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The Emission Control System:
Evaporation Emissions Control System (EVAP)
Fuel Tank and Gas Cap Re-Design Help Reduce Emissions
On most cars, the fuel tank has been redesigned to include added space at the top of the tank. The added “air dome” is where fuel vapors can collect without dramatically increasing the internal fuel tank pressure.  But if you’ve ever filled up you gas tank after driving on empty you likely heard the escape of fuel vapors as you opened the cap. Years ago you would have been less likely to hear that noise because gas caps allowed vapors to escape into the atmosphere. Newer caps create an airtight seal and help force vapors down a vent line to a charcoal canister. The vapor recovery line connects the fuel tank to the charcoal canister.
When the engine is shut off, fuel vapors again collect in the charcoal canister until they are again ready to be used.
 During normal operation, fuel vapors can develop as the result of an increase in temperature inside the fuel tank or after the engine is turned off, excess fuel vapors not burned during the combustion process can collect inside the fuel line . In the past, vehicles manufactured before EVAP systems became standard, were frequently designed to vent fuel vapors directly into the atmosphere from both the gas cap and carburetor .
Evaporation Emissions Control devices are designed to function as a closed loop recycling system to prevent fuel vapors from leaking into the atmosphere. Fuel vapors directly contribute to increased levels of hydrocarbon emissions. To reduce harmful emissions, EVAP systems have become increasingly efficient. The result has be a gradual increase in fuel efficiency and the reduction of emissions.
 To recycle fuel vapors, they must be collected and stored in a way that makes them relatively easy to re-introduce into the combustion process.
At the center of the EVAP system is a canister chocked-full of activated charcoal. Activated charcoal is basically the same stuff used in most odor-eater shoe inserts and the concept works just about the same.
 Both shoe inserts and our charcoal canister take advantage of charcoal's ability to readily absorb vapors. As fuel molecules heat and vaporize, they travel down a re-cycling tube and enter the canister through a one-way valve. Another tube on the other side of the canister is connected to the intake manifold.
When the engine starts, a powerful vacuum draws fuel vapor that had collected in the activated charcoal through a connecting tube and into the intake manifold. |
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1. Emission Control
2. Types Of Pollutants Created By Your Engine
3. 6 Ways In Which Emissions Are Reduced
4. Exhaust Gas Recirculation (EGR)
5. Air Injection And Catalytic Converter
7. Positive Crankcase Ventilation (PCV)
8. Automotive Emissions Wrap Up
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