Back pressure
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Back pressure refers to the resistance to a moving fluid by obstructions or tight bends in the confinement vessel along which it is moving, such as piping or air vents, against its direction of flow.
Because it is really resistance, the term back pressure is misleading as the pressure remains and causes flow in the same direction, but the flow is reduced due to resistance. For example, an automotive exhaust muffler with a particularly high number of twists, bends, turns and right angles could be described as having particularly high back pressure [1].
Back pressure caused by the exhaust system (consisting of the exhaust manifold, catalytic converter, muffler and connecting pipes) of an automotive four-stroke engine has a negative effect on engine efficiency resulting in a decrease of power output that must be compensated by increasing fuel consumption; however, while the contemporary exhaust system may increase the level of strain on both the local economy and the global environment by requiring an increase in the purchase, consumption and venting of hydrocarbon fuel and its carbon dioxide byproduct, most automobile saturated societies see this as an acceptable and necessary trade-off. Although the exhaust system indirectly requires more fuel and that releases more CO2 pollution into the upper atmosphere, the catalytic converter greatly reduces the heavier chemical byproducts produced by the engine that would otherwise remain much closer to the ground and disperse much more slowly causing a local pollution known as smog and with out mufflers, any area that is heavily trafficked by motor vehicles would become a highly dangerous environment for any people and perhaps animals as well who were not utilizing professional hearing protection. However, the recent trend of making precision gas engines that run quieter and more efficient along with the current introduction of hybrids and fully electric cars is diminishing the importance of the exhaust system.
In a two-stroke engine however, a certain amount of exhaust backpressure is needed to prevent unburned fuel/air mixture from passing right through the cylinders into the exhaust.
Back pressure in information technology
The term is also used analogously in the field of information technology to describe the build-up of data behind an I/O switch if the buffers are full and incapable of receiving any more data; the transmitting device halts the sending of data packets until the buffers have been emptied and are once more capable of storing information [2]. It also refers to an algorithm for routing data according to congestion gradients (see Backpressure Routing).
See also
References
- ↑ Muffler at How Stuff Works
- ↑ Back pressure at Webopedia
