Application of an Inter-Turbine Burner Using Core Driven Vitiated Air in a Gas Turbine Engine

Abstract

An Inter-Turbine Burner (ITB) that is capable of increasing the thrust of a gas turbine engine with minimal effect on SFC has been developed. Gas turbine engines using multistage turbine sections have the inherent disadvantage of temperature loss through the turbine section. This occurs when each successive turbine stage extracts energy from the superheated mass airflow stream. The net result is limited energy potential due to the first stage turbine temperature limits. An Inter-Turbine Burner (ITB) is able to utilize constant temperature burning through the turbine section by adding burners between the turbine stages. The resultant engine is suited for missions requiring large amounts of constant or intermittent power extraction. The Spytek ITB incorporates a modified version of an Ultra-Compact Combustor (UCC) [1] (high-g burner) which was originally developed by the Air Force Research Laboratory in Dayton, Ohio. The ITB has been incorporated into a gas turbine engine and has been successfully tested operating at a near constant temperature (NCT) cycle. The engine/ITB is specifically configured and packaged for high power density use. Temperature rises across the ITB (T6-7) were tested in ranges from 421K-588K with representative increases in power take-off noted. The burner, positioned directly upstream of the ITB turbine, operates with vitiated air taken directly from the core engine exhaust stream. The engine tested is a two spool turbo-jet (ITB shaft inclusive), in the 1334(N) class. The ITB is cross shaft linked to an axial compressor booster stage, attached to the engine inlet which super-charged the core engine. The two major areas addressed in development were the ability to provide air into the primary burn zone of the ITB to sustain combustion and second, the ability to successfully entrain the combustion products from the ITB vortex chamber into the main air stream without causing undue restrictions or hot-streak problems which can affect the life of the ITB turbine. Flexibility in ITB testing is further enhanced through the use of two adjustable test features, 1) a variable flow splitter, capable of adjusting the amount of air diverted into the ITB combustor, and 2) a variable nozzle guide vane pack upstream of the ITB turbine. A proprietary entrainment system rapidly mixes the ITB combustor products with the main stream dilute flow products without any undo effects on the ITB turbine. The Mark#1 version of the ITB system exhibits power on demand increases of 16%–22%.