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 feedback control system is used to alter the air/fuel mixture to compensate for changes in the operating conditions (altitude, temperature, state of tune, etc). A 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 air injection system is used to allow fuel that did not burn during the power stroke to continue burning in the exhaust manifold. This is accomplished by introducing fresh air near the exhaust valve, thus giving the fuel more oxygen to burn with.
The anti-afterburn system is used to prevent excessive amounts of fuel from being dumped into the engine during deceleration or downshifting. This system allows extra air into the intake manifold during times of high manifold vacuum.
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.