An linear instability analysis is made in Part II of a moving thin viscous liquid sheet of uniform thickness in an inviscid gas medium. It shows that surface tension always opposes the onset and development of disturbances. Existence of surrounding gas and relative velocity between the sheet and gas is required for the onset of instability. If gas Weber number, We_g, is smaller than the density ratio of gas to liquid, ρ, liquid viscosity enhances instability. If We_g is just slightly larger than ρ, aerodynamic and viscosityinduced instabilities interact with each other, displaying the complex effects of viscosity via Ohnesorge number. For We_g » ρ, aerodynamic instability dominates, liquid viscosity reduces disturbance growth rate, and increase the dominant wave length. From the derived dispersion relation, a disturbance Mach num ber, M_d, is defined. If M_d > 1, the liquid sheet is unstable. If M_d = 1, it is neutral. Whereas for M_d < 1, the sheet is stable.

Through maximum entropy formalism, droplet probability distribution function (PDF) in sprays is formulated in Part III. If only conservation of mass is considered, the derived analytical droplet size PDF is Nukiyama-Tanasawa type. If conservation of mass, momentum and energy is all taken into account, joint droplet size and velocity PDF is obtained for isothermal sprays without resorting to the details of atomization processes. The joint PDF predicted depends on Weber number, and compares favorably with measurements. Droplet velocity PDF is truncated Gaussian for any specific droplet size. As droplet size increases, mean velocity approaches a constant value and velocity variance decreases, i.e., velocity becomes more uniform. Computed droplet size PDF vanishes as droplet size goes to zero. Mean droplet diam eters calculated from the predicted PDF agree well with observations and im ply that the discrepancy among the empirical correlations of Sauter mean diameter may be due to the differences in the experimental conditions (different W eber num ber ranges and source values). The computation also indicates that atomization efficiency is very low, and usually less than 1%. Droplet size, velocity and tem perature PDF in sprays under combustion has also been derived. Effects of combustion on PDF occur mainly through the heat transferred into liquid sheet prior to its breakup. Resulting joint PDF is Gaussian-like for velocity, exponential for temperature, but very complicated for droplet size. A method is presented for estim ating the am ount of heat transferred between liquid (sheet portion) and its environment.

Part IV reports experimental studies on the interaction between spray and various annular air flows. Three different categories of spray envelopes are identified and data correlation is obtained. It shows bluff-body type of combustor has ability and easement to control aerodynamically spray angle, shape and droplet trajectories. As a result, spray combustion characteristics including the heat transfer to the wall can be controlled aerodynamically.