Exhaust-System Design

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A passenger-car exhaust system consists basically of three main components:

Catalytic Converter

The catalytic converter serves as an exhaust-gas cleaning device for spark ignition (SI) engines (as does nowadays the oxidation catalytic converter in diesel engines). It is mounted as close as possible to the engine so that it can quickly reach its operating temperature and therefore be effective in urban driving. It is fitted as supplementary equipment in place of the front muffler, whose acoustical functions it also takes over in addition to its exhaust-gas cleaning function. The acoustical changes in the vehicle must meed legal requirements.

Mufflers

Depending on the size of the vehicle and the engine, one or several mufflers are used. In V-engines the left and right cylinder banks are frequently run separately, each being fitted with its own catalytic converter of muffler, and only brought together at the end of the vehicle in one large muffler.

Exhaust Pipes

The exhaust pipes are the third and last component in the exhaust system. They combine the exhaust-gas outlets in the cylinder head into one or more pipes (manifolds), and also connect the catalytic converter(s) and the mufflers to each other. The length and cross-section of the pipes, as well as the type of junction used, influence the vehicle’s performance characteristics and acoustic behavior. Exhaust systems for vehicles with larger swept volumes are therefore often fitted with twin pipes. The pipes, the catalytic converter, and muffler are connected to the main body of the system by means of insert connections and flanges. Many original-equipment (OE) systems are welded into one complete element for faster mounting.

The entire exhaust system is connected with the underbody of the vehicle via flexible suspension elements. The fixing points must be carefully selected, as otherwise vibration can be transmitted to the bodywork and thus generate noise in the passenger compartment. The exhaust-system noise at the exhaust-emission point (tailpipe) can also cause bodywork resonances.

The total volume of the passenger-car Muffler system is approximately three to eight times the engine’s swept volume. Depending on swept volume and the type of muffler, the exhaust system weighs between 8 and 40 kg.

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