SUBJECT :- THERMAL ENGG.- II

SEMINAR ONCATALYTIC CONVERTOR FOR

SI ENGINE

SUBMITTED BY:- SUMIT WAGHBRANCH :- HEAT POWER ENGINEERING

What is Catalytic Convertor

A catalytic converter is an emissions control device that converts toxic pollutants in exhaust gas to less toxic pollutants by catalyzing a redox reaction (oxidation or reduction).

Catalytic converters are used with internal combustion engines fueled by either petrol (gasoline) or diesel including lean-burn engines as well as kerosene heaters and stoves

Catalyst is a substance that increase rate of chemical reaction without itself undergoing any permanent chemical change.

Brief History of the Catalytic Converter

The catalytic converter was first invented by Eugene Houdry in the 1950’s.

Tetra-ethyl lead present in gasoline "poisoned" the converter by forming a coating on the catalyst's surface, effectively disabling it.

The catalytic converter was further developed by John J. Mooney and Carl D. Keith at the Engelhard Corporation, creating the first production catalytic converter in 1973.

Types of Catalytic Converters.

Two Way Catalytic Converter

A two-way catalytic converter has two simultaneous tasks.

Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2

Oxidation of unburnt hydrocarbons (unburnt and partially-burnt fuel) to carbon dioxide and water: CxH(2x+2) + [(3x+1)/2] O2 → xCO2 + (x+1) H2O

(a combustion reaction)Unable to control NOx gases.

Three Way Catalytic Converter

Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2

Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2

Unwanted reactions can occur in the three-way catalyst, such as the formation of odiferous hydrogen sulfide and ammonia.

Anatomy of Catalytic Converter for SI Engines

All catalytic converters are built in a honeycomb or pellet geometry to expose the exhaust gases to a large surface made of one or more noble metals: platinum, palladium and rhodium.

Rhodium used to remove NO and platinum used to remove HC and CO.

Lead and sulfur in the exhaust gas severely inhibit the operation of a catalytic converter (poison).

Catalytic Convertor

The honey-comb surface increases the amount of surface area available to support the catalyst, and therefore is often called a catalyst support.

A washcoat is used to make converters more efficient, often as a mixture of silica and alumina.

Platinum is the most active catalyst & is widely used.Platinum and palladium are used as an oxidization

catalyst.Platinum & Rhodium are used as a reduction catalystCerium, iron, manganese and nickel are also used.

Uses of Catalytic Converter

A catalytic converter is a device used to reduce the toxicity of emissions from an internal combustion engine.

Catalytic converters are most commonly used in motor vehicle exhaust systems.

Catalytic converters are also used on generator sets, forklifts, mining equipment, trucks, buses, trains, and other engine-equipped machines.

A catalytic converter provides an environment for a chemical reaction wherein toxic combustion by-products are converted to less-toxic substances.

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