A comparison of spatially-resolved drop size and drop velocity measurements in an isothermal chamber and a swirl-stabilized combustor

A liquid fuel air-assist atomizer is characterized in both an isothermal spray chamber and a swirl-stabillized combustor. The objective is to asses the extent to which the isothermal characterization represents atomizer performance under reacting conditions and in the presence of strong, aerodynamic swirl. The technique employed for the point measurements of droplet size and droplet velocity is phase Doppler interferometry. In the isothermal chamber, comparative measurements are conducted using laser diffraction (Malvern). To explain the differences in spray behavior observed in the combustor, the droplet measurements are complemented with laser anemometry measurements of the axial and azimuthal velocity fields, and thermocouple measurements of the temperature field. The results show that, except for initial Sauter mean diameter (SMD), the spray behavior in the combustor is substantially different than that observed in the isothermal chamber. In particular, (1) the spray field in the combustor has a hollow-cone structure, (2) the radial spread of the spray widens, (3) the number density decreases by at least an order of magnitude, and (4) the SMD at points displanced from the centerline is reduced. These differences are explained by the presence of heat release and the aerodynamically induced recirculation. In addition, the droplets and fuel vapor in the widened spray boundary are found to be important to combustor stability and performance. The results establish the importance and potential of characterizing sprays within the practical, operating environment. © 1988 Combustion Institute