Transcript Two Stroke Internal Combustion Engines - BruceAg

Two Stroke
Internal Combustion Engines
*How a two stroke engine works
*Advantages/Disadvantages
From foukeffa.org
GA Ag Ed Curriculum Office
To accompany Georgia Agriculture Education Curriculum Lesson
July 2002
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.
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
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
The two stroke cycle
• The two stroke engine ignites every
revolution of the crankshaft. These engines
overlap operations to reduce parts while
maintaining power.
The two stroke cycle
• After the fuel air
explosion, the piston is
driven down. As the
piston reached the
bottom of it’s stroke,
the exhaust port is
uncovered. Most of
the gases are driven
out.
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.
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.
The two stroke cycle
• Simply put, in a two stroke engine you have
only:
– Compression
– Combustion
• Thus, Two Strokes.
2 stroke compared to 4 stroke
• In two stroke engines
• In four stroke engines
the crankcase is a
the crankcase is
pressurization
separate from the
chamber to force
compression chamber.
fuel/oil/air into the
This allows the use of
cylinder. Here you
heavy oil for
mix oil and gas to
lubrication.
lubricate internal parts.
Disadvantages of a two stroke
• The engines do not last as long due to poor
lubrication.
• You have to mix two cycle engine oil with
gasoline. $$$$$
• The engines do not use fuel efficiently.
• These engines produce a lot of pollution.
Summary
• Two stroke engines are great for the power
to weight ratio and their simple design,
however, due to there pollution concerns
these engines will be harder to find.
Source
www.howstuffworks.com