Effect of internal geometry of the pressure-swirl duplex nozzle on the atomization characteristics of jet a-1 fuel

The effects of the geometric parameters of a pressure-swirl duplex nozzle (dual orifice) on the spray characteristics of Jet A-1 fuel were studied. Two pilot nozzles with different shapes and two main nozzles with different shapes were evaluated. The spray characteristics were analyzed using laser diagnostic techniques, a phase Doppler particle analyzer (PDPA) and planer laser sheet imaging. Atomizer performance including flowrate, discharge coefficient, spray structure, resulting droplet size, and velocity distribution were analyzed. Comparison of the atomization characteristics under various injection conditions and nozzle geometry revealed great major alteration in spray characteristics. This type of atomizers is mainly used as fuel injectors in gas turbine combustors. The discharge coefficients of the pilot nozzles minimally affected by the injection pressure, while the discharge coefficient of the combined pilot and main nozzle was considerably influenced by the injection pressure. The discharge coefficient of the cone-shaped pilot nozzle was slightly higher than that of the flat-shaped pilot nozzle at low injection pressures. The spray cone angle of the cone-shaped pilot nozzle was higher than that for the flat-shaped pilot nozzle due to the well-matched flow condition, producing higher swirl intensity. The nozzle with the counter-rotating flow configuration formed a larger spray cone angle owing to the interaction of the two sprays having opposing rotational directions. The nozzle with the counter-rotating flow configuration demonstrated lower axial and radial velocities compared to those for the nozzle with the co-rotating flow configuration due to the energy losses incurred by the shear flow of the two sprays having a counterrotating flow configuration. A cone shape tip inside the swirl chamber helped swirl intensity and consequently wider spray and finer atomization when the opposing orientation of swirlers causes energy loss, turbulence, shear flow, and accordingly a wider range of droplet size with marginally lower velocity.