Planar Laser-Induced Fluorescence (PLIF) of H2
Contents
1. An Example of WinView 32 Display Averaging of Five PLIF Images of Six Cases without Ceramic PLIF Images of Six Cases with Ceramic Position of Ceramic Table 3 1 Results LIST OF TABLES 3 2 Correlation Chart for Flowmeters 40400009 1X FWHM HBW ICCD KrF LED VUV NOMENCLATURE diameter of a lens focal length of a lens temperature dependent Boltzmann fraction of the absorbing state full width at half maximum half bandwidth intensified charge coupled device krypton fluoride laser emitting diode mass flow rate of mass flow rate of fluorescence signal per pixel temperature ultra violet vacuum ultra violet OH mole fraction INTRODUCTION As lasers become increasingly available and reliable laser spectroscopy becomes promising in the diagnostic probing of combustion processes Laser based techniques are capable of remote non intrusive in situ spatially and temporally precise measurements of chemical parameters unlike physical probing methods such as thermocouples that have been traditionally utilized to investigate and characterize combustion phenomena 1 Laser induced fluorescence is presumably the most well known technique for2. REE 20 DISCUSSION E 27 4 CONCLUSIONS AND 5 222 22 20040 0000 29 AAC ONCIUSIONS 29 4 2 Recommendations 014223 akan neha ei 29 Appendix A EXPERIMENTAL 1 1 012 31 COMPEX 150 EXCIMER LASER OPERATION PROCEDURE 35 WINVIEW 32 22 24 41 REFERENCES ket ale 45 5 47 vii Figure 1 1 1 2 24 2 2 2 3 2 4 2 9 2 6 2 7 3 1 3 2 3 3 3 4 3 5 LIST OF ILLUSTRATIONS State View of Laser Induced 1 Basic Arrangement of PLIF 2 PLIF Setups easements Sectional View of McKenna Flat Flame Schematic Diagram of Experimental Setup forthe Plat Elame E eases Gas Handling ICCD Test with 3 D Image Acquisition System
3. 45 zi 5 5 1 765 7 4 481 9 4 543 Case 11 MR 5 918 Figure 3 3 PLIF Images of Six Cases without Ceramic Rod 25 a Case 2 3 627 b Case 4 MR 2 448 c Case 6 MR 1 765 d Case 8 MR 4 481 e Case 10 MR 4 543 Case 12 MR 5 918 Figure 3 4 PLIF Images of Six Cases with Ceramic Rod 26 Figure 3 5 Position of Ceramic Rod 3 2 Discussion The flame was asymmetric for the cases without the ceramic rod but this was because the flame was non uniform the flame was always generated on the right side of the burner seen from the ICCD However after inserting the ceramic rod the flame became more uniform The flame in Fig 3 4 is more uniform than that in Fig 3 3 The stoichiometric mixture ratio of 8 was not achieved due to restriction of the gas handling system or the burner In both Figs 3 3 and 3 4 it can be seen that lower the mixture ratio MR the larger is the flame image As mentioned in section 1 1 3 the measured quantity of the 27 fluorescence signal is written as Spp const The fluorescence signal is directly proportional to the mole fraction of OH and a temperature dependent function in bracket As the MR increases both adiabatic flame temperature T and OH mole fraction increase In this situation it is difficult to separate the term from th
4. AJAA Journal Vol 39 No 10 pp 1926 1935 October 2001 Houwing A F P Smith D R Fox J S Danehy P M amp Mudford N R Laminar boundary layer separation at a fin body junction in a hypersonic flow Shock Waves Vol 11 pp 31 42 2001 Bessler W G Hildenbrand F amp Schulz C laser induced fluorescence imaging of vibrational temperatures in a NO seeded flame Applied Optics Vol 40 No 6 pp 748 755 2001 Rothe E W and Andresen P Application of tunable excimer lasers to combustion diagnostics a review Applied Optics Vol 36 No 18 pp 3971 4033 1997 Bombach R Laser Spectroscopy in Combustion Research Ch 2 Paul Scherrer Institut Switzerland Internet URL http cdg web psi ch Summerschool chap2 pdf Anderson P Bath A Groger W et al Laser induced fluorescence with tunable excimer lasers as a possible method for instantaneous temperature field measurements at high pressures checks with an atmospheric flame Applied Optics Vol 27 No 2 pp 365 378 1988 Houwing A F P Palma P C et al Fluorescence imaging based flow diagnostics applications to free piston shock tunnel flows 22 International Symposium of Shock Waves Imperial College London UK July 18 23 Paper 0890 1999 45 10 11 12 13 14 15 16 17 18 E S and Khokhlov A M Deflagrations Hot Spots and th
5. In Setup Hardware Interface tab select High Speed In Setup Hardware Controller Camera tab select ST 138 for Controller Type 576x 384 3ph for Camera Type Electronic for Shutter Type and check Full Frame for Readout Mode Go to Acquisition Experimental Setup In Main tab select 0 1 sec for Exposure Time 1 for Number of Images and 1 for Accumulations Also check Use Full Chip for CCD Readout b In Timing tab select Free Run for Timinig Mode and Normal for Shutter Control c In Data File tab type in Data File Name a file name you want to create such as 073103Test Click on Enable for Auto Increment File Name and set Current 42 Value to 1 This will facilitate the file handling by adding the suffix with incrementing numbers from 1 as 073103Test1 073103Test2 and so on In ROI tab select 1 for New Pattern 1 380 and 5 for X and 1 575 5 for Y 4 The proper position of the ICCD can be checked with Flat Field images although flat field is not used for the right purpose With the room lights on take flat field by Acquisition Acquire Flat Field You will see high intensities caused by fluorescent lights on the sides of the burner on the image Using these clues move the ICCD to the right position 5 Acquire background for background correction by selecting Acquisiti
6. Planar Laser Fluorescence Imaging of Combustion Gases Applied Physics B Vol 50 pp 441 454 1990 46 BIOGRAPHICAL INFORMATION Takashi Yokomae received his Master of Science in Aerospace Engineering from the University of Texas at Arlington UTA in December 2003 He was born in Japan and upon completing high school there he came to the United States to study in the University He received his Bachelor of Science in Aerospace Engineering from UTA in May 2003 Culturally diverse UTA community allowed him to be more broad minded during his 6 year stay at UTA He likes to play various kinds of sports for example basketball tennis baseball softball swimming and rollerblading 47
7. system configuration is presented in Fig 2 7 below Monitor TAXI Cable 580099007 ST 138 Detector Controller PCI Interface Card HostComputer 118214 with WinViewi32 cc 100 Coolant Circulator ICCD Detector Figure 2 7 Image Acquisition System Configuration 2 5 2 Image Processing PI systems are adjusted so that data have a small offset This offset assures that small signals will not be missed and can be subtracted after the signal is acquired to specified number of pixels in each direction will be combined to form super pixels for greater sensitivity 17 18 prevent it from having any influence on the data The background subtraction feature automatically subtracts any constant background in the signal This includes not only constant offsets caused by the amplifier system in the controller but also time dependent buildup of dark charge The background subtract equation is expressed as follows 17 Corrected image data Raw image data Background Another data correction technique flatfield correction which divides out non uniformities in gain from pixel to pixel was also available in WinView 32 but was not used because this was found to be unnecessary The corrected images are displayed in WinView 32 Gray scale images can be displayed in false color which varies with the light intensity or the fluorescence signal Five frames of images are averaged since the flame f
8. 1 Check the beam path 2 Turn on main switch of the laser assembly at the utility supply 3 Turn on main switches and key switches of both Amplifier and Oscillator 4 Switch on the designated computer PC and the monitor Always turn on the laser assembly before turning on the computer to prevent data ring diagnosis failure see section II 1 below 5 Wait until DOS prompt C gt and a blinking cursor appears 6 Type cd lambda to change directory 7 Type 1 150 to start the COMPex150 software II Booting the Local Software After the software started it passes three tests 1 Data ring diagnosis also called dynamic fiber loop check The data ring of the COMPex 150 is a local area network LAN which links the modules of the laser assembly with fiber optics lightwave guides To test it the PC sends a light signal and checks if it passes the LAN If this test fails a window DYNAMIC FIBER LOOP CHECK appears When this happens turn off both the PC and the laser assembly and wait for about 30 minutes and turn them back on If everything is all right the program enters the module availability check 36 2 Module Availability Check This tests what modules of the laser assembly are recognized by the PC If any of them does not respond NOT INSTALLED is displayed and a beep tone is displayed However because the last one F2 SOURCE is not installed just hit G to continue if everything else is YES The
9. Colors are assigned according to intensity of fluorescence captured by the ICCD low intensity being black and high being red The range of the intensity level was kept at 300 to 1200 after examining all the images Vertical and horizontal cross sections profile the intensity at the strips where the cursor shown as a big white cross is placed High intensities shown at the bottom of the image can be assumed to be the fluorescence emitted at the beam stop see Fig 2 1 that reflected back and is removed during further processing 22 073103Test4 384 X 576 X 1 x 226 Y 242 2 1 672 2 Fig 3 1 Example of WinView 32 Display Figure 3 2 demonstrates averaging of five images for Case 1 The reason why the averaging was done is because the flame flickers somewhat Figures 3 3 and 3 4 show the averaged images for the twelve cases At each MR a ceramic rod was inserted to stabilize the flame 18 Fig 3 4 The position of the rod is 0 44 in above the burner surface and 0 31 in to the right from the vertical centerline of the burner as described in Fig 3 5 The burner is outlined with white lines in each image For Cases 7 and later the ICCD was accidentally moved and the image frame also moved slightly 23 4 1 in i a Test 1 b Test 2 E 5 Test 3 Test 4 Test 5 f Average Figure 3 2 Averaging of Five Images 24 Z a Case 1 MR 3 627 b Case 3 MR 2 448
10. Fuel P Se Se a Cooling Water Cooling Water Flowmeter Pressure Regulator Flashback Arrestor Oxidizer Shielding Gas Figure 2 3 Schematic Diagram of Experimental Setup for the Flat Flame Burner 11 Regulator for H2 Regulator for O2 Flowmeter for Flowmeter for H2 Flowmeter for H2 Flash arrestor for Flash arrestor for Figure 2 4 Gas Handling System Oxygen and hydrogen gas cylinders with pressure regulators are fixed on the side of the combustion table The millboard 40 inch wide by 42 inch high is erected between the burner and the gas cylinders for safety The gases from two cylinders are joined at a tube union and hence pre mixed before ignited at the burner To prevent backflash upon ignition two flash arrestors are installed one between the cylinder and the union the other between the and the union In addition to adjust the flow rates of gases correlated flowmeters with standard valves Cole Parmer catalog nos A 12 03216 22 for and gt and 03216 32 for installed vertical tangential locator line of a flowmeter ensures accuracy in reading the float position 2 3 Optical System The optical system consists of spatial filtering laser sheet generation and image collection List of Equipment a Spherical plano convex objective lens f 350 mm d 2 in CVI Laser b Pinhole 40 um diameter
11. Induce d 250 1 1 1 2 Planar Laser Induced 3 1 1 3 Fluorescence Dependence of Temperature and Mole Fraction 44 0120 4 1 1 4 5 5 2 EXPERIMENTAL 5 7 2 4 1 8 7 2 2 CoMmb sti n Syste 9 2 2 11 9 2 2 2 Combustion Gas Handling 10 13 2 3 1 5 E 13 2 3 2 Laser Sheet edie na 14 mape Collecion 15 2 4 ICCD Intensified Charged Coupled 15 2 5 Image Acquisition and 1 17 2 5 1 Image 17 2X2 mage 18 3 RESULTS AND DISCUSSION 20 SINS RG SUIS
12. c Cylindrical plano concave lens f 81 4 mm d 1 in CVI Laser Spherical plano convex imaging lens f 50 mm d 1 in CVI Laser e Band pass filter center wave length 296 7 10 nm HBW or FWHM d 1 in CVI Laser f Optical table rails amp carriers Thermo Oriel 2 3 1 Spatial Filtering Spatial filters eliminate random fluctuations from the intensity profile of a laser beam which increases resolution significantly Optical defects and particles in the air cause intensity variations of laser beams Spatial filtering is fairly simple see the schematic shown in Fig 2 5 An ideal coherent collimated laser beam behaves as though produced by a distant point source Spatial filtering consists of focusing the 13 beam producing an image of the source with all the imperfections in the optical path defocused in an annulus about the axis A pinhole blocks most of the noise 14 OBJECTIVE PINHOLE INPUT BEAM SCATTERING CLEAN PR FROM DUST DIRTY Newport Corporation Figure 2 5 Spatial Filters In this research a 2 inch diameter fused silica singlet lens PLCX 50 8 180 3 UV from CVI Laser Corporation is the objective lens and 40 um diameter pinhole 15 employed 2 3 2 Laser Sheet Generation PLIF requires the generation of a laser sheet A cylindrical lens is used to do this In the experiment 1 inch diameter VUV CaF round singlet lens CLCC 25 4 38 1 CFUV from CVI Laser is
13. mol 32 mol 3 627 2 mol where 22400 ml is the volume occupied by 1 mole of a gas assuming an ideal gas and molecular weight of is 32 g mol 2 g mol Table3 1 Results Case mm ml min mm O2 ml min mm N ml min Ceramic MR The maximum flow of O2 was 20 mm or 749 ml min for this setup When the flow rate was increased over that value the burner started making a whistling noise and the flame became unstable which eventually might have been put out On the other hand the flow rate could not be lowered less than 18 mm 1639 ml min while it could go up to the flowmeter limit 65 mm 13 6 l min shielding gas No was 21 kept constant at 60 mm or 13 4 l min for the first six cases where the flame was relatively larger and lowered to 40 mm or 96 1 l min for relatively small flame Table3 2 Correlation Chart for Flowmeters Scale Reading ml min O2 ml min ml min mm 65 13600 3761 13412 60 11875 3395 12724 55 10360 3051 12049 50 9302 2727 11252 45 7600 2400 10450 40 6450 2098 9608 35 5176 1787 8753 30 4162 1451 7777 25 3000 1108 6748 20 2025 749 5626 15 1060 459 4502 10 430 251 3313 5 178 120 2056 example of WinView 32 display is shown in Fig 3 1 below The image is rotated 90 degrees counter clockwise
14. operation procedure Open the valves of and cylinders Set the pressure regulators to about 15 psi 100 kPa Open the gas lines Open the flowmeter valve for and ignite the burner with a long match The flowmeter reading should be about 20 mm Turn off the room lights in order to see the flame better Open the flowmeter valve for too and adjust it to about 15 mm Always ignite fuel H2 first Open the flowmeter valve for and adjust it to the maximum value 60 mm or until you do not see orange flame any more Orange flame means it is reacting with ambient air and the shielding is not sufficient Fire the laser See Appendix B for the laser operation procedure Acquire the image with WinView 32 See Appendix C for the WinView 32 procedure 33 15 Change mixture ratio of the and acquire more images and repeat Also insert ceramic rod to stabilize the flame 18 16 After the experiments turn off everything Do not forget to close the water valve as well 17 After turning off the ST 138 controller keep flushing the ICCD with nitrogen at a flowrate of at least 2 liters min for at least 30 minutes This keeps moisture condensation from forming on the ICCD until it reaches room temperature 34 APPENDIX 150 EXCIMER LASER OPERATION PROCEDURE 35 I Starting the Laser Assembly Keep in mind that the laser assembly consists of Amplifier and Oscillator
15. or equal to 10 ppm compressed nitrogen of grade ultra high purity from Airgas is used The ICCD is controlled by the detector controller Model ST 138 S from PI which sends information to a computer through a TAXI cable and PCI interface card 16 The ICCD was tested visible light with a Nikon lens with a focal length of 1 meter 3 28 ft with all the room lights shut off The UV filter was removed and the laser was not firing Figure 2 6 shows a 3 D object Garfield also shown in Fig 2 1 acquired Figure 2 6 ICCD Test with 3 D Garfield 2 5 Image Acquisition and Processing The ICCD controller is managed by WinView 32 software from PI The fluorescence images acquired are stored on the host computer Windows98 processed and displayed 2 5 1 Image Acquisition The WinView 32 software also from PI is installed on the host computer Windows98 The PCI interface card installed in the host computer permits communication between the computer and the ST 138 controller The controller accepts 17 input from the computer or WinView 32 and converts it to the proper control signals for the camera These signals can be adjusted to specify the readout rate binning parameter regions of interest gain and array temperature Data acquired in the camera is transmitted to the controller where it is processed It then is passed on to the computer displayed in the WinView 32 window and can be stored on disk 17 The
16. radical species measurements It has been in use considerably since the early 1980s because of its merits of providing high spatial resolution typically 0 1 mm high temporal resolution typically less than 100 ns and high sensitivity typically concentrations in the ppm range 2 1 1 Planar Laser Induced Fluorescence 1 1 1 Laser Induced Fluorescence Laser induced fluorescence LIF is an established selective and sensitive approach for identifying species concentration from reactive flow systems without perturbing the system under study 3 5 LIF is a sequence of molecules or atoms being excited to higher electronic energy states via laser absorption followed by spontaneous emission of fluorescence The spectral absorption regions are discrete because the energy states of molecules and atoms are quantized Typically fluorescence occurs at wavelengths greater than or equal to the laser wavelength Therefore LIF offers the possibility to investigate species of interest by selecting the appropriate wavelength Shown in Fig 1 1 below is the state view of LIF As the species under investigation are usually molecules or radicals not atoms the electronic levels are divided into sub levels according to the molecular vibrational and rotational energy Due to quantum mechanical effects electronic vibrational and rotational energies are quantized 1 0 1 2 6 Figure 1 1 also shows energy state description of LIF The molecule
17. 0 mm from the image intensifier of the ICCD with the convex side facing the ICCD Since the bandpass filter is mounted on the ICCD the imaging lens is almost touching the ICCD 4 Power the laser assembly designated computer and monitor for the laser Open the water valve See Appendix B for the details of the laser operation 5 Ensure all the valves of the four flowmeters are closed 6 Open the nitrogen cylinder valve Adjust the pressure regulator to about 15 psi 1 bar Then open the gas line 7 Power the ST 138 detector controller switch on the cooling of the ST 138 and power coolant circulator CC 100 The ST 138 will be ready temperature is thermostated to within 0 050 C of preset value in this case 30 C in about 10 minutes when the status LED is turned from orange to green 32 10 11 12 13 14 Immediately after procedure 8 open the valve of the flowmeter of the nitrogen for the ICCD and set it to 1 2 liters min for at least 10 minutes and then lower to 0 75 1 liters min The flowmeter is for air molecular weight of about 28 8 g mol but it can be used in the same way since it is close to that of nitrogen 28 g mol and accurate flow rate is not required One division equals 1 liters min Power host computer for WinView 32 and monitor Start the WinView 32 software If you start WinView 32 before you turn on ST 138 you will see Controller is not responding See Appendix C for WinView 32
18. 8 nm Excitation of the OH radical at 248 nm not only minimizes the dependence of the resulting fluorescence on quenching effects but also maximizes the predissociation dominated decay process Predissociation occurs when the potential energy curve for a bound molecular state is crossed by the curve of a repulsive or unbound state 2 Selecting this particular LIF approach enables the specifically sensitive measurement of OH concentration in the flow This approach has previously been used in OH measurement of an automobile engine in a laboratory scale supersonic Ho air combustion tunnel etc 2 The laser pulse energy is maximum at 380 mJ pulse at low repetition rates lt 10 Hz or pulses sec However the laser was operated at 20 Hz with a constant pulse 8 energy of 50 mJ pulse set by designated computer for the laser Pulse length is typically 22 nm which is fast enough to freeze flows 2 2 2 Combustion System 2 2 1 Flat Flame Burner A laboratory standard 2 McKenna flat flame burner is used as shown below in Fig 2 2 120 mm 4 72 in 60 mm Burner plate 2 36 in Ring for shielding gas W ater cooling Shielding gas chamber Combustion gas chamber Holthuis amp Associates Figure 2 2 Sectional View of McKenna Flat Flame Burner The burner is made up of a 6 cm diameter sintered porous stainless steel plug and a 1 4 cm width sintered porous bronze shroud ring T
19. F2 source is an extra part that could generate the fluorine F2 gas when the laser is turned on but in our configuration the F gas in the gas cabinet is used Upon pressing G the program continues with the self test 3 Self Test The self test shows the results of the data ring diagnosis and checks the COMPex watchdogs Afterwards it sets the stepper motor of the grating to its last position Motor reference position once failed The grating is controlled via a small stepper motor When the laser is powered on this motor will drive in one direction until it sees an optical flag and then stop This is the motor s way of finding home If it doesn t find home then the software will give this error This problem was solved by turning the drive motor pulley with fingers in such a direction to drive the grating in the opposite direction about half an inch with the main power off Then turn on the main power and watch the motor move the grating If the test results are OK the program begins to wam up the thyratron and enters the Main Menu It takes about 8 minutes to warm up 37 Main Menu Central Program Menu 1 Check current settings on Main Menu 2 Press M to open the Data Menu Notice that both laser devices Ampl for Amplifier and Osc for Oscillator are represented with their own page The Oscillator page is the master page parameters in Amplifier are ignored Check Parameter Setting of the Oscillator as fo
20. Model ICCD 576 E from Princeton Instruments PI has 384 x 576 pixel format The front enclosure of the ICCD detector includes the image intensifier and the CCD The image intensifier is coupled to the CCD using a fiber optic window on both the output of the image intensifier and the front side of the CCD Due to thel 1 coupling ratio the fiber optics translates the output of the image intensifier to the input of the CCD at the same size This type of coupling is the most efficient possible as well as eliminating lens effects such as vignetting The CCD array in an ICCD camera is cooled by a _ Peltier effect thermoelectric cooler driven by closed loop proportional control circuitry A thermal sensor attached to the cooling block of the detector monitors its temperature The coolant block is made of Delrin to prevent condensation but this also prevents heat transfer from the thermoelectric cooler to the atmosphere Water or other coolant is therefore necessary to carry away heat generated by the thermoelectric cooler 16 The ICCD is typically operated cooled gt 45 C with chilled water circulation with the help of a coolant circulator Model CC 100 also provided by PI The ICCD needs continuous flushing of the detector with nitrogen while operating cooled Even if the detector is not powered flushing is required whenever the coolant is circulating in order to prevent moisture condensation Since PI recommends nitrogen with less than
21. PLANAR LASER INDUCED FLUORESCENCE PLIF OF H2 O2 COMBUSTION The members of the Committee approve the master s thesis of Takashi Yokomae Frank K Lu Supervising Professor Donald R Wilson Seiichi Nomura Copyright by Takashi Yokomae 2003 All Rights Reserved PLANAR LASER INDUCED FLUORESCENCE PLIF OF H2 O2 COMBUSTION by TAKASHI YOKOMAE Presented to the Faculty of the Graduate School of The University of Texas at Arlington in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN AEROSPACE ENGINEERING THE UNIVERSITY OF TEXAS AT ARLINGTON August 2003 ACKNOWLEDGEMENTS I wish to express my appreciation to my supervising professor Dr Frank Lu for giving me an opportunity to work on this research at the Aerodynamics Research Center ARC for being patient with my slow progress and for his technical guidance I would also like to thank Drs Wilson and Nomura for being members of my thesis committee Special thanks go to Qiong Joan Wei who has shared her knowledge with me I really appreciate those individuals who have assisted me at the ARC Rod Duke Jason Meyers Chris Roseberry and Philip Panicker just to name a few I am grateful to my mother Tsugiko for financial and emotional support from home back in Japan I would also like to acknowledge the teaching assistantship for the first year and the graduate fellowship for the two years of my graduat
22. e fg T T term since when increases 1 T decreases while varies with temperature too In the experiments it appears that the temperature effect was dominant In other words as MR increased increased but the fg T T term decreased much causing the fluorescent to decrease It is problematic to say that the OH concentration is directly proportional to the fluorescence signal The spatial filters discussed in Section 2 3 1 were not used because the strong laser burned the pinhole After removing the pinhole and the objective lens decent laser sheet was still generated and the experiment was continued From personal communication with Dr D R Wilson who used hypersonic air breathing propulsion code 28 CHAPTER IV CONCLUSIONS AND RECOMMENDATIONS 4 1 Conclusions The objective of the study was to visualize the hydroxyl OH formation within the hydrogen oxygen combustion by means of PLIF which is suitable for use in pulsed facilities The conclusions drawn from the investigation are summarized as follows 1 Stoichiometric mixture ratio of 8 was not attained 2 As the MR increased the fluorescence signal decreased 3 The planar laser induced fluorescence of the OH radical was acquired successfully however if it can be directly reflected in OH concentration is in question 4 2 Recommendations for Future Work The burner needs repairing in order to get a uniform flat flame as well as to reac
23. e Transition to Detonation 17th International Colloquium on the Dynamics of Explosions and Reactive Systems Heidelberg Germany July 25 30 1999 Internet URL http www iwr uni heidelberg de icders99 program papers 001 050 03 1 pdf Databank Oxydex Internet URL http www databank oxydex com science_mathematics_references excimer_lasers html Lambda Physik User Manual COMPex 150 Ft Lauderdale Nov 1997 Chen Y C Mansour M S Topology of turbulent premixed flame fronts resolved by simultaneous planar imaging of LIPF of OH radical and rayleigh scattering Experiments in Fluids Vol 26 pp 277 287 1999 Prucker S Meier W amp Stricker W flat flame burner as calibration source for combustion research Temperatures and species concentrations of premixed H air flames Review of Scientific Instruments Vol 65 No 9 pp 2908 2911 Sept 1994 Newport Corporation Spatial Filter Internet URL http www newport com file_store PDFs tempPDFs Spatial_Filters_e3873 pdf Lambda Research Optics Inc Internet URL http www lambda cc PAGES1 htm Roper Scientific ICCD Detector Operation Manual 1999 Internet URL ftp ftp roperscientific com manuals files 5CO009v3f pdf Roper Scientific WinView Princeton Instruments Imaging Software 2001 Internet URL ftp ftp roperscientific com manuals files 5C0046v25b pdf Hanson R K Seitzman J M amp Paul P H
24. e study granted by the Mechanical and Aerospace Engineering Department at the University of Texas at Arlington August 18 2003 iv ABSTRACT PLANAR LASER INDUCED FLUORESCENCE PLIF OF H2 COMBUSTION Publication No Takashi Yokomae M S The University of Texas at Arlington 2003 Supervising Professor Frank K Lu The fluorescence in the 297 nm wavelength in burning flame is imaged A laser sheet is generated when the 248 nm KrF excimer laser beam passes through a cylindrical lens Hydroxyl OH radical is excited by the laser sheet across flame produced by a flat flame burner The excited radical emits fluorescence which is captured by the ICCD camera However the fluorescence signal depends on temperature as well as OH concentration In the present work only fluorescence images are obtained of the combustion process Further work is needed to distinguish between concentration and temperature effects in the fluorescence images TABLE CONTENTS ACKNOWLEDGEMENTS scons aie ae ae aes iv ABSTRACT adas EIS OF ILEUS TRATIONS LIS DOE TABLES eiii ix NOMENCLATURE a a EER x Chapter L INTRODUC TON aae 1 1 1 Planar Laser Induced 1 1 1 1 Laser
25. h stoichiometric mixture ratio In addition a UG 11 Schott glass filter may be useful to block the 445 nm second transmission band of the 297 nm bandpass filter as employed in experiments in 2 where they have the same experimental setup the same KrF excimer laser and the same 297 nm filter 29 Although the images were taken by single shot Free Run mode the whole image acquisition setup can be integrated by introducing a PG 200 pulse generator The pulser can synchronize the laser ICCD detector and ST 138 detector controller when used as a master trigger This will eliminate the possibility of missing the fluorescence signal by the ICCD Further study should be performed for the future applications of PLIF With more sophisticated equipment temperature and velocity measurements can be achieved 30 APPENDIX EXPERIMENTAL PROCEDURE 31 1 Ensure the following connections a Connect a 25 pin ICCD cable from the ICCD to Detector of the ST 138 controller b Connect a TAXI cable from J7 of the ST 138 controller to the PCI interface card of the computer with WinView 32 software installed Ensure the coolant hoses and hose are connected to the ICCD 2 Place the cylindrical lens about 23 5 inches from the burner with the concave side facing the laser 3 Place the ICCD camera as close to the burner as possible about 20 inches at the right angle to the laser sheet Also place the imaging lens about 5
26. he reactant mixture consisting 9 of pre mixed oxidizer O2 and fuel H2 is introduced into the bottom of the burner distributed over the cross section by the sintered plug Any existing surge in the reactant stream is settled in the cavity located below the sintered plug Passing a concentric inert gas N2 around the flame holder through the bronze plug ring enables shielding of the flames produced from entrainment effects and stabilizes the flame above the sintered plug This shielding gas is also brought into a cavity in the bottom of the burner in order for any surge present to be damped out The cooling water is supplied to the burner by a stainless steel tubing where it is rolled in a spiral shape with equally spaced rings and embedded in the sintered plug The plane of the coil is parallel to the surface of the burner to ensure that radial temperature gradients do not occur 13 2 2 2 Combustion Gas Handling System List of Equipment a Compressed hydrogen 200 ft cylinder Airgas b Compressed oxygen 80 ft cylinder Airgas Compressed nitrogen 200 ft cylinder Airgas d Pressure Regulators e Flashback arrestors Ibeda Inc f Correlated flowmeter with standard valve Cole Parmer g Copper steel and plastic tubing h Standard temperature millboard McMaster Carr 10 Figure 2 3 illustrates the setup for the combustion system Fig 2 4 is the picture of the gas handling system Be
27. indrical lens and transforms into a laser sheet The laser sheet spreads across the H2 O2 flame produced by a flat flame burner where it excites the radical causing it to emit fluorescence The fluorescence signals are acquired by an intensified CCD camera A UV filter and an imaging lens are placed in front of the ICCD to filter and focus the photo signals The images captured by the ICCD are transmitted to a computer for processing FLUORESCENCE Cylindrical lens Flow facility Burner ICCD camera Display Figure 1 2 Basic Arrangement of PLIF 1 1 3 Fluorescence Dependence of Temperature and Mole Fraction The measured quantity of the fluorescence signal in photons per pixel from a single ICCD camera frame can be written as 2 Spp const The fluorescence signal is directly proportional to the mole fraction of OH and a temperature dependent function in brackets Experimental efficiencies such as transmission efficiency of the collection lens and filter the camera s photo cathode quantum efficiency and the electronic gain on the camera are considered constant for a given experimental setup 2 1 1 4 Disadvantages of PLIF Just as nothing is perfect PLIF is not without blemish either The main disadvantage of PLIF is quenching of fluorescence at higher pressures by numerous collisions of molecules Such quenching effects can be avoided easily by exciting the molecule to a fast p
28. llows a Excimer gas and its wavelength KrF 248 nm b Buffer gas Ne for KrF Repetition rate 20 Hz d Trigger mode internal e Running mode and its preset parameter Energy Constant mode at 50mJ It is possible to change the gas values but it is not recommended since the preset gas values are carefully optimized 3 Laser Firing a Open the water valve over the stairs The laser has to be cooled with water at repetition rates higher than 10 Hz b Open the beam shutter c Type S and then Y to confirm The laser now needs a few seconds to initialize the power supply The menu changes to the Running Menu Then is begins emitting laser light with the given 38 repetition rate It be recognized by clicking noise The higher the repetition rate is the faster the clicking will be All the gas valves remain closed while firing the laser d Ifthe laser beam seems weak New Gas Fill has to be performed IV Conditions Before Starting New Fills 1 The laser must not be firing 2 Make sure that all the four required gases are available Do not use gas cylinders with less than 74 psi 5 bar since the impurities from gas cylinder walls can contaminate the tube 3 Turn on the vacuum pump of the gas cabinet 4 Open all the four gas cylinder valves in the gas cabinet 5 Close all the four pressure regulators in the gas cabinet 6 Ensure all the four pressure regulators are set to about 60 psi 4 bar 7 Open all
29. luctuate even with nitrogen shielding mostly because of air conditioning 19 CHAPTER RESULTS AND DISCUSSIONS This chapter presents the PLIF results obtained and the interpretation of the results The experimental procedures are detailed in Appendices A C 3 1 Results The laser repetition rate 20 Hz laser energy 50 mJ pulse camera position and focus and camera filters are kept constant during the experiments The PLIF technique was employed to capture images of fluorescence emitted by the 248 nm KrF excimer laser excitation while varying mixture ratio or controlling the volumetric flow rates of hydrogen and oxygen Mixture ratio MR is defined as the ratio of the oxidizer to fuel mass flow rates 2 A ceramic rod was also inserted in the flames perpendicular to the laser sheet to stabilize the flame 18 the case of the fuel being and the oxidizer the reaction is expressed as 2 H O2 gt 2 So the stoichiometric MR for combustion is calculated as 8 _ lmol 32g mol _ 2 thy 2mol 2g mol A number of PLIF images were taken at various mixture ratios listed in Table 3 1 The values for volumetric flowrates ml min in Table 3 1 are taken or interpolated 20 from the correlation charts provided by Cole Parmer Table 3 2 and the mixture ratios MR are calculated as follows taking case one for example 459 ml min mo 22400ml mol hy 2025ml min 22400 ml
30. n waves CHAPTER II EXPERIMENTAL SET UP The PLIF set up without combustion system is shown in Fig 2 1 below The combustion system is depicted in section 2 2 Ceramic rod Cylindrical lens Beam shutter Exci xcimer laser Beam stop or Flat 4 flame burner ICCD Coolant circulator ICCD detector controller Figure 2 1 PLIF set up 2 1 KrF Excimer Laser Excimer stands for excited dimer a diatomic molecule usually of a rare gas atom and a halide atom that are bound in excited states only ArF KrF XeCl and XeF the most important excimers because they dissociate releasing the excitation energy through UV photons 10 energy is high intensity beams of UV light with wavelengths ranging from 193 to 351 nm 11 When compared with visible light sources UV lasers are capable of detecting minor species such as OH NO and CO 12 The OH radical is naturally occurring 2 and one of the most abundant in flames 6 In this experiment a COMPex 150T KrF Excimer Laser Lambda Physik was used because its center wavelength and bandwidth are tunable between 248 0 and 248 8 nm and it coincides with some of the OH A X 3 0 band system 12 The absorption line of OH is excited at 248 nm 2 3 v 0 and detected at 297 nm A d v 3 gt v 0 Despite the weaker strength of this OH transition than others that could be used such as 284 and 308 nm there are advantages of using 24
31. on Acquire Background Then in Acquisition Experimental Setup Data Correction tab select the background file Make sure the Flat Field box is unchecked Flat Field feature is not used because it does not improve the images in this particular experiment 6 Turn off the room lights ignite the burner adjust the flowrates to desired mixture ratio and fire the laser Acquire images by selecting Acquisition Acquire A black and white picture will be shown on display 7 Change flowrates of the and gases and repeat 5 Also insert a ceramic rod to stabilize the flame 18 and repeat 5 8 Gray scale images can be converted to color images by color icon 9 In Display Display Layout General tab Axes Cross Sections and Info Bar boxes are checked to make analysis easier 10 In Display Display Layout Range tab Intensity level can be manually selected 43 11 Since WinView 32 be run only Windows 98 machine we license only on Windows 98 press Print Screen on the keyboard paste onto wordpad and save as Word 6 file in order to make color copy This can be seen and edited in Microsoft Photo Editor on other machines 44 REFERENCES Eckbreth Laser Diagnostics for Combustion Temperature and Species Abacus Press Kent UK and Massachusetts USA 1988 Cohen L M Jassowski D M and Ito J I Performance of a Titan rocket engine using laser induced fluorescence of
32. redissociating state from which fluorescence is emitted only during the predissociation lifetime For sufficiently short predissociation lifetimes collisions do not occur which means no quenching within the lifetimes In some environments where PLIF is unsuitable other laser techniques such as coherent anti Stokes Raman scattering CARS or Rayleigh scattering are recommended 7 1 2 Objective In long duration facilities flow parameters could be measured with physical probes that are placed spatially through the flow However this method is not suitable for pulsed flow facilities because of their short flow duration A desirable alternative to such probe based methods in pulsed facilities is PLIF imaging which yields instantaneous measurements at a large number of points in a laser illuminated plane 8 The development of pulse detonation engines is underway at the Aerodynamics Research Center The initiation of detonation is believed to occur at hot spots 9 where heat and pressure are sufficient to trigger a rapid chemical reaction In hydrogen systems that involve chemical activity a large population of OH is expected This OH formation can be studied by the use of PLIF since OH is one of the species that can be detected in PLIF measurements The objective of this research is to visualize OH formation within oxy hydrogen combustion by means of PLIF as a stepping stone to the next phase of experiments in detonatio
33. s or radicals are excited by laser absorption to the metastable state and then drop down to the stable ground state emitting fluorescence excited state collisional electronic Absorption Fluorescence rotational levels 1 vibrational 1 ground levels vi 0 state Rolf Bomback RET rotational energy transfer Paul Scherrer Institut Switzerland VET vibrational energy transfer Figure 1 1 State View of Laser Induced Fluorescence 1 1 2 Planar Laser Induced Fluorescence The planar laser induced fluorescence PLIF is a derivative of the LIF technique which necessitates the generation of a laser sheet from the probe laser beam in order to facilitate imaging of the fluorescence PLIF involves illuminating the flow with a thin sheet of laser light tuned to excite electronic transitions in a chemical species in the flow The OH radical is accessed in this experiment A radical is an atom or a group of atoms that is a usually very reactive species which contains one or more unpaired electrons The fluorescence emitted by the laser excitation is focused onto an intensified charge coupled device ICCD camera to produce an image of the fluorescence in that region Besides the species concentration temperature pressure and velocity could be measured with prudent choice of transition and subsequent image processing 3 A basic arrangement of PLIF is illustrated below in Fig 1 2 laser beam passes through a cyl
34. the gas lines marked with post it notes V New Gas Fill automatic 1 Go to the Main Menu and press M to enter the Data Menu 2 Press N and select the page with KrF Osc or KrF Ampl that needs a new fill 39 New Fill procedure fills the laser device that is actually the upper most page on the Data Menu You have to fill Oscillator and Amplifier separately To change the page on the Data Menu hit N for next page 3 Push Q to leave the Data Menu Now you are on the Main Menu 4 Push G to open the Gashandling Menu 5 Push N to start a new fill The laser tube is evacuated to 30 mbar If the evacuation exceeds 12 minutes there may be a gas leak The gases will be filled one by one for the amount specified The new fill will stop automatically when it is filled to 3330 mbar 40 APPENDIX C WINVIEW 32 OPERATION PROCEDURE 41 1 Start WinView 32 Unless the 8 138 is powered Controller Is Not Responding will appear If the ST 138 is and the message still shows up the pins of the TAXI cable is most likely torn Check the pins of the cable with continuity test of a multimeter TAXI cable has only four wires in it pin 2 connects to pin 4 on the opposite side pin 7 connects to pin 9 on the opposite side pin 4 connects to pin 2 on the opposite side pin 9 connects to pin 7 on the opposite side Once you find discontinuities dismantle the both ends of the cable and solder the pins
35. used Calcium fluoride negative cylindrical lenses are appropriate for anamorphic expansion at vacuum ultra violet wavelengths They are ideal for use with excimer lasers 15 14 The excimer laser first passes through the objective lens cleaning the scattering from dust particles 14 It then goes through the pinhole creating a clean 14 spatial profile Subsequently it passes through the cylindrical lens producing the laser sheet 2 3 3 Image Collection A narrow band interference filter with center wavelength of 296 7 10 nm 10 296 7 3 1 00 from CVI Laser is selected see Section 2 1 ICCD camera with the filter mounted onto is placed at right angles to the laser sheet This will let only the selected fluorescence pass and block undesirable ambient light scattered laser light at 248nm and emission from the flame 2 A 1 inch diameter fluorescence imaging lens fused silica single lens PLCX 25 4 25 8 UV from CVI Laser is placed about 50 mm away from the ICCD intensifier with the convex side facing the ICCD and focuses the image into the ICCD The optical table rail and carrier were used to fix the lens onto the table 2 4 ICCD Intensified Charged Coupled Device List of Equipment a ICCD detector Princeton Instruments b ICCD detector controller Princeton Instruments c Coolant circulator Princeton Instruments d Ultra high purity compressed nitrogen Airgas 15 The ICCD detector
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