An axisymmetric capsule, consisting of an incompressible liquid droplet, surrounded by an infinitely thin elastic membrane having a Mooney constitutive behaviour, is suspended into another incompressible Newtonian liquid subjected to an elongational shear flow. The motion and the deformation of the capsule are determined numerically by means of a boundary-integral technique. It is thus possible to reach large deformations, and to study the influence of the initial geometry of the particle, as well as that of the constitutive behaviour of the membrane. In all cases considered here, it appears that there exists a critical value of the non-dimensional shear rate (the capillary number) above which no steady solution can be obtained, and where the capsule continuously deforms. This phenomenon is interpreted as the outset of burst. The model shows also the importance of the sphericity index for the determination of the overall capsule deformability.

The Effervescent atomizer, which is a type of internal-mixing twin-fluid atomizer, has been showed to work well with biofuels in terms of lower droplets size at relatively low injection pressure. The two phase flow inside the atomizer was numerically simulated using the volume of fluid model. Validation with experimental work was performed. The present results showed that the gas to liquid mass ratio (GLR) is one of the major contributory factors affecting the atomizer performance. The two phase flow was identified as slug flow in the discharge passage at low GLR (.08%). The flow evolved to slug-annular flow at GLR= 0.5%. At relatively high GLR (0.8%) the annular flow was distinguished. The mixing between phases was augmented with increasing GLR. Finally the liquid film thickness at the atomizer outlet was calculated and compared with the conventional aviation Jet-A1 fuel. The results showed that the liquid film thickness almost remains unchanged at low GLRs, though the higher biofuel viscosity, order of four. But, for higher GLRs, the liquid film thickness slightly changed. Finally, the results unveil the superiority of effervescent atomizer with Jatropha biofuel.

In the current work, three-dimensional simulations of the internal flow inside effervescent atomizer are performed. For this purpose, the volume of fluid model combined with the two equation realizable ݇-ߝ turbulence model are adopted. Validation with previous work in the literature is performed and the current results compare well. The internal flow results are then compared for both jet-A1 fuel and jatropha biofuel, as alternative fuel for commercial aviation. The present results show that the flow inside the atomizer evolves with gas to liquid mass ratio (GLR). Slug flow is identified for both fuels at low GLRS (below 0.3%) while annular flow is obtained at higher GLRs (above 0.3%). The effect of biofuel viscosity on the flow is obvious at GLRs below 0.3% and is relatively inhibited at higher values of GLR (0.8%). Finally the current results show the capability of effervescent atomizer in handling jatropha biofuel, in terms of internal flow. KEY WORDSJatropha biofuel, effervescent atomizer, two-phase flow, volume of fluid and aviation * Assist. Lecturer,