An emission system helps control gas fumes and cleans the air
Emission control systems or EVAP system as there are called have been
incorporated into automobiles to prevent pollution by limiting the amount of
un-burnt and evaporated gases into the atmosphere. These systems have been
efficient in reducing the air pollution caused by automobiles to a large extent.
Increased engine efficiency and lighter vehicle construction has also
contributed to help reduce emissions. Air pollution gases produced
by cars consist of carbon monoxide, hydrocarbons, carbon dioxide and nitrogen
oxide. Tailpipe emissions are measured in parts per million or PPM.
What Goes Wrong?
The emission system depends on a series of chemical reactions, sensors and
vacuum control solenoids to operate correctly. In time chemical
reactions fade as the device loses its effectiveness and rubber hoses can
deteriorate causing leaks in the sealed EVAP system. Either of these failures
cause a check engine light to come on
How Does It Work?
1. Charcoal Canister
A charcoal canister is a device that is filled with a fume absorbing material
that has the ability to condensate gas fumes gathered from inside the gas tank. Once
condensed the fumes are turned back into liquid fuel and transferred back into
the tank. This canister is usually located at the rear of the car near the fuel
tank and is constructed of plastic.
2. Oxygen Sensor
is designed to monitor engine exhaust gases and send this
information to the
main computer PCM
so adjustments can be made to the fuel mixture controlling
un-burnt fuel. Because these sensors are
emerged in hot exhaust gases they have a high failure rate and
to keep the system working correctly.
3. EVAP Control Solenoid
An EVAP solenoid
is controlled by the main engine computer and located near the intake manifold.
This solenoid is connected to the charcoal canister using a vacuum hose to draw raw gas vapor from the fuel tank
and into the charcoal canister.
4. Catalytic Converter
is designed to convert partially burned gases to completely
burned gases. This is done when the converter becomes hot unitizing a thermo
reaction due to the catalyst material inside the unit. Some cars use an electric air pump
which injects air into the exhaust system just after the exhaust ports of the
to help heat up the catalyst and optimize efficiency.
5. Mass Air Flow Sensor
mass air flow sensor
monitors airflow that enters the engine by measuring
resistance across a hot wire that is cooled when different amounts of air pass
over it. This feedback data trim adjustments to further help clean emission
outputs by not allowing excess fuel to enter the engine during excessive
6. Gas Cap
A gas cap seals liquid fuel and fumed gases from escaping the fuel tank. This
cap is designed with an automatic tightening mechanism to support the minimum
tension the cap must be installed at while sealing against the tank filler neck using an O ring
7. EGR Valve
An EGR valve stands for exhaust gas recirculation which is use to allow engine exhaust to enter the intake manifold.
This recalculation cools combustion temperatures and lowers emissions. Many cars have done
away with this valve by being able to
control valve timing
which achieves the
same objective. An EGR valve is used is to lower KNOX (NO2) gases which occur
when the combustion chamber
temperature reaches over 3500°.
Got any Questions?
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emission system questions
, please visit our forum. If you need
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Article first published 2017-06-27