2-Stroke Engine

Above: Timing Diagram for a 2-stroke Engine Cycle 

Stages	Piston Motion	Temp. Of Compressed Air (°C)	Pressure of Compressed Air (Bar)	Exhaust Valve	Scavenge Port
Compression	Upwards	550	80-90	Closed	Covered
Combustion	Downwards	-	-	Closed	Covered
Expansion	Upwards	1700	130-160	Closed	Covered
Exhaust & Scavenge	Downwards	-	-	Open	Uncovered

Compression Stroke: 

·         Fresh air is compressed from BDC to TDC (80-90bar) with its temperature raised to around 550°C.

·         Scavenge port are just covered, exhaust valve is closed and fuel injector is shut.

Combustion stroke:

·         Fuel oil is injected into the hot air, igniting it.
         (Click here for further elaboration on combustion)

Expansion Stroke:

·         After combustion, the air pressure goes up to 130-160bar with its temperature reaching to about 1700°C.

·         Piston is pushed downwards by the force from the expansion of gases.

·         Gases fall in pressure as they expand.

Exhaust & Scavenge:

·         Exhaust valve open towards the end of expansion stroke.

·         Due to differential pressure during blow-down period, exhaust gases are pushed out of the cylinder into exhaust manifold.

·         Once scavenge ports are uncovered, the scavenge air pushes the remaining  gases out of cylinder and filling it up with fresh air for the next cycle.