This document discusses methods for controlling vehicle emissions, including thermal converters and catalytic converters. It explains that thermal converters promote the oxidation of carbon monoxide and hydrocarbons by keeping exhaust gases above 600-700°C. Catalytic converters contain platinum, palladium, or rhodium, which accelerate chemical reactions to convert carbon monoxide, hydrocarbons, and nitrogen oxides in exhaust into less harmful emissions like carbon dioxide and water vapor. Particulate traps are also used to reduce particulate emissions from diesel engines.

2. IT IS KNOWN THAT THE CAUSE OF SMOKE IS INCOMPLETE
BURNING OF FUEL INSIDE THE COMBUSTION CHAMBER.THE
TWO MAJOR REASONS FOR INCOMPLETE COMBUSTION ARE,
 INCORRECT AIR FUEL RATIO
 IMPROPER MIXING
THE FOLLOWING ARE THE FACTORS RESULTS SMOKE,
o INJECTION SYSTEM
o LOAD
o FUEL
o FUEL-AIR RATIO
o ENGINE TYPE AND SPEED
o MAINTENANCE

3. EMISSION CONTROL METHODS
 Thermal converters
 Catalytic converters
 Particulate traps

4. THERMAL CONVERTER
• These are essentially enlarged exhaust manifolds connected
to the exhaust ports, to minimize heat losses and keep the
exhaust gas from cooling to non reacting temp.
• They promote oxidation of the CO&HC .
• For the CO,
CO+1/2O2 CO2
• For the above reaction to occur at a useful rate, the temp.
must be held above 700°C.
• For HC,
CxHy+ZO2 xCO2+1/2yH2O
where, Z=x+1/4y
• the above reaction needs a temp. above 600°C for at least
50msec to substantially reduce HC.
• Nox emissions cannot be reduced using a thermal converter.

5. Used in CI engines in their exhaust flow to reduce the amount of particulates
released to the atmosphere.
Made of ceramic, in the form of monolith or else made of metal wire mesh.
Remove 60 to 90 percentage of particulates
As trap catch soot they slowly get filled up and resist exhaust gas flow and
raise back pressure.
High back pressure causes engine to run hotter and increase fuel consumption
To reduce this, regeneration is done.

7.  They are chambers mounted in the flow system through which the exhaust
gases pass through.
 These chambers contain catalytic material which promotes the oxidation of
the emissions contained in the exhaust flow.
 They are usually a stainless steel container mounted somewhere along the
exhaust pipe.
 Inside the container is a porous ceramic structure through which the
exhaust gas flows.
 Its volume is half the displacement volume of the engine.
 Alumina is the base ceramic material used. It can withstand high
temperatures, remains chemically neutral, very low thermal expansion &
does not thermally degrade with age.
 CO and HC can be oxidized to CO2 and H2O.

10.  A catalyst is a substance that accelerates a chemical reaction by lowering
the energy needed for it to proceed.
 Most commonly used catalyst materials are platinum, palladium &
rhodium.
 Palladium & platinum promote the oxidation of CO & HC.
 Rhodium promotes the reaction of NOx in one or more of the following
reactions.
 NO + CO ½ N2 + CO2
 2NO + 5CO + 3H2O 2NH3 + 5CO2
 2NO + CO N2O + CO2
 NO + H2 ½ N2 + H2O
 2NO + H2 N2O + H2O
 CO + H2O CO2 + H2

11.  Some catalysts promote the conversion of SO2 to SO3, which
eventually gets converted into sulphuric acid. This degrades the
catalytic converter.
 New catalysts are being developed that promote the oxydation
of HC & CO, but do not change SO2 into SO3.