Editing Turbofan (section)

=== Afterburning turbofan ===
{{further|Afterburner}}
[[File:Pratt & Whitney F119.JPEG|thumb|[[Pratt & Whitney F119]] afterburning turbofan on test]]

Since the 1970s, most [[jet fighter]] engines have been low/medium bypass turbofans with a mixed exhaust, [[afterburner]] and variable area exit nozzle. An afterburner is a combustor located downstream of the turbine blades and directly upstream of the nozzle, which burns fuel from afterburner-specific fuel injectors. When lit, large volumes of fuel are burnt in the afterburner, raising the temperature of exhaust gases by a significant degree, resulting in a higher exhaust velocity/engine specific thrust. The variable geometry nozzle must open to a larger throat area to accommodate the extra volume and increased flow rate when the afterburner is lit. Afterburning is often designed to give a significant thrust boost for take off, transonic acceleration and combat maneuvers, but is very fuel intensive. Consequently, afterburning can be used only for short portions of a mission.

Unlike in the main engine, where [[stoichiometric]] temperatures in the combustor have to be reduced before they reach the turbine, an afterburner at maximum fuelling is designed to produce stoichiometric temperatures at entry to the nozzle, about {{cvt|2100|K|R °F °C|sigfig=2}}. At a fixed total applied fuel:air ratio, the total fuel flow for a given fan airflow will be the same, regardless of the dry specific thrust of the engine. However, a high specific thrust turbofan will, by definition, have a higher nozzle pressure ratio, resulting in a higher afterburning net thrust and, therefore, a lower afterburning specific fuel consumption (SFC). However, high specific thrust engines have a high dry SFC. The situation is reversed for a medium specific thrust afterburning turbofan: i.e., poor afterburning SFC/good dry SFC. The former engine is suitable for a combat aircraft which must remain in afterburning combat for a fairly long period, but has to fight only fairly close to the airfield (e.g. cross border skirmishes). The latter engine is better for an aircraft that has to fly some distance, or loiter for a long time, before going into combat. However, the pilot can afford to stay in afterburning only for a short period, before aircraft fuel reserves become dangerously low.

The first production afterburning turbofan engine was the [[Pratt & Whitney TF30]], which initially powered the [[General Dynamics F-111 Aardvark|F-111 Aardvark]] and [[Grumman F-14 Tomcat|F-14 Tomcat]]. Low-bypass military turbofans include the [[Pratt & Whitney F119]], the [[Eurojet EJ200]], the [[General Electric F110]], the [[Klimov RD-33]], and the [[Saturn AL-31]], all of which feature a mixed exhaust, afterburner and variable area propelling nozzle.