Cylinder and Piston Drive Engines
by Ron Kurtus (revised 9 September 2017)
The cylinder and piston configuration is a vital part of many types of engines. It is also a form of machine, converting an input force into an output.
A cylinder is typically a tube that is closed on one end. The piston is a solid cylindrical object that slides inside the cylinder. Pressure from expanding gas or from a liquid causes the piston to move within the cylinder. The movement can be used to drive a shaft or turn a wheel.
Questions you may have include:
- What is the cylinder-piston configuration?
- What are ways to expand the gas?
- How can the process be repeated?
This lesson will answer those questions. Useful tool: Units Conversion
The cylinder and piston form a machine that converts pressure inside the cylinder into motion.
Pressure inside cylinder pushes piston forward
The pressure inside the cylinder is usually from expanding gases and sometimes liquids.
Ways to expand gas
Gases and liquids expand when heated. There are several ways to heat the material and cause the expansion that will move the piston and rod.
Heat the cylinder
You can externally heat the cylinder, which will in turn heat the gas or liquid inside the cylinder, causing it to expand. A Stirling engine uses this method.
Inject gas under pressure
Another method is to attach a tube into the cylinder and inject steam or some gas under pressure that will then move the piston. An air-pressure engine and a steam engine are examples that use this method.
A third method to create pressure inside the cylinder is to inject a fuel-air mixture and then ignite it. The explosion would create pressure to drive the piston forward. A gasoline engine is an example using this method.
Pressure inside the cylinder can create work by pushing the piston forward or outward. However, this is a single action. You want to be able to repeat the action. That would require the piston to be pulled inward and then repeat the outward action.
A piston rod that is moving back and forth has minimal use. It would be better to be able to have the rod turn a wheel, which would result in more useful work.
Having the piston rod churn a wheel is a major principle of most engines.
The cylinder and piston configuration is also a form of machine, converting an input force into an output. It is what drives many forms of engines.
A cylinder is a tube that is closed on one end, while the piston is a solid cylindrical object that slides inside the cylinder. Pressure from expanding gas or from a liquid causes the piston to move within the cylinder. The movement can be used to drive a shaft or turn a wheel.
Improve your knowledge
Resources and references
Basic Engine Parts - HowStuffWorks.com
How Cars Work - Links and videos on the functions of automobiles
Engine Cylinder - Wikipedia
Piston - Wikipedia
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Cylinder and Piston Drive Engines