Modeling of a Shape Memory Alloy Reciprocating Engine

John M. Boyle Jr

Advisor: Dr. Kathleen Issen

Co-Advisor: Dr. Garrett Hall

Collaborator: Sandra Martinez B.S. Mechanical Engineering 
 

Clarkson University

Department of Mechanical and Aeronautical Engineering

Potsdam, NY 13699

Motivation

Utilize waste heat to power a shape memory alloy reciprocating engine.  
 

Shape Memory Alloys (SMA's) have been around for nearly 50 years, though it has only been within the last 15 to 20 years that significant applications have been developed. The property that makes SMA's unique is the ability to actually change its crystalline structure by simply loading or unloading the specimen, or by applying a temperature gradient. This shape memory effect and pseudo elastic behavior lends itself to many possibilities, such as orthodontics, surgical and medical instruments, mobile communications, sealing applications, and many uses as actuators. New applications are found constantly as the human imagination finds new creative uses for these curious Materials. As the understanding of SMA' s increase, along with the rise of better technology, the future of SMA' s looks very bright. One of the more interesting applications of SMA' s is to harness waste energy for SMA use. Since the alloys can be induced to change phase using only a temperature gradient, utilizing the waste heat from existing systems is a remarkable method to both increase efficiency and reduce waste simultaneously.  
 

A novel example is to use the waste heat from an automobile engine to power a small SMA heat engine. This smaller engine could be used to handle some smaller tasks of the larger engine, thereby alleviating some of the burden and increasing efficiency. Several different SMA engines have been proposed in the past. Some examples include an early helical spring engine model, the Banks Engine3, offset disk engines, and an interesting reciprocating engine proposed by Sakuma and Iwata5. These engines commonly operate in hot and cold-water baths that cause the SMA' s to induce phase change. The cold state, called Martensite (M), is softer than the hot state, Austenite (A), and can be easily strained to perform some work. Arranging the alloys in a way so that when some of the elements are M, others are A, it is possible to heat the M and cool the A thus causing the M to contract into A. This is the basic theory of a SMA heat engine. The main problems associated with these applications are heating and cooling the metals fast enough to make the engine output useful. This is usually overcome by using relatively thin elements to increase heat dissipation, but the disadvantage is that with thinner alloys, the power output is usually lower, making the engine less desirable. Because of this reason, widespread use of SMA engines has yet to occur.

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