Chemical Science and Technology Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899, USA

The statistical behavior of droplets in a kerosene pressure-atomized spray was investigated under swirling and burning conditions. This case was studied in order to better understand individual droplet transport processes downstream of the fuel spray flame. A two-component phase-Doppler particle sizing system was employed to provide information on the droplet size and velocity distributions as well as interarrival-time statistics. Time-resolved information is presented on the instantaneous values of diameter, and the respective axial and radial velocity components. The results provide some evidence of nonsteady interarrival-time statistics (associated with droplet clustering) immediately downstream of the fuel nozzle and at radial coordinates near the center of the spray. This unsteady statistical behavior was most prominent within the shear layer formed near the inner spray boundary. Decomposition of the results into size classes indicated that clustering (attributed to entrainment by recirculating gases) occurred only for the smallest droplets, 020/tm in diameter. For larger droplets, analysis on the random nature of the spray process revealed that droplet transport generally follows steady Poisson statistics. Furthermore, the information provided here shows that size-class decomposition is important in the analysis of spray behavior.