Turbine Fuel Ignition and Combustion Facility for Extremely Low Temperature Conditions

Abstract

As the temperature of combustion air and fuels are reduced, the ability to achieve ignition within gas turbine engines becomes increasingly difficult. Several factors share responsibility, related largely to the physical characteristics of fuel emerging from nozzles, whereby an increasing fuel viscosity with temperature reduction results in larger average fuel droplets. The ensuing reduced surface area hinders fuel evaporation within an environment where evaporation is already impeded by low partial pressures due to low ambient temperature conditions and/or depending on the mode of operation, due to a high altitude environment. To study the effects of extremely low air and fuel temperatures on gas turbine fuel ignition performance, a dual mode (namely for cold start and altitude relight) test rig has been designed and commissioned. Its main components include a turbo-jet combustion chamber section, fuel system, ignition system, fuel/air cooling systems, and data acquisition/instrumentation. For airflow within the combustion chamber, two alternate sources are used, depending on the mode of operation. As such, this rig allows key parameters related to gas turbine ignition, such as fuel flow, fuel viscosity, ignition characteristics, airflow, and pressure conditions to be monitored and recorded. Highlights of this test rig include a General Electric J-85 combustion chamber section with quartz windows, fuel and air cooling via cryogenic liquids (LN2 for the fuel, LN2 and LOx for air), fuel and air closed loop temperature control, high speed data acquisition, a gas turbine exciter or, as selected, a custom programmable ignition system. Airflow is provided either by twin 11 HP blowers providing up to 0.5 kg/s of airflow to simulate sea level start conditions, or through the entrainment of high velocity air to simulate relight conditions at up to 21000 feet altitude. This rig is capable of achieving minimum inlet air temperatures and fuel temperatures lower than −45°C. A series of commissioning tests was undertaken with the rig in both ground start and altitude (low pressure) configurations. In order to study viscosity effects on ignition performance, two common gas turbine fuels were utilized, namely JP-4 (F-40) and JP-8 (F-34). Ignition fuel flows as well as lean blowout flows for a stock injector design are presented for these fuels across a matrix of fuel and air temperatures. Conclusions are drawn and future developments are described.