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5.20: External Combustion Engines

Difficulty Level: At Grade Created by: CK-12
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This picture was taken in 1899 (the color was added later). The picture shows the inventor of an early automobile, along with his wife, driving one of his inventions. The man and woman were on their way to the top of Mount Washington, the highest mountain in the eastern U.S. The purpose of the trip up the mountain was to get publicity for the steam-powered automobile. The inventor and his wife were the first people to ever reach the top of the mountain by car. Steam engines are not used very much anymore, because more efficient and powerful engines have been developed. But inventors and engineers learned a lot from these early combustion engines.

Q: How else were steam engines used?

A: Starting in the 1700s and up until the early 1900s, steam engines were commonly used to run factory machines, train locomotives, and ships. Their power led to a revolution in industry and transportation.

What Is a Combustion Engine?

A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the thermal energy to do work. There are two types of combustion engines: external and internal. A steam engine is an external combustion engine.

How External Combustion Engines Work

An external combustion engine burns fuel externally, or outside the engine. The burning fuel releases thermal energy, which is used to heat water and change it to steam. The pressure of the steam moves a piston back and forth inside a cylinder. The kinetic energy of the moving piston can be used to turn a vehicle’s wheels, a turbine, or other mechanical device. The Figure below explains in greater detail how this type of engine works. 

Diagram illustrating how an external combustion engine works

Q: What type of energy does the piston have when it moves back and forth inside the cylinder?

A: Like anything else that is moving, the moving piston has kinetic energy.

Summary

  • A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the thermal energy to do work.
  • An external combustion engine burns fuel externally, or outside the engine.
  • An external combustion engine burns fuel to heat water and produce steam. The steam is under pressure and is used to push a piston back and forth inside a cylinder. As the piston moves back and forth, it moves a piston rod, which can do work.

Review

  1. Define combustion engine.
  2. What is an external combustion engine?
  3. Explain how an external combustion engine works.

Resources

 

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Vocabulary

combustion engine

Complex machine that burns fuel to produce thermal energy and uses the thermal energy to do work.

external combustion engine

Engine that burns fuel externally, or outside the engine.

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Description
Difficulty Level:
At Grade
Grades:
7 , 8
Date Created:
Nov 01, 2012
Last Modified:
Aug 17, 2016
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