Fuel Evaporation Control For Models With Catalytic Converter
The fuel evaporation control line of the fuel tank is connected to an activated carbon filter, in which the fuel vapors which accumulate in the tank are collected. The activated carbon filter is linked by means of 2 further lines to the 2 air manifolds. A fuel evaporation control valve is installed in each of these 2 lines. When a fuel evaporation control valve is open, the vacuum in the air manifold draws in fresh air through the activated carbon filter. The fresh air flushes out the fuel collected in the filter and routes it to the engine for combustion. See Fig 1 .
Since this additionally supplied mixture influences combustion to a considerable extent, the fuel evaporation control valve consists of a non-return valve and an electrically operated valve. Due to the non-return valve, the fuel evaporation control valve is initially closed when no power is applied. The non-return valve prevents fuel collecting in the air manifold when the vehicle is parked. The non-return valve opens as the vacuum in the air manifold increases. Electric actuation takes place separately for both rows of cylinders dependent on the engine speed and load. The venting cycle (flushing phase) begins as soon as the emission (lambda) control system is active. On completion of one cycle, the valve is closed for approximately one minute (rest phase).