Effects of compressibility on the atomization of liquid jets

the effect of compressibili ty of fluids on the atomization of a liquid jet emanating from a nozzle into the ambient gas is investigated by use of linear stability analysis. An increase in the compressibility of the liquid gas is shown to promote the generation of smaller droplets, although at a slower rate. It is shown that in some parameter ranges, a small change in compressibility may result in a qualitative change of the mechanism of atomization. TOMIZATION is a process of breaking up a liquid jet into droplets of diameter much smaller than the jet di- ameter. This process is widely used in industrial applications including fuel injections in internal combustion engines. A good knowledge of the fundamental mechanism of atomiza- tion is essential for raising the combustion efficiency and re- ducing the environmental pollution. Our understanding of atomization is not yet complete. A concise review of experimental and theoretical work on atomization was given by Reitz and Bracco.1-2 A more ex- tensive exposition of the subject can be found in the work of Lefebvre.3 The atomization process as the consequence of the aerodynamic instability of a jet emanated into ambient gas was investigated by Taylor,4 Levich,5 and others. They con- sidered instability with respect to temporally growing dis- turbances. Atomization as the consequence of convective in- stability caused by spatially growing disturbances was studied by Lin and Kang,6 Lin and Lian,7 and Lin and Creighton.8 In all of the theoretical works mentioned above, the fluids are assumed to be incompressible. On the other hand in many applications, the jet speed is such that the Mach number of the ambient gas relative to the jet may reach transonic. For future applications it may even reach supersonic. Therefore, the compressibility of the fluids must be taken into account. Here, we investigate the effects of compressibility on atom- ization. The problem of instability of an inviscid compressible jet emanating into an inviscid compressible gas is formulated in the next section. The disturbance is allowed to grow both tem- porally and spatially. The results of the solution to the formu- lated problem are used to demonstrate that the compressibility brings about not only quantitative but also qualitative differences in the mechanism of atomization at its onset.