Manifold
A manifold is an optimized exhaust manifold . The engine output and the torque curve can be improved through optimized manifold pipe lengths, diameters and guides for each individual cylinder, which are tailored to the vehicle purpose. The manifold uses the principle of interference .
functionality
The exhaust gas emissions in a reciprocating piston engine are not continuous. During the gas exchange , when the exhaust valve opens, there is a strong pressure gradient between the cylinder and the exhaust system. This valve pre-outlet creates a pressure wave in the exhaust system. The pressure wave propagates through the exhaust system at the speed of sound. As a result, gas congestion and reflections cause the pressure wave to return. If the reflected pressure wave arrives at the outlet valve again at the wrong time, the gas exchange is impeded. Exhaust gas from the same cylinder or from neighboring cylinders can even flow back.
The formation of interference is encouraged by the dimensions and shape of a fan manifold. At the right time (when the exhaust valve opens), these generate a negative pressure in the respective exhaust pipe. The exhaust gases can leave the cylinder without significant counter pressure, the piston needs less force to expel the exhaust gas. There are hardly any residual gases left, so the filling with fresh gas and thus the internal cylinder cooling are better; the latter also reduces the tendency to knock . The energy saved and the better combustion (less residual gases) result in an increase in performance.
construction
The exhaust pipes of the cylinders with the greatest possible ignition interval are grouped and flow into a line (2 to 3 each, depending on the engine type). The largest ignition interval is 360 ° for the four-cylinder and 240 ° for the six-cylinder. As a result, cylinders 1 and 4 and 2 and 3 are combined in the four-cylinder in-line engine. The exhaust pipes of six-cylinder in-line engines are often grouped according to the scheme 1, 2 and 3 as well as 4, 5 and 6. These thicker pipes , also known as Y- pipes , can also be brought together again later. The cross-sectional area of this exhaust pipe is greater than the sum of the cross-sectional areas of the combined pipes. Even the type of merging can still determine the characteristics of the engine, e.g. B. change the torque curve. In high-performance racing engines, instead of grouping individual pipes, all exhaust pipes from a cylinder bank are fed into a collecting funnel with a subsequent diffuser . When designing a manifold, the aim is to have the same length of all exhaust pipes. As a result, optimized bends always have a very curved, sweeping shape. However, this type of construction is often not feasible in series vehicle construction due to a lack of space or manufacturing problems.
application
In contrast to manifolds made of cast iron , manifolds cannot be manufactured inexpensively by machine, which is why they are mainly used in motor sports and in sporty vehicles .
Exhaust manifolds came z. B. in the Audi 90 (2.3 liter 20V), in the Opel Astra F GSI as well as in the Kadett E 16V and Calibra 16V (2.0 liter 16V), in the Escort RS2000 16V , in the Ford Capri (1.6GT, 2.6RS) and in the Peugeot 206 RC (called 206 GTI 180 in some markets). Nowadays Mazda installs a 4-2-1 (fan) manifold in the Skyactiv gasoline engines. This enables higher compressions of up to 14: 1 in this engine concept (as of 2017). Otherwise (as described above) there would be a risk of knocking burns from the hot exhaust gases .
literature
- Richard van Basshuysen, Fred Schäfer: Handbook Internal Combustion Engine Basics, Components, Systems, Perspectives. 3rd edition, Friedrich Vieweg & Sohn Verlag / GWV Fachverlage GmbH, Wiesbaden 2005, ISBN 3-528-23933-6
- Gert Hack: make cars faster. 2nd Edition. Motorbuch Verlag, Stuttgart 1995, ISBN 3-613-01548-X