Evaporative Emissions System: Description and Operation

The ventilation line of the fuel tank is connected to an activated carbon filter (carbon canister), in which the fuel vapors produced in the tank are collected. The activated carbon filter is connected by a further line to the air manifold. A tank ventilation valve is integrated in this line.

When the tank ventilation valve is open, fresh air is drawn in via the activated carbon filter due to the vacuum in the air manifold. The fresh air flushes out the fuel collected in the filter and feeds it to the engine for combustion.

Since this additionally supplied fuel-air mixture has a considerable effect on combustion, the tank ventilation valve is designed as an electrically controlled valve. The tank ventilation valve is closed when no power is applied.

After starting, the first flushing phase is initiated in that the tank ventilation valve is activated for approx. 6 minutes (348 seconds). The valve is then closed for 100 seconds in order 10 implement basic adaptation. Once basic adaptation has been completed successfully, the subsequent flushing phase has a duration of 90 minutes (5400 seconds). Otherwise a further short flushing phase (approx. 6 minutes) takes place. In order to conclude basic adaptation successfully, the engine must idle and run in the part-load range.