Atomization of a small-diameter liquid jet by a high-speed gas stream.

摘要

The situation of a small-diameter liquid jet exposed to a large-diameter high-speed gas jet is investigated experimentally. Flow visualization and particle-sizing techniques are employed to examine both the initial breakup process and subsequent secondary atomization of the liquid. It is shown that nearly all of the breakup takes place in the near-field and that the bulk of the atomization is completed within the potential cone of the gas jet. The resultant drop size depends primarily on the gas velocity and to a weaker extent on the liquid mass flux. It is argued that the mechanism of primary atomization is similar to that of a liquid drop suddenly exposed to a high-speed gas stream. A phenomenological breakup model is proposed for the initial droplet size, based on the accelerative destabilization of the liquid jet surface by the Rayleigh-Taylor instability. Measurements of droplet sizes and surface wavelengths are shown to be in good agreement with the model predictions.; The downstream evolution of the droplet-size distribution is also investigated, with consideration given to several secondary mechanisms including turbulent breakup, droplet-droplet collisions, and droplet acceleration. It is argued that the relative acceleration of droplets of different size classes, and energetic collisions between droplets, are together responsible for the experimentally observed variation of the mean drop size with downstream distance from the injection plane in the far-field of the spray.; The feasibility of coaxial liquid-gas injection for pulse detonation engine (PDE) applications is additionally considered. The performance of coaxial atomizers under transient operating conditions appropriate to PDEs is analyzed along with the capability of this injection scheme to produce sufficiently small droplet sizes within restricted flow regimes. The ability to tailor the radial distributions of both the liquid mass flux and droplet sizes through the addition of swirl to the coaxial gas flow is examined, and the behavior of these jet flows in confinement tubes is also investigated. The results of this study indicate that from the standpoint of good atomization quality and controllability, coaxial injection is indeed a feasible solution for meeting the transient fuel-injection needs of the PDE.