MODELING OF GAS-TURBINE FUEL NOZZLE SPRAY

Satisfactory performance of the gas turbine combustor relies on the ca reful design of various components, particularly the fuel injector. It is, therefore, essential to establish a fundamental basis for fuel in jection modeling that involves various atomization processes. A two-di mensional fuel injection model has been formulated to simulate the air flow within and downstream of the atomizer and address the formation and break up of the liquid sheet formed at the atomizer exit. The shee t break up under the effects of air blast, fuel pressure, or the combi ned atomization mode of the air-assist type is considered in the calcu lation. The model accounts for secondary breakup of drops and the stoc hastic Lagrangian treatment of spray. The calculation of spray evapora tion addresses both droplet heat-up and steady-state mechanisms, and f uel vapor concentration is based on the partial pressure concept. An e nhanced evaporation model has been developed that accounts for multico mponent, finite mass diffusivity and conductivity effects, and address es near-critical evaporation. The present investigation involved predi ctions of flow and spray characteristics of two distinctively differen t fuel atomizers under both nonreacting and reacting conditions. The p redictions of the continuous phase velocity components and the spray m ean drop sizes agree well with the derailed measurements obtained for the two atomizers, which indicates the model accounts for key aspects of atomization. The model also provides insight into ligament formatio n and breakup at the atomizer exit and the initial drop sizes formed i n the atomizer nearfield region where measurements are difficult to ob tain. The calculations of the reacting spray show the fuel-rich region occupied most of the spray volume with two-peak radial gas temperatur e profiles. The results also provided local concentrations of unburned hydrocarbon (UHC) and carbon monoxide (CO) in atomizer flowfield, inf ormation that could support the effort to reduce emission levels of ga s turbine combustors.