Power on Two Stroke Cycle

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The power stroke starts after the piston passes TDC. Figure 25 illustrates the power stroke which continues until the piston reaches 91° ATDC, at which point the exhaust valves start to open and a new cycle begins.

A two-stroke engine requires one rotation of the crankshaft to complete one cycle. The events occur as follows:
Intake - the piston is near BDC/before dead center and exhaust is in progress. The intake valve or ports open and the fresh air is forced in. The exhaust valves or ports are closed and intake continues. 
Compression - after both the exhaust and intake valves or ports are closed, the piston travels up towards TDC/top dead center. The fresh air is heated by the compression.

Fuel injection - near TDC the fuel is injected by the injectors and the fuel starts to burn, further heating the gasses in the cylinder.

Power - the piston passes TDC and the expanding gasses force the piston down, rotating the crankshaft.
Exhaust - as the piston approaches BDC the exhaust valves or ports open and the exhaust gasses start to flow out of the cylinder.