Atomization characteristics on the surface of a round liquid jet

Abstract

Fundamental mechanisms of liquid jet breakup are identified and quantified. The quality of the atomization of liquids is an important parameter of many technological processes and is, e.g. for fuels and propellants critical in defining engine performance. This investigation takes a look at the jet behavior for a single injector element to determine the influence of the injection conditions on a round liquid jet. The study focuses on the atomization of a liquid forming a classical spray. To adjust the relative velocity between the liquid jet and the gaseous ambient a wind tunnel-like coaxial flow configuration was used. This made it possible to distinguish between effects of aerodynamic forces, chamber pressure and jet velocity, which determine the liquid Reynolds number and thereby the internal jet turbulence. Shadowgraphy and a novel image-processing approach was used to determine the jet surface characteristics: wavelength and amplitude. The absolute injection velocity of the jet seems to affect the structures the most with an increasing velocity causing the wavelengths to be smaller. An increase in chamber pressure seemed to have little influence on the jet with no relative velocity between the gas and liquid jet, but increased the amplitude and drop formation frequency at other testing conditions with relative motion. The wave amplitude trends provide information about the likelihood of drop formation but are limited in maximum size due to this breakup phenomenon of the jet. The study of the direction of the relative velocity demonstrated that injector performance cannot simply be described by scalar geometrical and operational injection parameters (e.g., We , Re or Oh), but has to include the injection direction of the atomizing fluids in relation to each other and to the ambient (e.g., combustion chamber). The undisturbed jet length and the spread angle were investigated, and a correlation for the droplet separation position was proposed. The data led to an extended classification of liquid jet breakup regimes. Large wave instabilities were experimentally analyzed and compared with linear stability theory.