Characterization of atomization inside a dry low emission (DLE) premixer

Dry low emission combustion systems, which allows fuel flexibility, have been developed to reduce the NOx and other emissions in gas turbine engines. In such systems, the required fuel-air mixing and flame stabilization is achieved by specially designed 'premixers'. The present work investigates the internal two-phase flow in a premixer and its influence on the spray structure at the premixer exit using various laser flow diagnostic techniques. The premixer geometry involves coaxially mounted counter-rotating swirler, through which air flow ensues into a convergent “shroud”. Multiple liquid jets issue from a central fuel stem and the atomization of the liquid jets occurs in presence of the swirling air cross flow. A transparent shroud is used for optical access in the present case. Time-resolved volumetric laser induced fluorescence imaging is adopted to visualize the internal flow field of the premixer. The internal and external air flow field is characterized by particle image velocimetry and laser Doppler velocimetry. Shadowgraph imaging is adopted to obtain the external spray structure. Liquid jet trajectory, penetration length, and the jet curling angle are estimated at different air -to-liquid ratios. Apart from the liquid jet atomization, a wall wetting is observed on the center body, depending on the air-fuel ratio for test done at atmospheric conditions. A transition is observed in the external spray structure over the range of flow conditions depending on air-fuel ratio.