Catalytic Converter: Description and Operation

Fig. 9 Catalytic converter:

Fig. 10 Fuel tank filler safety neck.:

Fig. 11 Mini catalytic converters:

The catalytic converter serves two purposes: it permits a faster chemical reaction to take place and although it enters into the chemical reaction, it remains the same, ready to repeat the process. The catalytic converter combines hydrocarbons (HC) and carbon monoxide (CO) with oxygen to form water and carbon dioxide.

The catalyst is structured in the form of a honeycomb monolith, Fig. 9. The catalyst consists of a porous substrate of an inert material, coated with platinum and other metals, the catalytically active materials.

This device, located in the exhaust system between the exhaust manifold and muffler, requires the use of heat shields, in some cases, due to its high operating temperatures.

The heat shields are necessary to protect chassis components, passenger compartment and other areas from heat related damage.

A smaller diameter fuel tank filler tube neck, Fig. 10, is incorporated to prevent the larger service station pump nozzle, used for leaded fuels, being inserted into the filler tube, thereby preventing system contamination.

Since the use of leaded fuels contaminates the catalysts, deteriorating its effectiveness, the use of unleaded fuels is mandatory in vehicles equipped with catalytic converters. The catalytic converter can tolerate very small amounts of leaded fuels without permanently reducing the catalyst effectiveness.

Some vehicles incorporate two mini-oxidation catalytic converters in conjunction with the main underfloor converter. Their main purpose is to initiate exhaust gas oxidation before the gases reach the underfloor converter. The mini-ox, Fig. 11, is a single biscuit catalytic converter and is shaped so that only one small biscuit can fit inside the can.

The "hybrid" converter, Fig. 11, utilizes a larger biscuit and a smaller biscuit. A Power Heat Control Valve is incorporated to increase the flow of exhaust gases through the left-hand exhaust manifold to rapidly bring the mini-catalyst up to operating temperature.

CAUTION: Operation of any type, including idling, should be avoided if engine misfiring occurs. Under this condition, the exhaust system will operate at abnormally high temperature, which may cause damage to the catalyst or other underbody parts of the car.

Alteration or deterioration of the ignition or fuel systems, or any type of operating condition, which results in engine misfiring must be corrected to avoid overheating the catalytic converter. Proper maintenance and tune-up according to manufacturer's specifications should be made to correct the condition as soon as possible. Interrupting the ignition at high speeds with the transmission in gear can be expected to result in a catalyst overheat condition.