Emission Control Systems: Description and Operation

Emission Control System:

SYSTEM OPERATION

For reduced CO, HC, and NOx emissions, there are many emission control systems as shown in the figure.

1. Air injection system (AIS).
This system helps continue combustion of spent exhaust gases by introducing fresh air into the exhaust port or main converter.
2. Positive crankcase ventilation (PCV).
When the engine is running at idle, the purge control valve is opened slightly and a small amount of blow-by gas is drawn into the combustion chamber. At high engine speed or heavy-load conditions, the purge control valve is further opened and a larger amount of blow-by gas is drawn into the combustion chamber.
3. Evaporative emission control system (EVAP)
This system takes fuel vapors generated by the fuel in the fuel tank and stores them in a charcoal cannister while the engine is not running. The fuel vapor is stored in the cannister until it is drawn into the combustion chamber by intake manifold vacuum and burned when the engine is running.
4. Catalytic converter (TWC).
There are two three-way catalytic converters used to reduce CO, HC, and NOx emissions. They reduce CO and HC through oxidation and NOx by chemical reaction.