Two-Stroke EnginesTwo-Stroke Engines

TransportationTransportationMr. O’RourkeMr. O’Rourke

Two-StrokeTwo-Stroke

ApplicationsApplications

Two stroke engines are found on:Two stroke engines are found on: Weed trimmersWeed trimmers SnowmobilesSnowmobiles Older dirt bikesOlder dirt bikes ChainsawsChainsaws Nitro R/C CarsNitro R/C Cars Small outboardsSmall outboards Older Jet skisOlder Jet skis

The BasicsThe Basics

Two stroke engines operate on the same principles as a Two stroke engines operate on the same principles as a four stroke engine. four stroke engine.

Intake- Fuel mixture is drawn into Intake- Fuel mixture is drawn into crankcasecrankcase during during upstrokeupstroke Compression- mixture is compressed in the Compression- mixture is compressed in the crankcase crankcase during during

downstroke and again during upstroke before combustiondownstroke and again during upstroke before combustion Combustion-fuel is recompressed and ignited in cylinder during Combustion-fuel is recompressed and ignited in cylinder during

upstrokeupstroke Exhaust- burned mixture is forced out by Exhaust- burned mixture is forced out by fresh mixture being being

forced in during downstrokeforced in during downstrokePiston fires once every revolution. No traditional valves like a four-Piston fires once every revolution. No traditional valves like a four-

stroke. Piston serves as a “valve” by covering the ports.stroke. Piston serves as a “valve” by covering the ports.

Two-StrokeTwo-Stroke

Upstroke (compression)Upstroke (compression)

One-way valve opens and fuel mixture is One-way valve opens and fuel mixture is drawn into crankcasedrawn into crankcase

Transfer port is coveredTransfer port is covered

Fuel mixture is compressed (again) and Fuel mixture is compressed (again) and ignitedignited

Piston covers exhaust port during Piston covers exhaust port during compressioncompression

Downstroke (Combustion)Downstroke (Combustion)

Combustion forces piston down Combustion forces piston down compressing fuel mixture in crankcasecompressing fuel mixture in crankcase

Intake port is covered and valve is forced Intake port is covered and valve is forced closedclosed

Transfer port is uncovered forcing fuel Transfer port is uncovered forcing fuel mixture into cylindermixture into cylinder

This fuel mixture pushes the exhaust out This fuel mixture pushes the exhaust out the exhaust portthe exhaust port

Two-StrokeTwo-Stroke

AdvantagesAdvantages

Less parts = Lighter Less parts = Lighter

Fires once every revolution = 2x power of Fires once every revolution = 2x power of four strokefour stroke

Cheaper, less complex and easier to work Cheaper, less complex and easier to work onon

Can work in any orientation (upside down, Can work in any orientation (upside down, sideways)sideways)

DisadvantagesDisadvantages

No dedicated lubrication system (not as No dedicated lubrication system (not as durable)durable)

Not fuel efficient and require expensive oil Not fuel efficient and require expensive oil to be mixed with gas (one gallon oil/1,000 to be mixed with gas (one gallon oil/1,000 miles)miles)

Produce a lot of pollution due to burning of Produce a lot of pollution due to burning of gas and oil.gas and oil.

Two-StrokeTwo-Stroke

http://www.animatedengines.com/http://www.animatedengines.com/twostroke.htmltwostroke.html

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