Carbon adsorber
The carbon adsorber contains activated charcoal. Activated charcoal is made using a special oxygen treatment technology. Oxygen treatment opens up millions of microchannels between carbon atoms, dramatically increasing the active surface area of the charcoal and its absorption capacity. After this treatment, the charcoal becomes "activated." To ensure that the North American vehicle meets environmental requirements, higher quality charcoal is used in its adsorber.
On-board fuel vapor regeneration system during refueling
To comply with On-Board Evaporative Removal (ORVR) requirements, the fuel tank and associated components are designed to minimize fuel evaporation losses during refueling. This is accomplished by blocking direct fuel vapor leakage from the fuel tank into the atmosphere. Instead, the fuel vapor is directed to the EVAP canister and stored there until periodically discharged into the engine intake manifold.
When refueling the vehicle, the narrow filler neck tube of the fuel tank, located below the fuel distribution pipe area, forms a hermetic seal that does not allow vapors to pass through. A control valve, also located in the filler neck tube, opens in the direction of fuel supply, preventing splashes.
As the fuel tank fills, fuel vapors are directed to the EVAP canister carbon filter, where they are adsorbed by activated carbon granules. Hydrocarbons from the fuel vapors are trapped in the canister, and only purified air is released into the atmosphere through the canister vent line. Hydrocarbons that accumulate in the canister are periodically discharged into the engine and burned in it.
The EVAP canister purge valve is located in the engine compartment. The engine control module (ECM) controls the valve and ensures that fuel vapor is discharged from the EVAP canister into the engine for combustion. The discharge rate (the amount the purge valve opens) is determined by engine operating conditions. The vapor discharge rate is adjusted to maintain optimum engine performance and exhaust toxicity. The following engine operating conditions affect the discharge rate:
- crankshaft speed and load
- engine coolant temperature
- time elapsed since engine start
- closed circuit fueling
Since the capacity of the EVAP canister is limited:
- nAS derivative - 2.5 L
- derivative version ROW - 0.7 l
- the carbon filter is constantly regenerated
Regeneration occurs with the engine running: air is pumped through the EVAP canister and ventilation pipe, 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 and fuel systems for leaks when the ignition is off.
The monitoring system includes the previously described EVAP system elements and the following additional elements:
(Details can be found on the website LRman.ru)
- air pump
- dust filter
The pump is connected to the EVAP canister vent line and includes:
- pTC (positive temperature coefficient) heating element
- switching valve
- measuring diaphragm
The pump operates only when the ignition is off, under the control of the ECM. In addition, the ECM monitors the operation of the pump and the switching valve, controlling malfunctions. A dust filter protects the pump from 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
- the filling volume of the fuel tank ranges from 15 to 85 percent
- outside air temperature above 0°C (32°F) and below 40°C (104°F)
- the engine has not been started for at least 3 hours prior to the last run cycle
The pump increases the pressure in the fuel tank, the electric current that ensures the pump operation is measured by the switching valve in different states. Comparison of the current selection in each of the states indicates the intensity of fuel leaks; if necessary, the ECM records an appropriate diagnostic trouble code (DTC).
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