Emission Control Systems: Description and Operation

These vehicles are equipped with emission control systems to reduce the various pollutants produced as either a byproduct of combustion or by evaporation.
The oxygen sensor system is used to alter the air/fuel mixture to compensate for changes in the operating conditions (altitude, temperature, state of tune, etc). The fuel injection system control unit uses an exhaust gas oxygen sensor and other inputs to determine the outputs necessary to maintain the fuel mixture within a vary narrow operating range. This minimizes the production of unwanted pollutants as well as keeping the catalytic converter operating at peak efficiency.
To prevent the introduction of leaded fuel into the system, a fillpipe restrictor is installed. This prevents the larger diameter fuel nozzles used for leaded fuel from entering the fillpipe. Leaded fuel will permanently contaminate the oxygen sensor and the catalytic converter.
To reduce the formation of oxides of nitrogen (known as NOx) during the combustion process, inert exhaust gasses are re-introduced into the combustion chambers by the EGR system.
The emissions created by the evaporation of raw fuel is controlled by the use of a closed ventilation system for the fuel tank, and a canister filled with activated charcoal to capture the fuel vapors. The charcoal canister captures and stores the vapors as they expand. When the engine is started, a valve is opened allowing the engine to draw air through the charcoal canister thereby also drawing in and burning the stored fuel vapors.
Some products of combustion escape past the piston rings. These are known as 'blowby'. These various gasses and contaminants are drawn into the engine by the PCV system, and burned during normal running.