Carbon adsorber
The charcoal adsorber contains activated charcoal. In the manufacture of activated carbon, a special oxygen treatment technology is used. Oxygen treatment opens up millions of microchannels between carbon atoms, dramatically increasing the active surface of the carbon and its absorption capacity. After this treatment, the coal becomes «activated». In order for the North American vehicle to meet environmental requirements, its canister uses higher quality charcoal.
On-board fuel vapor recovery system for refueling
To comply with onboard EVAP requirements (ORVR) the design of the fuel tank and related elements minimizes the loss of fuel evaporation during refueling. To do this, the direct leakage of fuel vapors from the fuel tank into the atmosphere is blocked. Instead, fuel vapor is directed to the canister of the fuel vapor control system (EVAP) and are there until periodically occurring unloading into the intake manifold of the engine.
When the vehicle is refueled, the narrow fuel filler tube below the fuel rail area forms a vapor tight seal. A check valve, also located in the filler tube, opens in the direction of the fuel supply to prevent splashing.
As the fuel tank fills, fuel vapors are directed to the EVAP canister's carbon filter where they are adsorbed by activated carbon granules. Hydrocarbons from fuel vapors are retained in the adsorber, and only purified air is released into the atmosphere through the adsorber vent pipe. Hydrocarbons accumulating in the adsorber are periodically unloaded into the engine and burned in it.
The EVAP canister purge valve is located in the engine compartment. Engine control module (ECM) operates the valve and ensures that fuel vapors are discharged from the EVAP canister into the engine for combustion. Unloading intensity (purge valve opening) determined by the operating conditions of the engine. The intensity of the discharge of vapors is adjusted to maintain optimal dynamic performance of the engine and exhaust toxicity. The following engine operating conditions affect the unloading intensity:
- crankshaft speed and load
- engine coolant temperature
- time elapsed since engine start
- closed loop refueling
Since the capacity of the EVAP canister is limited:
- NAS derivative - 2.5 L
- derived version of ROW - 0.7 l
- the carbon filter is constantly regenerated
Regeneration occurs while the engine is running: air is pumped through the EVAP canister and vent line, enters the engine, and is burned.
Fuel tank leak monitoring
Fuel tank leak monitoring is required by law in NAS vehicles. The monitoring system periodically checks the EVAP system and fuel system for leaks when the ignition is off.
The monitoring system includes the previously described elements of the EVAP system and the following additional elements:
- air pump
- dust filter
The pump is connected to the EVAP canister vent line and includes:
- PTC heating element (with a positive temperature coefficient)
- switching valve
- measuring diaphragm
The pump only works when the ignition is off, controlled by the ECM. In addition, the ECM monitors the operation of the pump and the switching valve for faults. The dust filter protects the pump from the ingress of moisture and foreign particles.
Fuel tank leak monitoring is performed under the following conditions:
- the engine has been running for at least 10 minutes and is currently not running
- fuel tank fill volume is between 15 and 85 percent
- outdoor temperature above 0°C (32°F) and below 40°C (104°F)
- the engine has not been started for at least 3 hours before the last cycle of operation
The pump raises the pressure in the fuel tank, the electric current that makes the pump work is measured by the switching valve in various states. Comparison of the current selection in each of the states indicates the intensity of fuel leakage; if necessary, the ECM sets the appropriate DTC (DTC).
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