Mufflers are also referred to as resonators and silencers, although the term muffler is usually used. A muffler contains perforated pipes, baffles and resonance chambers, which are designed to break up the pulsating effect of the exhaust gases and so reduce the noise. At the same time, this must be done with as little restriction as possible, because restrictions would cause backpressure and inhibit gas flow.
Many mufflers have a combination of baffles and pipes, which are perforated so that the pattern of the gas flow is altered, but not restricted. The construction of one type of muffler is shown in Figure14.21. This is a reverse-flow muffler, where the direction of flow of the exhaust gases is changed within the muffler. Gases entering through the inlet pipe have to reverse their direction of flow before they can leave through the outlet pipe.
Catalytic converters are fitted in the exhaust system in same way as mufflers (Fig. 14.22). They are fitted to vehicles that operate on unleaded fuel and are used to control exhaust emissions.
One of the features of catalytic converters is that done they operate at higher temperatures than mufflers. They are fitted with a heat shield to prevent heat from radiating to the bodywork and adjacent parts, but care should be taken to avoid burns when working on or near a hot exhaust system.