Session: 01-12 Whole Engine Performance and Novel Concepts III

Paper Number: 100807

100807 - Water Enhanced Turbofan: Improved Thermodynamic Cycle Using Hydrogen as Fuel 

The main challenge for aviation in this century is to reduce absolute emissions and climate impact while the demand for air transportation will increase steadily. The innovative “Water-Enhanced-Turbofan” (WET) concept is a promising way forward to improve the efficiency of turbofan engines beyond the potential that can be expected from evolutionary improvements in the future. A WET uses the exhaust heat of the core flow to vaporize liquid water, which is injected upstream of the combustion chamber. The injected water is recovered from the exhaust mass flow using a condenser to create a closed water cycle within the gas turbine engine. This process leads to a higher specific power of the core engine whereby the turbines can provide more power and the bypass ratio is increased significantly for a constant fan diameter. Thus, the overall engine efficiency increases and the CO2 emissions decreases. Published studies regarding the WET investigate the concept with conventional kerosene but the combination of the WET with hydrogen could lead to further improvements in efficiency.

The design and integration of a Heat Recovery Steam Generator (HRSG) and a condenser for the WET are challenging. In addition, providing hydrogen as a gaseous fuel is a further hurdle, as it is stored in liquid form (LH2) at 20 K in the aircraft fuselage. The use of the low temperature of LH2 as a heat sink for condensation and separation of water within the WET is a promising possibility with many uncertainties. Besides, the combustion of hydrogen produces a considerable amount of additional water vapor, which in turn can have an impact on the engine's water circulation. It is not known to what extent hydrogen and a WET application can be combined to take advantage of both innovations in aircraft engines.

To evaluate the potential of a Hydrogen-WET, a WET using kerosene as fuel is designed at the thermodynamic cycle level. Subsequently, a Hydrogen-WET-Engine is presented, that utilizes the higher water content of the combustion process and the heat sink of the LH2 to improve the thermodynamic cycle and the condensation process. Furthermore, emerging effects from the use of hydrogen are addressed to create understanding of the new technology.

The hydrogen fueled WET shows benefits in the thrust-specific energy consumption compared to the design for kerosene. Since the LH2 temperature is very low, it is beneficial to use the hydrogen evaporation process as an additional heat sink during the condensation process of the exhaust flow. The extreme temperature difference leads to a high heat transfer and therefore to a smaller condenser. In addition, the combustion of hydrogen produces 3 to 4 times more water as kerosene for the same amount of energy. Due to the higher water loading, it is possible to cool the exhaust less while separating the identical quantity of liquid water compared to the kerosene WET. This effect leads to an even smaller condenser. Following the thermodynamic cycle calculation, an estimation for the heat transfer surfaces of the HRSG and the condenser along with the LH2 conditioner are presented.

Presenting Author: Alexander Görtz German Aerospace Center

Presenting Author Biography: 05/20 – present:
Scientist at the German Aerospace Center; Institute of Propulsion Technology:
- Thermodynamic analysis of future propulsion systems
- Performance of hydrogen combustion engines

11/18 – 08/19:
Student assistant at the Technical University Berlin; Chair of Aero Engines:
- Installation of a wind tunnel for calibration procedures
- Assistance for measurement technology within aero engines

04/18 – 05/20:
Studies in mechanical engineering (M.Sc.) at the Technical University Berlin:
- Master thesis: Spline based 1-D compressor modeling in preliminary aero engine design

10/13 – 03/18:
Studies in mechanical engineering (B.Sc.) at the Technical University Dortmund:
- Bachelor thesis: Analysis of hydraulic losses in oil injected screw compressor

Authors:

Alexander Görtz German Aerospace Center
Jannik Häßy German Aerospace Center
Marc Schmelcher German Aerospace Center
Mahmoud El-Soueidan German Aerospace Center