1. Intake and Compression:
* Intake: As the piston moves down, it creates a partial vacuum in the crankcase. This vacuum draws in a mixture of fuel and air through a transfer port into the crankcase.
* Compression: As the piston moves up, it compresses the fuel-air mixture in the crankcase. At the top of the stroke, a port opens, connecting the crankcase to the combustion chamber.
* Transfer: The compressed mixture is forced into the combustion chamber through the transfer port, pushing out any remaining exhaust gases.
2. Power and Exhaust:
* Power: At the end of the compression stroke, the spark plug ignites the fuel-air mixture, causing combustion and pushing the piston down. This is the power stroke.
* Exhaust: As the piston moves down, it uncovers the exhaust port, allowing the spent exhaust gases to escape.
Key Differences:
* No Separate Intake Stroke: The two-stroke engine combines intake and compression into a single stroke, unlike the four-stroke engine which has separate intake and compression strokes.
* Scavenging: The transfer of the compressed fuel-air mixture into the combustion chamber pushes out the exhaust gases in a process called scavenging.
* Lubrication: Two-stroke engines typically use pre-mixed fuel and oil for lubrication, as there is no separate oil sump.
Benefits:
* Simpler Design: Fewer moving parts, making them lighter and cheaper to manufacture.
* Higher Power-to-Weight Ratio: The shorter cycle allows for higher engine speeds and thus more power.
Drawbacks:
* Higher Emissions: Two-stroke engines produce more unburned fuel and oil emissions than four-strokes.
* Lower Fuel Efficiency: They consume more fuel for a given amount of power output.
* Higher Maintenance: The pre-mixed oil can foul spark plugs and require more frequent cleaning.
Summary:
While both two-stroke and four-stroke engines use internal combustion, they achieve the power stroke through different mechanisms. The two-stroke engine accomplishes intake, compression, power, and exhaust in just two strokes, making it a simpler but less efficient design compared to the four-stroke engine.
