Date of Award


Document Type


Degree Name

Master of Science


Department of Aeronautics and Astronautics

First Advisor

Marc D. Polanka, PhD.


A study of the efficiency and energy losses of a selection of five small (40 - 200 cm3 displacement) single cylinder, four-stroke engines was accomplished. The study was performed as part of a larger effort to improve the range and endurance of small internal combustion engines (ICE) that power Group II Unmanned Aerial Vehicles (UAVs). Little is known about the performance, efficiency, and allocation of energy losses for four-stroke ICEs in this size range. The goal of the study was to characterize these parameters for use in future research efforts. Three research objectives were developed to guide the study contained herein. The first objective was to reliably measure the brake power output of each engine and compare the measurements to the manufacturers advertised power ratings. The second objective was to perform an energy balance, experimentally measuring the fuel energy entering the system (engine), and all of the energy exiting the system. Energy exiting the system was categorized as useable energy (brake power), or energy losses due to exhaust sensible enthalpy, thermal losses, or incomplete combustion. The third objective (which encompassed the first two) was to perform as series of parametric sweeps on the engines, examining the effect of varying engine speed, equivalence ratio, combustion phasing, cylinder head temperature, and throttle position. The characterization data from the five engines was then used to develop a set of correlations that could be used to predict brake mean effective pressure (BMEP), fuel conversion efficiency (nf), exhaust sensible enthalpy losses, thermal (cooling load) losses, and incomplete combustion losses as a percentage of fuel energy for small four-stroke engines with displacement volumes of 40 - 200 cm3. Accurate correlations for this size class currently do not exist in the literature.

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