Editing Combustor (section)

==Types==
[[File:CanCombustor.svg|thumb|right|Arrangement of can-type combustors for a gas turbine engine, looking axis on, through the exhaust. Teal color (dark cyan) indicates the cooling-air flow path, orange the combustion gas flow path.]]

===Can===
Can combustors are self-contained cylindrical combustion chambers. Each "can" has its own fuel injector, igniter, liner, and casing.<ref name="nasa">Benson, Tom. [https://www.grc.nasa.gov/WWW/K-12/airplane/burner.html Combustor-Burner]. NASA Glenn Research Center. Last Updated 11 Jul 2008. Accessed 6 Jan 2010.</ref> The primary air from the compressor is guided into each individual can, where it is decelerated, mixed with fuel, and then ignited. The secondary air also comes from the compressor, where it is fed outside of the liner (inside of which is where the combustion is taking place). The secondary air is then fed, usually through slits in the liner, into the combustion zone to cool the liner via thin film cooling.<ref>Flack, p. 442.</ref>

In most applications, multiple cans are arranged around the central axis of the engine, and their shared exhaust is fed to the {{not a typo|turbine(s)}}. Can-type combustors were most widely used in early gas turbine engines, owing to their ease of design and testing (one can test a single can, rather than have to test the whole system). Can-type combustors are easy to maintain, as only a single can needs to be removed, rather than the whole combustion section. Most modern gas turbine engines (particularly for aircraft applications) do not use can combustors, as they often weigh more than alternatives. Additionally, the pressure drop across the can is generally higher than other combustors (on the order of 7%). Most modern engines that use can combustors are [[turboshafts]] featuring [[centrifugal compressor]]s.<ref>Flack, pp. 442–3.</ref><ref>Henderson and Blazowski, p. 106.</ref><ref>https://armyaviation.tpub.com/AL0993/Figure-1-20-Can-Annular-Combustion-Chamber-134.htm</ref><ref>https://www.aircav.com/gencombu.html</ref>

===Can-annular===
[[File:CanAnnularCombustor.svg|thumb|right|Cannular combustor for a gas turbine engine, viewing axis on, through the exhaust]]

The next type of combustor is the "can-annular"<ref>Federal Aviation Administration, FAA-H-8083-32A, Aviation Maintenance Technician Handbook - Powerplant Volume 1, p.1-44</ref> combustor. Like the can-type combustor, can-annular combustors have discrete combustion zones contained in separate liners with their own fuel injectors. Unlike the can combustor, all the combustion zones share a common ring (annulus) casing. Each combustion zone no longer has to serve as a pressure vessel.<ref>Mattingly, Heiser, and Pratt, pp. 377–8.</ref> The combustion zones can also "communicate" with each other via liner holes or connecting tubes that allow some air to flow circumferentially. The exit flow from the can-annular combustor generally has a more uniform temperature profile, which is better for the turbine section. It also eliminates the need for each chamber to have its own igniter. Once the fire is lit in one or two cans, it can easily spread to and ignite the others. This type of combustor is  also lighter than the can type, and has a lower pressure drop (on the order of 6%). However, a can-annular combustor can be more difficult to maintain than a can combustor.<ref>Flack, pp. 442–4.</ref> Examples of gas turbine engines utilizing a can-annular combustor include the [[General Electric J79]] [[turbojet]] and the [[Pratt & Whitney TF30]] and [[Rolls-Royce RB.183 Tay|Rolls-Royce Tay]] [[turbofans]].<ref>Henderson and Blazowski, pp. 106–7.</ref>

===Annular===
[[File:AnnularCombustorNew.png|thumb|right|Annular combustor for a gas turbine engine, viewed axis on looking through the exhaust. The small yellow circles are the fuel injection nozzles, while the larger orange ring is the continuous liner for the combustion zone.]]

The final, and most-commonly used type of combustor is the fully annular combustor.  Annular combustors do away with the separate combustion zones and simply have a continuous liner and casing in a ring (the annulus). There are many advantages to annular combustors, including more uniform combustion, shorter size (therefore lighter), and less surface area.<ref>Henderson and Blazowski, p. 108.</ref><ref>Mattingly, p. 757.</ref> Additionally, annular combustors tend to have very uniform exit temperatures. They also have the lowest pressure drop of the three designs (on the order of 5%).<ref>Flack, p. 444.</ref> The annular design is also simpler, although testing generally requires a full size test rig. An engine that uses an annular combustor is the [[CFM International CFM56]], the [[General Electric F110]] and the [[Pratt & Whitney F401]]. Almost all of the modern gas turbine engines use annular combustors; likewise, most combustor research and development focuses on improving this type.

====Double annular combustor====
One variation on the standard annular combustor is the ''double annular combustor'' (DAC). Like an annular combustor, the DAC is a continuous ring without separate combustion zones around the radius. The difference is that the combustor has two combustion zones around the ring; a pilot zone and a main zone. The pilot zone acts like that of a single annular combustor, and is the only zone operating at low power levels. At high power levels, the main zone is used as well, increasing air and mass flow through the combustor. GE's implementation of this type of combustor focuses on reducing {{NOx}} and {{CO2}} emissions.<ref>[http://www.cfm56.com/press/news/cfms+advanced+double+annular+combustor+technology/198?page_index=23 CFM'S Advanced Double Annular Combustor Technology] {{webarchive|url=https://archive.today/20120728235534/http://www.cfm56.com/press/news/cfms+advanced+double+annular+combustor+technology/198?page_index=23 |date=2012-07-28}}. Press Release. 9 Jul 1998. Accessed 6 Jan 2010.</ref> [https://engineering.purdue.edu/~propulsi/propulsion/images/jets/basics/combust.jpg A good diagram of a DAC is available from Purdue]. Extending the same principles as the double annular combustor, triple annular and "multiple annular" combustors have been proposed and even patented.<ref>Ekstedt, Edward E., et al (1994). {{US patent|5323604}} Triple annular combustor for gas turbine engine].</ref><ref>Schilling, Jan C., et al (1997). {{US patent|5630319}} Dome assembly for a multiple annular combustor].</ref>