Back pressure#Back pressure in automotive .28four-stroke engine.29 exhaust
{{Short description|Force opposing the flow of fluid through pipes}}
{{for|the routing algorithm|backpressure routing}}
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.{{cite journal |url=http://www.ijamejournals.com/pdf/rpj161130.pdf |last1=Shekhar |first1=Ravi |first2=Paramvir |last2=Singh Dhugga |first3=Kashish |last3=Malik |title=CFD analysis of Back Pressure due to bend in exhaust Pipe of 4 stoke petrol engine |journal=Int. J. Aerosp. Mech. Eng |volume=3 |issue=4 |year=2016 |pages=1–3}}
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. {{Cite book |title=Fundamentals of Software Architecture: An Engineering Approach |date=2020 |publisher=O'Reilly Media |isbn=978-1492043454}}
Explanation
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.{{cite report |url=https://apps.dtic.mil/sti/pdfs/ADA542327.pdf |archive-url=https://web.archive.org/web/20210624053025/https://apps.dtic.mil/sti/pdfs/ADA542327.pdf |url-status=live |archive-date=June 24, 2021 |last=Hield |first=Peter |title=The effect of back pressure on the operation of a diesel engine |publisher=Defence Science and Technology Group |year=2011}}{{cite book |chapter-url=https://books.google.com/books?id=Dt4LCwAAQBAJ&pg=PA367 |pages=367–374 |chapter=The influence of exhaust backpressure upon the turbochargers boost pressure |first1=Levente-Botond |last1=Kocsis |first2=Dan |last2=Moldovanu |first3=Doru-Laurean |last3=Baldean |title=Proceedings of the European Automotive Congress EAEC-ESFA 2015 |year=2015 |isbn=9783319272764 |publisher=Springer International Publishing}}
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.{{cite book |url=http://books.sae.org/book-r-161/ |title=Design and Simulation of Two-Stroke Engines |year=1996 |first=Gordon |last=Blair |publisher=SAE International |isbn=978-1-56091-685-7 |archive-url=https://web.archive.org/web/20121025072735/http://books.sae.org/book-r-161/ |archive-date=25 October 2012 |url-status=dead}}{{cite journal |url=https://bura.brunel.ac.uk/bitstream/2438/13696/1/Fulltext.pdf |last1=Dalla Nora |first1=Macklini |first2=Thompson Diórdinis Metzka |last2=Lanzanova |first3=Hua |last3=Zhao |title=Effects of valve timing, valve lift and exhaust backpressure on performance and gas exchanging of a two-stroke GDI engine with overhead valves |journal=Energy Conversion and Management |volume=123 |year=2016 |pages=71–83|doi=10.1016/j.enconman.2016.05.059 |bibcode=2016ECM...123...71D }}
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.{{cite journal |last1=Majors |first1=Ronald E |title=Column Pressure Considerations in Analytical HPLC |journal=LCGC North America |date=2007 |volume=25 |issue=11 |pages=1074–1092 |url=https://www.chromatographyonline.com/view/column-pressure-considerations-analytical-hplc-0 |access-date=10 March 2022}} 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.{{cite journal |last1=Neue |first1=Uwe D. |title=Kinetic Plots Made Easy |journal=LCGC North America |date=2009 |volume=27 |issue=11 |pages=974–983 |url=https://www.chromatographyonline.com/view/kinetic-plots-made-easy-1 |access-date=10 March 2022}}
See also
References
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