Emission Control Systems: Description and Operation
Emission Controls began in the early 1960's, due to the alarm of the decreasing quality in the atmospheres air we breathe.
Photochemical-Smog is the main by-product of tailpipe emissions, and is produced when Hydrocarbons and Oxides of Nitrogen are mixed and exposed to sunlight. This type of pollution was first noticed in the 1940's. As the pollutants increased both in intensity and frequency, it posed more of a problem. California took the lead in combating Smog by becoming the first state to place controls on motor vehicle emissions. As Smog began to appear in other parts of the country, the Federal Government became active in the area of Regulations and Control.
Vehicle manufacturers are now developing and producing more sophisticated components to help reduce the level of harmful exhaust pollutants. Fuel and ignition systems have also been modified to help in this effort. Since the introduction of electronic Fuel Injection and Computerized Engine Controls, today's vehicles are producing less emissions and better fuel economy, while maintaining performance and power.
HYDROCARBONS or HC
A chemical compound made up of Hydrogen and Carbon molecules. Hydrocarbons, a major pollutant given off by an automobile, are mostly unburned portions of fuel or raw fuel (gasoline). Hydrocarbons are the only major automotive air pollutant that can come from sources other than the engine's exhaust. While the majority of HCs are produced by the evaporation from the fuel system (20%) and the engines exhaust (60%), another source is the oil and gasoline fumes/vapors within the crankcase.
CARBON MONOXIDE or CO
Is a chemical compound of gasoline and oxygen and is an odorless colorless poisonous gas. It is formed when the combustion process is less than complete, due to an improper air/fuel mixture ratio, or poorly tuned engine. CO is measured primarily at the tailpipe, but may also escape into the crankcase in the form of blow-by gases.
OXIDES OF NITROGEN or NOx
Is a chemical compound of Nitrogen and Oxygen, both present in atmospheric air. NOx forms during the combustion process when engine temperatures become excessively high. Oxides of Nitrogen is the major contributor to Photochemical-Smog, but is very difficult to measure from the tailpipe.
CRANKCASE EMISSIONS CONTROL
Beginning with 1961 new model vehicles, California Legislature required control over crankcase emissions. This control became standard for the rest of the United States with 1963 new model vehicles. The control was accomplished through a Positive Crankcase Ventilation (PCV) Valve. The Valve is designed to eliminate the emission of fumes, vapors, and blow-by gases from the crankcase into the atmosphere. The crankcase is vented through hoses to the air cleaner.
Fresh air from the air cleaner is drawn in to be mixed with the blow-by gases in the crankcase. When the PCV Valve opens, the mixture is then routed from the crankcase, through the PCV Valve, and into the combustion chamber to be reburned.
AIR INJECTION/CATALYTIC CONVERTERS
The Air Injection Systems originated in the mid 1960's. This system is designed to put fresh air into the exhaust stream to help reduce the Hydrocarbons and the Carbon Monoxide level.
The additional oxygen, combined with the heat of the exhaust manifold, causes the excess HC and CO to be converted to water vapor (H2O) and Carbon Dioxide (CO2) through chemical reaction.
In the 1970's catalytic converters were introduced as another alternative to help in reducing HC and CO emissions. Later the three-way catalytic converter was developed which reduces NOx as well as HC and CO.
EVAPORATIVE EMISSION CONTROL
Evaporative Emission Controls (EEC or EVAP) were first used in the 1960's. After the EVAP System was refined to a "sealed housing" in 1970, vehicles bought or sold in the state of California were required to be equipped with a working EVAP System. This requirement was extended to the rest of the Nation with the 1971 model vehicles.
The purpose of the EEC system is to trap gasoline vapors (Hydrocarbons) that would otherwise escape into the atmosphere. The vapors are vented from the fuel tank into a charcoal canister for storage. Once the engine is running and has reached operating temperature, the vapors are purged from the canister and routed into the intake manifold. The fuel vapors become part of the intake air/fuel mixture and are consumed during the combustion process.
EXHAUST GAS RECIRCULATION
The EGR System is designed to control Oxides of Nitrogen (NOx), by diluting the air/fuel mixture with exhaust gas. At specific engine operating modes a small portion of exhaust gases are recirculated into the induction system. Since exhaust gases do not contain the needed oxygen for the combustion process, the air/fuel ratio becomes less by volume. This lowers peak combustion temperatures, which prevent the formation of NOx.
ENGINE DESIGN/IMPROVED COMBUSTION SYSTEM (IMCO)
Starting in the 1960's a group of engine modifications were designed to improve combustion and reduce HC and CO in the exhaust. It included a heated primary air system, carburetor design changes, fuel injection, engine "breathing" refinements and spark timing controls.