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The SAfer FUEL system

Final Report Summary - SAFUEL (The SAfer FUEL system)

Executive Summary:
Air travel is today the safest form of transport worldwide. However, safety can never be taken for granted. Constant effort is needed to maintain the highest safety level, taking into account the global air transport industry and its changing operational context (i.e. new technologies, the evolution of flight conditions and climate changes).

To this end 13 organizations across Europe have joined forces to address future air transport constraints such as changing flight conditions, emerging technologies, and more exposure to hazardous weather, in order to meet the needs for European-led research and development in fuel system safety.

Partly funded by the 7th Framework Programme of the European Commission, the SAFUEL project aims to develop, test and validate technologies for the Safer Fuel System of the future.

The fields of application of these technologies are:
- Water and ice management
- Flammability reduction means
- Ignition source reduction

The main outcomes of this project, achieved with the involvement of the 13 partners are:
- A TRL3 technology for water in fuel measurement
- The release of the 1st set of design rules aiming at reducing the hazard of ice release in the fuel system
- A TRL3 technology for oxygen sensing
- A TRL3 architecture of an inerting system
- TRL2 and TRL3 technologies for gauging systems

All these technologies have been developed based on high level requirements and the maturity levels have been approved with external reviewers.

Project Context and Objectives:

All Fuel System (FS), subsystems and components, added over time, have to work together and also have to work with other aircraft critical systems such as engine bleed air supply systems and engines. When a new system, subsystem or component is introduced, its impacts on and its interconnections with the other FS subsystems and components and the overall FS are not always thoroughly investigated and anticipated. For instance, the inter-dependence of the current Fuel Tank Inerting System (FTIS) and the fuel venting subsystem is not fully understood. As a result, the complexity of the FS could jeopardize the perfect management of failure hazards. Consequently, the approach to add more systems, subsystems and components to the already complex FS has reached its limit:
• It is not adequate when considering safety as a top priority,
• Such an approach to prevent ice and failure will add more complexity to an already highly complex FS (with several new subsystems having to be added for ice and failure hazard prevention),
• Such an approach also has negative impacts on aircraft operating costs for:
o Fuel consumption due to FS weight penalty (e.g. 50 KG on a single aisle aircraft for the harness made of metal wiring of the fuel gauges)
o Expensive and time consuming scheduled maintenance. Today FS subsystems require:
▪ Operations to be performed by skilled staff (refueling and operational check before take-off). But, current economic constraints can lead some contractors to outsource tasks to subcontractors who do not necessarily have experienced employees, increasing the risk of human error.
▪ Costly scheduled maintenance to guarantee FS subsystems’ optimum functional level (e.g. the FTIS maintenance cost is in the top five operating costs for airlines). Again, current economic constraints can lead some operators to postpone tasks, increasing the risk for FS subsystem malfunctions.

SAFUEL objectives:
Addressing air transport constraints and answering needs for European-led research and technological development in FS safety, the overall objective of the SAFUEL project is to develop, test and validate the Safer Fuel System of the future.
Fully compliant with safety requirements, this Safer Fuel System will be able to deal with more extreme temperatures, stronger temperature gradients, higher humidity and more frequent exposure to lightning, due to:
• Future flight conditions
Flight conditions are changing due to the opening of new routes at higher altitude or routes crossing the Arctic. Also, during landing and take-off, faster climbing and approaches are required to optimise the flight routes.
• More exposure to hazardous weather conditions
• Emerging technologies

The hazards of fire, ice and FS failure are addressed by the SAFUEL project while integrating the needs of future aircraft platforms such as usage of alternative fuels, more composite aircraft or more electrical aircraft.

Consequently, SAFUEL has the following overarching technological objectives:
1. Improve water detection in fuel tank and gain knowledge on icing phenomena in the fuel system
2. Enhance flammability protection in the fuel tank and improve reliability, robustness and performance of inerting system
3. Remove possible ignition sources from the fuel tank
4. Verify and validate full compatibility of the results with Composite Aircraft and More-Electric Aircraft requirements, considering the increased exposure to lightning and induced arcing in these new technologies
5. Verify the compliance of results with Alternative Fuel standards.

The work is organised in four technical work packages (WP), all driven by the SAFUEL overall objectives to develop the new generation of safer FS (robust and integrated) which can better protect an aircraft against hazards (‘Ice’, ‘Fire’ and ‘Failure’). WP2 develops the water management function, gaining scientific and technical knowledge about ice in the FS with associated recommendations for FS design and developing an electrically passive optical water in fuel sensor. WP3 develops the in-tank wire-free dual oxygen/temperature sensor (electrically passive) and the optimised FTIS architectures. WP4 develops the electrically passive metal-free gauging. WP5 provides the High Level Requirements to WP2, WP3 and WP4 and assesses the results against Safety, emerging technologies and technological breakthrough (Technology Readiness Level (TRL) and integration level reviews) at system level. Assessment is performed by independent reviewers external to the project.

Three non-technical WP respectively manage:
• Dissemination (WP6 notably prepares the Public Forums at M21 and M42 and maintains the SAFUEL public website to widely disseminate results),
• Exploitation (WP7 maintains the SAFUEL Knowledge Register recording ownership and access/use rights to SAFUEL Foreground, verifying the Foreground is protected to fully support the exploitation plan),
• Management and the coordination of the Consortium (WP1).

Project Results:
A dedicated report has been delivered describing the main scientific and technical achievements: D7.4 Final Public Technical Report. This is a public deliverable aiming at the dissemination of the SAFUEL activity. Please refer to this document.

Potential Impact:
Water in fuel sensor:
The sensor is able to measure the quantity of dissolved water in the fuel. For this purpose, it is not possible to use this sensor to measure the quantity of undissolved water.
The sensor could be used for other applications, such as the monitoring of the quality of the fuel in the airports. This technology could also be used to monitor the quality of the fuel in the automotive industry and in the fuel distribution network.
A Background patent application on the technology: patent has been granted to partner ASTON in Japan (7/14) and USA (8/14). Commercial exploitation in the short to medium term is likely to be in less demanding applications than onboard aircraft. Discussions have been held with a major aircraft sensor system supplier but they considered the current TRL to be too low for them to take on. Aston University are maintaining and advertising the patent on this technology and still hope to realise development work averaging 50k€ going forward.

Icing phenomena:
The two PhD researchers in CRAN-U will either remain at CRAN-U as knowledgeable and skilled members of staff able to generate revenue and impact for the University or go on to work in industry where experience suggests they may turn to CRAN-U in the future for research and knowledge based services (150k€ p.a). The team have generated impact and are involved with publishing aspects of the work leading to new networking and business opportunities and peer review related funding (80k€ p.a).
The laboratory facilities and local retained knowhow will help CRAN-U offer capability in the fuels area to address future research (200k€ p.a). There is also a significant spin off in terms of other complex flow problems with phase changes, where fluid and solid properties are equally important such as slurry management, food processing, medicine and some important geological problems (200k€ p.a).

The test bench developed in TUHH will be available to aeronautic industry and can be used for any other systems in non-accessible areas. The test bench itself is for research purposes only; there is no assessment via TRL. Potential further developments are new or alternative measurement methods to measure the level of ice accretion in aircraft FS components (valves, pumps) and adjustments for full scale experiments and/or lower test temperatures. The size of the aeronautical industry susceptible to be interested in the bench is difficult to be estimated. However, further projects and funding can likely be attracted to TUHH (250 – 500k€).
The scientific knowledge gained from the test rig will be content of a PhD thesis. The thesis will be available probably in spring 2017. In addition, two publications are expected. The laboratory equipment will be used for further research and for educational purposes.

The design rules elaborated by ZODIAC have been presented during the last internal project review. This first set of rules can be applied from now on. This know-how will be used for the design of the next generation aircraft. It will be a part of the technical promotion that is done during the business competition.

Oxygen sensor:
NLR will perform further research and development of the gauging sensors and corresponding interrogator in order to provide a mature design towards a higher TRL level.
Further research and development needs to be performed to optimize the optical path as well as improvements or alternatives of the disk.
The fibre optical oxygen sensor will be further explored towards a Flight Test Instrumentation sensor to support oxygen measurement in a fuel tank during flight tests for certification.
The operational introduction of an optical oxygen sensor in an inerting application is expected to be completed in 5-10 years whereas the completion of the sensor development is expected to be completed in 3-5 years.
Another application of the sensor has been identified, leading to a patent application.

Oxygen closed loop inerting:
The architecture showed a minor gain on short flights, but a big potential gain for long flights. Once the development of the oxygen sensor will be completed, it will be possible to propose this technology to manufacturers for long range aircraft.

Acoustic gauging:
The accuracy depends on many physical parameters that are difficult to master. Nevertheless, this technology could be used for basic sensors such as level detectors.
From the current TRL3, the TRL6 for a level detector based on acoustic technology could be met in the coming three years.

Optical gauging:
The vibration testing conducted on the optical sensor during SAFUEL will lead to an upgrade of experimental methodologies, new opportunities of participation to national and international projects, and finally improvements in education (more students and exposure for the University) for UNIPARTH. It is difficult to estimate, but 70k€ could be conceivable.

NLR will perform further research and development of the gauging sensors and corresponding interrogator in order to provide a mature design towards a higher TRL level.

The fibre optical gauging sensor will initially be further explored for an application as an independent high/low fuel level sensor in the aircraft fuel system. A level sensor will consist of only a few Total Internal Reflection (TIR) elements. Research will be performed on optical multiplexing with Photonics on Chip (POC) to industrialize and ruggedize the level probe in combination with a technically simplified interrogator compared to the Optical Time Domain Reflectometry (OTDR) applied in SAFUEL. The research and development for the application of a TIR based optical level gauging sensor are expected to be completed in 3-5 years.

On a long term research path, the industrialization of the gauging probe will be investigated to eliminate the drawback of the complex mechanical integration. The research and development for the application of a TIR based optical fuel gauging sensor is expected to be completed in 10-15 years.

Pressure based gauging:
This technology is still very far from an aircraft application.
New studies could be undertaken to build a very accurate and ruggedized pressure sensor combined with a very accurate accelerometer.

List of Websites:
SAFUEL Project website:

SAFUEL Project Coordinator:
Bruno Reynard, Zodiac Aerotechnics SAS