Emission Control Systems: Description and Operation

Various emission control systems are used in modern automobiles to help reduce the amount of harmful pollutants released into the atmosphere. These systems can be grouped into four general categories:

1. Crankcase emission controls, which provide a means of venting the
excessive blow-by gases and oil vapors from the crankcase, without
releasing them into the atmosphere. This is accomplished by directing
the vented gases through the intake system, where they can be burned
again, and expelled through the exhaust system.

2. Evaporative control systems, which prevents raw fuel vapors (hydro
carbons) from escaping into the atmosphere from the fuel tank and fuel
system. Fuel vapors are collected and returned to the fuel system, or
directed into the intake system for combustion.

3. Exhaust emission controls, which help to convert some of the
pollutants, present in the exhaust system, into non-poisonous compounds.

4. Combustion control systems, which help control conditions within
the combustion chamber, keeping them as close to ideal as possible,
promoting complete burning of fuel at reduced combustion temperatures.

The following systems are commonly used on pollution controlled motor vehicles.
CATEGORY 1:
Positive Crankcase Ventilation (PCV)
CATEGORY 2:
Evaporative control system (ECS)
CATEGORY 3:
Air Injection Reactor system (AIR)
Three Way Catalyst (TWC)
CATEGORY 4:
Early Fuel Evaporation system (EFE)
Exhaust Gas Recirculation (EGR)
Temperature Controlled Air Cleaner (TCA)
Computerized Engine Control Systems (CEC) [*]

[*] There are many types of computerized engine control systems available from the different automobile manufacturers, and although they all perform similar functions, they operate differently. The one common attribute is that they all incorporate the use of an "Oxygen Sensor" to monitor the concentration of Oxygen in the exhaust gases, and use this information, compared with information stored in the computers memory, to regulate the fuel system, and in some cases, the ignition and other emission control systems.