Exhaust system

The exhaust system of an internal combustion engine in a motor vehicle is referred to as exhaust (Pl. exhausts ).

Construction

The components of a conventional car with a gasoline engine in the direction of the exhaust flow:

• Exhaust manifold
• Y-pipe
• Catalyst
• Middle silencer ( muffler )
• Silencer
• Tailpipe

For smaller engines like mopeds, the manifold opens directly into the muffler.

Exhaust manifold

The exhaust manifold is connected directly to the cylinder head. Sealing is achieved by embossed metal seals or coated fabric seals. The manifold is made of cast iron or stainless steel. The shape varies from a single manifold and complex shapes, which summarizes the outlet ducts in different ways. When and exhaust ports which are put together depends on the number of cylinders, the firing order and the construction of the engine. On engines with supercharging the exhaust lines are combined, for example, before the turbocharger. In the construction of manifolds, the exhaust pipes are designed to merge be the same length. This shape prevents a negative influence of the charge cycle. If the merging of the exhaust gases downstream of the manifold is not yet completed, the exhaust manifold is followed by a Y-pipe. In the simple variants of this component is omitted. To meet the stringent emissions standards and a further reduction of fuel consumption, there is an exhaust gas recirculation in newer engines. The valve for sitting at the exhaust manifold and connects it to the intake.

Y-pipe

The Y-pipe is rigidly bolted to the exhaust manifold. The seal is the same as the manifold. The name " Y-pipe " is derived from the most double-flow design, similar to a pair of pants. Like a trouser send the inputs to a single output. The oxygen sensor is often found at the bottom of the pant tube. Here, the temperatures required for the proper function can be achieved early. The transition to the next component, the catalyst is mainly for newer vehicles via a flexible connection. This can be a flexible metal hose or a cone or ball sealing. This decouples the connection of the motor and roll vibrations of the exhaust system attached to the sub-floor. In older vehicles can be found between Y-pipe and catalyst usually a rigid, inflexible screw. However, in order to still be able to catch vibrations, the Y-pipe is additionally supported springy.

Catalyst

The catalyst is the component that converts the exhaust gases in the interaction with the oxygen sensor. The so-called catalytic converter is barrel shaped and has a funnel-shaped inlet and outlet. Since he can warm up very quickly and thus have a very high temperature, it is surrounded by top and bottom generally with a heat shield. Inside is a porous ceramic block with small, parallel to the longitudinal axis channels. This monolith is coated with the noble metals platinum, rhodium and palladium, and causes a chemical reaction in the exhaust gas.

Soot filter

In diesel engines, particulate filters are increasingly being used. The particle filter is installed upstream of the exhaust system. The structure, with an inner monolith similar to a normal catalyst. The carbon black with the adhering polycyclic aromatics is collected in the filter, however, by the Zumengen additives burned for fuel or heating of the filter above the ignition temperature at regular intervals.

First and middle silencer

Before the catalyst technology found its way into our vehicles, the center or muffler were installed in place of the catalyst. Middle silencer absorb the sound through the use of insulation material. The structure resembles a large tin can. The exhaust pipe goes straight through the lid of the barrel through. Inside the tube is perforated and changes its cross section. The space between the pipe and the outer wall is filled with steel wool, basalt fibers, or, in yet older vehicles with asbestos fibers. Through the perforated tube of the exhaust gas stream is expanded, and slows down the attenuated vibration. The main function of Vorschalldämpfern is the absorption ( neutralization) of high-frequency sound waves.

First of all two-stroke engines, like the Trabant, in addition to the middle silencer have also a silencer. This has no sound insulation, but also expands the exhaust gas stream and the reflected sound waves so that they reinforce each other by interference. This creates a suction which favors the outflow of the combustion gases from the combustion chamber.

Silencer

In the construction of muffler silencer ( muffler reflection ) and middle silencer (absorption silencer ) combine. Where this is not the norm. Likewise muffler are frequently produced in pure reflection or absorption design. Absorption mufflers are very often used in the form of sports silencers that help due to their lower back pressure and more favorable flow characteristics in improved sound and can cause an increase in performance. Its external shape is varied between the different vehicles in order to adapt to the subfloor. Within the reflection damper is divided into a plurality of outwardly insulated chambers. The exhaust gas is then forced to split into several different lengths of streams, causing the sound waves partially cancel each other (interference effect due to phase-shifted superposition ). As a result, a high attenuation is at a low backpressure. Developers of exhaust systems can be influenced by well-defined cross-sections and shapes the noise and engine performance.

Sound

An important ( emotional ) factor when buying a car is the sound of a vehicle, which is heavily influenced by the exhaust. For this reason, automobile manufacturers have been cut exhaust note on the vehicle with a high development effort. Meanwhile, there is also the possibility to change the sound with special speakers in Exhaust: The exhaust can be considerably quieter, but it can also sound components are admixed. The first production vehicle that has such a special speaker in the exhaust, the Audi A6 Avant.

Laying

The components of the exhaust system are connected to the exhaust pipe. At certain points between the components of the pipes are inserted into each other. With a pipe clamp they are secured and sealed. For cost reasons, modern exhaust systems are installed in new cars as an individual part, that is, the pipes between the components (catalyst, muffler ) are firmly welded together. For replacement of individual components, the pipes must be cut. The spare parts are reattached with pipe clamps. Exhaust pipes are laid in road vehicles, under the vehicle cabin up to behind the person, in order to prevent an advance of the exhaust gases to the occupant. For trucks the exhaust can therefore gentle between the axles. For larger engines, such as 6 -, 8 - or 12 - cylinder V- engines, the exhaust systems are designed from front to back -flow ( with two tubes ). Either catalysts and rear muffler then also double-flow or duplicated. The pipes and the silencer are resiliently mounted with rubber on the underbody to counteract cracks in the system and the transmission of vibrations to the body. The lower floor is used for protection against heat in the area of the exhaust pipe with zinc or aluminum sheets. In some trucks, buses, tractors and other special vehicles, the exhaust gases are directed upward to avoid the blowing of persons or objects. In such cases, the exhaust ends often have a lid to prevent the ingress of rain and so as to protect components such as catalytic converters and motors. For cars that are manufactured in countries with left-hand traffic (as in Japan), is often observed that the tail pipe facing the sidewalk. Hang the tailpipes or muffler right and left on the sides, it is called sidepipes. These are available in Germany by the Road Traffic Licensing Regulations ( Road Traffic Licensing Regulations ) only allowed if: 1 mounted only as dummies, so not connected to the exhaust stream. 2 is mounted when connected to the exhaust system, the right ( passenger) side to the outlet opening downwards so that persons standing at the roadside can not be bothered with exhaust gases. In addition, must not be shortened or changed the original exhaust system and the connection must be made after the last silencer. Everything of course, only with the "blessing" by the Technical Control Board (TÜV / DEKRA ) with entry in the vehicle documents.

Tasks

Two main functions of the exhaust is the derivative of the combustion exhaust gases from the vehicle and the damping of the pressure surges arising in the explosive combustion in the combustion chambers in order to reduce the sound emission.

A closer look at the operation of an internal combustion engine processes taking place the exhaust has an important meaning. The exhaust has a significant impact on the available torque in the usable speed range of the drive unit. In motor sport, where the performance and power delivery is in the foreground, which is particularly exploited.

The exhaust is passively involved in gas exchange, by its shape determines which take place in it vibrations of the exhaust gases. These vibrations may assist the outflow of combustion gases from the combustion chamber with the exhaust valve is open, but also to counteract them. The suction can be so strong that even the inflow of fresh gases is supported simultaneously with the discharge valve open. By appropriate design of the exhaust system and vote to other components like timing but can also be the filling of the combustion chambers to increase, and at the same time reducing consumption by scavenging losses are kept low. The gas flow is in this case only be supported by the negative portion of the vibration gas to push back during the subsequent positive part of the gases before the valve is closed. This principle is also the basis to operate a two-stroke engine at all, because in him the charge cycle is mainly determined by flow-related processes. There are no valves, and the piston can support the outflow of the burned gases through its stroke, or only very little.

In the field of manufacturing exhaust there are a variety of manufacturing companies. The most popular are Hamann, Eberspacher, Remus - Sebring, Bosal and high performance motor sport.