With the aviation industry ever growing the climate impact of the aviation industry grows too. Although most innovations focus on reducing the CO2 emissions, non-CO2 emissions play a large role in shaping the climate impact of flying. Contrail formation due to aviation is the primary non-CO2 factor, but there is a large amount of uncertainty in determining the impact of contrails. Currently most contrail formation theory is based on using the Schmidt-Appleman criteria (SAC), but the underlying thermodynamic assumptions are being increasingly challenged by new turbofan engines with ever higher and higher bypass ratio’s. This thesis aims to evaluate the impact of the bypass ratio on the mixing physics and contrail formation in the near field, and see if a relation between bypass ratio and contrail occurrence can be found. To evaluate the relation between bypass ratio and contrail formation, 4 different modern and future turbofan engines were simulated in the Fluent CFD solver, all with a thrust rating of about 120kN and designed for short-to-medium range aircraft such as the A320. 2D Axisymmetrical meshes were made in ICEM of around 300.000 cells for each of the engines. Grid independence was evaluated using the Grid Convergence Index method and the results were proven to be independent of the grid. To evaluate which turbulence model to use two experimental cases were used from which the κ − ω − SST-model was chosen as the most accurate one. A validation case for the CFM56-3 based on research by Cantin et al. was used to check the validity of the flow field results obtained using Fluent. Contrail modeling was performed based on thresholds for Gibbs free energy, temperature and relative humidity over ice. These thresholds were used to determine the area of possible contrail formation, and again checked against the same case from Cantin et al. . The contrail analysis model presented here showed good agreement with the verification case, although it does overestimate the contrail a bit The contrail analysis model showed that there was a relation between bypass ratio and contrail formation, with higher bypass ratio engines having a higher absolute plume intensity. The presence and intensity of a shock in the nozzle seems to correlate better with the possible contrail formation volume and plume intensity. The SAC diagrams showed that the SAC underestimated the slope of the mixing lines as calculated from the flow field. Since the plume did not return to ambient conditions at the end of the domain, no statement could be made on the persistency of the contrail. The impact of H2 was also researched, as well as the impact of relative humidity on contrail characteristics.