Further development of the WET concept by the Institute for Propulsion Technology © MTU Aero Engines AG
One of the most promising ideas for reducing the climate impact of aviation is MTU Aero Engines' revolutionary Water-Enhanced Turbofan (WET) propulsion concept. The WET concept is a gas turbine-based propulsion system that can run on hydrogen or Sustainable Aviation Fuels in addition to kerosene and can be used in all classes of aircraft. In addition to the Institute of Propulsion Technology, five other DLR institutes and the industrial partner MTU Aero Engines are working on the further development of this concept. The associated DINA2030plus project is funded by the German Federal Ministry of Economics and Climate Action (BMWK) as part of the LuFo VI-2 project.
The Water-Enhanced Turbofan (WET) uses the residual heat from the engine's exhaust to increase the engine's efficiency. The WET concept combines the Joule-Brayton cycle with a parallel Clausius-Rankine cycle (Cheng cycle). Superheated water vapour is injected into the combustion chamber to participate in both combustion and power generation in the turbines. The liquid water is recovered from the exhaust gas upstream of the thrust nozzle, pumped to high pressure and then evaporated in a heat exchanger using the residual heat from the exhaust jet and returned to the combustion chamber. The result is a closed water cycle. Overall, the thermal efficiency of the propulsion system is improved and the power density of the core engine is increased, allowing higher by-pass ratios for the same fan diameter.
Benefits of the WET concept: reduced fuel consumption and climate-damaging emissions
Initial studies show a significant potential reduction in mission fuel consumption compared to next-generation geared turbofans. In addition to the carbon dioxide savings, the climate impact of non-CO2 effects should also be reduced by reducing nitrogen oxide emissions and condensation trails.
The DLR Institute of Propulsion Technology is active in several areas:
Thermodynamic overall system evaluation: Scientists are developing an overall thermodynamic model to simulate the interaction of individual components and determine an optimal thermodynamic cycle. The results of detailed investigations of individual components are integrated into the overall system model and the simulated operating behaviour is included in the climate assessment. In addition to paraffin operation, the use of hydrogen as an energy carrier is also evaluated and synergy effects are sought.
Simulation of the evaporator: The evaporator for heat recovery is a key component of the WET concept and represents a novelty in the field of aeronautics. An aeronautical application has completely different requirements in terms of space, weight and integration into the overall system compared to stationary applications. In order to meet these requirements and to be able to evaluate different designs, the researchers are evaluating compact heat exchangers using a clever combination of correlation-based preliminary design methods and CFD.
Experimental study of the evaporator: At the Institute of Propulsion Technology, a similarity experiment for an aircraft evaporator is being designed and built. The experimental investigations will be used to validate and calibrate design methods and simulations. In addition, the feasibility of evaporator concepts will be investigated and important foundations for further technology development will be laid.
The work is carried out in close cooperation with the collaborating partners and other DLR institutes. At the DLR Institute of Combustion Technology, a demonstrator for the WET concept will be built step by step on the basis of a retrofitted helicopter engine. Researchers at the DLR Institute of Atmospheric Physics will calculate the overall climate impact of a future aircraft with WET technology and assess the potential savings compared to conventional gas turbines. The DLR Institute of Air Transport is developing a 3D emissions register to map the use of WET engines at fleet level. The DLR Institute of Materials Research is investigating the durability of materials. In parallel, the DLR Institute of Vehicle Concepts is investigating the benefits of combining WET technology with a free-piston composite cycle engine concept (CCE).