EXHAUST AND EMISSION CONTROL
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 todays vehicles.
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.
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.
emissions that are considered major pollutants are as follows:
(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
of nitrogen (NOX ) 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.
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.