LDA measurement of fuel droplet sizes and velocities in a combustion field

Abstract

Laser doppler anemometry was applied to simultaneous measurement of fuel droplet size and its velocity in two kinds of continuous mini burners. Droplet size was determined from the scattered light intensity ( Ip) and number of Doppler burst waves ( N) that was required to correct the effect of different particle trajectories in the measuring volume. Prior to the experiments, calibrated lines for representative droplet diameters were made with regard to Ip and N. The two burners had different types of air assist fuel injectors. One had the injector with the swirler which provides assist air with a tangential velocity component. Another had the injector without the swirler and the air had no tangential component. These combustion flow fields were then compared. Downstream of the injector in both burners, Sauter mean diameter (SMD) varies as follows. In a combustion field it is larger than that in unburned condition and reaches a maximum, after which it decreases until all the droplet evaporate rapidly. These features agree with the results of numerical calculations for fuel droplet evaporation. In combustion fields, the SMD of the droplets from the swirler injector is about 10 μm smaller than that from the no-swirler injector. Therefore the droplets evaporate earlier than those from the no-swirler injector in the burner. Temperature measurement with a thermocouple shows that the temperature in the swirler-equipped burner is about 100 K higher than that in the swirlerless burner. The swirler provides a circular cone extension of droplets with high densities and high velocities. A higher temperature zone is formed just outside the cone end.