Effect of inner and outer airflow characteristics on high liquid pressure prefilming airblast atomization

The objective is to provide a better understanding of the hybrid atomization process to support the development of fuel injectors for future high-performance/low-emissions gas turbine combustors. In this type of fuel injector, both airblast forces and high liquid injection pressure are combined to achieve satisfactory performance over the entire range of combustor operation. The investigation involved conducting an experimental study using a fuel injector with the capability of reversing the direction of rotation of each of the two air swirlers used in the design, in addition to reducing the how area of each swirler. The experimental investigation was supported by analytical calculations that provided information on the fuel injector flowfield characteristics and relative motion between the swirling air and liquid fuel film. The results demonstrated that a combination of corotating inner airstream and counterrotating outer airstream with respect to the rotational direction of the enclosed liquid film yields the finest sprays as compared to other swirler configurations. The least efficient atomization was achieved when both airstreams were swirling in opposite direction to that of the liquid film. The study showed that in addition to air/liquid relative motion, other important aspects such as liquid injection pressure, direction of rotation of swirling air, and droplet coalescence should be considered in the design of a successful hybrid fuel injector.