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Exhaust system: Everything you need to know about parts and function of the exhaust system

The exhaust system of the car directs the flow of exhaust gases away from the vehicle and reduces the resulting noise. A modern exhaust system also contains components that help reduce the pollutants in the exhaust gas produced during combustion. In this article you will learn all about the different exhaust parts, where they can be found and what function each part has.

The path of exhaust gases through the exhaust pipe

Today, a modern exhaust system must meet a whole range of requirements at the same time. For example, the system should reliably dissipate the amount of exhaust gases produced and limit the noise emissions generated. The parts of the exhaust system are subjected to enormous stresses, but spare parts are readily available new or used. Additional components within the exhaust system are intended to reduce the emission of pollutants, while at the same time the exhaust should have low flow resistance. Compared to the past, the modern exhaust system consists of many more components, which also increases the number of necessary spare parts.

  • Exhaust manifold: The exhaust manifold is the first component of the exhaust system, located directly behind the engine. Here, the manifold is directly connected to the cylinder head by bolted joints. The exhaust gases produced in the cylinders are emitted by the engine and discharged through the exhaust manifold. It also brings together the exhaust gases from the different cylinders.
  • Y-pipe: A Y-pipe in the exhaust system combines two exhaust gas streams. For this purpose, the part has two inlets and one outlet. It is often installed at the end of the manifold if the manifold discharges the exhaust gas streams via two outlets. A Y-pipe is also often used in engines with multiple cylinder banks.
  • Flex pipe: The flex pipe is a flexible connecting element in the exhaust. The structure often consists of a metal mesh or is designed as a corrugated pipe. The flex pipe connects various exhaust parts without allowing oscillations and vibrations to be transmitted between the parts. In the case of the car’s exhaust, the flex pipe often couples the manifold and catalytic converter.
  • Lambda sensor: The lambda sensor measures the level of residual oxygen in the exhaust gas, and provides the data to the engine control unit. Thanks to this technology, the engine runs under optimal conditions with low emissions. The lambda sensor is located inside the exhaust system upstream of the catalytic converter. Some models have a second lambda sensor.
  • Exhaust pipe: Various pipes in the exhaust system are referred to as exhaust pipes. As a rule, these are specially shaped pipe sections that connect the various components of the exhaust system. Exhaust rubbers serve as bearings. Due to strong thermal and external influences, the parts are heavily stressed, but spare parts are readily available.

Muffler of the exhaust system

Every engine produces an exhaust noise after combustion due to the pulsating emission of exhaust gases. If the exhaust gases were simply discharged through pipes without any other components, noises with an enormous volume would be generated. These would be perceived as noise. For this reason, an exhaust system always contains one or more silencers.

  • Pre-silencer: The pre-silencer is the first silencer located directly behind the exhaust manifold. This muffler is designed to absorb the high-frequency part of the exhaust noise. In modern vehicles with catalytic converters, the pre-silencer is not required.
  • Center muffler: A muffler in the center of the exhaust system is referred to as a center muffler. In most cases, this silencer is also positioned centrally under the vehicle. Center mufflers are often designed as absorption mufflers.
  • Rear muffler: The rear muffler, also known as the rear silencer, is one of the final components of the exhaust system. This silencer provides the final attenuation of noise before the exhaust gases leave the tailpipe.

Exhaust gas purification in the exhaust system

In modern vehicles with internal combustion engines, exhaust gas purification takes place directly inside the exhaust system. The catalytic converter and other components are now an integral part of the exhaust aftertreatment system. These parts of the exhaust system are

  • Catalytic converter: The catalytic converter is the most important part of modern exhaust gas treatment. Within the exhaust system, the catalytic converter ensures that harmful exhaust gas components such as nitrogen oxides are converted before they are emitted from the exhaust. The catalytic converter is subject to constant wear in the car. Used catalytic converters are sought-after spare parts.
  • Catalytic converter pump: The catalytic converter pump is part of the secondary air system in modern gasoline engines. With the aid of the pump, oxygen-rich ambient air is blown in behind the engine’s exhaust outlet during the cold-running phase of the engine. The resulting afterburning reduces the emission of pollutants during cold engine running.
  • Secondary air valve: The engine control unituses the secondary air valve to determine when air is to be blown into the exhaust tract. When the valve is open, the secondary air pump or catalytic converter pump blows in oxygen-rich air for afterburning. When closed, the valve prevents exhaust gases from flowing back out of the exhaust system.

Exhaust gas recirculation

With exhaust gas recirculation, a portion of the exhaust gases is returned and fed back into the combustion process. This effectively reduces emissions such as nitrogen oxides. Exhaust gas recirculation is often necessary to ensure that internal combustion engines meet the applicable exhaust gas standards. In automotive engineering, exhaust gas recirculation is referred to as EGR or EGR.

  • EGR cooler: The EGR cooler ensures that the hot engine exhaust gases are cooled before they are fed back into the combustion process. The cooler often becomes clogged with combustion residues or leaks, but is readily available as a replacement part.
  • EGR cooler tube: The EG R cooler tube connects the EGR valve to the EGR cooler. Due to the stresses of running the engine, the tube sometimes tears or leaks. EGR cooler tubes are available as used spare parts even for older vehicles.
  • EGRvalve: An EGR valve controls the recirculation from the exhaust system to the intake tract. Depending on requirements, the EGR valve is opened or closed by the engine management system. This ensures that the right amount of exhaust gases always enters the intake tract at the right time.

Special exhaust gas purification for diesel engines

Exhaust gas aftertreatment in diesel engines differs in some respects from that in gasoline engines. Since diesel engines emit soot as well as pollutants such as nitrogen oxides, a soot particle filter is installed in many modern vehicles with diesel engines. Exhaust gas aftertreatment by injecting a urea solution is also standard in modern diesels.

  • Particulate filter: The diesel particulate filter or soot particle filter filters the soot particles contained in exhaust gases from diesel engines out of the exhaust gas stream. The particles, which are considered carcinogenic, remain in the filter for the time being, which in turn regenerates itself.
  • Adblue tank: An Adblue tank is a small tank in which the urea solution for exhaust gas aftertreatment is stored. The term Adblue is a registered trademark under which urea solution is available directly at many service stations in Germany.

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