ABSTRACT BOYETTE, WESLEY RYAN. Thrust and Specific Impulse Optimization of Eight- Centimeter Valveless Pulsejets at Low Subsonic Flight Speeds. (Under the direction of Dr. William L. Roberts). The purpose of this research was to develop a method of accurately measuring the thrust and specific impulse of valveless pulsejets that are approximately eight centimeters in length. Previous methods of doing such were largely unsuccessful. A vertically arranged thrust stand and electronic balance were ultimately able to produce reliable results. Seven inlets were then tested on a forward facing arrangement. The maximum thrust achieved was 24.4 mN and specific impulse peaked at 295 seconds. Comparison revealed that increasing inlet length has a positive effect on pulsejet performance. Each inlet was tested at simulated forward flight speeds as well, showing that shorter inlets perform optimally at lower speeds than longer inlets. Additionally, a relationship between pulsejet performance, frequency and exhaust temperature was identified. Similar tests were performed on hybrid configurations as well, which combine forward- facing and rearward-facing inlets. Of the five hybrid configurations tested, maximum thrust was 31.2 mN and maximum specific impulse was 232 seconds. This series of tests revealed that these configurations also showed improvement in performance at higher forward flight speeds and at smaller inlet areas. In all cases, hydrogen was used as the fuel, due to its very short chemical time. Pulsejets at this scale are also shown to be capable of operating on acetylene, although with reduced performance. Thrust and Specific Impulse Optimization of Eight-Centimeter Valveless Pulsejets at Low Subsonic Flight Speeds by Wesley Ryan Boyette A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science Aerospace Engineering Raleigh, North Carolina 2008 APPROVED BY: Dr. Andrey V. Kuznetsov Dr. Terry Scharton Dr. William L. Roberts Chair of Advisory Committee ii Biography The author was born Wesley Ryan Boyette on June 27,1980 in Hudson, North Carolina to Warren and Ruby Boyette. He was the youngest of three with two older sisters; Lara and Katie. At the age of nine, his family moved to Wendell, North Carolina where he stayed until graduating from East Wake High in 1998. He then attended the University of North Carolina at Chapel Hill for four years, obtaining a B.S. in Biology and a B.A. in Geography. In 2003, he enrolled full-time at North Carolina State University studying Aerospace Engineering and received his B.S. in 2006, graduating Magna Cum Laude. Immediately following graduation, he began his Master’s work under the direction of Dr. William Roberts. “Chance favors only the prepared mind.” – Louis Pasteur iii Acknowledgements Firstly, I would like to thank Dr. Roberts for offering his wealth of knowledge and assistance during my studies and research at NCSU. I would also like to thank Dr. Scharton and Dr. Kuznetsov for their help. Tim Turner has been a tremendous help and a large part of my research was made possible by the financial contribution of his company, Permafuels. I also appreciate Mike Breedlove and Skip Richardson for their professional and expeditious help with getting my hardware machined. Of course, none of this would have been possible without the support of my loving family. Finally, I would like to thank my friends for keeping me level-headed throughout this process. iv Table of Contents List of Figures .......................................................................................................................... vi List of Tables..........................................................................................................................viii 1 Introduction....................................................................................................................... 1 1.1 Theory of Operation..............................................................................................................1 1.2 History .......................................................................................................................................5 1.3 Related Work...........................................................................................................................6 1.4 Previous Research at AERL .................................................................................................8 1.5 Objectives............................................................................................................................... 13 2 Experimental Apparatus..............................................................................................15 2.1 Pulsejet Designs................................................................................................................... 15 2.1.1 Forward Facing..............................................................................................................................15 2.1.2 Rearward ..........................................................................................................................................18 2.1.3 Modified Rearward.......................................................................................................................19 2.1.4 Optimized .........................................................................................................................................22 2.1.5 Four Centimeter.............................................................................................................................23 2.1.6 Pertinent Design Dimensions and Ratios ...........................................................................24 2.2 Air Delivery System ............................................................................................................ 24 2.2.1 Cautionary Considerations .......................................................................................................27 2.2.2 Velometer .........................................................................................................................................27 2.3 Fuel Delivery System.......................................................................................................... 29 2.3.1 Flowmeters and Valves ..............................................................................................................29 2.3.2 Fuel Injectors ..................................................................................................................................29 2.4 Spark Ignition....................................................................................................................... 32 2.4.1 Transformer and Switch ............................................................................................................32 2.4.2 Igniter.................................................................................................................................................33 2.5 Electronic Balance .............................................................................................................. 35 2.6 Load cell.................................................................................................................................. 36 2.7 Thrust stand.......................................................................................................................... 38 2.7.1 For Load Cell ...................................................................................................................................38 2.7.2 For Mass Balance...........................................................................................................................41 2.8 Heating apparatus............................................................................................................... 42 2.9 Sound Level Meter............................................................................................................... 44 2.10 Startup procedure............................................................................................................... 44 3 Forward Facing Configuration...................................................................................49 3.1 Evolution of a Methodology ............................................................................................. 49 3.1.1 Load Cell............................................................................................................................................49 3.1.2 Electronic Balance ........................................................................................................................53 3.1.3 Final Apparatus..............................................................................................................................56 3.1.4 Difficulties and Considerations...............................................................................................58 3.2 Thrust and Specific Impulse Results............................................................................. 61 v 3.3 Performance as a Function of Inlet Diameter............................................................ 80 3.4 Performance as a Function of Inlet Length................................................................. 82 3.5 Performance as a Function of Fuel Flow Rate............................................................ 87 3.6 Performance as a Function of Simulated Forward