Evaporative Emissions System: Description and Operation

EVAPORATIVE & ORVR EMISSION CONTROL SYSTEM DESCRIPTION
On-Board Refueling Vapor Recovery (ORVR) system is properly designed to prevent the fuel tank vapor (HC) emission during refueling at the gas station.

This system consists of fuel vent valve (ORVR), fuel shut-off valve, fuel cut valve (roll over), two way valve (pressure/vacuum relief), fuel liquid/vapor separator which is installed beside the filler pipe, charcoal canister which is mounted under the rear floor LH side member with protector, tubes and miscellaneous connections.

While refueling, the flow and column of the refueling draws the ambient air into the filler pipe so as not to emit fuel vapor in the air. The fuel vapor in the tank is then forced to flow into the canister via the fill vent valve and the fuel liquid/vapor separator which isolates liquid fuel ingredient and transfers the pure vapor to the carbon canister.

While the engine is operating, the trapped vapor emission in the canister is drawn and fed by the intake manifold vacuum into the engine combustion chamber. According to this purge process, the carbon canister is purged and recovers its adsorbing capability.


EVAPORATIVE CONTROL SYSTEM
The evaporation control system prevents the emission of fuel tank vapor into the atmosphere. When fuel evaporates in the fuel tank, the vapors pass through vent hoses or tubes to a charcoal filled evaporative canister. The canister temporarily holds the vapors. The ECM allows intake manifold vacuum to draw vapors into the combustion chambers during certain operating conditions.

Fuel tank
The fuel tank is located under the rear of the vehicle. The fuel pump, fuel level sending unit and fuel tank pressure sensor are installed on the upper part of the fuel tank.

Fuel filler cap
A ratchet tightening device on the threaded fuel filler cap reduces the chances of incorrect installation, which would prevent sealing fuel vapors. After the gasket on the fuel filler cap and the fill neck flange contact each other, the ratchet produces a loud clicking noise indicating the seal has been set.

Evaporative emissions canister
The EVAP canister is filled with granules of an activated carbon mixture. Fuel vapors enter into the EVAP canister are absorbed by the charcoal granules. Fuel tank pressure vents into the EVAP canister and are temporarily held in the canister until they can be drawn into the intake manifold.

Canister close valve
The Canister Close Valve (CCV) closes off the air inlet to the Evaporative Emissions Canister for the Evaporative Emissions System leak detection inspection function. The CCV also prevents fuel vapors from escaping from the Evaporative Emissions Canister when the vehicle is not operating.

Purge solenoid valve
This valve is actuated by the purge control signal from the ECM and controls fuel vapor from the EVAP Canister to the intake manifold.

Fuel tank pressure sensor
The Fuel Tank Pressure Sensor (FTPS) is an integral part of the monitoring system. The FTPS checks Purge Solenoid Valve operation and leak detection in the Evaporative Emissions System by monitoring pressure and vacuum levels in the fuel tank during and between Purge Solenoid Valve operating cycles.