Positive Crankcase Ventilation

Positive Crankcase Ventilation







General Information

During combustion, every engine blows some of the combustion gases past the piston towards the crankcase - these gases are called blow-by gases. If these gases were not drawn off, the pressure in the crankcase would increase considerably. A vent connection is installed in the crankcase for this reason. For environmental protection reasons, these gases are not released into the atmosphere but are sent back to the engine for combustion via the intake system.

Of course, these positive crankcase ventilation gases contain a high proportion of engine oil and other combustion residues as well as a lot of fuel residues in some cases. If these gases get into the intake duct, they will contaminate the intake air and can then impair running smoothness, exhaust emissions and reduce knock resistance. It is obvious for these reasons why effective oil separation is important for the engine.

Positive Crankcase Ventilation System - Naturally Aspirated Engine







The two pre-separators, which are integrated in the cylinder head cover, are used to draw off most of the transported oil into the crankcase. The remaining blow-by gases are fed to the fine separator via hoses.

The hoses have a larger diameter compared with the hoses used in the Cayenne and as a result, air speed is reduced and less oil is transported in the gases.

PCV Oil Separator







The various parts of the oil separator are pointed out in the above illustration.







If there is only a small amount of blow-by gases, these go into the cyclone, where air is separated from oil. The oil goes into the reservoir, while the air is channelled out of the tank and fed back to the engine by the intake system.







For example, if the blow-by gases increase as a result of higher engine speeds, the two pressure control valves open and an additional bypass is activated in order to separate the oil. The air is again fed to the engine and the oil goes into the reservoir. The oil reservoir is always drained whenever there is a vacuum in the system, but never at full throttle.







The valve, which opens or closes the reservoir depending on whether or not there is a vacuum in the system, is installed beneath the oil reservoir. The size of the reservoir is designed so that even if the vehicle is only driven at full throttle (whereby the reservoir is never drained), a correspondingly large amount can be taken in until the vehicle needs to be refuelled.

Positive Crankcase Ventilation System - Turbo Engine







The diagram shows that the positive crankcase ventilation system in the turbo engine essentially works in the same way as in the naturally aspirated engine. However, there is not always a vacuum in the intake system of the turbo engine, but overpressure in the charger area. Additional check valves are therefore installed here. As a result, separation can be performed in the intake area, just like on a naturally aspirated engine, and between the air cleaner and turbocharger in the charger area.

Additionally, the aeration and ventilation system PCV is also used in the Panamera Turbo. This system ventilates the crankcase with a steady stream of fresh air, which evaporates fuel that is carried in. For this purpose, fresh air is removed between the charge air cooler and throttle valve and is delivered to the crank chamber via a line. The pressure that exists at any time between the removal point and the crankcase causes a steady flow of fresh air through the crankcase.