Emission Control Systems: Description and Operation

EMISSION BI-PRODUCTS
The three types of emission bi-products being controlled in gasoline engines are:

1. Hydrocarbons
These are particles, usually vapors, of gasoline that have not been fully burned. They are present in tailpipe emissions and crankcase vapors. Raw gas that evaporates from the tank or throttle body is considered an HC.

2. Carbon Monoxide
Carbon Monoxide (CO) is a poisonous chemical bi-product from the burning of fuel and air (carbon, in gasoline, and oxygen in the atmosphere). It forms in the engine when the burning of air/fuel (combustion) is less than complete. CO is measured at the tailpipe and is a bi-product of combustion, but traces of CO may also be found in the crankcase.

3. Oxides Of Nitrogen
Various compounds of nitrogen and oxygen, both present in the air, used for combustion, are formed in the combustion chamber during excessively high engine temperatures, and are part of the tailpipe emissions. They become part of the tailpipe emissions if not reduced by the EGR, Spark Timing, or Catalytic Converter systems.

EMISSIONS CONTROL SYSTEMS
This vehicle is equipped with the following system emissions control components:

Positive Crankcase Ventilation ([1][2]PCV)
The PCV system removes gases that "blow by" the pistons into the crankcase. These gases are recirculated into the induction system.

Three Way Catalytic Converter (TWC)
The three way catalyst reduces NOx as well as HC and CO.

Evaporative Emissions (EVAP) Control System
The evaporative emissions control system traps HC emissions from the fuel tank in a charcoal cannister and purges the fuel vapors into the intake manifold during specific engine operating conditions.

Exhaust Gas Recirculation (EGR)
EGR is strictly a control for NOx within the exhaust gases. It reduces NOx by diluting the air/fuel mixture with inert exhaust gases. This reduces peak combustion chamber temperatures to limit NOx formation.