NDLI: Forced and Self-Excited Instabilities From Lean Premixed, Liquid-Fuelled Aeroengine Injectors at High Pressures and Temperatures

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Hochgreb, Simone Dennis, David Ayranci, Isil Bainbridge, William Cant, Stewart
Copyright Year	2013
Abstract	Measurements of unsteady pressure and chemiluminescence during flow forced operation of aeroengine lean direct injection fuel spray nozzles were made, with a goal to determine the response of the flame, subject to a range of air fuel ratios, fuel flow splits between pilot and mains injectors, and cooling flows. A rotating shutter installed at the downstream choked nozzle provided the excitation for forcing the mass flow rate between 100 to 600 Hz, at normalized intensities of 0.1 to 0.7 relative to the mean velocity at the injector. The experiments were performed at inlet conditions of 800 K and 5.7 bar. Self-excitation created by the coupling between the flame and the combustor cavity was observed, in the form of a broad peak around 275 Hz. Numerical studies indicate that the peak is associated with an entropy spot (a region of non-uniform temperature) travelling from the flame to the choked nozzle, followed by the ensuing expansion wave towards the injector and amplification of the excitation. Investigation of previous studies suggests that similar phenomena may have been present in other studies at high pressure. The main impact of the self-excitation is the significant amplification of the velocity fluctuations from 0.1 of the mean velocity away from the self-excitation frequency to around 0.7 at the peak. The flame response, represented by the ratio of the fractional fluctuations in OH* chemiluminescence to the fractional velocity fluctuations at the injector, can be determined under conditions where the self-excitation heat release contributes only a small portion of the forced heat release, based on the measured background. The flame response shows a significant dependence on both air fuel ratio and fuel splits, with a decreasing gain towards higher frequency. The results show that it is possible to generate high amplitude fluctuations on the flow using this method, and demonstrate the role of entropy spots during normal operation in lean direct injection systems. Finally, the results suggest that there is an interaction between the forcing frequency and the self-excitation, which may behave in a non-linear manner, and which deserves further investigation.
Sponsorship	International Gas Turbine Institute
File Format	PDF
ISBN	9780791855119
DOI	10.1115/GT2013-95311
Volume Number	Volume 1B: Combustion, Fuels and Emissions
Conference Proceedings	ASME Turbo Expo 2013: Turbine Technical Conference and Exposition
Language	English
Publisher Date	2013-06-03
Publisher Place	San Antonio, Texas, USA
Access Restriction	Subscribed
Subject Keyword	Temperature Cooling Sprays Chemiluminescence Entropy Fuels Flow (dynamics) Pressure Waves Cavities High pressure (physics) Flames Heat Ejectors Fluctuations (physics) Nozzles Excitation Combustion chambers
Content Type	Text
Resource Type	Article

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