Design and application of low pressure and low temperature facility to study aeronautical flame during pull-away.

Abstract

Ignition and re-ignition in aeronautical engines are vital for ensuring operability, especially under high-altitude conditions where low pressure, low temperature, and reduced flow rates impact fuel atomization and evaporation, leading to potential flame instability or extinction. To address this, a High Altitude Re-ignition for gas Turbine (HARTur) facility is developed to replicate conditions at altitudes of up to 30 000 ft and to study the pull-away phase of re-ignition where the engine accelerates from wind-milling to idle conditions. This facility simulates thermodynamic conditions similar to those in aeronautical combustion chambers during pull-away, with pressures as low as 30 kPa and temperatures down to 248 K. HARTur has been designed to characterize the performance of rich-quench-lean injection systems through global combustion efficiency analysis and extinction limits. This study details the facility setup, calibration, and experimental results for four operating conditions during pull-away. Combustion efficiency is estimated from burned gas temperature measurements obtained via pressure drop across a nozzle at the combustion chamber exit. Operating points near atmospheric conditions achieve higher combustion efficiencies compared to low-pressure and low-temperature conditions, where the flame is more susceptible to extinguishing from minor disturbances, which narrows the pull-away corridor. In-depth local analyses of spray and flame structures, performed using advanced optical diagnostics (laser tomography, planar laser-induced fluorescence, and particle image velocimetry), revealed that low-temperature, low-pressure conditions widen spray angles, degrade atomization, and destabilize recirculation zones, leading to potential flame extinction. These findings underscore the importance of optimizing injector designs and metering strategies to enhance engine operability under extreme conditions.