: 5 min
JETSCREEN: understanding the impact of SAF on fuel systems
Sustainable Synthetic Fuels (SSF), more commonly known under the acronym SAF ("Sustainable Aviation Fuels"), refer to aeronautical fuels having received certification confirming that their production has a significantly reduced impact – sustainably – on the environment in comparison with conventional fuel. They therefore offer an effective and immediate solution to help eliminate carbon in the aviation sector.
However, two major questions arise concerning the use of SAFs: are they sufficiently available? And how compatible are they with current and future aircraft? Because although all aircraft can operate with no modification to the equipment using a 50/50 mixture of kerosene and sustainable fuels in their tank, what happens when the tank is filled 100% with SAF?
It's this last question which has come under scrutiny from the different stakeholders involved in JETSCREEN ("JET Fuel SCREENing and Optimization"). Launched by the European Commission as part of the "Horizon 2020" initiative, this research project has involved a consortium including several Group companies, in order to draw up the first reference base for the behavior of sustainable fuels in comparison with kerosene and to understand their effects on aircraft equipmen
"The objective of the JETSCREEN project was to develop solutions to help support the rapid approval of new fuels produced using a wide range of raw materials. This will help guide the sector to greater sustainability", the European Commission reminds us in its report.
In addition to the engine, several aircraft systems can be affected by changing fuel, including in particular the fuel distribution and gaging system. Safran Aerosystems, a leader in fluid management systems, has carried out two projects to test the compatibility of its products with SAFs.
Testing the limits of gaging
"Several types of sustainable fuels can be used in aviation, each with a chemical composition and physical characteristics which differ from those of kerosene. However, our fuel systems have been designed for and operate based on the physical characteristics of kerosene" explains Thierry Rouge-Carrassat, innovation director at Safran Aerosystems. "As part of JETSCREEN, we have sought to understand the possible effects of these variations in chemical and physical properties on the operation of our products and their life expectancy."
The first step for the Safran Aerosystems teams was to test the operation of the fuel control equipment, and particularly the sensors, which make it possible to display information concerning the volume and quality of the fuel in the tank. "We have developed a specific test installation to observe the limits of the gaging of biofuels", explains Gilles Saint Aubin, R&T Manager at Safran Aerosystems. "In an aircraft, the sensors make it possible to discover the mass of fuel in the tank, using a calculation model based among the things on the mass density of the kerosene with the height of the fuel in the tank. We have therefore performed a precise comparative study involving several sustainable fuels, subjecting them to temperature variations, and noted the measurement variations of our sensors to build calculation models enabling us to determine the mass of the different SAFs in the reservoir."
Focusing on the pumping system
The second test was performed on the Safran Aerosystems site at Roche-La-Molière (Loire) where all of the fuel distribution systems are manufactured.
"We converted a test bench to monitor the behavior of pumps, valves and taps operating with SAFs", continues Gilles Saint-Aubin.
In a tank which can hold between 500 and 2,000 liters of fuel, the teams ran the fuel pumps with SAFs for 1,200 hours. "That's the equivalent of several months' flight time! This endurance test should enable us to study the effects of using biofuels on the life expectancy of our products."
The Safran Aerosystems teams compared their equipment before and after the test to verify their hypotheses. "Biofuels are particular in that they are free of aromatics which contribute to creating a seal, but are also free of sulfur which is a natural lubricant."
During this test, the fuels and equipment were also subjected to variations in temperature and altitude. "At very low temperatures, we noted that certain biofuels can become very dense, which makes pumping them more complicated."
"This initial experimental exploratory phase enabled us to identify trends and themes which will need to be confirmed in our future research work", concludes Gilles Saint-Aubin.
Two approaches may potentially be envisaged when considering the use of SAFs: either the fuel system's equipment is modified to operate using these new sulfur-free and aromatic-free fuels, or the composition of the SAFs is adapted to make them compatible with current equipment.
Next step: the Volcan project
The conclusions from the JETSCREEN project were submitted in 2020. This collaborative work resulted in the development of preliminary design tools making it possible to understand the way the fuel behaves with different equipment, and in the development of a fuel control platform. The next step is to now take the collection of technical data further by expanding the range of SAFs tested and by testing all of the equipment comprising the fuel system together in order to identify and assess any possible modifications to be made to this equipment.
This is the subject of the VOLCAN project launched by Airbus with a consortium including ONERA, Dassault and Safran, with the participation of teams from Safran Aerosystems, Safran Aircraft Engines, Safran Helicopter Engines, Safran Filtration Systems, and Safran Tech. The VOLCAN project will also attempt to identify the influence of variations with the different components used in the composition of a SAF on the operation of the fuel system equipment.
The VOLCAN project is focusing on the use of 100% SAF, without aromatics or sulfur, the quantification of their benefits in terms of emissions and contrails, and the identification of any possible adaptations to current and future commercial aircraft.
As part of this project, the French aeronautical operators will be flying a single-aisle aircraft with 100% SAF by the end of the year.