000128530 001__ 128530
000128530 005__ 20190509132212.0
000128530 0247_ $$2doi$$a10.5075/epfl-thesis-4249
000128530 02470 $$2urn$$aurn:nbn:ch:bel-epfl-thesis4249-7
000128530 02471 $$2nebis$$a5673292
000128530 037__ $$aTHESIS
000128530 041__ $$aeng
000128530 088__ $$a4249
000128530 245__ $$aExperimental investigation of unstrained diffusion flames and their instabilities
000128530 269__ $$a2009
000128530 260__ $$bEPFL$$c2009$$aLausanne
000128530 300__ $$a171
000128530 336__ $$aTheses
000128530 520__ $$aIn this thesis, thermal-diffusive instabilities are studied experimentally in diffusion flames. The novel species injector of a recently developed research burner, consisting of an array of hypodermic needles, which allows to produce quasi one-dimensional unstrained diffusion flames has been improved. It is used in a new symmetric design with fuel and oxidizer injected through needle arrays which allows to independently choose both the magnitude and direction of the bulk flow through the flame. A simplified theoretical model for the flame position, the temperature and the species concentration profiles with variable bulk flow is presented which accounts for the transport properties of both reactants. The model results are compared to experiments with a CO2-diluted H2-O2 flame using variable bulk flow and inert mixture composition. The mixture composition throughout the burning chamber is monitored by mass spectrometry. An elaborate calibration procedure has been implemented to account for the variation of the mass spectrometer sensitivity as a function of the mixture composition. The calibrated results allow the effective mixture strength of the diffusion flames to be measured with a relative uncertainty of about 5 %. In order to properly characterize the flame produced, the velocity and temperature distribution inside the burning chamber are measured. The resulting species concentration and temperature profiles are compared to the simplified theory and demonstrate that the new burner configuration produces a good approximation of the 1-D chambered diffusion flame, which has been used extensively for the stability analysis of diffusion flames. The velocity profiles are also used to quantify the residual stretch experienced by the flame which is extremely low, below 0.15 s-1. Hence, this new research burner opens up new possibilities for the experimental validation of theoretical models developed in the idealized unstrained 1-D chambered flame configuration. The thermal-diffusive instabilities observed close to extinction are investigated experimentally and mapped as a function of the Lewis numbers of the reactants. The use of a mixture of two inerts (helium and CO2) allows for the effect of a wide range of Lewis numbers to be studied. A cellular flame structure is observed in hydrogen flames when the Lewis numbers is relatively low with a typical cell size between 7 and 15 mm. The cell size is found to scale linearly with the diffusion length, in good agreement with theoretical predictions. When the Lewis number is increased by using a higher helium content in the dilution mixture, the instabilities observed are planar intensity pulsation. The use of methane allowed pulsating flames to be generated for a wide range of bulk velocities and transport properties. The pulsating frequencies measured are in the 0.7 to 11 Hz range and were found to scale linearly with a diffusion frequency defined as U2/Dth multiplied by the square root of the Damköhler number. The experimental results presented here are the first observations of thermal-diffusive instabilities in such a low-strain flame. They constitute a unique dataset that can be used to quantitatively validate theoretical models on diffusion flame stability developed in the simplified one-dimensional configuration.
000128530 586__ $$aABB, 2009
000128530 6531_ $$athermal-diffusive instability
000128530 6531_ $$aunstrained
000128530 6531_ $$adiffusion flame
000128530 6531_ $$aexperimental
000128530 6531_ $$ainstabilités thermo-diffusives
000128530 6531_ $$aflamme de diffusion
000128530 6531_ $$aétirement
000128530 6531_ $$aétude expérimentale
000128530 700__ $$0245111$$g129902$$aRobert, Etienne
000128530 720_2 $$aMonkewitz, Peter Alexis$$edir.$$g105889$$0240474
000128530 8564_ $$uhttp://vpaa.epfl.ch/Jahia/site/vpaa/op/edit/lang/fr/pid/34588$$zAward
000128530 8564_ $$uhttps://infoscience.epfl.ch/record/128530/files/EPFL_TH4249.pdf$$zTexte intégral / Full text$$s4643938$$yTexte intégral / Full text
000128530 909C0 $$xU10317$$0252381$$pLMF
000128530 909CO $$pthesis-bn2018$$pDOI$$ooai:infoscience.tind.io:128530$$qDOI2$$qGLOBAL_SET$$pthesis
000128530 918__ $$dEDME$$cIGM$$aSTI
000128530 919__ $$aLMF
000128530 920__ $$b2008
000128530 970__ $$a4249/THESES
000128530 973__ $$sPUBLISHED$$aEPFL
000128530 980__ $$aTHESIS