Exhaust systems

Your vehicle’s exhaust system primarily routes exhaust gases away from the engine, but it performs a number a number of other important functions as well.

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How exhaust systems work

Internal combustion, by which fuel-burning engines derive power, can be a messy process. Fuel from the vehicle’s gas tank is drawn into the combustion chamber or cylinder within the cylinder head, where it is mixed with air drawn in from outside the vehicle through the air filter.

From there a spark plug produces a spark from the vehicle’s electrical system, namely the distributor cap and wires, which ignites the fuel-air mixture, producing a small explosion.

This explosion drives the piston – which is seated flush in the cylinder – up, which translates the force of the explosion into the crankshaft. The crankshaft translates this power into a circular motion, eventually reaching the transmission, which transfers this power to the wheels. Finally, the remaining fuel-air mixture, both burned and unburned, exits through the exhaust port, and the cycle begins anew. This happens thousands of times a minute when a vehicle’s engine is running.

But what happens once the exhaust gases exit the engine’s combustion chambers? First, it travels out of the engine via the exhaust manifolds (Figure A below), also known as exhaust headers or simply headers. Since most vehicles have multiple cylinders, each combusting their own fuel-air mixture and thereby producing their own exhaust, the exhaust manifold collects the spent fuel from each cylinder. The exhaust is then sent further down the exhaust system via a single tube known as the tailpipe.

Reducing polluting emissions

Exhaust gases undergo an important change before they exit the vehicle’s exhaust system. One of the most important in the process is the catalytic converter (Figure B below), which reduces the amount of toxic pollutants emitted into the air. In the U.S., automobiles are the primary source of air pollution. That’s one reason the EPA began regulating vehicle emissions and fuel standards under the Clean Air Act starting in 1970. Following the act’s passage, vehicle manufacturers began adding catalytic converters to the exhaust systems of their vehicles.

The catalytic converter doesn’t use moving parts to scrub exhaust gases. Instead, it utilizes chemical reactions to almost totally eliminate toxic pollutants such as nitrogen oxide, carbon monoxide and hydrocarbon in a vehicle’s exhaust. Within the catalytic converter a series of planes covered in catalytic metals such as platinum, rhodium or palladium chemically converts the pollutants into less harmful nitrogen, carbon dioxide and water, thereby reducing the amount of polluting emissions.

Reducing noise pollution

After leaving the catalytic converter, the exhaust gases travel further down the exhaust system tailpipe to the muffler (Figure D below). Much like its name suggests, the primary purpose of the muffler is to reduce the noise produced by the combustion process. Have you ever been to a stock car race or drag strip and noticed how loud it is? The main reason you’ll need ear protection anytime you’re in the vicinity of race cars is their lack of muffler.

Although a the muffler is the most easily visible component, it’s only one portion of a vehicle’s exhaust system.(Photo by Fred Patton)

A muffler turns down the volume on the vehicle by passing exhaust gases through a series of tubes and filters, which progressively absorb, diminish or delete the sound waves produced by the engine. Because the absorption of sound waves also produces back pressure, a muffler that operates properly is an integral component in a vehicle’s engine operating efficiently.

Once the exhaust gases have passed through the muffler and out via the remaining tailpipe through an exhaust tip or resonator tip, the exhaust system process is complete.

Your vehicle’s exhaust system