Performance assessment of electrically-driven fans with heat recuperation

Abstract

This thesis investigates the uninstalled performance potential of integrating heat exchangers within a ducted fan flow path, applied to a fuel-cell driven propulsion architecture. The main objective is to find out if the effects of heat utilization enhance the engines efficiency by generating additional thrust from waste heat. The benefits of heat transfer are weighted against the penalties of total air side pressure losses, forming the major design challenge, as for low pressure losses low Mach numbers are required. In order to decelerate the flow to low Mach levels, entering the HEX, a linear diffuser is applied here. The latter diffusor type leads to long ducts and thus necessitates long overall engine length to provide needed diffusion. A cycle-level performance model is established, using a cycle level simulation tool to size the engine and estimate pressure losses of the heat exchanger and the linear diffuser duct. With that, parametric studies varying the fan pressure ratio and the heat exchanger inlet Mach number at cycle design level are carried out to investigate performance trade-offs and understand the interdependencies of integrating heat exchangers within the propulsor flow path for thrust augmentation. When compared to the reference engine without heat recuperation, the engine with low fan pressure ratio of 1.2 and medium heat exchanger inlet Mach number 0.125 resulted in the most significant feasible performance improvement of 8% in uninstalled overall efficiency.