EXHAUST AND EMISSION CONTROL SYSTEMS

LEARNING OBJECTIVE: Identify components of the exhaust and emission control systems. Describe the operation of the exhaust and emission control systems.

Over the past several years, exhaust and emission control has greatly increased because of stringent antipollution laws and EPA guidelines. This has made the exhaust and emission control systems of vehicles invaluable and a vital part of today’s vehicles.

The waste products of combustion are carried away from the engine to the rear of the vehicle by the exhaust system where they are expelled to the atmosphere. The exhaust system also serves to dampen engine noise. The parts of a typical exhaust system include the following: exhaust manifold, header pipe, catalytic converter, intermediate pipe, muffler, tailpipe, hangers, heat shields, and muffler clamps.

The control of exhaust emissions is a difficult job. The ideal situation would be to have the fuel combine completely with the oxygen from the intake air. The carbon would then combine with the oxygen to form carbon dioxide (CO₂ ); the hydrogen would combine to form water (HO); and the nitrogen present in the intake would stand alone. The only other product present in the exhaust would be oxygen from the intake air that was not used in the burning of the fuel. In a real life situation, however, this is not what happens. The fuel never combines completely with the oxygen, and undesirable exhaust emissions are created as a result.

The most dangerous of the emissions is carbon monoxide (CO) which is a poisonous gas that is colorless and odorless. CO is formed as a result of insufficient oxygen in the combustion mixture and combustion chamber temperatures that are too low.

Other exhaust emissions that are considered major pollutants are as follows:

• Hydrocarbons (HC) are unburned fuel. They are particulate (solid) in form, and, like carbon monoxide, they are manufactured by insufficient oxygen in the combustion mixture and combustion chamber temperatures that are too low. Hydrocarbons are harmful to all living things. In any urban area where vehicular traffic is heavy, hydrocarbons in heavy concentrations react with the sunlight to produce a brown fog, known as photochemical smog.
• Oxides of nitrogen (NO_X ) are formed when nitrogen and oxygen in the intake air combine when subjected to high temperatures of combustion. Oxides of nitrogen are harmful to all living things.

The temperatures of the combustion chamber would have to be raised to a point that would melt pistons and valves to eliminate carbon monoxide and carbon dioxide emissions. This is compounded with the fact that oxides of nitrogen emissions go up with any increase in the combustion chamber temperature. Knowing these facts, it can be seen that emission control devices are necessary.