Biofuels in civil aviation is actively studied in recent years to identify potential alternative jet fuels to meet stringent environmental regulations imposed to tackle degraded air quality caused by fossil fuel combustion. In this context, the aviation industry prefers to develop ‘drop-in’ fuels which may not require substantial modifications in existing jet engine technologies. The thesis aims at evaluating the atomization characteristics of camelina- and jatropha-derived drop-in biofuels discharging from simplex swirl atomizer used in aircraft gas turbine engines. The test fuels are characterized in detail and all fuels meet current ASTM D7566 specifications. The experiments are conducted by discharging fuel spray into quiescent atmospheric air in a fuel spray booth to obtain spray characteristics such as fuel discharge behaviour, spray cone angle, breakup behaviour of swirling fuel sheet and spray drop size distribution. The characteristics of sheet breakup are deduced from the captured images of biofuel sprays and the measurements of spray droplet size distribution are obtained using Spraytec (laser-diffraction instrument). A systematic comparison is made between the biofuel sprays and the 100% Jet A-1 (conventional aviation kerosene) sprays to evaluate the drop-in feature of the biofuels. All the measured spray characteristics of the biofuel sprays follow the Jet A-1 both in qualitative and quantitative terms which ensure the drop-in nature of the tested biofuels. The minor differences observed in the comparison of the quantitative spray measurements are attributed to the variation in the fuel properties. This claim is supported using the predictions obtained from the liquid film breakup model and the empirical correlation reported in the literature for the determination of sheet breakup characteristics and mean drop size for sprays discharging from simplex swirl atomizers.