PRE-RELEASE
Brief description
| Brief description |
Certain markets have legal requirements governing emissions that are released into the air when refuelling (emission legislation varies on different markets). Hydrocarbons that evaporate in conjunction with refuelling must be handled by the car and not released in to the air. Cars on certain regulated markets are equipped with a system called ORVR (Onboard Refuelling Vapour Recovery), which takes care of the fuel vapour that is released while refuelling. The fuel vapour is collected in an evaporative emission canister through which air passes while the car is being driven to transport the petrol vapour back to the intake system for igniting in the engine.
It is important to ensure the integrity of the tank and its components to prevent emissions into the air. The evaporative emission system has therefore been designed to detect any leaks. A leak corresponding to a hole larger than 0.5 mm (0.020") in diameter must be detected by the evaporative emission system. See Tank integrity diagnosis .
System description
Fuel is filled through the fuel filler pipe and passes through the check valve down to the tank. The fuel filler pipe acts as an ejector. Fuel flowing down into the tank is accompanied by air from outside and prevents fuel vapour from being emitted to the surroundings via the opening in the fuel filler pipe. The fuel being filled forces the gaseous hydrocarbons and the air being drawn down into the tank through the float valve into the EVAP emission canister. The hydrocarbons are absorbed in the emission canister and the air is let out through the shut-off valve.At a certain fuel level, the float valve will close and increase the pressure in the tank. The fuel will now rise in the filler pipe and turn off the flow of fuel when it reaches the nozzle. The check valve in the filler pipe prevents fuel from being ejected from the mouth of the filler pipe when the nozzle closes.
The pressure remaining in the tank is led through the float valve into the evaporative emission canister. As the pressure in the tank is gradually reduced, fuel will run from the filler pipe until it is empty.
When the engine starts, the evaporative emission canister is gradually purged by air being drawn into it via the shut-off valve. Hydrocarbon/air mixture passes through the EVAP canister purge valve into the engine and is ignited.
