WP5: Innovative On-Board Thermal & Energy Management
Involved partners: ESA-ESTEC
For hypersonic cruise vehicles, and particularly, for civilian transport airplane, the thermal management for the overall system is a key point. As a matter of fact, it is mandatory to provide all needed cooling for passenger cabin but also for on-board equipment while facing very high heat fluxes everywhere on the external surface of the fuselage as well as inside the propulsion system. The high heat fluxes emanating from friction inherent to high-speed flights will have to be carried away to avoid too high structural temperatures within the vehicle and in particular for the passengers’ cabin where the ambient temperature needs to be well regulated within narrow margins.
At the same time, during the main part of the flight (hypersonic acceleration, cruise and deceleration), the dual-mode ramjet propulsion system is not able to directly provide mechanical or electrical power to supply all energy consumers on board. Since there is a strong need for on-board energy sources, one of the options is fuel cells. This path is currently being followed by several organizations around the world, for example by the FCH JU (Fuel Cells and Hydrogen Joint Undertaking), public private partnership which supports research, technological development and demonstration activities in fuel cell and hydrogen energy technologies in Europe. Fuel is the only cold source on-board and has to absorb the main part of the heat entering the vehicle. At the same time, the needed electrical power on board can be huge (~1MW) but can only absorb a part of this heat entering the vehicle. But for high-speed transport, this technology needs to be compatible with a particularly stringent environment, consequently requiring additional specific expertise brought by HIKARI consortium.
5.1.1 Electrical Energy sources (ESTEC): The approach consists in converting the heat entering the fuselage external structure into on-board power demands. In the frame of ATLLAS-studies, a preliminary generic concept was worked out allowing using the heat penetration as a potential energy source for on-board power generation. On this basis, ESTEC will elaborate further on this conceptual design and analyze in a generic way several potential energy conversion routes for which different parameters will be addressed, i.e. cruise speed, medium, fuel type, external surfaces, cabin volumes, passenger number. ESTEC will pursue previous task with the generic design of an actively closed cooling system for power generation which absorbs the heat at crucial places within the vehicle, i.e. structures and the passengers’ cabin. The criticality of this heat availability/collection will strongly depend on the point along the trajectory. For system using a coolant medium, a specific attention will be paid to the increase of its enthalpy which must be high enough at any times to drive the on board power demands, including electrical drives of fuel pumps, hydraulics, etc.
5.1.2 Use of fuel to cool the Airframe structure and provide right cabin environment (MBDA): MBDA will study different options to directly use the fuel as heat sink to cool the structure. That will combine some preliminary design of the fuselage thermal protection system and structure (using technologies and materials already under development within other programs), design of closed loop cooling systems with suitable coolant medium (air, nitrogen) bringing collected heat to the fuel tank. The different technological options will be identified, assessed and down selected.
5.2.1 On the basis of WP51 results but also results issued from WP62, MBDA will establish a methodology of design for a complete thermal and energy management system combining the different possible options identified and down-selected in order to ensure the right thermal management and provide a large and reliable source of on-board energy.
The activity will include:
- elaboration of relevant models of each component of the thermal and energy management system.
- development of a time-based simulation providing all needed operation parameters all along the trajectory.
- Implementation of an efficient design optimization process.
This activity will also take into account the possibility to use a buffer system (probably a hybrid battery/super-capacitors system) to relax the design constraints for the electric power generation system and then, optimize its operation on the overall trajectory. Different approaches of efficiency assessment and optimization will be considered (time-based simulation, energy analysis, etc.). When the needed models and corresponding methodology and tool are be available, an optimization of the combined system to provide the required cooling and energy while minimizing mass, volume and safety, reliability and maintenance issues will be carried out for two generic cases based on ZEHST, Mach 5 vehicle concept and on LAPCAT II Mach 8 vehicle concept.
Benefiting from the experience gained in Europe and Japan, through projects such as ATLLAS for example, HIKARI will intend to:
- Investigate different technological options so as to capture entering heat fluxes based on fuel preheating (or evaporation for self-pressurization) or on electric/mechanical energy conversion and
- Develop and apply a methodology to design a complete thermal and energy management system, combining these different options, so as to get an optimum architecture in terms of efficiency, mass, volume, fuel thermal charge.
The proposed activities will provide a clear view on the different elements which can contribute to absorb the massive heat fluxes entering the vehicle from atmosphere during the long high-speed cruise: on-board thermal to electric energy conversion, fuel preheating and self-pressurization.
After having reached a good understanding of potential use of these elements, a global optimization approach will allow defining the best combination of such technologies to provide an efficient thermal and energy management ensuring suitable environment for passengers and on-board subsystems all along the trajectory.
Finally, new devices could be used in standard aircraft if that leads to lighter planes for example. Energy management concepts which do not need gear boxes to drive components (i.e. oil & hydraulic pumps, generators) but indirect power transfer will increase the efficiency and reliability. This could be done by means of fuel cells, heat recovery etc.