Emissions control systems are used in the automobile industry in reference to a mechanisms put in place to limit discharge of noxious gases from the internal combustion engine or other components. The gases are called evaporative emissions and are generally released when gasoline slowly evaporates in the fuel tank and the fuel lines. These gases can come from 3 sources;
1. The exhaust pipe – the engine exhaust discharges both burned and unburned hydrocarbons, nitrogen oxides, carbon monoxide and oxides of sulfur as well as minor traces of several acids, phenols and alcohols.
2. The crankcase – this is only second to the engine exhaust in discharge of unburned hydrocarbons. It also emits carbon monoxide to a lesser extent.
3. The fuel tank and carburetor (for older automobiles) – these discharge minor but significant quantities of hydrocarbons.
The fuel used in automobiles usually contains up to 150 chemicals most of which are harmful if inhaled. These chemicals can cause dizziness, headaches, breathing complications and even death if inhaled in large amounts. For these reasons, all cars are required by law to be fitted with emission control systems also known as evaporative (EVAP) emission systems. The main function of EVAP systems is to 1.) Store and 2.) Dispose of the harmful vapors before they can be released into the air/atmosphere.
How emissions control systems work
An EVAP system typically comprises a small canister filled with charcoal, hoses and valves with vents lining up the fuel lines and a fuel tank cap that is completely sealed. With this arrangement, excess vapors coming from a fuel tank are moved to the canister where they are stored until it is deemed safe to move them back to the car engine. Once back in the engine, they are combusted in the fuel + air mixture.
The re-circulated exhaust gases usually lower the temperature of the combustion process, a condition that helps in cutting on the production of nitrogen oxide as a byproduct. A major drawback of this re-circulation process, however is that it lowers the efficiency of the engine. This is because a large percentage of the re-introduced pollutants are burned with no additional power generated.
Valves help develop a vacuum in the engine while the vents with the help of the valves serve to draw fresh air into the engine. EVAP systems can be controlled either mechanically or by use of engine computers.
Finally, EVAP systems just like any other human made system can go wrong. Sometimes a canister may fail to purge, sometimes it purges but in the wrong conditions interfering with the emissions and consequently with the performance of the car. In such circumstances, the entire emissions control system has to be replaced.