The piston moves downwards, creating a vacuum in the upper part of the cylinder. The Intake valve is open - the exhaust valve is closed. The vacuum draws an atomized mixture of air and fuel into the cylinder.

Compression Stroke

The piston moves upward in the cylinder. Both valves are closed. The trapped air/fuel mixture is compressed by the motion of the piston. At maximum compression, the air/fuel mixture is ignited by an electric spark.

Power Stroke

The piston is forced downward by the exploding air/fuel mixture. Both valves are closed. The crankshaft is forced to turn.

Exhaust Stroke

The piston is pushed back up by the rotating crankshaft. The exhaust valve is open, the intake is closed. The piston forces the burned air/fuel mixture out of the cylinder.

Intake Stroke

The piston moves downward in the cylinder, creating a vacuum. The intake valve is open, the exhaust valve is closed. Air ONLY is drawn into the cylinder.

Compression Stroke

The piston moves back up in the cylinder. Both valves are closed. The air becomes compressed in the cylinder and becomes extremely hot due to the high compression ratio of the diesel engine. At maximum compression, a small amount of diesel fuel is injected directly into the cylinder and is ignited by the super-heated air.

Power Stroke

The piston is forced downward by the explosion. Both valves are closed.

Exhaust Stroke

The piston is forced back up by the rotating crankshaft. The exhaust valve is open, the intake is closed. The burned gases are forced out of the cylinder by the piston.

Intake

As the rotor spins, it creates a vacuum and draws an air/fuel mixture through the intake port and into the chamber below the rotor.

Compression

As the rotor continues to turn, the tips of the rotor seal the chamber, and the trapped air/fuel mixture is compressed, and then ignited by an electric spark.

Power

The rotor is forced to turn by the expanding gases.

Exhaust

Once the tip of the rotor clears the exhaust port, the exhaust gases are then forced out of the chamber by the spinning rotor.

Up Stroke

Above the Piston

Any air/fuel mixture above the piston is trapped, compressed, and then ignited by an electric spark.

Below the Piston

The upward motion of the piston creates a vacuum in the crankcase, which causes a mixture of air and fuel (and lubricating oil) to be drawn past the Reed Valve, and into the area below the piston.

Down Stroke

Above the Piston

The force of the explosion pushes the piston down in the cylinder. Once the piston clears the exhaust port, the burned gases begin to force their way out of the cylinder.

Below the Piston

Pressure is created in the crankcase area by the downward movement of the piston. This causes the Reed Valve to be pushed closed. The trapped air/fuel mixture is now forced up through the intake (or transfer) port and refills the cylinder - helping to force out (scavenge) the exhaust gases.