STRUCTURE OF REACTING AND NONREACTING SWIRLING AIR-ASSISTED SPRAYS

A detailed characterization of a methanol spray produced by an air-assist atomizer with swirling atomizing air has been conducted. This study is the third of a series which examines the structure of sprays produced by a standardized atomizer which can be operated in three modes, pressure swirl, non-swirling air-assist, and swirling air-assist. Measurements of drop size and three components of velocity, three components of the gas phase velocity, the concentration of hydrocarbons within the spray, and time resolved droplet measurements are obtained at axial locations of 7.5, 15, 25, 35, 50, 75, and 100mm. These measurements are obtained for both reacting and non-reacting cases. In addition, the atomizing air flow in the absence of the spray is characterized. Primary observations from the present study are that (1) the presence of the drops alters the structure of the gas phase turbulence, including the degree of isotropy, (2) the presence of reaction strongly impacts the axial and radial velocity components, while having little impact on the azimuthal component, (3) reaction reduces the mean diameter of the distributions at all locations, (4) a strong dependence of the axial and radial velocity upon drop size exists, whereas little dependency is observed for the azimuthal component, and (5) detailed examination of the droplet arrival indicates clustering of drops. Finally, it is observed that the findings from the present study both agree and contradict with the results of others. This is indicative of the inherent complexity of reacting sprays, and suggests that a more methodical approach to studying the impact of swirl and geometrical changes is required to understand the effects of atomizing air, swirl, vaporization, and phase interaction such as that undertaken in the present effort. A detailed characterization of a swirling air-assisted spray has been conducted. This study reflects one part of a study which removes fuel type, geometry, and stoichiometry from the list of variable, and concentrates on the role of the atomizer type. Where possible, results from this study are compared to the findings of other studies which provide spatially resolved measurements in reacting sprays. The comparison of results indicate that (1) only a small number of data sets are available against which to compare the current results, and (2) consistency between data sets has not yet been reached. The majority of the studies do find that (1) droplets modulate the gas phase mean and fluctuating properties in a complex fashion, (2) the drops have less impact on the swirling component of velocity than on the radial or axial components, (3) reaction causes large increases in axial and radial velocities, and (4) the presence of reaction tends to increase the local drop size distribution means at the locations where measurements were obtained. Also, it is evident that the complexity of spray flames will require additional studies such as the present one to separate system specific effects. © 1992, Taylor & Francis Group, LLC. All rights reserved.