Editing Combustor (section)

===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>