Effects of fuel nozzle displacement on pre-filming airblast atomization

In gas turbine combustors, optimum arrangement between a fuel nozzle and a swirler/prefilmer module must be sought to achieve satisfactory ignition and stability characteristics in addition to reduced level of emissions. However, due to thermal expansion of the combustor or misalignment of the fuel nozzle, the location of a fuel nozzle may vary. Displacement of a fuel nozzle may change the amount of fuel injected to the pre-filming device (usually the inner swirler wall) and the location of attachment, which in turn affects the thickness of pre-filming liquid sheet on the wall. As a result, the spray structure formed by pre-filming airblast atomization may be significantly changed. An experimental investigation is carried out to study the effects of fuel nozzle displacement on the structure of a spray formed by a dual orifice pressure atomizer and a counter-rotating dual swirler: The inner wall of the swirler is designed to be used as a pre-filming device. The behavior of droplets, the flow characteristics of the swirling air flow, and the interaction between droplets and the flow are studied. Optical diagnostic methods including a flow visualization and an Adaptive Phase/Doppler technique are used. Distributions of droplet size, number density, and liquid phase volume flux are presented for various fuel nozzle displacements, in addition to gas phase velocity.