Crankcase ventilation

crankcase ventilation

The emission of unburned fuel to the atmosphere from the crankcase of an internal combustion engine.

Formerly a large source of hydrocarbons to the atmosphere, the rate of escape has been greatly reduced by recycling of the escaped gases to the cylinders by means of a device called the positive crankcase ventilation (PCV) valve. Crankcase ventilation contributes around 5% of unburned hydrocarbon emissions to the atmosphere.

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1. A gaseous envelope gravitationally bound to a celestial body (e.g., a planet, its satellite, or a star).