Suppression of Instabilities in Liquid Fueled Combustors by Variation of Fuel Spray Properties

This paper describes an experimental investigation of the feasibility of using “slow” active control approaches, which change liquid fuel spray properties, to suppress combustion instabilities. The objective of this control approach is to break up the feedback between the combustion process heat release oscillations and the combustor oscillations that drives the instability by changing the characteristics of the combustion process (i.e., characteristic combustion time). To demonstrate the feasibility of such control, this study used a proprietary fuel injector (Nanomiser™), which can independently vary its fuel spray properties, and investigated the dependence of acoustics-combustion process coupling, i.e., the driving of combustion instabilities, upon the fuel spray properties. The results of this study showed that by changing the spray characteristics it is possible to significantly damp combustion instabilities. Furthermore, using Abel’s deconvolution, this study showed that the instabilities were mostly driven in regions where the mean axial flow velocity was approximately zero, in the near field of the vortices that were generated in the combustor. The results of this study strongly suggest that a “slow” active control system that employs controllable injectors could be used to prevent the onset and/or damp detrimental combustion instabilities.