Modification of the Reaction Zone Using a Smart Fuel Injector for Control of Instabilities in Liquid Fueled Combustors

This paper describes an experimental investigation of suppressing combustion instabilities in a liquid fueled (n-heptane) atmospheric combustor incorporating an array of “smart” fuel injectors. These injectors were designed so that their spray properties could be manipulated without changing the overall operating conditions (power, mass flow rates, equivalence ratio, etc.) of the combustor. The dependence of these spray properties upon the smart injector settings was determined for a single injector using a series of cold flow experiments, including spray images and PDPA measurements of spray velocities and droplet sizes. The stability characteristics of a combustor incorporating seven such injectors were then determined and correlations were drawn between these characteristics, the single injector spray properties, and combustion behavior measurements taken for a single injector. It was shown that both longitudinal and tangential instability modes were excited in this combustor; the mechanisms of excitation and damping of these modes were then further investigated using high speed photography and spectroscopy measurements. Finally, suppression of both modes of instabilities in this combustor were demonstrated by slow tuning of the injector spray properties.