Brief description, fuel evaporation
| Brief description, fuel evaporation |
Legal requirements
ORVR, Onboard Refueling Vapor Recovery, is a legal requirement that came into force in the USA from M98. The legal requirement governs the emission of hydrocarbons in conjunction with refuelling.All M00 4-cyl cars are LEV (=Low Emission Vehicle).
On cars intended for markets with any legal requirements on tank integrity diagnosis, the software in T7 will turn on the CHECK ENGINE lamp. On markets without such legal requirements, the CHECK ENGINE lamp will not come on but a DTC will be generated.
Applies to all: Hydrocarbons that vaporize while refuelling must be dealt with in the car and not released into the atmosphere. Max. 0.2 g hydrocarbon per gallon of fuel may escape while refuelling 15-38 litres (4-10 gallons) of fuel per minute. The tank must be able to be filled at 15-38 litres (4-10 gallons) per minute to 95% of its total volume without the fuel nozzle shutting off too early so that subsequent topping up is required.
The system must be able to detect a leak corresponding to a hole greater than 1 mm (0.040”) in diameter. ORVR without tank integrity diagnosis (see below) will recycle the fumes but the system will not detect a leak.
System description
Fuel is filled through the fuel filler pipe and passes through a check valve into the tank. The fuel filler pipe acts as an ejector. The fuel flowing down to the tank will take with air from outside and prevent any fuel vapour from escaping into the atmosphere via the filler opening. The fuel being filled forces out the gaseous hydrocarbons and accompanying air through a float valve and on to the evaporative emission canister. The evaporative emission canister absorbs the hydrocarbons and the air passes out through the shut-off valve (not fitted on ORVR without tank integrity diagnosis).At a certain level (about 95%) the float valve closes, whereupon the pressure in the tank rises. The fuel now rises in the filler pipe, and the dispenser nozzle closes when the fuel reaches it. The check valve in the filler pipe prevents ”back-spit” when the dispenser nozzle closes.
The positive pressure that remains in the tank exits slowly through the roll-over valve into the evaporative emission canister. As the fuel level in the tank drops, fuel flows in from the filler pipe which is thus emptied.
When the engine is started, the evaporative emission canister is gradually ventilated by sucking air into the evaporative emission canister via the shut-off valve and then passing the mixture of hydrocarbons and air through the purge valve into the engine where it is burned.
The diagnosis on ORVR cars is in two variants, normal and special, depending on the engine coolant temperature and the intake air temperature. This is meant to counteract the effect of the evaporating fuel vapour as much as possible.
An evaporative emission canister fitted by the tank is used on ORVR cars to store approx. 130 g hydrocarbons. The canister is filled with approx. 70-90 g hydrocarbons during normal refuelling. This is subsequently purged while the car is being driven so that it is normally empty the next time the car is refuelled.
There are three variations of emission requirements from M01:
1. OBD II LEV for US/CA. Full ORVR with tank integrity diagnosis and fuel vapour recycling. CHECK ENGINE comes on for emission-related DTCs.
2. E-OBD, EC2000 for EU/NO/CH. ORVR with fuel vapour recycling but without tank integrity diagnosis, which means that car with this variant of ORVR do not have a shut-off valve or tank pressure sensor. CHECK ENGINE is on only in certain cases.
3. L-OBD for other markets. L-OBD is identical to E-OBD but it does not turn on the CHECK ENGINE lamp for emission-related DTCs.
On cars with full ORVR and ORVR without tank integrity diagnosis, the evaporative emission canister is on top of the tank. On cars without fuel vapour recycling, the canister is under the front right wing.
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B205E
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B205L
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B205R
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B235R
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Filler pipe
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Without fuel vapour recycling.
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X
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With fuel vapour recycling. Without EVAP diagnosis
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X
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X
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With fuel vapour recycling and EVAP diagnosis
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X
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X
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X
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Fuel tank
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Without fuel vapour recycling.
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X
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With fuel vapour recycling. Without EVAP diagnosis
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X
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X
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With fuel vapour recycling and EVAP diagnosis
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X
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X
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X
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Evaporative (EVAP) emission canister
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Without fuel vapour recycling.
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X
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With fuel vapour recycling
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X
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X
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X
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