Design modification of the air diffuser in the burners of a fuel oil power plant. Part II: Interaction with the liquid spray

Standard fuel oil industrial burners normally include an air diffuser to condition the air flow so that it satisfies the requirements for combustion. Primary air has to mix efficiently with the fuel droplets, confining them in a defined volume and ensuring their complete consumption in a determinate residence time. A widely used technique to achieve these objectives is to induce a swirling motion to the co-flowing air to create a recirculation zone. This work analyzes how a modification in the original design of the diffuser currently in use in a Cuban power plant, already studied in the first part of this investigation and consisting in the addition of a finned swirler ring, modifies the interaction of the air stream with the liquid spray. To this end, experiments were performed in a wind tunnel with a 1/3 scaled down burner model. To simulate the burner nozzle, a commercial air-assisted hollow cone one was used. Droplet Sauter mean diameter (SMD) was measured with laser diffractometry, and the three components of the average velocity of the droplets without and with co-flowing air were calculated with stereo particle image velocimetry (SPIV) in a complete diametric plane, divided in seventy 35 mm × 26.5 mm zones. The analysis of the results indicates that the presence of the swirler ring improves the performance, enhancing the rotation of the air flow, reducing the axial velocity and recirculating a fraction of the droplets closer to the exit nozzle.