Two Stroke Internal Combustion Engines

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Two Stroke Internal Combustion Engines
From foukeffa.org
GA Ag Ed Curriculum Office To accompany Georgia
Agriculture Education Curriculum Lesson July
2002 Edited by CTAE Resource Network February 2011
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About this lesson.

• This lesson contains hypertext links to
  www.howstuffworks.com.
• If you are connected to the internet, click on
  the link icon and scroll to the animation at the
  sight.

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Introduction to the Two Stroke Engine

• This type of engine is commonly found in
  applications such as
• lawn and garden equipment
• dirt bikes
• small outboard motors

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Introduction to the Two Stroke Engine

• Two stroke engines have advantages over four
  stroke
• simplified construction (no valves)
• fire once every revolution for a significant
  power boost
• Great power to weight ratio

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The Two Stroke Cycle

• The two stroke engine ignites every revolution of
  the crankshaft. These engines overlap operations
  to reduce parts while maintaining power.

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The Two Stroke Cycle

• After the fuel air explosion, the piston is
  driven down. As the piston reached the bottom of
  its stroke, the exhaust port is uncovered. Most
  of the gases are driven out.

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The Two Stroke Cycle

• When the piston has bottomed out, the intake port
  is uncovered. The new fuel enters and is ready
  for compression and combustion.

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The Two Stroke Cycle

• When the fuel mixture is being compressed, a
  vacuum is created in the crankcase. The vacuum
  opens a reed valve and sucks air/fuel/oil in from
  the carburetor.

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The Two Stroke Cycle

• Simply put, in a two stroke engine you have only
• Compression
• Combustion
• Thus, two strokes.

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Two Stroke vs. Four Stroke

• In two stroke engines the crankcase is a
  pressurization chamber that forces fuel/oil/air
  into the cylinder. Here you mix oil and gas to
  lubricate internal parts.

• In four stroke engines the crankcase is separate
  from the compression chamber. This allows for
  the use of heavy oil for lubrication.

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Disadvantages of a Two Stroke

• Does not last as long due to poor lubrication.
• You have to mix two cycle engine oil with
  gasoline.
• Does not use fuel efficiently.
• Produces a lot of pollution.

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Summary

• Two stroke engines are great for their power to
  weight ratio and their simple design. However,
  due to the pollution concerns these engines will
  be increasingly harder to find.

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Source

• www.howstuffworks.com