Cryogenic Hydrogen in Aero Engine Performance Calculations

Abstract

In this paper, the impact of cryogenic hydrogen preconditioning on aero engines is investigated using thermodynamic models of three fuel system architectures. Furthermore, highly simplified approaches that are useful for preliminary studies and conceptual design work are developed and evaluated.

Fuel systems for cryogenic hydrogen require fuel pre-heating in addition to the fuel-oil heat exchanger. Three options are in vestigated: electric, bleed, and combustion pre-heating. All are modeled in the GasTurb performance software using property functions and thermodynamic change-of-state equations. The reduction in thrust-specific energy consumption of the hydrogen engine compared to the kerosene reference engine depends on the required injection temperature. Without pre-heating, a reduction of 4% would be achievable in cruise. With pre-heating to an injection temperature of 273.15K, a reduction of 1.7% is achieved with electric pre-heating, and up to 3% with bleed or combustion pre-heating. The results are compared to highly simplified approaches in which the fuel preconditioning is approximated by adjusting mechanical efficiencies, secondary air system inputs, and the fuel heating value. The errors introduced by these simplifications are well below 0.5% in fuel flow at operating points such as take-off and cruise, thus, such simplified approaches are often justified.

In summary, heat release varies strongly with fuel temperature, especially for cryogenic hydrogen, and the associated power and bleed offtakes for fuel-preheating must be included in performance calculations. This paper presents both simplified approaches and rigorous models to achieve this.