CATALYTIC CONVERTERS

Catalytic Converters: Last month we saw the role of the EGR and how it reduces the harmful effects of exhaust gases. Continuing with emission issues, we'll now focus on catalytic converters, a key factor in significant changes occurring in exhaust systems. A development which was initiated in the early seventies, manufacturers realised that besides controlling emissions converters also muffled exhaust note.

A catalytic converter is located ahead of the muffler unit. Extreme heat inside the cat-con oxidises exhaust gases. The catalysts in the cat-con bring about a chemical change in the elements of the exhaust gases converting them to harmless exhaust vapours.

Different catalysts have different effects on pollutants like palladium or platinum which react with HC and CO to form water and carbon dioxide, whereas metal rhodium reduces NOx to harmless nitrogen and oxygen.

Reactions within the catalyst produce additional heat that reaches temperatures of 900O which is required for the catalyst to operate at complete efficiency. To safeguard the underbody from these high temperatures, the catalytic converter is made of stainless steel and special heat shields are also used.

Types of catalytic converters: The two basic types of catalytic converters used in modern cars are the two-way and three-way types, which both employ a monolith or pellet design. Monolith cat-cons use catalysts shaped in the form of a honeycomb while the pellet design uses pellets as catalyst.

A two-way cat-con uses only platinum and palladium as catalysts to reduce hydrocarbons and carbon monoxide and does not reduce nitrogen oxide. The three-way catalytic converter reduces nitrogen oxide in addition to hydrocarbons and carbon monoxide.

Precautionary measures: One must take care to use only unleaded petrol with catalytic converters as the lead in leaded fuels hampers effectiveness of the catalytic converter. The engine must also be properly tuned as misfiring causes the cat-con to overheat. Even prolonged idling with the spark plug wires removed damage to the cat-con.

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