Design and Performance Evaluation of a Two-Position Variable Geometry Turbofan Combustor

Abstract

Variable geometry combustors offer the potential for reductions in ignition and lean blowout fuel-air ratios required for expanded operational envelopes, while maintaining acceptable levels of combustion efficiency and pattern factor at high-temperat ure-rise operating conditions. Following a screening procedure that evaluated simulated variable geometry configurations, a variable geometry mechanism was incorporated into the combustion system and test evaluated. The testing included ground level ignition, altitude ignition, stability, combustion efficiency, and discharge temperature quality as functions of three fuels: JP-4, JP-5R, and a blend of JP-5R and DF2. The test conditions were consistent with high-temperature-rise, advanced turbofan engine systems operating over a wide flight envelope. The test results showed a definite improvement in combustion performance and the variable geometry system functioned properly and sealed adequately. The lean blowout fuel-air ratio goal of 0.002 was achieved for the majority of test conditions with JP-4 fuel and the ignition fuel-air ratio goal of 0.008 was achieved for all conditions. The temperature spread factor and combustion efficiency as well as liner temperatures were within the normal operating limits for maximum power conditions. A slight degradation in combustor operating characteristics was noted after changing to JP-5R fuel and further degradation after changing to JP-5R/DF2.