Evaporative Emissions System: Operation

Expanded fuel, caused by high ambient temperatures, is collected in the expansion tank. This fuel is returned to main tank by venting action as fuel is used from main tank.

Fig 1: Porsche 924 and 924 Turbo Fuel Evaporation System

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Fuel vapors produced in fuel tank pass through a vent line to a carbon canister where they are stored in the activated charcoal in the canister. A second vent line connects carbon canister to air cleaner.

When engine is running, intake vacuum draws fresh air through carbon canister. This fresh air mixes with fuel vapors and is drawn into intake system where it enters the combustion system and is burned.

This action purges the activated charcoal and renews its storage capacity. On air-cooled models fresh air is blown through charcoal canister from blower housing to aid in purging action.