29. November 2021

First in-flight 100 per­cent sus­tain­able-fu­els emis­sions study of pas­sen­ger jet shows ear­ly promise

DLR Falcon 20E in the exhaust plume of the Airbus A350
DLR Fal­con 20E in the ex­haust plume of the Air­bus A350
Image 1/5, Credit: © Airbus/S. Ramadier

DLR Falcon 20E in the exhaust plume of the Airbus A350

DLR Fal­con 20E in the ex­haust plume of the Air­bus A350, which flies on 100 per­cent sus­tain­able fu­el (SAF).
Measurement aircraft Falcon 20E D-CMET
Mea­sure­ment air­craft Fal­con 20E D-CMET
Image 2/5, Credit: © Airbus/S. Ramadier

Measurement aircraft Falcon 20E D-CMET

The Fal­con 20E, equipped with mul­ti­ple in­stru­ments, fol­lowed the Air­bus A350 in April this year. Now, in Novem­ber, the mea­sure­ment flights over the Mediter­ranean Sea have been re­sumed.
Falcon 20E D-CMET measurement aircraft in the A350’s exhaust plume
Fal­con 20E D-CMET mea­sure­ment air­craft in the A350’s ex­haust plume
Image 3/5, Credit: © Airbus/S. Ramadier

Falcon 20E D-CMET measurement aircraft in the A350’s exhaust plume

The Fal­con 20E flew to with­in 100 me­tres of the A350 at cruis­ing al­ti­tude. The tur­bu­lence that oc­curs there makes fly­ing this close hard work for the pi­lots.
The Falcon takes off on its mission
The Fal­con takes off on its mis­sion
Image 4/5, Credit: DLR (CC BY-NC-ND 3.0)

The Falcon takes off on its mission

The Fal­con flights help to bet­ter anal­yse the cur­rent­ly large­ly clean at­mo­sphere, which is on­ly slight­ly pol­lut­ed with emis­sions from in­dus­try and trans­port, in­clud­ing avi­a­tion. This gives re­searchers a unique op­por­tu­ni­ty to bet­ter un­der­stand the ef­fects of in­creased emis­sions pri­or to the Coro­n­avirus lock­down.
Refuelling the Airbus A350-900
Re­fu­elling the Air­bus A350-900
Image 5/5, Credit: ©Airbus/S. Ramadier

Refuelling the Airbus A350-900

In Toulouse, the Air­bus A350-900 is re­fu­elled with 100 per­cent sus­tain­able avi­a­tion fu­el for its first flight.
  • In November 2021, flight tests are again taking place with the DLR research aircraft Falcon 20E conducting emission measurements behind an Airbus A350.
  • Initial results show that the engines release fewer particulates under all operating conditions when using pure sustainable fuels.
  • Sustainable aviation fuels have the potential to reduce the climate impact of air transport.
  • Focus: Aeronautics, climate-friendly flight, sustainable fuels

Toulouse, 29 November 2021 – Initial findings from a world-first study of the impact of 100 percent Sustainable Aviation Fuel (SAF) on both engines of a commercial jet have provided promising early results.

The ECLIF3 study, involving Airbus, Rolls-Royce, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and SAF producer Neste, marks the first time 100 percent SAF has been measured simultaneously on both engines of a commercial passenger aircraft – an Airbus A350 powered by Rolls-Royce Trent XWB engines.

In-flight emissions tests and associated ground testing on the ECLIF3 programme began earlier this year and have recently resumed. The interdisciplinary team, which also includes researchers from the National Research Council of Canada and the University of Manchester, plans to publish its results in academic journals towards the end of next year and in 2023.

Findings from the study will support efforts currently underway at Airbus and Rolls-Royce to ensure the aviation sector is ready for the large-scale use of SAF as part of the wider initiative to decarbonise the industry. Aircraft are currently only allowed to operate on a 50 percent blend of SAF and conventional jet fuel, but both companies support the drive to certify 100 percent SAF use.

In April, the A350 flew three flights over the Mediterranean Sea pursued by a DLR Falcon chase plane to compare in-flight emissions of both kerosene and Neste’s Hydro-processed Esters and Fatty Acids (HEFA) sustainable fuel. The team also carried out compliance tests using 100 percent SAF and no operational issues were experienced.

Video – First in-flight emis­sion mea­sure­ments with 100 per­cent sus­tain­able avi­a­tion fu­el
In the ECLIF3 project, 100 per­cent Sus­tain­able Avi­a­tion Fu­el (SAF) was test­ed for the first time with both en­gines dur­ing flight op­er­a­tions of a pas­sen­ger air­craft. An Air­bus A350 pow­ered by two Rolls-Royce Trent XWB en­gines served as the re­search air­craft. Close be­hind, the DLR Fal­con 20E mea­sure­ment air­craft flew in the tur­bu­lent ex­haust plume. This al­lowed re­searchers from the DLR In­sti­tute of At­mo­spher­ic Physics to di­rect­ly mea­sure the emis­sions in flight and com­pare them with those of reg­u­lar air­craft kerosene.

In-flight emission tests using 100 percent SAF and a HEFA/Jet A-1 fuel blend resumed this month, while ground-based emissions testing to quantify the benefits of SAF on local air quality were also performed. The research team found SAF releases fewer particulates than conventional kerosene at all tested engine operating conditions, which points to the potential for reduced climate impact and improvement in air quality around airports.

In addition, SAF has lower density but higher energy content per kilogram of fuel compared to conventional kerosene, which brings some aircraft fuel-efficiency advantages due to lower fuel burn and less fuel mass on board to achieve the same mission. Detailed analysis by the team is on-going.

"Engines and fuel systems can be tested on the ground but the only way to gather the full set of emissions data necessary for this programme to be successful is to fly an aircraft in real conditions," said Steven Le Moing, New Energy Programme Manager at Airbus. "In-flight testing of the A350 offers the advantage of characterising direct and indirect engine emissions, including particulates from behind an aircraft at high altitude."

Simon Burr, Rolls-Royce Director of Product Development and Technology, Civil Aerospace, said: "This research adds to tests we have already carried out on our engines both on the ground and in the air which have found no engineering obstacle to our engines running on 100 percent SAF. If we are to truly decarbonise long-haul air travel, then 100 percent SAF is a critical element and we are committed to supporting its certification for service."

The DLR Falcon chase aircraft is equipped with multiple probes to measure emissions at cruise level down to a distance of only 100 metres from the A350 and feed them into scientific instrumentation for analysis.

"SAF has been shown to have a significantly lower carbon footprint over its life cycle compared to conventional jet fuel and now we are seeing it is advantageous in reducing non-carbon-dioxide effects too," said Markus Fischer, DLR's Divisional Board Member for Aeronautics. "Tests such as these are continuing to develop our understanding of 100 percent SAF and its use in flight, and we are seeing positive signs for its potential in climate mitigation. We look forward to studying the data from the second series of ECLIF3 flights, which restarted with a first chase flight above the Mediterranean earlier this month."

In 2015, DLR performed the ECLIF1 campaign, investigating alternative fuels with its Falcon and A320 ATRA research aircraft. These investigations continued in 2018 with the ECLIF2 campaign which saw the A320 ATRA flying with a mixture of standard jet fuel and up to 50 percent HEFA. This research showed the advantageous emission performance of fuel mixtures up to 50 percent SAF and paved the way for the 100 percent SAF test flights for ECLIF3.

Notes for editors: In-flight video footage of the DLR Falcon aircraft taking measurements from behind the 100% SAF-powered A350 aircraft is available to broadcast/online media.

DLR – research for climate-neutral air transport

The consequences of climate change demand action for climate-neutral air transport. This involves new technologies that will also ensure global mobility in the future. With its 25 institutes and facilities in the field of aeronautics research, DLR is driving this change forward with technologies for sustainable, environmentally compatible flight. Expertise from DLR's research programmes in space, energy and transport will also play an important role in this.

DLR has systems expertise in aeronautics research and sees itself in the role of an architect. DLR's goal is 'emission-free air transport', in order to achieve the climate targets that have been set. In doing so, the results of research must flow directly into the development of new products.

There is a considerable need for research and development on the path to climate-compatible air transport, which requires continuous funding and support. Much of this needs to be researched at a fundamental level, tested in practice and approved. DLR can do this with large-scale facilities such as its research aircraft, propulsion demonstrators and large-scale computers. In 2020, DLR published the white paper 'Zero Emission Aviation' together with the German Aerospace Industries Association (Bundesverband der Deutschen Luft- und Raumfahrtindustrie; BDLI). DLR is currently working on a Zero Emission strategy.

Climate impact of condensation trails

One third of the climate impact of air transport is due to carbon dioxide, while two thirds is caused by non-carbon-dioxide effects. Condensation trails and the resulting contrail cirrus clouds are the most significant factor. Aircraft engines emit soot particles, and these act as condensation nuclei for small, supercooled water droplets, which immediately freeze into ice crystals and become visible as contrails in the sky. The ice crystals in the condensation trails can persist for several hours in cold and humid conditions at altitudes of approximately eight to 12 kilometres and form high clouds, referred to as contrail cirrus. Depending on the position of the Sun and the characteristics of the underlying ground surface, these clouds can have a localised warming or cooling effect. Numerous research studies have shown that, globally, the warming effect predominates. The occurrence of these clouds is extremely variable in both time and space, and a relatively small number of contrails are responsible for a large part of the warming effect. For many years, DLR and its partners have been systematically investigating ways to reduce soot emissions and the climate impact of the resulting contrail formation. Together with NASA, DLR was able to demonstrate for the first time that the use of a 50-50 mixture of kerosene and Sustainable Aviation Fuel (SAF) halves the number of ice crystals in contrails under real flight conditions, which leads to a 20 to 30 percent reduction in the climate impact of the contrails.

  • Falk Dambowsky
    Head of Me­dia Re­la­tions, Ed­i­tor
    Ger­man Aerospace Cen­ter (DLR)

    Cor­po­rate Com­mu­ni­ca­tions
    Telephone: +49 2203 601-3959
    Linder Höhe
    51147 Cologne
  • Prof. Dr. Christiane Voigt
    Head of De­part­ment
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of At­mo­spher­ic Physics
    Cloud Physics
    Münchener Straße 20
    82234 Oberpfaffenhofen
  • Aeron Haworth
    Me­dia Re­la­tions Man­ag­er
    Air­bus UK
    Telephone: +44 (0)7711 063752

  • Bill O’Sullivan
    Com­mu­ni­ca­tions Man­ag­er – Air­lines
    Telephone: +44 796 87 67 172
Dossiers on this topic


Stay up to date and sub­scribe to the DLR newslet­ter with ar­ti­cles from the DLR ed­i­to­ri­al team in Ger­man and En­glish.

Main menu