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The swirl cup airblast fuel injector is widely used in modern low-emission gas turbine combustors. It is important to understand the underlying physics in the interaction between fuel spray and complex swirling airflow. The present study investigates a swirl cup airblast fuel injector's swirling flow and spray atomization characteristics. Various laser-based diagnostics, including planar Mie scattering, phase-Doppler particle analyzer, and high-speed particle imaging velocimetry, were employed for this purpose. The swirl cup airblast fuel injectors, featuring different outer swirler swirl numbers (0.8 < S N < 1.8) and inner–outer relative swirling directions, were investigated in an air Reynolds number ranging from 0.77 × 106 to 1.16 × 106 and a 2 kg/h constant kerosene mass flow rate. The results showed that, since the swirler relative direction showed a significant influence on the inner swirler induced central toroidal recirculation zone and outer swirler induced swirling jet zone, the interaction between spray and swirling airflow was changed. Therefore, spray angle, Sauter mean diameter, and droplet velocity were changed by the swirler relative direction. Moreover, the effect of swirl number on the spray characteristics was found to be different for co- and counter-direction swirler configurations. [ABSTRACT FROM AUTHOR]

To investigate the influence of swirling air flow field on the spray characteristics and the droplet behaviors of the swirl cup airblast fuel injector, a single swirler cup and a double swirlers cup airblast injector were operated in a wide range of fuel mass flow rates ( m f ) and relative air pressure drops ( Δ P a ). Various laser based diagnostics, including planar Mie scattering, phase-Doppler particle analyzer, and high speed particle imaging velocimetry, were employed to provide the information of spray angle, droplet Sauter mean diameter (SMD), droplet velocity, and air flow velocity. The results show that the air flow field was characterized by central toroidal recirculation zone (CTRZ), the double swirlers cup airblast injector generated stronger CTRZ than single swirlers cup airblast injector. The spray characteristics and the droplet behaviors with different size classes were significantly affected by the air flow field. The larger droplets (25–100 μm) with higher initial momentum were likely to keep its velocity when passing through CTRZ, when the m f increased, more large fuel droplets could pass through the CTRZ and expanded to both sides, resulting an increase in a spray angle. On the other hand, smaller droplets (<25 μm) with lower initial momentum were trend to be enrolled by the CTRZ; therefore, the spray droplets at lower m f were confined in the CTRZ. These droplets trend to coalesce with each other resulting in an increase of SMD in this region. [ABSTRACT FROM AUTHOR]

Lean combustion has been applied in gas turbine combustors to meet increasingly stringent regulations for pollutant emissions. As a representative low-emission technology, stratified partially premixed (SPP) combustion is capable of effectively reducing NOx emissions while still providing robust flames. In this work, the flow and spray processes inside an SPP combustor were experimentally investigated to further reveal the role of main stage swirl in flow development and fuel placement. Particle image velocimetry (PIV) and Planar Mie scattering (PMie) techniques were applied to provide the velocity distributions and droplet distributions under isothermal conditions with a relative pressure drop ranging from 1% to 5%. A spray post-processing algorithm was developed to acquire the characteristic parameters of the sprays without clear boundaries. Results show that the strong swirl from the main stage leads to the radial flow of pilot air streams and dominates the formation of central toroidal recirculation zone (CTRZ). With the addition of the main stage swirl, a proper flow structure including jet zones, recirculation zones and shear layers is formed, which promotes the widening of droplet radial distribution and the increase of the spray cone angle. The spray distribution therefore transforms from a bubble shape into a cone shape. The findings and conclusions could promote the understanding of interactions between pilot and main stage swirls for stage combustors and contribute to the optimization of such SPP injectors. [ABSTRACT FROM AUTHOR]