Assessment of fuel as alternative heat sink for future aircraft

Abstract

Fuel is assessed as alternative heat sink for future aircraft applications to avoid excessive drag from conventional cooling systems. Two cooling concepts using fuel as a heat sink are investigated for a hybrid electric aircraft platform with entry into service of year 2035+, 180 PAX and a design range of 1300 nm. The hybrid electric propulsion system produces a maximum heat power of 126.1 kW. Concept 1 uses active hot fuel circulation underneath the wing surfaces for cooling, whereas Concept 2 uses heat exchangers placed inside the existing tanks. Concept 1 is subdivided based on the fuel flow architecture into series and parallel configuration. Thermodynamic modeling is based on semi empirical methods combining effects of internal and external convection, conduction and radiation to an overall heat transfer model. A partial dependence analysis is performed to ensure the model's integrity. The cooling power potential of both concepts is evaluated at five mission points for the reference aircraft. Concept 1 provides sufficient cooling power for all operating points within the operational limits of the fuel temperature except for the Taxi case, in which the required cooling power is 85% fulfilled. The series and parallel sub configurations of Concept 1 are capable of equal cooling powers in all operating points. The parallel option requires less than half the hydraulic power of the series option. The final system needs a pump providing 2.3 kW of hydraulic power. Concept 2 fails to provide the required cooling power at any mission point other than Take-Off due to low fuel fill levels. Concept 1 is compared to a reference cooling system using a ram air cooler on aircraft level. A mass and drag sensitivity assessment shows that Concept 1 performance is in the range of 0.0% to +0.6% in fuel burn compared to the ram air cooling system depending on the mass considerations for Concept 1.