges as one of the most promising solutions, introducing new thermodynamic cycles where, unlike the Brayton cycle, pressure increases across the combustion process. This can lead to a lower entropy raise, benefiting the overall cycle efficiency.Several PGC concepts are currently studied by the combustion community, ranging from deflagration, such as constant volume combustion (CVC), to detonation, including Rotating Detonation Combustion (RDC) and Pulse Detonation Engine (PDE). Numerical simulation is used to assess the performance of these systems as well as better understand their behavior for improvements before performing experimental tests. Large Eddy Simulation (LES) has assumed an increasingly significant role in combustion science thanks to its high capability in capturing reacting flows. However, with the increasing complexity of combustion systems, advanced physical models are crucial to ensure predictive simulations.In this work, constant volume combustion technology is assessed and the main numerical challenges posed by these combustion systems are scrutinized. Ignition, high pressure combustion, dilution, flame-turbulence interaction, flame-stretch effects, heat fluxes are just part of the physics that CVC systems encompass and their interplay leads to complex physical phenomena that have to be modeled. The numerical models developed in this work are primarily scrutinized in simple test cases and then applied in complete 3D LES framework to compute the constant volume combustion chamber CV2, operated at Pprime laboratory (Poitiers, France).First, novel boundary conditions, based on NSCBC formalism, are derived from nozzle theory to mimic intake and exhaust valve effects. With this strategy no moving part is introduced in the LES and the flow properties are imposed both at the inlet and the outlet of these valves-controlled systems.Second, a two-step chemistry for propane/air mixtures is derived for multiple pressure, temperature and composition of fresh gases. The chemical kinetics is optimized for different concentration of dilutants, composed by burnt products such as carbon dioxide and water vapor. Like piston engines, constant volume chambers operate cyclically and each combustion event is affected by the residual burnt gases coming from previous cycles. For this reason, a numerical model to detail the local composition of diluted flammable mixtures is proposed to provide all the fresh gas information required by the kinetics and the combustion model. Based on a generalization of the classical Thickened Flame (TF) model, a new combustion model, the Stretched-Thickened Flame (S-TF) model, is developed to overcome the TF model limitations in predicting stretch effects on the laminar flame burning velocity. This is crucial to well capture transient events of propagating flames, which are fundamental in CVCs.Eventually, the ignition modeling is assessed and the Energy Deposition model is coupled with the S-TF model by tracking the kernel size in time.The models developed in this thesis are then applied to the CV2 chamber, highlighting their positive impact in capturing the unsteady physics involved in such systems
Nanduri, Jagannath Ramchandra. "A COMPUTATIONAL STUDY OF THE STRUCTURE, STABILITY, DYNAMICS, AND RESPONSE OF LOW STRETCH DIFFUSION FLAME." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1132237973.
Full textAmato, Alberto. "Leading points concepts in turbulent premixed combustion modeling." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52247.
Full textHinton, Nathan Ian David. "Measuring laminar burning velocities using constant volume combustion vessel techniques." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:5b641b04-8040-4d49-a7e8-aae0b0ffc8b5.
Full textMarshall, Andrew. "Turbulent flame propagation characteristics of high hydrogen content fuels." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53859.
Full textTaylor, Simon Crispin. "Burning velocity and the influence of flame stretch." Thesis, University of Leeds, 1991. http://etheses.whiterose.ac.uk/2099/.
Full textli, zhiliang. "EXPERIMENTAL AND CFD INVESTIGATIONS OF LIFTED TRIBRACHIAL FLAMES." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3048.
Full textPh.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering PhD
Roldo, Ismael. "Estudo experimental e teórico de chamas em escoamento de estagnação imersas em meios porosos inertes." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/127905.
Full textThe interest in developing efficient combustion systems to reduce environmental pollution and increase the burning efficiency has called attention to the combustion in inert porous media. The heat recirculation, induced by the solid matrix, from the hot products to the incoming cold reactants, increases the flame temperature and improves its stability, allowing for the use of fuels with low heat content. A recent study shows theoretically that a flame stabilized by a stagnation plane immersed in a porous medium may, under certain conditions, to extend the flammability limits of a mixture of fuel and air. On the other hand, the stagnation plane imposes a certain strain rate on the flow field, which is relevant to various porous burner configurations. Therefore, the focus of this work is the study of combustion in a porous burner with a stagnation plane. An experiment is conducted with packing bed of spheres where a flame can be stabilized against a stagnation plane. The equivalence ratio and the strain rate are controlled by the flows of air and fuel and the distance between the injector and the stagnation plane. The flame position is approximately determined by the temperature field measured by thermocouples. In addition, it is performed a simplified numerical analysis of the problem in which one can see the effect of the strain rate on the stability of flames in porous burners. The results show that it is possible to stabilize flames within the porous medium with stagnation plane, however, it has not been possible to assign a temperature increase due to the increased strain rate.
Han, Bai. "An Experimental and Computational study on Burner-Generated Low Stretch Gaseous Diffuion Flames." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1112978301.
Full textBougrine, Sabre. "Modélisation 0D de la combustion des carburants alternatifs dans les moteurs à allumage commandé." Phd thesis, Ecole Centrale Paris, 2012. http://tel.archives-ouvertes.fr/tel-00740654.
Full textHan, Bai. "An experimental and computational study of burner-generated low stretch gaseous diffusion flames." online version, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1112978301.
Full textDemesoukas, Sokratis. "Modélisation 0D/1D de la combustion pour l’optimisation des systèmes de combustion des moteurs à allumage commandé." Thesis, Orléans, 2015. http://www.theses.fr/2015ORLE2024.
Full textNowadays, the design of Spark Ignition internal combustion engines is focused on the reduction of fuel consumption and low pollutant emissions, while conserving an adequate output power. The high cost of experimental testing comes in favor of the use of numerical simulations for the assessment of engine technologies. Phenomenological Zero-Dimensional combustion models allow evaluating various technical concepts since they take into account various aspects of spark ignition combustion such as chamber geometry, laminar flame characteristics (thickness and speed) and the impact of turbulence. Such models also calculate species concentration of the exhaust gases. In order to create a zero-dimensional combustion model, which can be able to describe correctly the physics of combustion, the key aspects of laminar and turbulent premixed combustion are identified. Three versions of typical combustion models are compared in terms of physical description of the combustion process. The result of this comparison indicated the most physically pertinent mod-el (the Flame Surface Density model). This model is retained and is enhanced with physical modeling of the several phenomena, which affect the heat release rate. Those phenomena are the wall-flame interaction, post-flame reactions and flame stretch. Finally, the proposed model is validated for several engine configurations. Each configuration has an impact on a specific engine parameter. This analysis shows which are the confidence intervals and the limitations of the proposed model
Foley, Christopher William. "Attachment point characteristics and modeling of shear layer stabilized flames in an annular, swirling flowfield." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54357.
Full textYAMASHITA, Hiroshi, Naoki HAYASHI, Tsutomu ISAYAMA, Kazuhiro YAMAMOTO, 博史 山下, 直樹 林, 勉. 伊佐山, and 和弘 山本. "対向流予混合火炎中のOH濃度と燃焼速度." 日本燃焼学会, 2007. http://hdl.handle.net/2237/19735.
Full textHickman, David Gary. "A study of lean burn combustion in a spark ignition engine." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388654.
Full textWeiler, Justin D. "Numerical Simulation of Flame-Vortex Interactions in Natural and Synthetic Gas Mixtures." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4774.
Full text藤田, 英之, Hideyuki FUJITA, 博史 山下, Hiroshi YAMASHITA, 友哉 中尾, and Tomoya NAKAO. "固体壁の小円孔を通過する予混合火炎の消炎に関する数値解析 (水素-空気予混合火炎の消炎機構)." 日本機械学会, 2003. http://hdl.handle.net/2237/8992.
Full textAbdel-Raheem, Mohamed A. "Numerical study of the characteristics of CNG, LPG and hydrogen turbulent premixed flames." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/19612.
Full textVarea, Emilien. "Experimental analysis of laminar spherically expanding flames." Phd thesis, INSA de Rouen, 2013. http://tel.archives-ouvertes.fr/tel-00800616.
Full textBariki, Chaimae. "Interaction entre une flamme de prémélange et une structure tourbillonnaire." Thesis, Orléans, 2018. http://www.theses.fr/2018ORLE2067.
Full textUnderstanding and predicting the different mechanisms at play in turbulent premixed flames is a tremendously difficult issue for sizing or optimizing many combustion systems. Turbulent reactive flows are characterized by a complex interaction between the fluid motion, the inherent heat generated by the flame and turbulence. This challenge being extremely difficult to meet, the study of the interactions between a flat flame and a toroidal vortex provide an ideal canonical framework to better understand the physical mechanisms at play. In this perspective, experimental studies were carried out using a stagnation burner fed by a premixed fuel and air (methane/air,propane/air, hydrogen/air). A panel of experimental techniques as well as numerical tools have been used to characterize thoroughly the flame/vortex interactions. By modifying the equivalence ratio, the mixture composition and the vortex intensity, the temporal evolution of the interaction enable the extraction of the flame surface, the flame front stretch and curvature as well as the displacement/consumption speeds. In addition, the internal flame structure is deeply investigated by decomposing the flame front into a preheat zone and a reaction zone
山本, 和弘, Kazuhiro YAMAMOTO, 悟. 石塚, and Satoru ISHIZUKA. "伸長・回転流れにおける圧力変化と火炎特性." 日本機械学会, 1997. http://hdl.handle.net/2237/9316.
Full textKochar, Yash N. "Laminar flame speed and stretch sensitivity of hydrocarbon fuels at high preheat, pressure and vitiation." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52216.
Full textJohnston, Michael C. "Growth and Extinction Limits: Ground Based Testing of Solid Fuel Combustion in Low Stretch Conditions in Support of Space Flight Experiments." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1511915506999995.
Full textKlarmann, Noah [Verfasser]. "Modeling Turbulent Combustion and CO Emissions in Partially-Premixed Conditions Considering Flame Stretch and Heat Loss / Noah Klarmann." München : Verlag Dr. Hut, 2019. http://d-nb.info/1194288723/34.
Full textBrequigny, Pierre. "Influence de la nature du carburant sur la combustion en moteur à allumage commandé : impact de l’étirement de flamme." Thesis, Orléans, 2014. http://www.theses.fr/2014ORLE2038/document.
Full textIn a context of decreasing pollutant emissions, the transport sector is facing an improvement of engine concept as well as a fuel diversification. The use of these different fuels often involves an impact on the combustion performance itself. In the case of Spark ignition engine, the efficiency is a function of the released heat, image of the combustion speed, i.e. the flame front speed consuming the air-fuel mixture. It is well known that every expanding flame is submitted to flame curvature and strain rate which are both contributors to flame stretch. As the answer of each air-fuel mixture (i.e. the fuel itself, the equivalence ratio, the dilution …) is different to flame stretch, the objective of this work is to understand flame stretch impact on fuel performance in Spark-Ignition engines. To achieve this goal, different fuel-air mixtures with similar unstretched laminar burning speed and thermodynamic properties but different responses to stretch were selected. Those mixtures were then studied with different experimental devices with different measurement techniques: single-cylinder metallic and optical engines, turbulent combustion spherical vessel. Results show that flame stretch sensitivity properties such as Markstein length and Lewis number, determined in laminar combustion regime, are relevant parameters to describe the flame propagation in turbulent combustion as in the combustion chamber of the Spark-Ignition engine and need to be taken into consideration to evaluate global performance of these fuels, experimentally and also in modeling simulation
Nan, Yu-Jyun, and 余峻南. "Measurements of Unsteady Stretch for Lean Premixed Turbulent Methane/Air Flames." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/64911772549777167573.
Full text國立中央大學
機械工程研究所
93
This thesis investigates experimentally the effect of unsteady stretch for lean premixed turbulent methane/air flames interacting with near-isotropic turbulence. We study the effect of Reynolds number (Ref) on local properties of lean premixed flames at two different turbulent intensities. The near-isotropic turbulence is generated in a large cruciform burner that includes a long vertical vessel and a large horizontal vessel equipped with a pair of counter-rotating fans and perforated plates. The long vertical vessel can be used to produce a downward propagating premixed flame to interact with near-isotropic turbulence. We apply high-speed particle imaging velocimetry (PIV) to measure flame-turbulence interactions, and thus the corresponding strain rate, curvature, stretch rate, and dilatation rate fields along the wrinkled flame front can be obtained. Results show that, at the equivalence ratio �� = 0.7, and the turbulent intensity u�S = 32.34 cm/s (Ref = 1020), no apparent correlations between the stretch rate and the dilatation can be observed. This differs with that found by Driscoll and his co-workers who used a single vortex interacting with a lean premixed flame. It is found that at Ref = 1020, the stretch rate is dominated by both the strain rate and the curvature term. This situation gradually changes as flame propagating, in which the curvature becomes more and more important that eventually dominates the stretch rate. For large values of Ref up to 1750 (u�S = 46.2 cm/s), the possible correlation between the stretch rate and the dilatation rate is even worse, and the strain rate term plays a more important role than the curvature term, indicating the effect of Reynolds number on the stretch rate.
Chang, Chung-Chien, and 張中千. "Stretch Measurements of Turbulent Premixed Methane/Air Flames Using High-speed PIV." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/81619478658634718494.
Full text國立中央大學
機械工程研究所
92
This thesis investigates experimentally the effect of unsteady stretch on laminar premixed flames interacting with turbulent flows. Using a turbulent wake burner and a large cruciform burner, a von Kármán turbulent wake and near-isotropic turbulent flows can be generated, respectively. We applied high-speed particle image velocimetry (PIV) and the laser tomography to quantitatively measure the corresponding strain rate, curvature, stretch rate, and dilatation rate along the interacting flame front with turbulent wake and near-isotropic turbulence. Experiments in the turbulent wake burner were conducted to study the effect of radiative heat losses on stretching of premixed CH4 flames by using two diluting gases, CO2 (large radiative heat loss) and N2 (small radiative heat loss),respectively. Note that the laminar burning velocities for both CO2- and N2-diluted flames are kept constant with SL = 10 cm/s at a fixed equivalence ratio Φ = 0.7. Experimental results reveal that the maximum burning rate that may be indicated by the maximum dilatation rate occurs in regions of high positive curvature rates. This confirms that the reaction rate of Le<1 flames is increased by the positive stretch, as already suggested by Law and many other researchers. The curvature team is more important than the strain rate term in the overall stretch consideration for the present lean CH4/air premixed flames with Le<1, at least for the ratio of the mean tangential velocity of the staggered vortex pair of the wake to the laminar burning velocity, uθ/SL , up to 2. By comparing CO2- and N2-diluted flames, the wrinkled flame propagation speeds and the peak values of the dilatation rate are largely decreased by the increase of radiative heat loss. Experiments in the cruciform burner were conducted to investigate the effect of unsteady stretch for rich (Φ = 1.45) methane/air flames interacting with near-isotropic turbulence, where the root-mean-square turbulent intensity u'=32.3 cm/s and u'/SL = 2.2. The experimental data suggest that the reaction of rich CH4 flames (Le>1) is strengthened by the negative strain rate, but the flame is burned more intensely near regions of the flame front whose curvature is positive. For the unsteady stretch of rich CH4 flames, the strain rate term plays a dominate role on the stretch rate in the beginning of the flame-turbulence interaction, but during the interaction the curvature term gradually becomes a dominate term.
Danby, Sean James. "Experimental quantification of transient stretch effects from vortices interacting with premixed flames." 2008. http://www.lib.ncsu.edu/theses/available/etd-09222008-105850/unrestricted/etd.pdf.
Full textJou, Luo Feng, and 羅豊州. "Effects of Flow Stretch on Premixed-Flame Propagation in Closed Tube." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/30504991709454040912.
Full text大葉大學
機械工程研究所
83
Here a hydrodynamic model was proposed for flame propagation in close tube effected by flow stretch. The flame is treated as a surface of discontinuity like in previous work. For the structure governing flame burning rate, large activation energy and large heat release assumptions are used in the model. It is well known that for laminar premixed flames with Lewis number smaller then one propagating in open space, the burning rate will increase when it is subjected to positive flow stretch and the reverse is true for negative flow stretch. And for flame with Lewis number bigger then one the trend is just the opposite. For flames propagating in open space the pressure is constant , while in present study the overall pressure is rising with the flame propagation . Present theoretical results suggest for flames propagating in closed tube the effect of flow stretch to the flame is the same as that in open space. That is for flame in closed tube positive flow stretch will increase the mass burning rate for flames with Lewis number smaller then one, and for flames with Lewis number bigger then one the mass burning rate will decrease. The trend will reverse for flames experiencing negative flow stretch.
De, Vries Jaap. "A STUDY ON SPHERICAL EXPANDING FLAME SPEEDS OF METHANE, ETHANE, AND METHANE/ETHANE MIXTURES AT ELEVATED PRESSURES." 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-05-601.
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