ID 398

Spray characteristics of a dual orifice swirl cup at elevated pressures and temperatures

 

Abstract:

The spray characteristics of a gas turbine fuel injector is investigated at realistic engine conditions to understand the droplet behaviour in elevated pressure and temperature environments. The swirl cup is a piloted prefilming airblast atomizer that is typically used in rich dome combustors of gas turbines, where a dual orifice nozzle is used as the pilot injector to generate the primary spray. This paper, reports results from experiments done to characterize the spatial and temporal features of the spray by time resolved direct laser light sheet imaging at 5 KHz. A phase Doppler interferometer is used to measure the droplet size and velocity distribution. Experiments are performed for low and high-power operating conditions, up to 7 bar and 623 K ambient at constant fuel air ratio (FAR). The spray structure is mainly dictated by the alignment of majority of droplets to the swirl shear layer at the swirl cup exit. The vortex shedding at the cup exit results in a clustered droplet motion in the downstream region. At high power conditions, the FAR increases and the recirculating spray structure is altered drastically, with the central region filled with droplets. The increase in liquid to gas momentum coupling results in ~50 % drop in the shear layer velocity and ~20 % increase in Sauter-mean-diameter compared to the low-power conditions. For constant FAR, increase in ambient pressure results in the formation of bigger droplets, with an expansion of the recirculation zone. Above 373 K, increase in air temperature results in fine droplets due to high evaporation rates.