Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 3-24-2012 Increasing Reliability of a Small 2-Stroke Internal Combustion Engine for Dynamically Changing Attitudes Steven C. Crosbie Follow this and additional works at: https://scholar.afit.edu/etd Part of the Aerospace Engineering Commons Recommended Citation Crosbie, Steven C., "Increasing Reliability of a Small 2-Stroke Internal Combustion Engine for Dynamically Changing Attitudes" (2012). Theses and Dissertations. 1038. https://scholar.afit.edu/etd/1038 This Thesis is brought to you for free and open access by the Student Graduate Works at AFIT Scholar. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of AFIT Scholar. For more information, please contact [email protected]. INCREASING RELIABILITY OF A SMALL 2-STROKE INTERNAL COMBUSTION ENGINE FOR DYNAMICALLY CHANGING ALTITUDES THESIS Steven C Crosbie, Captain, USAF AFIT/GAE/ENY/12-M08 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED The views expressed in this thesis are those of the author and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the United States Government. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. AFIT/GAE/ENY/12-M08 THESIS Presented to the Faculty Department of Aeronautics and Astronautics Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In Partial Fulfillment of the Requirements for the Degree of Master of Science in Aeronautical Engineering Steven C Crosbie Captain, USAF March 2012 APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. AFIT/GAE/ENY/12-M08 INCREASING RELIABILITY OF A SMALL 2-STROKE INTERNAL COMBUSION ENGINE FOR DYNAMICALLY CHANGING ALTITUDE Steven C Crosbie Captain, USAF March 2012 Approved: ___________________________________ ________ Dr. Marc Polanka (Chairman) date _______________________________________ ________ Dr. Paul King (Member) date _____________________________________ ________ Lt Col Frederick Harmon (Member) date AFIT/GAE/ENY/12-M08 Abstract Remotely Piloted Aircraft (RPA) typically utilize commercial internal combustion engines (ICE) as their power sources. These engines are designed to run at sea level, but these aircraft are often pressed into service at higher altitudes where the performance characteristics deteriorate. A Brison 95cc two-stroke engine’s performance characteristics at altitude are investigated using a test facility that can measure these characteristics over a range of pressures and temperatures. With its stock carburetor at sea level static (SLS) conditions, the engine makes 5.5 peak hp and brake specific fuel consumption (BSFC) ranged from 1.2-4.0 lb/(hp-hr). At 10,000 ft conditions, the peak hp drops 40% while off peak power conditions can see a drop of over 90%. As well, the carburetor makes operating at high altitudes unreliable and unpredictable. In order to increase reliability, a throttle body fuel injection (TBI) system was installed on the engine. The fuel injection system matched carburetor peak power at SLS conditions while increasing power by as much as 90% at low RPM and high altitude operating conditions. BSFC is decreased to a consistent 1.0 to 1.2 lb/(hp-hr) across all operating conditions. Lastly both reliability at high altitude and startup reliability are increased with the TBI system while eliminating the need for the tuning by the end user. iv Acknowledgements I would like to thank my research advisor, Dr. Marc Polanka, and the research sponsor, Dr. Fred Schauer, for allowing me the opportunity to work on this research with them. Thank you Dr. Polanka for the weekly meetings spending hours discussing the direction of the research, my understanding of how to conduct research, and how to best present the research. Thank you Fred for having the confidence in me from the start and letting me work in your facility. None of this research would be possible without the continued support of the key players that work in 5-Stand and D-Bay. Dr. John Hoke was instrumental helping me understand key concepts for the research as well as advising me on the appropriate direction to take the research. Thank you Paul Litke for taking the time to look at my data and help me understand the trends we were seeing. Dave Burris, thank you for all of your help troubleshooting LabVIEW code and your timeliness in fixing the areas we highlighted. To the guys in 5-Stand, thank you Adam Brown, Jacob Baranski, and Dr. Eric Anderson for showing me how things work in 5-Stand and helping me fit into the 5-Stand operating cycle. Thank you Captain Cary Wilson and JR Groenewegen for showing me the ropes with small engine research and allowing me to share the lab when operating schedules were tight this summer. Thank you Ben Naguy for helping me machine the parts I needed, often last minute, and teaching me how to use most of the equipment in the machine shop. Thank you Rich Ryman for always being available to answer questions regarding how to install hardware, which hardware to select, and where to find the hardware I needed. v Lastly, I would like to thank my parents. Thank you for listening to me vent about being covered in work from classes or my schedule being tight for working in the lab. Thank you for understanding why visits for holidays were shortened so I could get back to Ohio to work on this research. Without your continued support, none of this would be possible. vi Table of Contents Page Abstract .................................................................................................................. iv Acknowledgements ................................................................................................. v Table of Contents .................................................................................................. vii List of Figures ........................................................................................................ ix List of Tables ........................................................................................................ xii List of Symbols .................................................................................................... xiii List of Abbreviations ........................................................................................... xiv INCREASING RELIABILITY OF A SMALL 2-STROKE INTERNAL COMBUSTION ENGINE FOR DYNAMICALLY CHANGING ALTITUDES ........... 15 I. Introduction ....................................................................................................... 15 I.1 Objectives .......................................................................................................... 19 I.2 Methodology ...................................................................................................... 21 II. Theory and Previous Research ......................................................................... 24 II.1 Internal Combustions Engines ........................................................................... 24 II.2 Two-Stroke Spark Ignition Engines................................................................... 24 II.3 Four-Stroke Engines .......................................................................................... 29 II.4 Compression Ignition Engines ........................................................................... 29 II.5 Engine Parameters ............................................................................................. 30 II.6 Fuel Delivery ..................................................................................................... 35 II.6.1 Carburetor Theory .................................................................................. 36 II.6.2 Fuel Injection Theory ............................................................................. 38 II.6.3 Previous Fuel Metering Research .......................................................... 41 II.7 Pressure Impact .................................................................................................. 42 II.8 Temperature Impact ........................................................................................... 46 II.9 Combustion Background ................................................................................... 47 II.10 Impact of Air-to-Fuel Ratio and Previous AFR Research on Two-Stroke Engines ........................................................................................................................ 49 III. Test Setup and Apparatus ......................................................................... 51 III.1 Existing Test Facility ......................................................................................... 51 III.2 Initial Test Facility Upgrades............................................................................. 55 III.2.1 Fixing Altitude Chamber Pressure Leaks (Facility Objective 1) ........... 57 III.2.2 Getting the Engine to Start (Facility Objectives 2, 4, & 6).................... 60 vii III.2.3 Installing an Oil Cooler (Facility Objective 3) ...................................... 66 III.2.4 Addressing Starter Gear Jamming ......................................................... 67 III.3 Carburetor Testing ............................................................................................