Potential of Future Thermoelectric Energy Recuperation for Aviation

Abstract

Germany's Fifth Aeronautical Research Program (LuFo-V) gives the framework for the thermoelectric energy recuperation for aviation (TERA) project, which focuses on the positioning of thermoelectricity by means of a holistic reflection of technological possibilities and challenges for the adoption of thermoelectric generators (TEG) to aircraft systems. The aim of this paper is to show the project overview and some first estimations of the performance of an integrated TEG between the hot section of an engine and the cooler bypass flow. Therefore, casing integration positions close to different components are considered such as high-pressure turbine (HPT), low-pressure turbine (LPT), nozzle, or one of the interducts, where the temperature gradients are high enough for efficient TEG function. TEG efficiency is then to be optimized by taking into account occurring thermal resistance, heat transfer mechanisms, efficiency factors, as well as installation and operational system constrains like weight and space.

TEG Design for Waste Heat Recovery at an Aviation Jet Engine Nozzle

“…The occurrence of MW heat losses of turbofan engines [21], in contrast to the relatively low average electrical power requirements of today's mid-size aircrafts (180 PAX~45 kVA/engine) offers an attractive fuel saving potential from a direct conversion of engine heat into electrical energy by TEG. As shown in a previous work [22], the assumption of an efficient heat transfer by heat pipes (κ eff = 400 Wm −1 K −1 ) and conservative TEG material efficiency (ZT mean = 0.8) yields a specific TEG power output between 1 kWm −2 to 9 kWm −2 , which becomes attainable from of a first approximation of temperatures and heat fluxes on several sections of the reference engine: high-and low pressure turbine (HPT, LPT), interducts, and nozzle. The theoretically maximum available surface of the turbofan geometry would allow for an installation of approximately 15 kVA TEG power output per engine in total.…”

“…In order to quantify the reduction of the fuel consumption, combined numerical methods have been applied to forward simulation data to a parametric model of the aircraft using the Pacelab Aircraft Preliminary Design (APD) software environment [23]. As the reference engine, a second generation geared turbofan engine with an unmixed nozzle and design-freeze in 2030 was chosen, together with an appropriate mission profile [22]. The most influential parameters of today's civil turbofan engines (bypass ratio, overall pressure ratio, turbine entry temperature, etc.)…”

“…The most influential parameters of today's civil turbofan engines (bypass ratio, overall pressure ratio, turbine entry temperature, etc.) have been extrapolated to meet the prospective technology level in 2030 [22]. For definition of the geometry and the engine thrust requirements, the engine was designed with GasTurb [24] for top of climb as the design point (DP).…”

“…The lowered mechanical power, which is taken by the generator from the driving shaft, translates into an efficiency improvement, and this in turn leads to a reduction of the specific fuel consumption (SFC). According to the APD model of the reference aircraft the maximum saving on SFC equals 1% for a vanishing mechanical power usage by the conventional generator (total replacement by TEG) [22]. In this case, the TEG must provide the entire average power output of the generator, which equals 45 kVA per engine according to the APD model.…”

Evaluation of energy efficient propulsion technologies for unmanned aerial vehicles

“…On small-scale UAVs, mass budgets are typically very tight, so a lightweight generator onboard to buffer battery systems could be extremely advantageous. If a proof-of-concept can be developed at a small scale, and the TEGs are capable of recovering a tangible amount of lost heat, energy harvesting technology could prove to be a practical option for larger-scale applications (Bode et al 2017).…”