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 an d stability characteristics in addition to reduced level of emissions. Howe ver, 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 nozz le may change the amount of fuel injected to the pre-filming device (usuall y the inner swirler wall) and the location of attachment, which in turn aff ects the thickness of pre-filming liquid sheet on the wall. As a result, th e spray structure formed by pre-filming airblast atomization may be signifi cantly changed. An experimental investigation is carried out to study the e ffects of fuel nozzle displacement on the structure of a spray formed by a dual orifice pressure atomizer and a counter-rotating dual swirler: The inn er 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, an d the interaction between droplets and the flow are studied. Optical diagno stic methods including a flow visualization and an Adaptive Phase/Doppler t echnique are used. Distributions of droplet size, number density, and liqui d phase volume flux are presented for various fuel nozzle displacements, in addition to gas phase velocity.