###### Abstract  
There is renewed interest in hydrogen as an alternative fuel for aero engines, due to their perceived environmental and performance benefits compared to jet fuel. This paper presents a cycle, thermal performance, energy and creep life assessment of hydrogen compared with jet fuel, using a turbofan aero engine. The turbofan cycle performance was simulated using a code developed by the authors that allows hydrogen and jet fuel to be selected as fuel input. The exergy assessment uses both conservations of energy and mass and the second law of thermodynamics to understand the impact of the fuels on the exergy destruction, exergy efficiency, waste factor ratio, environmental effect factor and sustainability index for a turbofan aero engine. Finally, the study looks at a top-level creep life assessment on the high-pressure turbine hot section influenced by the fuel heating values. This study shows performance (64% reduced fuel flow rate, better SFC) and more extended blade life (15% increase) benefits using liquefied hydrogen fuel, which corresponds with other literary work on the benefits of LH\({}_{2}\) over jet fuel. This paper also highlights some drawbacks of hydrogen fuel based on previous research work, and gives recommendations for future work, aimed at maturing the hydrogen fuel concept in aviation. l 14 March 202122 April  
embrittlement in metals, its high volatility due to its low boiling point (\(-252.87\)\({}^{\circ}\)C), which means it can boil off in storage, and water vapor formation, or OH radicals which form a greenhouse gas. However, unlike with jet fuel, the contrail effect depends on the altitude, and the residence time of water vapor is relatively short [10; 11]. LH\({}_{2}\) also has a greater propensity to generate high NOx than jet fuel, due to its higher flame temperature at a given equivalence ratio [7; 11]. Another important limitation of LH\({}_{2}\) is cost, which includes production, transporting and storage costs [12; 13]. The cost factor could be overcome with technology advancement in the use of cheaper methods and foreseeable large-scale production and supplier competition [12; 14; 15]. When we consider other production options for LH\({}_{2}\), like electrolysis, which has less impact on the environment, the need to account for high energy losses from building new infrastructure and the liquefaction process must be justified to make economic sense, compared with jet fuel. Although the subject of LH\({}_{2}\) dates as far back as 1937 [10; 15], when the first aero-derivative gas turbine fueled by hydrogen was successfully run, the uptake of LH\({}_{2}\) as a fuel has been slow for aviation and is still in its infancy, due to the many limitations mentioned in the previous paragraph. It is, therefore, vital to develop both analytical and experimental tools to assess further mitigations and designs that would enable the LH\({}_{2}\) technology to mature for its use in aero engines. Interestingly, there are ongoing research discussions and publications around mitigating some of the drawbacks of LH\({}_{2}\), especially on combustor design, NOx mitigation or management, and the issue of high storage volume. Cranfield University has been at the forefront of combustor design and redesign studies for LH\({}_{2}\) aero-engine applications within the European Union (EU) CRYOPLANE and ENABLEH2 project [4; 11; 15; 16; 17]. One of the problems with facilitating lean combustion to reduce flame temperature, thereby reducing NOx emission, is the stability limit. Since LH\({}_{2}\) has a much greater stability limit, the primary combustion zone could be designed to realize lean combustion at all load conditions without approaching flameout. However, an imperfection in the fuel to air ratio (FAR) can create a localized fuel-rich and high-temperature flame pocket [6]. Hence, micromix combustors have been proposed to offer benefits that extend beyond NOx reduction.