ACOUSTIC AND OPTICAL FLAME TRANSFER FUNCTION MEASUREMENTS IN A HIGH-PRESSURE LEAN-BURN AERO-ENGINE COMBUSTOR FUELED WITH JET A

This paper reports flame transfer function (FTF) measurements obtained in a high-pressure lean-burn aero-engine combustor using acoustic and optical methods. A liquid fueled lean premixed pre-vaporized combustor was operated at various combustor fuel air ratios (FAR) relevant for supersonic transport. A high-pressure siren was employed to modulate the combustor inlet air flow at frequencies ranging from 30Hz up to 1050Hz. Acoustic FTFs were obtained via multi-microphone method using signals from multiple dynamic pressure sensors. Optical FTFs were obtained simultaneously with acoustic measurements by imaging OH*, CH* and C-2* chemiluminescence from the combustor., Specifically, line-of-sight chemiluminescence signal for each species was collected with a fiber optic probe and imaged onto photomultiplier tubes with 10nm bandpass filters centered at 310nm, 430nm and 515nm, respectively. Complementary 2D high speed OH* chemiluminescence images were also acquired using a high-speed camera to gain insight into the flame dynamics and support the interpretation of the FTF findings. A comparison of FTFs using the acoustic and optical methods show good agreement in phases and magnitude trends. The measured FTFs show significant variations with varying fuel-air ratios at various frequency ranges confirming a strong dependency of FTFs with flame shapes.