Increased public awareness and political concern about the environmental footprint of aviation have created very ambitious goals to reduce emissions in the future. This objective of this research project is to develop a multidisciplinary turbofan engine design and sizing tool for conceptual engine design. The tool will be used in a parametric analysis to determine how the main design parameters impact engine performance and sizing. Methods to improve the propulsive and thermal efficiency have been analyzed to assess the effect on engine characteristics. The bypass ratio, fan pressure ratio, overall pressure ratio and turbine inlet temperature have been analyzed in a parametric analysis. It was found that higher values of these design parameters improved engine performance at the cost of engine size and weight.