Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 6-19-2014 Measuring Scaling Effects in Small Two-Stroke Internal Combustion Engines Alex K. Rowton Follow this and additional works at: https://scholar.afit.edu/etd Recommended Citation Rowton, Alex K., "Measuring Scaling Effects in Small Two-Stroke Internal Combustion Engines" (2014). Theses and Dissertations. 539. https://scholar.afit.edu/etd/539 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]. MEASURING SCALING EFFECTS IN SMALL TWO-STROKE INTERNAL COMBUSTION ENGINES THESIS JUNE 2014 Alex K. Rowton, Captain, USAF AFIT-ENY-T-14-J-36 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio DISTRIBUTION STATEMENT A. 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-ENY-T-14-J-36 MEASURING SCALING EFFECTS IN SMALL TWO-STROKE INTERNAL COMBUSTION ENGINES 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 Alex K. Rowton, BS Captain, USAF June 2014 DISTRIBUTION STATEMENT A. APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. AFIT-ENY-T-14-J-36 MEASURING SCALING EFFECTS IN SMALL TWO-STROKE INTERNAL COMBUSTION ENGINES Alex K. Rowton, BS Captain, USAF Approved: ________________________//signed// ______________ ___30______ May 2014_____ Marc D. Polanka, PhD (Chairman) Date ____________________________//signed// __________ ____30 ______May 2014____ Timothy C. Radsick, LtCol, USAF (Member) Date ________________________//signed// ______________ ____30 ______May 2014____ Paul I. King, PhD (Member) Date AFIT-ENY-T-14-J-36 Abstract As internal combustion (IC) engine displacement decreases, cylinder surface area to swept volume ratio increases. Examining power output of IC engines with respect to cylinder surface area to swept volume ratio shows that there is a dramatic change in power scaling trends at approximately 1.5 cm-1. At this size, thermal quenching and friction losses are expected to dominate engine performance. As a result, power production and efficiency characteristics suffer. Furthermore, small IC engines (< 100 cc displacement) have limited technical performance data, so quantifying efficiency trends is difficult. Therefore, establishing accurate performance figures for a family of geometrically similar engines in the size class of approximately 1.5 cm-1 is beneficial in understanding the thermal losses as well as other phenomena that contribute to lower efficiencies in small IC engines. Three small two-stroke engines were considered in this scaling study. They spanned the transition size regime of 1.5 cm-1. The engines shared a similar design to reduce performance variability due to factors other than size. A performance baseline was established for each engine. Measured performance values were used to determine scaling relationships for engines of this size. The results of this study show that brake fuel conversion efficiency diminished with decreasing engine size. Furthermore, friction losses increased as engine size was reduced as a result of increasing cylinder surface area to swept volume ratio. Equivalence ratio was not held constant during testing due to the limitations of each engine’s carburetor. Therefore, definitive relationships concerning engine heat rejection were not realized. iv Acknowledgments I would like to thank all those who were involved with the support of this study. I am grateful for the advice and assistance of the following people who helped me to accomplish this research: Dr. Marc Polanka, Lt. Joseph Ausserer, Capt. Josh Rittenhouse, Mr. Paul Litke, Mr. Keith Grinstead, Mr. Adam Brown, Mr. JR Groenewegen, Lt. Col. Timothy Radsick, Dr. Paul King, Lt. Kevin Horn, and Lt. Anthony Trombley. I would like to specifically acknowledge the immense help of Mr. Rich Ryman for his patience and advice regarding test bench integration and hardware. I would like to thank Mr. Dave Burris for his help in developing and improving the LabVIEW control software without which this project would have been nearly impossible. Alex K. Rowton v Table of Contents Page Abstract .............................................................................................................................. iv Table of Contents ............................................................................................................... vi List of Figures .................................................................................................................. viii List of Tables ..................................................................................................................... xi Nomenclature .................................................................................................................... xii List of Abbreviations ....................................................................................................... xiv I. Introduction .....................................................................................................................1 1.1 Motivation ...........................................................................................................1 1.2 Research Objectives ............................................................................................4 1.3 Methodology .......................................................................................................5 1.4 Thesis Overview ..................................................................................................6 II. Literature Review ............................................................................................................7 2.1 Background on IC Engines .................................................................................8 2.1.1 Terminology ............................................................................................. 8 2.1.2 IC Engine Cycles .................................................................................... 11 2.1.3 Types of Ignition .................................................................................... 16 2.1.4 Fuel Delivery .......................................................................................... 19 2.1.5 Induction Methods.................................................................................. 23 2.1.6 Efficiency ............................................................................................... 26 2.2 Engine Performance ..........................................................................................30 2.2.1 Equivalence Ratio .................................................................................. 30 2.2.2 Ignition Timing ...................................................................................... 33 2.2.3 Abnormal Combustion ........................................................................... 34 2.2.4 Short-Circuiting ...................................................................................... 36 2.2.5 Blow-by .................................................................................................. 37 2.3 Performance Measurement ................................................................................38 2.3.1 Dynamometers ....................................................................................... 39 2.3.2 In Cylinder Pressure ............................................................................... 40 2.3.3 Exhaust Emissions.................................................................................. 40 2.4 Scaling Behavior ...............................................................................................42 2.4.1 Related Work in Small IC Engine Scaling ............................................. 46 III. Methodology ...............................................................................................................49 3.1 Engine Selection ................................................................................................49 3.2 Test Bench .........................................................................................................51 3.2.1 Air Flow ................................................................................................. 54 3.2.2 Fuel Flow................................................................................................ 58 vi 3.2.3 Ignition ................................................................................................... 59 3.2.4 Indicated Pressure Measurements .......................................................... 61 3.2.5 Drivetrain & Dynamometer ................................................................... 63 3.2.6 Engine Cooling & Thermal Loss ..........................................................