Diesel Catalytic Converters as Emission Control Devices.

INTRODUCTION:
Internal combustion engines are devices that generate work from
combustion reactions. Combustion products under high pressure produce
work by expansion through a turbine or piston. The combustion reactions
inside these engines are not necessarily neutralizing or complete and air
pollutants are produced.
There are three major types of internal combustion engine(1) in use today:
1) the spark ignition engine, which is used primarily in automobiles; 2) the
diesel engine, which is used in large vehicles and industrial systems where
cycle efficiency offers advantages over the more compact and lighter-weight
spark ignition engine and; 3) the gas turbine, which is used in aircraft due to
its high power/weight ratio and is also used for stationary power generation.
Each of these types of engine is an important source of atmospheric
pollutants. Automobiles are the one of the major source of carbon monoxide,
unburned hydrocarbons, and nitrogen oxides. Probably more than any other
combustion system, the design of automobile engines is now being guided by
requirements to reduce emissions of these pollutants. While substantial
progress has been made in emission reduction, automobiles remain important
sources of air pollutants.
2
In order to reduce emissions, modern cars have been designed to carefully
control the amount of fuel they burn. The goal is to keep the air-to-fuel ratio
very close to the “stoichiometric” point, which is the calculated ideal ratio of
air to fuel. Theoretically, at this ratio, all of the fuel will be burned using all of
the oxygen in the air. [The stoichiometric ratio is about 14.7 to 1, meaning
that for each Kilogram of fuel, 14.7 Kilogram of air will be burned. The fuel
mixture actually varies from the ideal ratio quite a bit during driving.
Sometimes the mixture can be “lean” (an air-to-fuel ratio higher than 14.7);
and other times the mixture can be “rich” (an air-to-fuel ratio lower than
14.7).]

Diesel Catalytic Converters as Emission Control Devices.