Transcript Two-Stroke Engine - Two Rivers High School

Two-Stroke Engines
• Two-stroke engines are
used only in applications
where the motor is not used
very often and a fantastic
power-to-weight ratio is
important Lawn and garden
equipment
What’s the Difference?
https://www.youtube.com/watch?v
=hV3LImCslpo
The Basics
• A two-stroke engine:
• Is an internal combustion engine
• Converts gasoline into motion
• Is the most common car engine type
• 2 piston strokes per cycle
• 1 crankshaft revolutions per cycle
Chain saws, leaf blowers, Trimmers, Snowmobiles, Dirt bikes
Mopeds, Jet skis, Small outboard motors, Remote controlled
planes
About 2-strokes
• Less moving parts
• No valves
• Oil is mixed in fuel for lubrication
• engine can operate at any angle
• Spark plug fires during every piston stroke!
• Hotter, faster, lighter than 4-stroke
• Wedged piston increases air movement for intake & exhaust
• Low fuel efficiency & increased emissions
• Lighter, simpler, cheaper
Operation of two-stroke engine
• Piston travels up
• Intake & Compression
• Piston travels down
• Power & Exhaust
• Plug fires EVERY piston revolution
• Requires proper amount of back-pressure
• Great power to weight ratio
• Twice power in half the time
Intake & Compression stroke
Intake. The fuel/air mixture is first drawn into
the crankcase by the vacuum created during the
upward stroke of the piston through the reed valve.
Compression. The piston then rises, driven by
flywheel momentum, and compresses the fuel
mixture. (At the same time, another intake stroke
is happening beneath the piston).
Power & Exhaust/Transfer Stroke
Power.
At the top of the stroke the
spark plug ignites the fuel mixture.
The burning fuel expands, driving
the piston downward.
Exhaust/Transfer:
Toward the end of the stroke, the piston exposes
the intake port, allowing the compressed fuel/air
mixture in the crankcase to escape around the
piston into the main cylinder. This expels the
exhaust gasses out the exhaust port, usually located
on the opposite side of the cylinder.
Operation of Two-stroke
How Stuff Works Link
Things to watch:
Spark plug firing
Piston acting as a valve
Where air/fuel/oil mixture enters
Why aren’t they used in cars?
• Wear out much faster
• Poor lubrication
• Hotter & faster
• Increased wear
• Two stroke oil is expensive
• 4 oz/gallon
• 1 gallon every 1,000 miles
• Inefficient
• Poor fuel economy
• Increased emissions
• Oil burning
• Unburnt fuel leaving engine
Mixing Gas & Oil
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2 stroke oil is different than 4 stoke oil
Never substitute 4-stroke oil in a 2 cycle engine
Mix to manufacturer recommendation
• Generally located on the gas cap or tag
• Too much = fouled plugs & poor performance
• Too little = poor protection, increased engine wear
Modern 2 stroke oils need to be mixed lighter on vintage
implements.
Synthetic blends require less oil but are more expensive
TCW-3
Quality oil will have a rating on the label.
This means the oil has been tested and meets
regulations
Avoid oils that have not been rated
How Much Oil do I Need?
Look at the side of the bottle
OR
(Gallons x 128) / Desired Mixture
= Ounces to add
How much oil do I add if I have
a 5 gallon gas can that is half
full to reach 40:1 mixture?
Generate a list of pros & cons
with your partner!