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2-Stroke Engine Operation
A two-stroke engine completes a power cycle in just two strokes of the piston (one revolution of the crankshaft), unlike the more common four-stroke engine that requires four strokes to complete a cycle.
Here's a breakdown of its operation:
1. Intake/Compression Stroke: As the piston moves upward, it compresses the air/fuel mixture in the combustion chamber. Simultaneously, the mixture (a blend of fuel and oil in the case of most two-stroke engines) is drawn into the crankcase through ports or valves opened by the descending piston.
2. Combustion/Power Stroke: As the piston reaches the top of its stroke, the spark plug ignites the compressed air/fuel mixture. The rapid expansion of gases from combustion forces the piston back down. This downward movement generates power that drives the crankshaft.
3. Exhaust/Scavenging Stroke: Towards the end of the power stroke, the exhaust ports, or valves open, and the high-pressure exhaust gases are expelled from the combustion chamber. Meanwhile, the piston continues downward, uncovering intake ports or valves, allowing a new mixture of air/fuel to enter the chamber, and the cycle repeats.
This design offers advantages in simplicity and power-to-weight ratio but tends to produce more pollution due to the mixing of fuel and oil and the incomplete burning of fuel in the combustion chamber.
Two-stroke engines are commonly used in smaller outboard boat motors due to their lightweight and high-power output relative to their size.