Periodic Reporting for period 3 - IMOTHEP (Investigation and Maturation of Technologies for Hybrid Electric Propulsion)
Período documentado: 2023-01-01 hasta 2024-06-30
Hybrid electric propulsion (HEP) emerged during the 2010's as a possible way to reduce aircraft fuel burn and CO2 emissions. It consists in the combination of electric and thermal energy sources and propulsors in the propulsion chain of an aircraft, which offers an increased freedom to optimise the propulsion integration and aircraft's performances. The primary goal of the IMOTHEP project was to achieve a key step in assessing the potential of HEP for reducing commercial aircraft fuel consumption beyond the performance of conventional propulsion technologies projected to 2035. For that, technical objectives included identifying the propulsion architectures and associated aircraft configurations for which HEP brings a benefit, but also investigating the most promising technologies for the components of a hybrid propulsion chain, as well as the tools and infrastructure required for its development. Finally, all these elements were assembled in a research and technology roadmap for HEP, which was the ultimate objective of IMOTHEP.
To achieve these ambitious goals, the four-year project was supported by seven R&D institutes, 11 industrial partners (from aviation and electric systems), a service SME and seven universities from nine European countries, plus the CNRC and the University of Toronto in Canada.
To achieve these ambitious goals, the four-year project was supported by seven R&D institutes, 11 industrial partners (from aviation and electric systems), a service SME and seven universities from nine European countries, plus the CNRC and the University of Toronto in Canada.
IMOTHEP assessed the benefit of hybridization on four different configurations of hybrid aircraft covering regional and short medium range (SMR) missions and representing different levels of disruption in aircraft design. This assessment was performed in close connection with the investigation and preliminary design of the electric components and architecture of the hybrid power train. From a first conceptual aircraft design, target specifications were defined for the architecture and components of the hybrid propulsion chain, triggering the investigation of technological solutions with a twenty-year timeframe perspective. The performance resulting from these analyses of the electric components and power chain were synthesized through two subsequent aircraft design loops, with an increasing level of fidelity, to assess the potential fuel burn reduction of the selected aircraft configurations, compared to conventional technologies extrapolated to 2035.
Designs were proposed for all the components of the propulsion chain, with performances that over-perform current state of the art and are generally close to the projections for 2035, using medium aggressive assumptions. Safe an operable electrical architecture could be designed for all the studied configurations. Solutions for power management scheme were also identified, covering various flight situations. Failure case analyses were performed and evidenced the need for increasing the reliability of electric components to avoid frequent failure occurrences in case of distributed propulsion. Thermal management of electrical machines also emerged as a key design issue for HEP power trains. Finally, two classes of systems emerge based on the involved power and the required voltage for power distribution. Regional aircraft involve electric machines with power up to one MW and seem feasible with 800 V electric distribution. Associated technologies are believed to reach TRL 6 by 2030. On the contrary, SMR aircraft require electric machine in the range from one to 10 MW and multi-kilovolt power distribution. Corresponding technologies are only believed to reach TRL 6 after 2035, pushing any SMR application to a longer term. Especially, electric wiring interconnection system (EWIS) appears as a critical challenge involving a disruption with current systems (540 V) and severe physical issues such as partial discharges or arcing.
Finally, when integrating all the power train's characteristics in the aircraft overall design and optimisation, none of the studied SMR configurations exhibited a benefit of hybridization compared to conventional technologies projected to 2025. Moreover, results from sensitivity analyses did not suggest that improving the performances of electric components beyond those reached by the design performed within IMOTHEP were likely to change significantly the conclusions. For regional aircraft, it was found that a purely turboelectric propulsion chain (i.e. using electricity produced on board the aircraft by turbomachinery) was not promising, while parallel hybrid, using electricity stored in batteries to assist thermal propulsion, could bring a fuel burn reduction in the order of 10%, but on short range only, typically 200 nm. The most promising configuration identified within IMOTHEP is a hybrid "plug-in" configuration, an aircraft flying in full electric mode over 200 nm and using a thermal range extender for 600 nm missions. Efficiency gain in block energy could reach 55% on 200 nm, while a 20% fuel burn reduction was possible on 600 nm.
Designs were proposed for all the components of the propulsion chain, with performances that over-perform current state of the art and are generally close to the projections for 2035, using medium aggressive assumptions. Safe an operable electrical architecture could be designed for all the studied configurations. Solutions for power management scheme were also identified, covering various flight situations. Failure case analyses were performed and evidenced the need for increasing the reliability of electric components to avoid frequent failure occurrences in case of distributed propulsion. Thermal management of electrical machines also emerged as a key design issue for HEP power trains. Finally, two classes of systems emerge based on the involved power and the required voltage for power distribution. Regional aircraft involve electric machines with power up to one MW and seem feasible with 800 V electric distribution. Associated technologies are believed to reach TRL 6 by 2030. On the contrary, SMR aircraft require electric machine in the range from one to 10 MW and multi-kilovolt power distribution. Corresponding technologies are only believed to reach TRL 6 after 2035, pushing any SMR application to a longer term. Especially, electric wiring interconnection system (EWIS) appears as a critical challenge involving a disruption with current systems (540 V) and severe physical issues such as partial discharges or arcing.
Finally, when integrating all the power train's characteristics in the aircraft overall design and optimisation, none of the studied SMR configurations exhibited a benefit of hybridization compared to conventional technologies projected to 2025. Moreover, results from sensitivity analyses did not suggest that improving the performances of electric components beyond those reached by the design performed within IMOTHEP were likely to change significantly the conclusions. For regional aircraft, it was found that a purely turboelectric propulsion chain (i.e. using electricity produced on board the aircraft by turbomachinery) was not promising, while parallel hybrid, using electricity stored in batteries to assist thermal propulsion, could bring a fuel burn reduction in the order of 10%, but on short range only, typically 200 nm. The most promising configuration identified within IMOTHEP is a hybrid "plug-in" configuration, an aircraft flying in full electric mode over 200 nm and using a thermal range extender for 600 nm missions. Efficiency gain in block energy could reach 55% on 200 nm, while a 20% fuel burn reduction was possible on 600 nm.
The key step in understanding the potential of HEP for reducing fuel burn of commercial aviation was largely attained. The work performed gives a much-improved view on the potential and challenges of hybridization, as well as on the aircraft missions that could benefit from it.
In particular, IMOTHEP showed that hybridization is not a candidate for SMR aircraft in the short to medium term. An aircraft concept and hybrid architecture that benefits from hybridization is still to identify for this class of aircraft, together with a revisited set of TLARs and operations. The technical challenges, especially associated to the required high voltage for power distribution, call for an incremental approach from lower power and voltage, and push the emergence of an operational aircraft to a longer-term horizon, beyond 2035-2040.
For regional aircraft, IMOTHEP identified a promising configuration exceeding initial project's targets. Fully electric aircraft with a thermal range extender ("plug-in" hybrid) offers an unrivaled energy efficiency over the 200 nm typical mission of regional aircraft and still achieves a fuel burn reduction with the extender mode over the 600 nm design mission. Regarding parallel hybrid, significant battery performances are required and the maximum foreseen benefit, about 10%, is mainly achievable on short-range missions. Both solutions, parallel hybrid and electric with range extender, strongly rely on battery performances. They are not too sensitive to the performance of other electric systems and the designs explored within IMOTHEP already offer a satisfying basis for further development, in particular for electric motors or power electronics, even with conservative technology assumptions. The most critical point for the feasibility of plug-in hybrid is EWIS, mostly due to volume and integration constraints associated to the required size of cables.
Based on the identified most promising targets for hybridization, IMOTHEP proposed a research and technology roadmap for maturing up to TRL 6 the required technologies. Although, exploratory research are certainly to be maintained on high power and high voltage systems, the roadmap mostly focuses on electric systems in the 1 MW and 1 kV class, which correspond to the selected regional aircraft configurations. This roadmap, established with the broad scope of European research, academic and industrial partners involved in IMOTHEP, is to serve as a guideline for the proposal and development of future projects towards the maturation of hybrid electric aircraft.
In particular, IMOTHEP showed that hybridization is not a candidate for SMR aircraft in the short to medium term. An aircraft concept and hybrid architecture that benefits from hybridization is still to identify for this class of aircraft, together with a revisited set of TLARs and operations. The technical challenges, especially associated to the required high voltage for power distribution, call for an incremental approach from lower power and voltage, and push the emergence of an operational aircraft to a longer-term horizon, beyond 2035-2040.
For regional aircraft, IMOTHEP identified a promising configuration exceeding initial project's targets. Fully electric aircraft with a thermal range extender ("plug-in" hybrid) offers an unrivaled energy efficiency over the 200 nm typical mission of regional aircraft and still achieves a fuel burn reduction with the extender mode over the 600 nm design mission. Regarding parallel hybrid, significant battery performances are required and the maximum foreseen benefit, about 10%, is mainly achievable on short-range missions. Both solutions, parallel hybrid and electric with range extender, strongly rely on battery performances. They are not too sensitive to the performance of other electric systems and the designs explored within IMOTHEP already offer a satisfying basis for further development, in particular for electric motors or power electronics, even with conservative technology assumptions. The most critical point for the feasibility of plug-in hybrid is EWIS, mostly due to volume and integration constraints associated to the required size of cables.
Based on the identified most promising targets for hybridization, IMOTHEP proposed a research and technology roadmap for maturing up to TRL 6 the required technologies. Although, exploratory research are certainly to be maintained on high power and high voltage systems, the roadmap mostly focuses on electric systems in the 1 MW and 1 kV class, which correspond to the selected regional aircraft configurations. This roadmap, established with the broad scope of European research, academic and industrial partners involved in IMOTHEP, is to serve as a guideline for the proposal and development of future projects towards the maturation of hybrid electric aircraft.