Fuel placement and atomization inside a gas-turbine fuel injector at realistic operating conditions

Abstract

The atomization process and fuel placement inside a gas turbine fuel injector are investigated at realistic operating conditions to understand the role of individual flow processes and hardware components. A high pressure, high temperature spray test facility is developed that can simulate a wide range of aero-engine operating conditions. The fuel injector is a swirl cup - dual orifice nozzle combination which is used in the rich dome combustors of various aero-engines. The internal flow field is captured using time-resolved laser induced fluorescence imaging and phase Doppler interferometry measurements. A stage-wise characterization is adopted to track the spray formation as the flow evolves through the swirl cup. The fuel placement at the cup exit is mainly decided by pilot nozzle spray characteristics and the relative momentum exchange between the gas and liquid phases. At the swirl cup exit, two class of droplets are formed: (1) droplets originated directly from the pilot nozzle, which are convected downstream by the primary air swirl, (2) droplets originated from the rim, which are atomized by the shear layer. The relative percentage of these two droplet classes depends on the pilot nozzle operation at low and high power conditions. The effect of primary spray and wall-filming are minimal towards improving the atomization. In both low and high power operating cases, the counter-rotating shear layer interactions are identified as the major mechanism that is improving the atomization process in swirl cup.