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          A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

  Exhaust stroke

TemperatureUp to approx. 700C (Diesel engine)
Up to approx. 900C (petrol engine)
Pressure5 - 3 bar (petrol engine)
Somewhat higher (Diesel engine)

The piston travels from BDC to TDC. The gases escape through pressure.
TDC = Top Dead Center, BDC = Bottom Dead Center

The animated working process.


In the exhaust stroke, as much burnt fuel mixture as possible should leave the cylinder with very little loss (except in the case of internal exhaust gas recirculation).


Like the induction stroke, this also lasts longer than a half a crankshaft rotation. It begins before bottom-dead center (BDC) through the opening of the exhaust valve and finishes at the end of the valve overlap after top-dead center (TDC). The burnt mixture is sent, as early as possible, to the exhaust system. Towards the end, the optimum speed of the spent gases should help to suck in the fresh gases. Once the fresh gases have filled the area up to the exhaust valve, this should actually close. This however, only functions completely in the RPM range of the maximum torque. Without special valve-lifting- or camshaft adjustment, below this RPM range the fresh gases turn back again, while above this range, too little gas is sucked in. 09/11

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

The angle from Io until Ec is called the valve overlap.
Io/Eo = Intake/exhaust opens, Ic/Ec = Intake/exhaust closes

Oil from the sump, which reaches the combustion chamber, is expelled during the exhaust stroke.               Top of page               Index
2001-2015 Copyright programs, texts, animations, pictures: H. Huppertz - E-Mail
Translator: Don Leslie - Email:

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