Editing Turbocharger (section)

===Turbine===
[[File:Turbo-turbine.jpg|thumb|upright=1.6|Turbine section of a [[Garrett_Motion|Garrett]] GT30 with the turbine housing removed]]

The [[turbine]] section (also called the "hot side" or "exhaust side" of the turbo) is where the rotational force is produced, in order to power the compressor (via a rotating [[shaft (mechanical engineering)|shaft]] through the center of a turbo). After the exhaust has spun the turbine, it continues into the exhaust piping and out of the vehicle. 

The turbine uses a series of blades to convert kinetic energy from the flow of exhaust gases to mechanical energy of a rotating shaft (which is used to power the compressor section). The turbine housings direct the gas flow through the turbine section, and the turbine itself can spin at speeds of up to 250,000 rpm.<ref>Mechanical engineering: Volume 106, Issues 7-12; p.51</ref><ref>Popular Science. Detroit's big switch to Turbo Power. Apr 1984.</ref> Some turbocharger designs are available with multiple turbine housing options, allowing a housing to be selected to best suit the engine's characteristics and the performance requirements.

A turbocharger's performance is closely tied to its size,<ref name="eight">{{cite web |last=Veltman |first=Thomas |title=Variable-Geometry Turbochargers |publisher=Coursework for Physics 240 |date=24 October 2010 |url =http://large.stanford.edu/courses/2010/ph240/veltman1/ |access-date=17 April 2012 }}</ref> and the relative sizes of the turbine wheel and the compressor wheel. Large turbines typically require higher exhaust gas flow rates, therefore increasing turbo lag and increasing the boost threshold. Small turbines can produce boost quickly and at lower flow rates, since it has lower rotational inertia, but can be a limiting factor in the peak power produced by the engine.<ref name="one">{{cite web|last=Tan |first=Paul |title=How does Variable Turbine Geometry work? |publisher=PaulTan.com |date=16 August 2006 |url =http://paultan.org/2006/08/16/how-does-variable-turbine-geometry-work/ |access-date=17 April 2012 }}</ref><ref name="two">A National Maritime Academy Presentation. [https://www.scribd.com/doc/17453088/How-Does-Variable-Turbine-Geometry-Work Variable Turbine Geometry].</ref> Various technologies, as described in the following sections, are often aimed at combining the benefits of both small turbines and large turbines.

Large diesel engines often use a single-stage [[axial turbine|axial inflow turbine]] instead of a radial turbine.<ref>{{Citation |last=Schobeiri |first=Meinhard T. |title=Introduction, Turbomachinery, Applications, Types |date=2012 |work=Turbomachinery Flow Physics and Dynamic Performance |pages=3–14 |editor-last=Schobeiri |editor-first=Meinhard T. |url=https://link.springer.com/chapter/10.1007/978-3-642-24675-3_1 |access-date=2024-12-13 |place=Berlin, Heidelberg |publisher=Springer |language=en |doi=10.1007/978-3-642-24675-3_1 |isbn=978-3-642-24675-3}}</ref>

====Twin-scroll====
A twin-scroll turbocharger uses two separate exhaust gas inlets, to make use of the pulses in the flow of the exhaust gasses from each cylinder.<ref>{{cite web |title=Twin-Turbocharging: How Does It Work? |url=https://www.carthrottle.com/post/twin-turbocharging-how-does-it-work/ |website=www.CarThrottle.com |date=11 October 2016 |access-date=16 June 2022 |language=en}}</ref> In a standard (single-scroll) turbocharger, the exhaust gas from all cylinders is combined and enters the turbocharger via a single intake, which causes the gas pulses from each cylinder to interfere with each other. For a twin-scroll turbocharger, the cylinders are split into two groups in order to maximize the pulses. The exhaust manifold keeps the gases from these two groups of cylinders separated, then they travel through two separate spiral chambers ("scrolls") before entering the turbine housing via two separate nozzles. The [[scavenging (engine)|scavenging]] effect of these gas pulses recovers more energy from the exhaust gases, minimizes parasitic back losses and improves responsiveness at low engine speeds.<ref>{{cite web |title=A Look At Twin Scroll Turbo System Design - Divide And Conquer? |url=https://www.motortrend.com/how-to/modp-0906-twin-scroll-turbo-system-design/ |website=www.MotorTrend.com |access-date=16 June 2022 |language=en |date=20 May 2009}}</ref><ref>{{cite web|last=Pratte |first=David |url=http://www.modified.com/tech/modp-0906-twin-scroll-turbo-system-design/ |title=Twin Scroll Turbo System Design |publisher=Modified Magazine |access-date=28 September 2012}}</ref>

Another common feature of twin-scroll turbochargers is that the two nozzles are different sizes: the smaller nozzle is installed at a steeper angle and is used for low-rpm response, while the larger nozzle is less angled and optimised for times when high outputs are required.<ref>{{cite web |title=BorgWarner's Twin Scroll Turbocharger Delivers Power and Response for Premium Manufacturers - BorgWarner |url=https://www.borgwarner.com/newsroom/press-releases/2020/02/18/borgwarner-s-twin-scroll-turbocharger-delivers-power-and-response-for-premium-manufacturers |website=www.borgwarner.com |access-date=16 June 2022}}</ref>

<gallery heights="150px" mode="packed">
File:Mitsubishi twin-scroll turbo.JPG |Cutaway view showing the two scrolls of a [[Mitsubishi Motors|Mitsubishi]] twin-scroll (the larger scroll is illuminated in red)
File:Twin-scroll turbo T-GDI.jpg |Transparent exhaust manifold and turbo scrolls on a [[Hyundai Gamma engine]], showing the paired cylinders (1 & 4 and 2 & 3)
</gallery>

====Variable-geometry====
[[File:VariableGeometryTurbo 1.JPG|thumb|Cutaway view of a [[Porsche]] variable-geometry turbocharger]]{{Main|Variable-geometry turbocharger}}
Variable-geometry turbochargers (also known as ''variable-nozzle turbochargers'') are used to alter the effective [[aspect ratio]] of the turbocharger as operating conditions change. This is done with the use of adjustable vanes located inside the turbine housing between the inlet and turbine, which affect flow of gases towards the turbine. Some variable-geometry turbochargers use a rotary [[Actuator#Electric|electric actuator]] to open and close the vanes,<ref>{{cite book|last=Hartman|first=Jeff|title=Turbocharging Performance Handbook|publisher=MotorBooks International|url=https://books.google.com/books?id=SvG0gq4DxecC&pg=PA95|year=2007|isbn=978-1-61059-231-4|page=95}}</ref> while others use a [[pneumatic actuator]].

If the turbine's aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of the turbine housing as the engine accelerates, the turbo's aspect ratio can be maintained at its optimum. Because of this, variable-geometry turbochargers often have reduced lag, a lower boost threshold, and greater efficiency at higher engine speeds.<ref name="eight"/><ref name="one"/> The benefit of variable-geometry turbochargers is that the optimum aspect ratio at low engine speeds is very different from that at high engine speeds.

==== Electrically-assisted turbochargers ====
An [[electrically-assisted turbocharger]] combines a traditional exhaust-powered turbine with an electric motor, in order to reduce turbo lag. Recent advancements in electric turbocharger technology,{{when|date=December 2024}} such as mild hybrid integration,<ref>{{Cite web |date=2018-07-04 |title=What is an electric turbocharger? |url=https://www.turbocharger.mtee.eu/what-is-an-electric-turbocharger/ |access-date=2024-12-10 |website=Mitsubishi Turbocharger |language=en-US}}</ref> have enabled turbochargers to start spooling before exhaust gases provide adequate pressure. This can further reduce turbo lag<ref>Truett, Richard, and Jens Meiners. “Electric Turbocharger Eliminates Lag, Valeo Says.” Automotive News, vol. 88, no. 6632, p. 34.</ref> and improve engine efficiency, especially during low-speed driving and frequent stop-and-go conditions seen in urban areas. This differs from an [[electric supercharger]], which solely uses an electric motor to power the compressor.