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MASS SPECTROSCOPY APPLIED to GAS LEAK DETECTION and FUEL IONIZATION by JAYANTH POTHIREDDY a THESIS PRESENTED to the GRADUATE

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MASS SPECTROSCOPY APPLIED to GAS LEAK DETECTION and FUEL IONIZATION by JAYANTH POTHIREDDY a THESIS PRESENTED to the GRADUATE MASS SPECTROSCOPY APPLIED TO GAS LEAK DETECTION AND FUEL IONIZATION By JAYANTH POTHIREDDY A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2003 Copyright 2003 by Jayanth Pothireddy To my friends ACKNOWLEDGMENTS I would like to sincerely thank Dr. Corin Segal for giving me this wonderful opportunity and for his unlimited support, understanding and incredible patience without which I would not have successfully completed my thesis. I would also like to thank Dr. David Mikolaitis and Dr. Martin Vala for their support and Dr. Norman Fitz-Coy for his valuable suggestions. Many thanks go to Mr. Jan Szczepanski for giving me “first lessons” on mass spectrometry, invaluable suggestions, tremendous support and help in developing the mass spectrometry system. My heartfelt thanks go to my friends Venkat, Sujith, Gopi, Anand, “Iranian bros” Amir and Omid, Weizhong, Sampath, Harsha, Adil, Anant, Sasidhar, Charan, Danny, Jonas, Nelson, Zhu Wei, Ron, “Dr” Amit, Errol, Anurag, Priya, Amit “Saale” and Balaji for their support and understanding. I thank Ron Brown for constructing a nice model of the Space Shuttle aft compartment and for his help in moving the mass spectrometer cart to and fro from “chemistry” to “aero.” iv TABLE OF CONTENTS Page ACKNOWLEDGMENTS.................................................................................................. iv LIST OF FIGURES...........................................................................................................vii ABSTRACT....................................................................................................................... ix CHAPTERS 1 INTRODUCTION............................................................................................................ 1 1.1 Introduction............................................................................................................ 1 1.2 Cryogenic Fuel Leaks ............................................................................................ 1 1.3 Ionization of Fuels ................................................................................................. 4 2 EXPERIMENTAL SETUP.............................................................................................. 9 2.1 Introduction............................................................................................................ 9 2.2 Aft-Compartment Model........................................................................................ 9 2.3 Ionization Tube .................................................................................................... 11 2.4 Mass-Spectrometer............................................................................................... 12 2.4.1 Ion Sources ................................................................................................ 14 2.4.2 Mass Analyzers.......................................................................................... 17 2.4.3 Detectors .................................................................................................... 18 2.5 The SRS Residual Gas Analyzer ......................................................................... 19 2.5.1 Ionizer ........................................................................................................ 20 2.5.2 Quadrupole Mass Filter: ............................................................................ 21 2.5.3 Ion Detector ............................................................................................... 23 2.5.4 Modes of Operation of SRS RGA ............................................................. 24 2.6 Vacuum System ................................................................................................... 25 3 RESULTS AND SUMMARY ....................................................................................... 26 3.1 Introduction.......................................................................................................... 26 3.2 Data Acquisition and Calibration......................................................................... 26 3.2 Leak Detection Tests............................................................................................ 28 3.3 Ionization Tests.................................................................................................... 30 3.5 Summary .............................................................................................................. 33 v APPENDIX A AFT COMPARTMENT MODEL ................................................................................ 35 B STANFORD RESEARCH SYSTEMS RESIDUAL GAS ANALYZER 300.............. 39 B.1 SRS Mass Spectrometer ...................................................................................... 39 B.1.1 Specifications ............................................................................................ 39 B.1.2 Internal Components ................................................................................. 40 B.2 Electrostatic Ion Lens System ............................................................................. 41 LIST OF REFERENCES .................................................................................................. 44 BIOGRAPHICAL SKETCH ............................................................................................ 46 vi LIST OF FIGURES Figure page 2-1. Aft compartment model- left side view...................................................................... 11 2-2. Ionization tube. .......................................................................................................... 12 2-3. Basic components of a mass spectrometer with feedback control carried by a computer. ................................................................................................................. 13 2-4. SRS Mass spectrometer.............................................................................................. 19 2-5. Ionizer Schematic. Reproduced from Ref. 4.............................................................. 20 2-6. Quadrupole rod connections. Reproduced from Ref. 4. ............................................ 21 2-7. Ion Detector Components. Reproduced from Ref. 4. ................................................ 24 2-8. Vacuum pumping system........................................................................................... 25 3-1. Analog scans- mass scale calibration......................................................................... 27 3-2. Helium leak detection concentration curve for L=1.3 cm.......................................... 29 3-3. Helium leak detection concentration curve for L=2.5 cm.......................................... 29 3-4. Butane (C4H10) ionization.......................................................................................... 31 3-4 (contd.). Butane (C4H10) ionization. ........................................................................... 32 3-5. Normalized fragmentation species pressure. ............................................................. 33 A-1. Hull............................................................................................................................ 35 A-2. Hull-front piece......................................................................................................... 36 A-3. Hull- rear piece.......................................................................................................... 36 A-4. Hull- side piece. ........................................................................................................ 37 A-5. Hull- shoulder piece.................................................................................................. 37 vii A-6. Hull- top piece........................................................................................................... 38 A-7. Hull- bottom piece. ................................................................................................... 38 B-1. Ionizer Components. ................................................................................................. 40 B-2. Quadrupole Mass Filter Components........................................................................ 40 B-3. Electrostatic ion lens system. .................................................................................... 41 B-4. ICP, ion sampling interface, and vacuum system. Reproduced from Ref. 21. ......... 42 B-5. Schematic of SRS mass spectrometer with the electrostatic ion lens assembly for ionization studies. .................................................................................................... 43 viii Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science MASS SPECTROSCOPY APPLIED TO GAS LEAK DETECTION AND FUEL IONIZATION By Jayanth Pothireddy August 2003 Chair: Corin Segal Major Department: Mechanical and Aerospace Engineering A quadrupole mass spectrometry system was evaluated for two distinct applications: gas leak detection in a scaled model of the space shuttle aft compartment and to characterize the effect of fuel ionization. Stanford Research Systems Residual Gas Analyzer 300 was evaluated in this study. The leak detection experiments were conducted by simulating He gas leaks for cryogenic fuel leaks, inside a model of the space shuttle aft compartment.
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