FLEX CYCLE COMBUSTOR DEVELOPMENT AND DEMONSTRATION

An innovative, ''flex-cycle'' combustion system has been developed for the Garrett Model 400-1 Integrated Power Unit (IPU), a 425 shp (317 k W) gas turbine engine designed for use on future fighter aircraft. Dem onstration of this system required real-time transient operation of th e combustor in a full-scale test rig. The transient testing was unique , having been performed with an electronic control, which modulated al l combustor operating parameters according to programmed engine compon ent maps, drag curves, fuel schedules, and selected ambient test condi tions. The axially injected annular combustor is capable of engine sta rts in two seconds, as well as producing 200 shp (149 k W) for emergen cy use at all altitudes up to 50,000 ft (15,240 m). The combustion sys tem is capable of switching operation from the emergency power stored energy (SE) mode to the normal-air breathing (NAB) auxiliary power mod e without loss of engine power. The flex-cycle combustor supplies emer gency power in the SE mode with a temperature rise of 2200-degrees-F ( 1222-degrees-C) and in the NAB mode with a temperature rise of 1600-de grees-F (889-degrees-C). Specific features that make these requirement s possible include air-assisted simplex airblast fuel atomizers with i ntegral check valves, and effusion-cooled combustor liner walls. This paper describes the flex-cycle combustion system design, test methods used, and significant test results. Steady-state performance, in both the SE and NAB operating modes, and real-time transient test results a re discussed. The transient testing included rapid starts as well as t ransitions from the SE to NAB operating regimes.