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.