As an educator, we know that you are extremely influential in the development of the minds and dreams of the students that you teach. We want to provide you with a teaching resource to encourage student’s interest in energy topics. We hope to promote creative thinking and help students to imagine the career possibilities in the energy savings, efficiency, green technology, science and engineering fields. This Big Teaching Ideas! segment on the amazing Stirling Engine is meant to provide a course outline for teachers to start discussions, project ideas and lab experiments with their students. Offering students these types of “outside the norm” introductions to energy and science topics can be fun and exciting. …We just might help to inspire the next energy visionary or inventor.
The Amazing Stirling Engine
Stirling engines convert heat energy into mechanical energy. Instead of burning fuels, these engines use external heat sources to pump the piston, turn the shaft and create mechanical energy. The Reverend Robert Stirling invented this engine in 1816 as an alternative to steam engines. Stirling was concerned about the dangers posed by steam engine explosions. They had a tendency to explode killing and maiming many people. Stirling invented this “hot air engine” as a safe alternative.
How It Works
These engines work by exploiting the way gases expand in hot temperatures and contract in cold temperatures. The Stirling engine is composed of a sealed cylinder filled with a working gas. Stirling originally used air but today’s Stirling engines may use helium or hydrogen gas. A mechanism moves the gas from the hot side to the cold side of the cylinder. There are different mechanisms that do this depending on the particular design of the engine. When the gas is on the hot side of the cylinder it expands and pushes a piston outward. This stroke of the piston is when the power is generated. The expansion of the gas forces some of it to the cold side of the cylinder. The gas contracts on the cold side and is compressed by a second piston linked to the first. The gas is then moved back to the heat source where it expands pushing the piston out again. As the gas continually expands and contracts, the power piston moves in and out turning the shaft and creating mechanical energy to do work.
There are a number of advantages to Stirling engines. First, the use of heat energy to create mechanical energy can be an efficient use of a waste byproduct. Heat is usually a byproduct of a process that cannot be recovered. The ability to recover heat energy and convert it back to mechanical energy is a major advantage of the Stirling engine. A second advantage is that alternative sources of energy can provide the heat. Geothermal, biogas or solar energy can be used to drive the engine. These engines operate cleanly, quietly and safely.
Stirling engines also have a number of disadvantages that have prevented their widespread adaptation. An external heat source is needed to power the engine. It is not practical to have such a heat source in most applications. In addition, the engine must warm up before it can run. Unlike a gasoline engine, which can vary its power output depending on how much fuel is injected into the engine, Stirling engines have a constant power output. These disadvantages have limited the practical use of the Sterling engine, however there has recently been a renewed interest in energy efficient applications for this type of engine.
There are a number of important applications of Stirling engines today. These engines are used on submarines to provide power to the vessel. They are also useful in situations where there are processes that generate a lot of heat as a byproduct. For instance, power plants generate a lot of wasted heat. This heat can be recovered by the engine and used to generate more power. The engine can also be reversed. Mechanical energy can be input and the engine used as a heat pump for a refrigeration system. Many more applications of this type of engine are in their research and development phases.
Cow Dung Powered Stirling Engine
Genius inventor, Dean Kamen, has a fascinating idea to provide people in the world’s developing countries with clean and fresh water. He’s developed a cow dung powered water purification system, run by a Stirling Engine. He calls it the Slingshot. With recent backing by Coca Cola, he has a chance to make a huge impact on the lives of millions of people in developing lands. For more details, see the Bluefaucet.com article on Dean Kamen’s Slingshot.
Build a Stirling Engine
Building a Stirling Engine is a great lab activity. It’s fun to build them and watching them work is fascinating. You can use them to illustrate the principles of physics and chemistry, while students enjoy an engaging hands on activity. Additionally, you can fuel their curiosity by challenging them to imagine applications in which Stirling Engines can be used. Check out this link for a great Stirling Engine kit and more info on topic.
Questions for your Stirling Engine student lesson:
What are the advantages and disadvantages of the Stirling Engine?
What are past and current applications that are using the Stirling Engine?
What other applications can use a Stirling Engine?
What is the benefit of the constant power output of the Stirling Engine?
What applications are there for using passive heat to drive the Stirling Engine?
Besides Dean Kamen’s Slingshot, what other creative ways can Stirling Engines be used?
How can Stirling Engines be powered from the heat exhaust of other engines, factories or manufacturing processes?
How can Stirling Engines be used in cars and other transportation vehicles?
How does the Stirling Engine provide energy savings?
Please share this page with other educators and provide us with feedback in our comments sections. We want to hear about your students and their ideas, lab work and experiences with Stirling Engines.
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