The Idaho Stirling Engine Homepage
Chris Daniel & Eric Johnson

Homepage Contents:

Engine Animation
Final Idaho Stirling Engine Design
The History of the Idaho Stirling Engine
               Background
               Problem Statement
               Design Process
               Pictures of Design Iterations

IDAHO STIRLING ENGINE ANIMATION:

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FINAL IDAHO STIRLING ENGINE DESIGN & DESCRIPTION:

The final design uses a 100 W halogen bulb for the heat source. The cold side of the engine is maintained by an ice water bath. A small aluminum displacer is sealed in a pressurized glass cylinder. The displacer is connected to a crankshaft with fishing line. At one end of the crankshaft is a flywheel and at the other is a bobbin which is used to show the work done by the engine. As the crankshaft rotates, fishing line (which is attached to a small weight) is wound up on the bobbin. The weight can be lifted up two feet along the side of the ruler.

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The History of the Idaho Stirling Engine

Abstract

Stirling engines, although they have not found their niche in modern commercialization, can be used as valuable teaching aids in the classroom. University of Idaho professor, Dr. Don Elger, organized three groups of ME430 students with the goal of designing, instrumenting, and modeling a Stirling engine that could be used as a teaching aid in his classes. As the system specialists on the Idaho Stirling Engine (ISE) team, our main objective was to design and construct a simple classroom Stirling engine. The goal was to design the teaching aid to be “cool and observable” rather than to design for maximum efficiency. An iterative design process was used. Each independent variable manipulation was empirically evaluated for its effect on the list of design parameters. The resulting model, named the Idaho Stirling Engine, was well-balanced in meeting all of the design parameters. The engine ran continuously at approximately 250 revolutions per minute. The engine will be very useful as a teaching aid in the classroom. However, there is always room for future improvements. The next design iteration should focus on improving the engine’s efficiency and the ease of which it can be mathematically modeled.

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Background

The concept of the Stirling engine originated in the early 1880s [1]. Since then, especially in the last 50 years, Stirling engine technology has come a long way [2]. However, modern uses of Stirling engines are almost invisible. Besides engines built for research, the only Stirling engines that have made an impact are those used as cryocoolers, those used to power small submarines, and those used in the classroom [1]. For Stirling engines to become commercialized, they will have to demonstrate reliability and reasonable cost. Although properly designed Stirling engines have a high efficiency, it is not much higher than that of the modern diesel engine [2]. Therefore, for Stirling engines to become more popular, their other advantages (low noise, low emissions, and the ability to use a wide variety of fuels) will have to outweigh the current disadvantages (high cost, unknown technology, and unproved reliability).

Although wide-spread production of Stirling engines does not appear promising in the near future, their use in classrooms is gaining attention. Simple, displacer type Stirling engines, operating between a small temperature difference, offer excellent educational value when used as teaching aids in the classroom. Dr. Don Elger, a professor at the University of Idaho, recognized the benefits of this Stirling engine application. He assigned three ME430 teams to his Stirling Engine research: System Specialists, Instrumentation Specialists, and Modeling Specialists. This web page reports on the findings of the System Specialists.

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Problem Statement

“Construct a simple, observable, cool engine that will be used as a teaching device. The work done by the engine must be visual and measurable. The engine should be designed for application in the classroom rather than for maximum efficiency.”

Objectives

Design and construct the “Idaho Stirling Engine.” Parameters (as stated by Dr.Elger):

· Work done is visual and measurable
· Heat in is electrical, observable, and measurable
· It is esthetic and fascinating to watch
· It is robust: comes to a steady state operating point and stays there
· It is easy to use in the classroom
· It is easy for others to construct
· It is reliable · It is straightforward to model
· It is safe (minimize hot surfaces and electrical exposure)
· Engine efficiency is as good as possible, while satisfying other constraints

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Design Process

To establish a starting point for designing the Idaho Stirling Engine, we began by modifying an existing Stirling engine that was developed by Ted Boyl-Davis, a graduate student at the University of Idaho.

Variables

The following independent design variables were manipulated during the iterative design process of the ISE and empirically evaluated. The variables were evaluated based on the previous list of design parameters:

· Type of energy source (Incandescent vs. Halogen light bulb)
· Type of pressurized container (Tin vs. Glass/Pyrex)
· Use of Insulation
· Size of energy source (50, 100, 150 or 200 W bulbs)
· Diaphragm material (balloon vs. inner-tube rubber)
· Ice water bath or air-cooling fins
· Solid vs. split displacer
· Base design for energy source (can vs. plaster/putty)
· Use of brass bushings
· Seal for pressurized container (rubber band vs. jar lid)

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PICTURES OF DESIGN ITERATIONS: