Estimation of mission fuel savings potential using thermoelectric recuperation in aero-engines

The reduction of fuel consumption represents a major challenge on the way to an environmentally friendly air transport system. Thermoelectric generators (TEG) can offer a robust solution for direct conversion of lost heat from an aero-engine to electricity, reducing the fuel burn fraction of engine offtake and thereby required mission fuel. The overarching goal of the TERA-project (Thermoelectric Energy Recuperation for Aviation) within Germanys fifth Aeronautical Research Program (LuFo-V) is thus to evaluate the potentials of TEG on engine and aircraft level. To that effect, integration between the hot section of the engine and the cooler bypass flow is considered to quantify achievable output power. Fundamentally, two aspects determine the success of the concept: Firstly, the gravimetric power density of the TEG, which depends on thermoelectric material properties and thermal conditions, determines whether a break-even performance can be reached. Beyond break-even, mission fuel is saved. Secondly, the total generated power, limited by the TEG size and available area, determines the overall fuel savings potential. In this contribution, a trade-study approach is presented. In order to evaluate the fuel savings potentials, an aircraft with entry-into-service in 2035 was defined and sized for future requirements as a baseline. Mission fuel is calculated as function of TEG power and weight of the TEG system. Two models are used: a simple model based on the Breguet range equation considering cruise phase only, and a more elaborate mission-based model, in which the aircraft is sized according to engine offtake and weight modifications. Results are presented for design and off-design missions and collated to expected TEG performance. From the trade studies, break-even power density is determined, and the fuel savings potential evaluated. Preliminary studies, based on a TEG integrated into the engine nozzle, indicate a fuel savings potential of one tenth of a percent.