Vehicle Emission Control System for Compliance to Standards

Clean Air Act has set standards for Emission Control System of carbon monoxide, nitrogen oxides and hydrocarbons for new automobiles. Environmental Protection Agency (EPA) tests automobile models for compliance with Emission Control System standards. Environment Canada also conducts detailed inspection of vehicle exhaust systems, air intake and overall integrity so as to determine the efficiency of diesel emission control devices.

What is Emission Control System?

In automobiles, Emission Control System is employed to limit the discharge of noxious gases from the internal combustion engine and other sources. There are three main sources of hazardous emissions: the engine exhaust, crankcase and the fuel tank and carburetor. The engine exhaust discharges burned and unburned hydrocarbons, carbon monoxide, nitrogen oxides and sulfur including various acids, alcohols and phenols. The crankcase is a secondary source of unburned hydrocarbons and to a lesser extent carbon monoxide while the fuel tank and the carburetor are a minor but insignificant source of pollutants. Below are general descriptions of Emission Control Systems that are inspected for compliance.

-        Air injection system

-        Exhaust gas recirculation system

-        Positive crankcase ventilation system

-        Catalytic converter

-        Fuel evaporative system

-        Thermostatic air cleaner system

Air injection System

This is designed to introduce outside air into the exhaust stream to assist the burning of gases produced by the engine. Air is injected into the exhaust system, cylinder head and exhaust manifold or directly into the catalytic converter.

Exhaust gas recirculation system

This technology is designed to reduce nitric oxide emissions from an engine when the temperature in the combustion chamber rises to 2,500 degrees Fahrenheit. At this temperature nitrogen and oxygen will chemically combine to produce nitrogen oxides which are a major pollutant. Recirculation of a small amount of exhaust gases into the combustion chamber helps cool it down to reduce the production of nitrogen oxides.

Positive crankcase ventilation system

This Emission Control System is designed to draw untreated gases or raw and untreated pollutants from the crankcase and reintroduce them to the intake stream. Once they enter the intake stream, they can be burned by the combustion process or through the air injection system or catalytic converters.

Catalytic converter

This is so far the most effective and fuel efficient among Emission Control Systems on a vehicle. When exhaust gases pass the honeycomb structure a chemical reaction takes place. Platinum or palladium that coats the honeycomb speeds the change of hydrocarbons and carbon monoxide into water and carbon dioxide. In order to pass emission inspections, car owners think they can simply change the catalytic converter but it should only be replaced if it not working efficiently.

Fuel evaporative system

About 20% of hydrocarbon emissions are caused by the evaporation of fuel. A fuel evaporative system is designed to hold hydrocarbon vapors and introduce them into the engine to be burned.

Thermostatic air cleaner system

This Emission Control System regulates air temperature flow into the engine. It draws heated air from around the exhaust manifold during a cold engine start up and as the engine warms up to normal operating temperature, a valve changes position to allow cool air to enter the engine.