Greenman M.D. Design and Construction of a Miniature Internal Combustion Engine

Submitted to the Department of Aeronautics and Astronautics in Partial Fulfillment of the Requirements for the Degree of Master of Science at the Massachusetts Institute of Technology, 1996. 137 p.Abstract
An emerging demand for micro-sized air vehicles has necessitated the development of lightweight power sources that provide a higher power density than conventional batteries. A practical hydrocarbon-fueled engine is proposed that is expected to surpass conventional lithium-cell batteries in terms of short-term power-to-weight ratio and long term duration. The design concept is a single-piston, oscillating miniature internal combustion engine. The engine is a tuned mass-spring system driven near resonance by a 2-stroke, port-scavenged power head. Electrical power is extracted directly from the piston by means of a linear alternator. A prototype engine having a bore of 1/16 inch, weighing 1.6 grams and producing 0.5 Watts of AC power is developed- Scaling relationships are developed to size the power head, and the spring and alternator components are sized to match accordingly. Thermal losses in both the power head and the alternator are estimated, and a method of cooling the alternator is proposed. A unique double-helical spring is designed to satisfy the frequency and amplitude requirements. A simple model of the engine dynamics is presented verifying the feasiblily of the concept. Some general scaling principles are presented for sizing the engine and some the limitations encountered in designing the prototype are discussed.AbstractList of Figures
List of TablesMotivation
Objective
Power Head Design
Piston Sizing
Compression Ratio
Estimated Heat Losses
Combustion Time
Scavenging System Design
Alternator Design
nitial Sizing
Magnet Design
Coil Design
Alternator Cooling
Spring Design
Design Concept
Preliminary Design
Material Selection
Detailed Design
Electrical Lead Spring Design
System Dynamics and Control
System Dynamics
Engine Control
Engine Starting
Discussion
Design Summary
Scaling Considerations
Conclusions