Positive Crankcase Ventilation: Description and Operation

Positive Crankcase Ventilation

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 fitted 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 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 and exhaust emissions and reduce knock resistance. It is obvious for these reasons why effective oil separation is important for the engine.

On the new flat engines this task is performed by the oil mist separator, which consists of a pre-separator and a fine separator.