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Intake Stroke

TemperatureApprox. 100°C
Pressure0,8 - 0,9 bar (naturally aspirated engine)
Up to approx. 2 bar (charged standard engine)
Up to approx. 5 bar (charged racing engine)

The piston travels from TDC to BDC. The gases flow in through vacuum.
TDC = top-dead-center, BDC = bottom-dead-center

The animated working process.


During the intake-stroke of the four-stroke engine, the cylinder should be as completely filled as is possible, in all operational areas, with fresh gas. Specific used gas proportions can then be introduced (internal exhaust gas recirculation) by the engine management in certain, exactly defined operational areas.


The air- fuel -mixture with indirect injection, or pure air with direct injection, is sucked in by the (relatively low) pressure difference between the inlet manifold and the cylinder. This is caused by the movement of the piston, whereby the combustion chamber volume is increased. 09/11

Reasons for the opening before TDC and the closing after BDC
The gas-column is relatively inert.
It reaches it's highest speed about one third before BDC.
Used gases help to suck in fresh gas.
Cam operated stroke-valves open and close relatively slowly.

The angle from Io to Ec is called valve overlap.
The anlgle Ic is particularly important for the performance development.
Io/Eo = Intake/Exhaust opens, Ic/Ec = Intake/Exhaust closes