When considering alternative fuels for aviation, factors such as the overall efficiency of the combustion process and the levels of emissions emitted to the atmosphere, need to be critically evaluated. The physical and chemical properties of a fuel influence the combustion efficiency and emissions and therefore need to be considered. The energy content of a biofuel, which is influenced negatively by the presence of oxygen in the molecular structure (i.e. oxygenated chemical compounds), is relatively low when compared with that of conventional jet fuel. This means that the overall efficiency of the process will be different. In this paper two possible scenarios have been investigated in order to assess the potential to directly replace conventional jet fuel with Methyl Buthanoate - MB (a short chain FAME representing biofuel) and a synthetic jet fuel (FT fuel) using Computational Fluid Dynamics (CFD) modelling in a typical Modern Air-Spray Combustor (MAC). In addition the impact of fuel blending on the combustion performance has been investigated. Computational Fluid Dynamics (CFD) has been verified and validated over past decades to be a powerful design tool in industries where experimental work can be costly, hazardous and time consuming, to support the design and development process. With recent developments in processor speeds and solver improvements, CFD has been successfully validated and used as a tool for optimizing combustor technology. Combustion of each fuel is calculated using a mixture fraction/pdf approach and the turbulence-chemistry interaction has been modelled using the Laminar Flamelet approach. Detailed chemical reaction mechanisms, developed and validated recently by the authors for aviation fuel including kerosene, synthetic fuel and bio-aviation fuel have been employed in the CFD modelling. A detailed comparison of kerosene with alternative fuel performance has been made.