Dense sprays

The phase Doppler method utilizes the wavelength of light as the basis of measurement. Hence, performance is not vulnerable to fluctuations in light intensity. The technique has been successfully appHed to dense sprays, highly turbulent flows, and combustion systems. It is capable of making simultaneous measurements of droplet size, velocity, number density, and volume flux. 

Recently, Razumovskid441 studied the shape of drops, and satellite droplets formed by forced capillary breakup of a liquid jet. On the basis of an instability analysis, Teng et al.[442] derived a simple equation for the prediction of droplet size from the breakup of cylindrical liquid jets at low-velocities. The equation correlates droplet size to a modified Ohnesorge number, and is applicable to both liquid-in-liquid, and liquid-in-gas jets of Newtonian or non-Newtonian fluids. Yamane et al.[439] measured Sauter mean diameter, and air-entrainment characteristics of non-evaporating unsteady dense sprays by means of an image analysis technique which uses an instantaneous shadow picture of the spray and amount of injected fuel. Influences of injection pressure and ambient gas density on the Sauter mean diameter and air entrainment were investigated parametrically. An empirical equation for the Sauter mean diameter was proposed based on a dimensionless analysis of the experimental results. It was indicated that the Sauter mean diameter decreases with an increase in injection pressure and a decrease in ambient gas density. It was also shown that the air-entrainment characteristics can be predicted from the quasi-steady jet theory. 

L. Martinelli, R. D. Reitz, and F. V. Bracco, Comparison of Computed and Measured Dense Spray Jets, in Dynamics of Flames and Reactive Systems, vol. 95 of Progress in Astronautics and Aeronautics, J. R. Bowen, N. Manson, A. K. Oppenheim and R. I. Soloukhin, eds., New York American Institute of Aeronautics and Astronautics, 1984, 484-512. 

Within the scope of this work, the initial spray breakup process, providing information about the dense spray core, will be investigated. The formation of fuel drops will be simulated based on first-principles and will offer detailed insight into primary atomization. The three-dimensional, transient calculation will track the interface evolution through droplet formation and breakup. Because the results will be based on conservation laws, they will be extremely general. This will lead to better models that can be used with confidence in the engine design process. 

Primary atomization, the formation of ligaments and drops by an atomizer, has already been a subject of study for over a century. The difficulty in experiments is that the numerous droplets reflect light, obscuring clear views of the atomization process. In addition, the high speed and small size of practical fuel injection means that the experimental images are often not clear. Dense sprays and non-spherical drops also make quantitative data difficult to obtain with laser-based diagnostics. 

Felton PG, Hamidi AA, Aigai AK. Measurement of drop-size distribution in dense sprays by laser diffraction. Proceedings, ICLAS-85. Third International Conference on Liquid Atomization and Spray Systems (The Institute of Energy, London, 1985), IVA/4/1. 

Apart from considerations in regard to drop deformation, many empirical and theoretical correlations have been obtained in an isolated-drop configuration. These correlations can be used for simulation of drop motion in very dilute sprays, where each drop can be assumed isolated, fii dense sprays, however, the drop spacings are small enough that isolated drop assumption is no longer valid. Therefore, in order to calculate the drop motion in such sprays a group of drops has to be considered as a whole. 

Catastrophic breakup has only been observed in shock tube experiments where extremely high initial relative velocities are possible. In [7], it is noted that such high velocities are not expected in typical dense sprays. Therefore, the practical applications of this breakup mode are limited. 

F.X. Tanner. Development and validation of a cascade atomization and drop breakup model for high-velocity dense sprays. Atomization and Sprays, 14(3) 211-242, 2004. 

F.X. Tanner, K.A. Feigl, S.A. Ciatti, C.F. Powell, S.-K. Cheong, J. Liu, and J. Wang, Structure of high-velocity dense sprays in the near-nozzle region. Atomization and Sprays, 16 579-597, 2006. 

Fig. 14.7 Classification of inner flame for a dense spray stream...

Jasuja, A. K., and Lefebvre, A. H., Influence of Ambient Pressure on Drop Size and Velocity Distributions in Dense Sprays. Twenty-Fifth Symposium (International) on Combustion, The Combustion Institute, Pittsburg, pp. 345-352. 

In the intermediate and dense spray regime, the local volume fraction of the liquid phase could be high and variations in the volume fractions should be accounted for in the gas-phase equations. Accordingly, the unfiltered mass and momentum conservation equations become [40-42]... 

Tanner FX (2004) Development and Validation of a Cascade Atomization and Drop Breakup Model fa- High-Velocity Dense Sprays. Atomization Sprays 14(3) 211-242... 

Santangelo, P. J., Sojka, P. E. (1994). Focused-image holography as a dense-spray diagnostic. Applied Optics, 33(19), 4132 136. 

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