Parts of The Stirling Engine

Sorry for the delay in posts, I've had numerous projects in my other classes due the last few days and although I've been reading the writing of these posts was delayed..

I continued my project by reading about the parts of a Stirling Engine and what each of their functions included. For this I went to the McMaster library to find some introductory books on Stirling Engines. While at McMaster I borrowed a number of books, of these I’ve only had time to look at one. The book I got the majority of my information for this post comes from STIRLING ENGINES written by Graham Reader and Charles Hooper in the 1980s. Before explaining the parts of the Stirling Engine I should note that there are many variations of the engine and for this post I will be referencing to the beta-type Stirling Engine. The beta-type Stirling Engine consists of 3 mechanical parts with an optional 4^th part that aids in efficiency which I will talk about in a later post. The Engine is a closed regenerative cycle heat engine that requires only a difference in temperature to create Net Work. Its’ cycle can be divided into 4 distinct phases which help show the purpose for each part. The beta-type Stirling Engine consists of a displacer, working piston, flywheel and an optional regenerator to increase efficiency.

The displacer is a large, loosely-fit piston within the large cylinder of the Engine. This large cylinder contains a gas (pressurized hydrogen and helium are optimal, however any gas can work) which is heated by an external heat source. As the Engine completes its cycle the displacer has two purposes; to move the gas into and out of contact with the heat source and to provide insulation between the heat source and the cooler side of the cylinder.

The working piston is the smaller piston on the Engine, and should be snugly fit within its cylinder. Ideally, no air should be able to move around the edges of the piston. The working piston is responsible for the mechanical energy within the Engine. This piston responds to changes in pressure from the heating and cooling of the concealed gas. As the pressure increases the force exerted by the gas within the cylinder also increases. Once the pressure becomes strong enough the gas pushes the piston upwards rotating a flywheel. This stroke does all of the work within the engine. The remaining 3 phases put energy back into the system using some of the converted mechanical energy.

The working pistons motion results in an increase in volume and less pressure. The flywheel continues to rotate using some of the mechanical energy to move the displacer down blocking the gas from the heat source and effectively cooling the gas. The cooler gas contains less pressure, resulting in the working piston returning to its lowest position. This phase also uses some of the mechanical energy of the flywheel. The final phase of the Engine is the flywheel pulling the displacer upwards, allowing the gas to come in contact with the heat source repeating the cycle again.

Understanding what each part of the Engine is and what it does was fairly complex and required a lot of google searches and re-reading of textbooks. Of the sources I visited there were 3 sources that proved to be the most useful. The first of these sources was from animatedengines.com which showed the cycle of the engine in an animated GIF and gave a very brief explanation of the different phases of the engine. I also visited robertstirlingengine.com which built from the animation showed at animatedengines.com. This site also explained the different parts of the engine in more detail. It was here where I found the proper names for different parts. My textbook itself started more complex and little of what I read was directly applicable to the basic knowledge of the Engine. I also first saw a PV diagram on this website which is explained in my next blog post.

Despite these sources the majority of my understanding came from actually watching the Stirling Engine I have at home and comparing it to what I was reading online and in the textbook. For some reason everything began to “click” after touching and watching the physical engine instead of just watching theoretical diagrams.

 

Sources:

Animated Engines. (n.d.). Low Temperature Differential Stirling Engine. Retrieved May 27, 2014 from “Animated Engines”: www.animatedengines.com

Hooper, C & Reader, T. G. (1983). STIRLING ENGINES. New York, NY: E. & F. N. Spon.

Stirling Engine. (n.d.). The operating principles of Stirling engine. Retrieved May 28, 2014 from “Robert Stirling Engine”: www.robertstirlingengine.com