Back pressure

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Back pressure (or backpressure) is the term for a resistance to the desired flow of fluid through pipes. Obstructions or tight bends create backpressure via friction loss and pressure drop. [1]

Contents

In distributed systems in particular event driven architecture, back pressure is a technique to regulate flow of data, ensuring that components do not become overwhelmed. [2]

Explanation

Two similar pipings with same pressure distance and head. The second pipe contains some obstructions for flow resulting in less discharge. Back pressure.jpg
Two similar pipings with same pressure distance and head. The second pipe contains some obstructions for flow resulting in less discharge.

A common example of backpressure is that caused by the exhaust system (consisting of the exhaust manifold, catalytic converter, muffler and connecting pipes) of an automotive four-stroke engine, which has a negative effect on engine efficiency, resulting in a decrease of power output that must be compensated by increasing fuel consumption. [3] [4]

In a piston-ported two-stroke engine, however, the situation is more complicated, due to the need to prevent unburned fuel/air mixture from passing right through the cylinders into the exhaust. During the exhaust phase of the cycle, backpressure is even more undesirable than in a four-stroke engine, as there is less time available for exhaust and the lack of pumping action from the piston to force the exhaust out of the cylinder. However, since the exhaust port necessarily remains open for a time after scavenging is completed, unburned mixture can follow the exhaust out of the cylinder, wasting fuel and increasing pollution. This can only be prevented if the pressure at the exhaust port is greater than that in the cylinder. Since the timing of this process is determined mainly by exhaust system geometry, which is extremely difficult to make variable, correct timing and therefore optimum engine efficiency can typically only be achieved over a small part of the engine's range of operating speed. [5] [6]

Liquid chromatography

Back pressure is the term used for the hydraulic pressure required to create a flow through a chromatography column in high-performance liquid chromatography, the term deriving from the fact that it is generated by the resistance of the column, and exerts its influence backwards on the pump that must supply the flow. Back-pressure is a useful diagnostic feature of problems with the chromatography column. [7] Rapid chromatography is favoured by columns packed with very small particles, which create high back-pressures. Column designers use "kinetic plots" to show the performance of a column at a constant back-pressure, usually selected as the maximum that a system's pump can reliably produce. [8]

See also

Related Research Articles

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The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values.

<span class="mw-page-title-main">Miller cycle</span> Thermodynamic cycle

In engineering, the Miller cycle is a thermodynamic cycle used in a type of internal combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, U.S. patent 2,817,322 dated Dec 24, 1957. The engine may be two- or four-stroke and may be run on diesel fuel, gases, or dual fuel. It uses a supercharger or a turbocharger to offset the performance loss of the Atkinson cycle.

<span class="mw-page-title-main">Two-stroke engine</span> Internal combustion engine type

A two-strokeengine is a type of internal combustion engine that completes a power cycle with two strokes of the piston in one revolution of the crankshaft. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.

<span class="mw-page-title-main">Exhaust gas recirculation</span> NOx reduction technique used in gasoline and diesel engines

In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. The exhaust gas displaces atmospheric air and reduces O2 in the combustion chamber. Reducing the amount of oxygen reduces the amount of fuel that can burn in the cylinder thereby reducing peak in-cylinder temperatures. The actual amount of recirculated exhaust gas varies with the engine operating parameters.

<span class="mw-page-title-main">Four-stroke engine</span> Internal combustion engine type

A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum in the cylinder through its downward motion.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.

In spark-ignition internal combustion engines, knocking occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel–air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.

Volumetric efficiency (VE) in internal combustion engine engineering is defined as the ratio of the equivalent volume of the fresh air drawn into the cylinder during the intake stroke to the volume of the cylinder itself. The term is also used in other engineering contexts, such as hydraulic pumps and electronic components.

<span class="mw-page-title-main">Exhaust manifold</span> Structure collecting an engines exhaust outlets

In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word manifold comes from the Old English word manigfeald and refers to the folding together of multiple inputs and outputs.

<span class="mw-page-title-main">Inlet manifold</span> Automotive technology

An inlet manifold or intake manifold is the part of an internal combustion engine that supplies the fuel/air mixture to the cylinders. The word manifold comes from the Old English word manigfeald and refers to the multiplying of one (pipe) into many.

<span class="mw-page-title-main">Reed valve</span> Type of check valve

Reed valves are a type of check valve which restrict the flow of fluids to a single direction, opening and closing under changing pressure on each face. Modern versions often consist of flexible metal or composite materials.

<span class="mw-page-title-main">Gasoline direct injection</span> Mixture formation system

Gasoline direct injection (GDI), also known as petrol direct injection (PDI), is a mixture formation system for internal combustion engines that run on gasoline (petrol), where fuel is injected into the combustion chamber. This is distinct from manifold injection systems, which inject fuel into the intake manifold.

Manifold vacuum, or engine vacuum in a petrol engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.

<span class="mw-page-title-main">Back-fire</span> Explosion in the exhaust of an engine

A backfire or afterburn is combustion or an explosion produced by a running internal combustion engine that occurs in the exhaust system, rather than inside the combustion chamber. It is also sometimes referred to as an afterfire, especially in cases where the word backfire is used to mean a fuel burn that occurs while an intake valve is open, causing the fire to move backward through the system and out through the intake instead of the exhaust. When the flame moves backward it may also be called a "pop-back". A backfire can be caused either by ignition that happens with an exhaust valve open or unburnt fuel making its way into the hot exhaust system. A visible flame may momentarily shoot out of the exhaust pipe. A backfire is often a sign that the engine is improperly tuned.

The two-stroke power valve system is an improvement to a conventional two-stroke engine that gives a high power output over a wider RPM range.

Cylinder head porting refers to the process of modifying the intake and exhaust ports of an internal combustion engine to improve their air flow. Cylinder heads, as manufactured, are usually suboptimal for racing applications due to being designed for maximum durability. Ports can be modified for maximum power, minimum fuel consumption, or a combination of the two, and the power delivery characteristics can be changed to suit a particular application.

<span class="mw-page-title-main">Ignition timing</span> Timing of the release of a spark in a combustion engine

In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke.

<span class="mw-page-title-main">Scavenging (engine)</span> Process used in internal combustion engines

Scavenging is the process of replacing the exhaust gas in a cylinder of an internal combustion engine with the fresh air/fuel mixture for the next cycle. If scavenging is incomplete, the remaining exhaust gases can cause improper combustion for the next cycle, leading to reduced power output.

The inertial supercharging effect is the increase of volumetric efficiency in the cylinder of an engine.

Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.

<span class="mw-page-title-main">Internal combustion engine</span> Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance. This process transforms chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.

References

  1. ↑ Shekhar, Ravi; Singh Dhugga, Paramvir; Malik, Kashish (2016). "CFD analysis of Back Pressure due to bend in exhaust Pipe of 4 stoke petrol engine" (PDF). Int. J. Aerosp. Mech. Eng. 3 (4): 1–3.
  2. ↑ Fundamentals of Software Architecture: An Engineering Approach. O'Reilly Media. 2020. ISBN   978-1492043454.
  3. ↑ Hield, Peter (2011). The effect of back pressure on the operation of a diesel engine (PDF) (Report). Defence Science and Technology Group. Archived (PDF) from the original on June 24, 2021.
  4. ↑ Kocsis, Levente-Botond; Moldovanu, Dan; Baldean, Doru-Laurean (2015). "The influence of exhaust backpressure upon the turbochargers boost pressure". Proceedings of the European Automotive Congress EAEC-ESFA 2015. Springer International Publishing. pp. 367–374. ISBN   9783319272764.
  5. ↑ Blair, Gordon (1996). Design and Simulation of Two-Stroke Engines. SAE International. ISBN   978-1-56091-685-7. Archived from the original on 25 October 2012.
  6. ↑ Dalla Nora, Macklini; Lanzanova, Thompson Diórdinis Metzka; Zhao, Hua (2016). "Effects of valve timing, valve lift and exhaust backpressure on performance and gas exchanging of a two-stroke GDI engine with overhead valves" (PDF). Energy Conversion and Management. 123: 71–83. Bibcode:2016ECM...123...71D. doi:10.1016/j.enconman.2016.05.059.
  7. ↑ Majors, Ronald E (2007). "Column Pressure Considerations in Analytical HPLC". LCGC North America. 25 (11): 1074–1092. Retrieved 10 March 2022.
  8. ↑ Neue, Uwe D. (2009). "Kinetic Plots Made Easy". LCGC North America. 27 (11): 974–983. Retrieved 10 March 2022.
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