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A turbo-compound engine is a reciprocating engine that employs a turbine to recover energy from the exhaust gases. Instead of using that energy to drive a turbocharger as found in many high-power aircraft engines, the energy is instead sent to the output shaft to increase the total power delivered by the engine. The turbine is usually mechanically connected to the crankshaft, as on the Wright R-3350 Duplex-Cyclone, but electric and hydraulic power recovery systems have been investigated as well.

As this recovery process does not increase fuel consumption, it has the effect of reducing the specific fuel consumption, the ratio of fuel use to power.^[1] Turbo-compounding was used for commercial airliners and similar long-range, long-endurance roles before the introduction of turbojet engines. Examples using the Duplex-Cyclone include the Douglas DC-7B and Lockheed L-1049 Super Constellation, while other designs did not see production use.

Concept

Most piston engines produce a hot exhaust that still contains considerable undeveloped energy that could be used for propulsion if extracted. A turbine is often used to extract energy from such a stream of gases. A conventional gas turbine is fed high-pressure, high-velocity air, extracts energy from it, and leaves as a lower-pressure, slower-moving stream. This action has the side-effect of increasing the upstream pressure, which makes it undesirable for use with a piston engine as it increases the back-pressure in the engine, which decreases scavenging of the exhaust gas from the cylinders and thereby lowers the efficiency of the piston portion of a compound engine.^[2]

Through the late 1930s and early 1940s one solution to this problem was the introduction of "jet stack" exhaust manifolds. These were simply short sections of metal pipe attached to the exhaust ports, shaped so that they would interact with the airstream to produce a jet of air that produced forward thrust. Another World War II introduction was the use of the Meredith effect to recover heat from the radiator system to provide additional thrust.

By the late-war era, turbine development had improved dramatically and led to a new turbine design known as the "blowdown turbine" or "power-recovery turbine". This design extracts energy from the momentum of the moving exhaust, but does not appreciably increase back-pressure. This means it does not have the undesirable effects of conventional designs when connected to the exhaust of a piston engine, and a number of manufacturers began studying the design.

History

The first aircraft engine to be tested with a power-recovery turbine was the Rolls-Royce Crecy. This was used primarily to drive a geared centrifugal supercharger, although it was also coupled to the crankshaft and gave an extra 15 to 35 percent fuel economy.^[3]

Blowdown turbines became relatively common features in the late- and post-war era, especially for engines designed for long overwater flights. Turbo-compounding was used on several airplane engines after World War II, including the Napier Nomad^[4]^[5] and the Wright R-3350.^[6]^[7] The exhaust restriction imparted by the three blowdown turbines used on the Wright R-3350 is equal to a well-designed jet stack system used on a conventional radial engine, while recovering about 550 hp (410 kW) at METO (maximum continuous except for take-off) power.^[2] In the case of the R-3350, maintenance crews sometimes nicknamed the turbine the parts recovery turbine due to its negative effect on engine reliability. Turbo-compound versions of the Napier Deltic, Rolls-Royce Crecy, Rolls-Royce Griffon, and Allison V-1710 were constructed but none was developed beyond the prototype stage. It was realized in many cases the power produced by the simple turbine was approaching that of the enormously complex and maintenance-intensive piston engine to which it was attached. As a result, turbo-compound aero engines were soon supplanted by turboprop and turbojet engines.

Some modern heavy truck diesel manufacturers have incorporated turbo-compounding into their designs. Examples include the Detroit Diesel DD15^[8]^[9] and Scania^[10] in production from 1991.^[11]^{[clarification needed]}

Starting with the 2014 season, Formula One switched to a new 1.6 liter turbocharged V6 formula that uses turbo-compounding. The engines use a single turbocharger that is connected to an electric motor/generator called the MGU-H. The MGU-H uses a turbine to drive a generator, converting waste heat from the exhaust into electrical energy that is either stored in a battery or sent directly to an electric motor in the car's powertrain.

List of types

Detroit Diesel
- DD15^[12]

Napier
- Napier Nomad
Wright Aeronautical
- Wright R-3350: The turbo-compound version was the only turbo-compound aero-engine to see mass production and widespread usage.
Dobrynin
- Dobrynin VD-4K
Zvezda
- Zvezda M503: Soviet-built 42 cylinder diesel naval engine used in the Osa-class missile boat
Renault
- Renault Energy F1: 1.6 liter turbocharged V6 engine built for Formula 1. Unlike its contemporaries, still uses a wastegate as an emergency measure to control boost pressure in case the turbo-compounding with the MGU-H fails.
Ferrari
- Ferrari 059: 1.6 liter turbocharged V6 engine built for Formula 1 for the Ferrari F14 T as well as the Sauber C33.
Mercedes-Benz
- Mercedes PU106: 1.6 liter turbocharged V6 engine built for Mercedes-Benz Formula 1 programme.
Honda
- Honda RA615H: 1.6 liter turbocharged V6 engine built for Formula 1 for the McLaren MP4-30.

References

^ Stimson, Thomas E., Junior (February 1956). "The Race of the Airliners". Popular Mechanics: 113–118. Retrieved 19 February 2016.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ ^a ^b Facts about the Wright Turbo Compound (PDF). Wood Ridge New Jersey: Curtiss-Wright Corporation:Wright Aeronautical Division. October 1956. Archived from the original (PDF) on 16 February 2010. Retrieved 19 February 2016.
^ "Rolls-Royce and the Sleeve Valve" (PDF). New Zealand Rolls-Royce & Bentley Club Inc (7–3): 15. 2007. Archived from the original (PDF) on 6 December 2010.
^ Gunston, Bill (30 April 1954). "Napier Nomad: An engine of outstanding efficiency". Flight: 543–551. Archived from the original (PDF) on 5 March 2016. Retrieved 19 February 2010.
^ E. E. Chatterton (22 April 1954). "Napier Diesels: An RAeS Lecture" (PDF). Flight: 552. Retrieved 19 February 2010.
^ "Ten Ideas That Failed: 2 Turbo-compound Piston Engine" (PDF). Flight. 16 December 2003. Retrieved 19 February 2010.
^ "Super Survivor" (PDF). Flight. 18 June 1997. Retrieved 19 February 2010. in its hey-day, the Connie was often called the world's best tri-motor
^ "DD15" (video). Detroit Diesel.
^ "DD15 Brochure" (PDF). Detroit Diesel.
^ "Scania Turbocompound". Scania Group. Archived from the original on 30 January 2010.
^ "Scania produces 4 ECO-point engine from Oct 2001". Scania Group. Archived from the original on 7 August 2011. With 440 hp, the new version of Scania's 12-litre turbocompound engine is suitable for Alpine terrain, as well as normal European long-haul and construction operations.
^ "The Turbo Compounding Boost". 2007.

[popmech0256-1] Stimson, Thomas E., Junior (February 1956). "The Race of the Airliners". Popular Mechanics: 113–118. Retrieved 19 February 2016.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[EH-2] Facts about the Wright Turbo Compound (PDF). Wood Ridge New Jersey: Curtiss-Wright Corporation:Wright Aeronautical Division. October 1956. Archived from the original (PDF) on 16 February 2010. Retrieved 19 February 2016.

[nzrrbc-3] "Rolls-Royce and the Sleeve Valve" (PDF). New Zealand Rolls-Royce & Bentley Club Inc (7–3): 15. 2007. Archived from the original (PDF) on 6 December 2010.

[Flight,_30_April_1954,_Napier_Nomad-4] Gunston, Bill (30 April 1954). "Napier Nomad: An engine of outstanding efficiency". Flight: 543–551. Archived from the original (PDF) on 5 March 2016. Retrieved 19 February 2010.

[Flight,_30_April_1954,_Napier_diesels-5] E. E. Chatterton (22 April 1954). "Napier Diesels: An RAeS Lecture" (PDF). Flight: 552. Retrieved 19 February 2010.

[Flight,_2003,_Ten_ideas_that_failed-6] "Ten Ideas That Failed: 2 Turbo-compound Piston Engine" (PDF). Flight. 16 December 2003. Retrieved 19 February 2010.

[Flight,_1997,_Super_survivor-7] "Super Survivor" (PDF). Flight. 18 June 1997. Retrieved 19 February 2010. in its hey-day, the Connie was often called the world's best tri-motor

[8] "DD15" (video). Detroit Diesel.

[9] "DD15 Brochure" (PDF). Detroit Diesel.

[10] "Scania Turbocompound". Scania Group. Archived from the original on 30 January 2010.

[11] "Scania produces 4 ECO-point engine from Oct 2001". Scania Group. Archived from the original on 7 August 2011. With 440 hp, the new version of Scania's 12-litre turbocompound engine is suitable for Alpine terrain, as well as normal European long-haul and construction operations.

[12] "The Turbo Compounding Boost". 2007.

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

@@ Line 1: / Line 1: @@
+{{Use dmy dates|date=September 2022}}
+{{Short description|Reciprocating engine combined with a blowdown turbine}}
 {{Use American English|date=April 2016}}
 [[Image:Napier Nomad.jpg|thumb|right|The [[Napier Nomad]] engine. The power-recovery turbine sits underneath a two-stroke diesel engine.]]
-A '''turbo-compound engine''' is a [[reciprocating engine]] that employs a [[turbine]] to recover energy from the exhaust gases. Instead of using that energy to drive a [[turbosupercharger]] as found in many high-power [[aircraft engine]]s, the energy is instead coupled to the output to increase the total power delivered by the engine. The turbine is usually mechanically connected to the [[crankshaft]], as on the [[Wright R-3350 Duplex-Cyclone]], but electric and hydraulic power recovery systems have been investigated as well.
+A '''turbo-compound engine''' is a [[reciprocating engine]] that employs a [[turbine]] to recover energy from the exhaust gases. Instead of using that energy to drive a [[turbocharger]] as found in many high-power [[aircraft engine]]s, the energy is instead sent to the output shaft to increase the total power delivered by the engine. The turbine is usually mechanically connected to the [[crankshaft]], as on the [[Wright R-3350 Duplex-Cyclone]], but electric and hydraulic power recovery systems have been investigated as well.
-As this recovery process does not increase [[fuel consumption]], it has the effect of reducing the [[specific fuel consumption (shaft engine)|specific fuel consumption]], the ratio of fuel use to power.<ref name="popmech0256">{{cite journal|last1=Stimson|first1=Thomas E., Junior|title=The Race of the Airliners|journal=Popular Mechanics|date=February 1956|pages=113–118|url=https://books.google.com/books?id=u-EDAAAAMBAJ&pg=PA113&dq=&hl=en&sa=X&ei=uoxET6-bFcPVgQf2s_i2BA&ved=0CEcQ6AEwBjgK#v=onepage&q&f=true|accessdate=19 February 2016}}</ref> Turbo-compounding was used for commercial airliners and similar long-range, long-endurance roles before the introduction of high-bypass [[turbofan]] engines replaced them in this role. Examples using the Duplex-Cyclone include the [[Douglas DC-7B]] and [[Lockheed L-1049 Super Constellation]], while other designs did not see production use.
+As this recovery process does not increase [[fuel consumption]], it has the effect of reducing the [[specific fuel consumption (shaft engine)|specific fuel consumption]], the ratio of fuel use to power.<ref name="popmech0256">{{cite journal|last1=Stimson|first1=Thomas E., Junior|title=The Race of the Airliners|journal=Popular Mechanics|date=February 1956|pages=113–118|url=https://books.google.com/books?id=u-EDAAAAMBAJ&pg=PA113|access-date=19 February 2016}}</ref> Turbo-compounding was used for commercial airliners and similar long-range, long-endurance roles before the introduction of [[turbojet]] engines. Examples using the Duplex-Cyclone include the [[Douglas DC-7B]] and [[Lockheed L-1049 Super Constellation]], while other designs did not see production use.
 ==Concept==
-Most piston engines have a hot exhaust that still contains considerable undeveloped [[energy]] that could be used for propulsion if extracted. A turbine is often used to extract energy from such a stream of gases. A conventional gas turbine is fed high-pressure, high-velocity air, extracts energy from it, and leaves as a lower-pressure, slower-moving stream. This action has the side-effect of increasing the upstream pressure, which makes it undesirable for use with a piston engine as it has the side-effect of increasing the back-pressure in the engine, which decreases scavenging of the [[exhaust gas]] from the cylinders and thereby lowers the efficiency of the piston portion of a compound engine.<ref name="EH">{{cite book|title=Facts about the Wright Turbo Compound|date=October 1956|publisher=Curtiss-Wright Corporation:Wright Aeronautical Division|location=Wood Ridge New Jersey|url=http://www.enginehistory.org/Wright/TC%20Facts.pdf|accessdate=19 February 2016|format=pdf|deadurl=yes|archiveurl=https://web.archive.org/web/20100216210835/http://www.enginehistory.org/Wright/TC%20Facts.pdf|archivedate=16 February 2010|df=}}</ref>
+Most piston engines produce a hot exhaust that still contains considerable undeveloped [[energy]] that could be used for propulsion if extracted. A turbine is often used to extract energy from such a stream of gases. A conventional gas turbine is fed high-pressure, high-velocity air, extracts energy from it, and leaves as a lower-pressure, slower-moving stream. This action has the side-effect of increasing the upstream pressure, which makes it undesirable for use with a piston engine as it increases the back-pressure in the engine, which decreases scavenging of the [[exhaust gas]] from the cylinders and thereby lowers the efficiency of the piston portion of a compound engine.<ref name="EH">{{cite book|title=Facts about the Wright Turbo Compound|date=October 1956|publisher=Curtiss-Wright Corporation:Wright Aeronautical Division|location=Wood Ridge New Jersey|url=http://www.enginehistory.org/Wright/TC%20Facts.pdf|access-date=19 February 2016|url-status=dead|archive-url=https://web.archive.org/web/20100216210835/http://www.enginehistory.org/Wright/TC%20Facts.pdf|archive-date=16 February 2010}}</ref>
 Through the late 1930s and early 1940s one solution to this problem was the introduction of "jet stack" exhaust manifolds. These were simply short sections of metal pipe attached to the exhaust ports, shaped so that they would interact with the airstream to produce a jet of air that produced forward thrust. Another [[World War II]] introduction was the use of the [[Meredith effect]] to recover heat from the radiator system to provide additional thrust.
-By the late-war era, turbine development had improved dramatically and led to a new turbine design known as the "blowdown turbine" or "power-recovery turbine". This design extracts energy from the momentum of the moving air, but does not appreciably increase back-pressure. This means it does not have the undesirable effects of conventional designs when connected to the exhaust of a piston engine, and a number of manufacturers began studying the design.
+By the late-war era, turbine development had improved dramatically and led to a new turbine design known as the "blowdown turbine" or "power-recovery turbine". This design extracts energy from the momentum of the moving exhaust, but does not appreciably increase back-pressure. This means it does not have the undesirable effects of conventional designs when connected to the exhaust of a piston engine, and a number of manufacturers began studying the design.
 ==History==
 [[Image:Wright R-3350 Cyclone Engine 1.jpg|thumb|right|[[Wright R-3350 Duplex-Cyclone]] Turbo-Compound [[radial engine]].]]
-The first aircraft engine to be tested with a power-recovery turbine was the [[Rolls-Royce Crecy]]. This was used primarily to drive a geared centrifugal supercharger, although it was also coupled to the crankshaft and gave an extra 15 to 35 percent fuel economy.<ref name=nzrrbc>{{Cite journal |title=Rolls-Royce and the Sleeve Valve |url=http://www.kda132.com/Praeclarum/NZ07-3.pdf |issue=07-3 |year=2007 |journal=New Zealand Rolls-Royce & Bentley Club Inc |page=15 |deadurl=yes |archiveurl=https://web.archive.org/web/20101206092033/http://kda132.com/Praeclarum/NZ07-3.pdf |archivedate=2010-12-06 |df= }}</ref>
+The first aircraft engine to be tested with a power-recovery turbine was the [[Rolls-Royce Crecy]]. This was used primarily to drive a geared centrifugal supercharger, although it was also coupled to the crankshaft and gave an extra 15 to 35 percent fuel economy.<ref name=nzrrbc>{{Cite journal |title=Rolls-Royce and the Sleeve Valve |url=http://www.kda132.com/Praeclarum/NZ07-3.pdf |issue=7–3 |year=2007 |journal=New Zealand Rolls-Royce & Bentley Club Inc |page=15 |url-status=dead |archive-url=https://web.archive.org/web/20101206092033/http://kda132.com/Praeclarum/NZ07-3.pdf |archive-date=6 December 2010 }}</ref>
 Blowdown turbines became relatively common features in the late- and post-war era, especially for engines designed for long overwater flights. Turbo-compounding was used on several [[airplane]] engines after [[World War II]], including the [[Napier Nomad]]<ref name="Flight, 30 April 1954, Napier Nomad" >
-{{cite journal |journal=[[Flight (magazine)|Flight]] |last=Gunston |first=Bill |authorlink=Bill Gunston |title=Napier Nomad: An engine of outstanding efficiency |chapter= |url=http://www.flightglobal.com/pdfarchive/view/1954/1954%20-%201215.html |format=PDF |date=30 April 1954 |pages=543–551 |ref=Flight, 30 April 1954, Napier Nomad |accessdate=19 February 2010
+{{cite journal |journal=[[Flight (magazine)|Flight]] |last=Gunston |first=Bill |author-link=Bill Gunston |title=Napier Nomad: An engine of outstanding efficiency |url=http://www.flightglobal.com/pdfarchive/view/1954/1954%20-%201215.html |format=PDF |date=30 April 1954 |pages=543–551 |ref=Flight, 30 April 1954, Napier Nomad |archive-url=https://web.archive.org/web/20160305034809/https://www.flightglobal.com/pdfarchive/view/1954/1954%20-%201215.html |url-status=dead |archive-date=5 March 2016 |access-date=19 February 2010
 }}</ref><ref name="Flight, 30 April 1954, Napier diesels" >
 {{cite journal
@@ Line 26: / Line 28: @@
   |author=E. E. Chatterton
   |title=Napier Diesels: An RAeS Lecture
-  |chapter=
   |url=http://www.flightglobal.com/pdfarchive/view/1954/1954%20-%201223.html
   |format=PDF
   |date=22 April 1954
-  |pages=552
+|pages=552
   |ref=Flight, 30 April 1954, Napier diesels
-  |accessdate=19 February 2010
+  |access-date=19 February 2010
-}}</ref> and the [[Wright R-3350 Duplex-Cyclone|Wright R-3350]]<ref name="Flight, 2003, Ten ideas that failed " >
+}}</ref> and the [[Wright R-3350 Duplex-Cyclone|Wright R-3350]].<ref name="Flight, 2003, Ten ideas that failed " >
 {{cite journal
   |journal=[[Flight (magazine)|Flight]]
   |title=Ten Ideas That Failed: 2 Turbo-compound Piston Engine
-  |chapter=
   |url=http://www.flightglobal.com/articles/2003/12/16/175396/ten-ideas-that-failed.html
   |format=PDF
   |date=16 December 2003
+|ref=Flight, 2003, Ten ideas that failed: 2 Turbo-compound piston engine
-  |pages=
+  |access-date=19 February 2010
-  |ref=Flight, 2003, Ten ideas that failed: 2 Turbo-compound piston engine
-  |accessdate=19 February 2010
 }}</ref><ref name="Flight, 1997, Super survivor " >
 {{cite journal
   |journal=[[Flight (magazine)|Flight]]
   |title=Super Survivor
-  |chapter=
   |url=http://www.flightglobal.com/articles/1997/06/18/4788/super-survivor.html
   |format=PDF
   |date=18 June 1997
+|ref=Flight, 1997, Super survivor
-  |pages=
-  |ref=Flight, 1997, Super survivor
   |quote=in its hey-day, the Connie was often called the world's best tri-motor
-  |accessdate=19 February 2010
+  |access-date=19 February 2010
-}}</ref> being examples.  The exhaust restriction imparted by the three blowdown turbines used on the Wright R-3350 is equal to a well-designed jet stack system used on a conventional [[radial engine]], while recovering about {{convert|550|hp|kW|abbr=on}} at METO (maximum continuous except for take-off) power.<ref name="EH"/> In the case of the R-3350, maintenance crews sometimes nicknamed the turbine the ''parts recovery turbine'' due to its negative effect on engine reliability. Turbo-compound versions of the [[Napier Deltic]], [[Rolls-Royce Crecy]], [[Rolls-Royce Griffon]], and [[Allison V-1710]] were constructed but none was developed beyond the prototype stage. It was realized in many cases the power produced by the simple turbine was approaching that of the enormously complex and maintenance-intensive piston engine to which it was attached. As a result, turbo-compound aero engines were soon supplanted by [[turboprop]] and [[turbojet]] engines.
+}}</ref> The exhaust restriction imparted by the three blowdown turbines used on the Wright R-3350 is equal to a well-designed jet stack system used on a conventional [[radial engine]], while recovering about {{convert|550|hp|kW|abbr=on}} at METO (maximum continuous except for take-off) power.<ref name="EH"/> In the case of the R-3350, maintenance crews sometimes nicknamed the turbine the ''parts recovery turbine'' due to its negative effect on engine reliability. Turbo-compound versions of the [[Napier Deltic]], [[Rolls-Royce Crecy]], [[Rolls-Royce Griffon]], and [[Allison V-1710]] were constructed but none was developed beyond the prototype stage. It was realized in many cases the power produced by the simple turbine was approaching that of the enormously complex and maintenance-intensive piston engine to which it was attached. As a result, turbo-compound aero engines were soon supplanted by [[turboprop]] and [[turbojet]] engines.
 Some modern heavy truck diesel manufacturers have incorporated turbo-compounding into their designs. Examples include the [[Detroit Diesel]] DD15<ref>
@@ Line 68: / Line 65: @@
   |url=http://www.detroitdiesel.com/pdf/engines/2009-dd15-brochure.pdf
   |title=DD15 Brochure
-  |format=pdf
   |publisher=Detroit Diesel
 }}</ref> and [[Scania AB|Scania]]<ref>
@@ Line 75: / Line 71: @@
  |title       = Scania Turbocompound
  |publisher   = Scania Group
- |deadurl     = yes
+ |url-status     = dead
- |archiveurl  = https://web.archive.org/web/20100130064711/http://www.scania.com/products-services/trucks/main-components/engines/engine-technology/turbocompound/index.aspx
+ |archive-url  = https://web.archive.org/web/20100130064711/http://www.scania.com/products-services/trucks/main-components/engines/engine-technology/turbocompound/index.aspx
+ |archive-date = 30 January 2010
- |archivedate = 2010-01-30
- |df          =
 }}</ref> in production from 1991.<ref>
 {{cite web
@@ Line 85: / Line 80: @@
  |publisher   = Scania Group
  |quote       = With 440 hp, the new version of Scania's 12-litre turbocompound engine is suitable for Alpine terrain, as well as normal European long-haul and construction operations.
- |deadurl     = yes
+ |url-status     = dead
- |archiveurl  = https://web.archive.org/web/20110807165744/http://www.scania.com/%28S%28ebn3pnjrzi4q5wm4hwql15y5%29%29/media/pressreleases/2001070614en.aspx
+ |archive-url  = https://web.archive.org/web/20110807165744/http://www.scania.com/%28S%28ebn3pnjrzi4q5wm4hwql15y5%29%29/media/pressreleases/2001070614en.aspx
- |archivedate = 2011-08-07
+ |archive-date = 7 August 2011
- |df          =
 }}</ref>{{clarify|date=June 2011}}<!--which Scania product?-->
-Starting with the 2014 season, [[Formula 1]] switched to a new 1.6 liter turbocharged V6 [[Formula One engines#2014|formula]] that uses turbo-compounding.{{citation needed|date=February 2015}} The engines use a single turbocharger that is connected to an electric motor/generator called the MGU-H. On harvesting, the MGU-H acts as a generator, converting wasted mechanical energy from the turbine into electrical energy that is stored in a battery. When the car accelerates, the MGU-H acts as a motor, using the stored electrical energy to spool up the turbine, eliminating lag.{{citation needed|date=February 2015}}
+Starting with the 2014 season, [[Formula One]] switched to a new 1.6 liter turbocharged V6 [[Formula One engines#2014–2021|formula]] that uses turbo-compounding. The engines use a single turbocharger that is connected to an electric motor/generator called the MGU-H. The MGU-H uses a turbine to drive a generator, converting waste heat from the exhaust into electrical energy that is either stored in a battery or sent directly to an electric motor in the car's powertrain.
 ==List of types==
@@ Line 126: / Line 120: @@
 * [[Turbocharger]]
 * [[Gas turbine]]
+* [[Electric turbo-compound]]
 ==References==
-{{reflist}}
+{{Reflist}}
 {{Piston engine configurations}}

Latest revision as of 07:26, 17 September 2024

Concept

History

List of types

See also

References