Session: 01-13: Thermal Management and Aero-engine Oil Systems II

Submission Number: 175072

Integration of a Liquid Hydrogen Conditioning System Into the Performance Calculation of a Turbofan Engine Using a Secondary Fluid 

Hydrogen powered propulsion is an important area of research where the hydrogen’s use itself varies, e.g. powering a fuel cell or direct combustion. Several authors in the literature agree that climate-neutral aircraft will fly with liquid hydrogen as fuel in the future. In its liquid form, hydrogen is stored in the aircraft’s fuselage at 20 K, but combustion requires much higher temperature. Conditioning of the hydrogen needs a large amount of thermal energy and large heat exchanger have to be integrated into the engine. The most common concepts of heat exchanger integration utilize waste heat recovery or inter compressor cooling.

Burning and conditioning hydrogen directly in the core engine of a turbofan leads to several challenges. These range from safety issues to the formation of ice on the outer walls of heat exchangers. One solution to overcome those challenges is to use a secondary fluid cycle transferring the waste heat to the hydrogen. However, integrating this type of conditioning system requires additional heat exchangers, pumps and/or compressors, which increases the complexity of the overall system. Furthermore, the secondary fluid cycle can be enhanced to use additional heat sources as the engine oil and air for the environmental control system (ECS). Although some data on the thermodynamic state of hydrogen after conditioning is available in the literature, the impact of the secondary cycle state on the conditioning system is unknown. Interesting design values include the secondary fluid temperature, pressure, and mass flow rate, as well as the maximum and minimum achievable hydrogen temperatures.

This paper proposes an architecture for a liquid hydrogen conditioning system in a turbofan engine that uses nitrogen as a secondary fluid. While the exhaust is the main heat source, engine oil and ECS provide additional heat to secondary cycle.

To address the potential of this architecture, the first step is to design a reference engine for short- to medium-range applications on a thermodynamic cycle level. Then, models for the main components of the conditioning system are developed and presented. These components include cryogenic pumps, nitrogen compressors, and heat exchangers. The reference engine is adapted so that the conditioning system can be integrated into the cycle analysis of the engine. Using the engine's thermodynamic model, this paper will address the following research questions:

-         - What is a suitable architecture of the conditioning system on a thermodynamic level?

-         - What impact do specific design values have on the overall system?

-         - What are the operating conditions of the heat exchangers and pumps during different flight phases?

-         - What are possible limits of the hydrogen conditioning system?

Presenting Author: Alexander Görtz German Aerospace Center (DLR), Institute of Propulsion Technology

Presenting Author Biography: - B.Sc. in Mechanical Engineering at Technical University Dortmund
- M.Sc. in Mechanical Engineering at Technical University Berlin
- Currently Researcher at German Aerospace Center in Cologne

Authors:

Alexander Görtz German Aerospace Center (DLR), Institute of Propulsion Technology
Jannik Häßy German Aerospace Center (DLR), Institute of Propulsion Technology
Marc Schmelcher German Aerospace Center (DLR), Institute of Propulsion Technology
Mahmoud El-Soueidan German Aerospace Center (DLR), Institute of Propulsion Technology
Florian Herbst German Aerospace Center (DLR), Institute of Propulsion Technology