Initial findings from a world-first study of the impact of 100 per cent sustainable aviation fuel (SAF) on both engines of a commercial jet have provided “promising” early results.

The ECLIF3 study, involving Airbus, Rolls-Royce, German research centre DLR and SAF producer Neste, marks the first time 100 per cent SAF has been measured simultaneously on both engines of a commercial passenger aircraft – an Airbus A350 aircraft 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 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 per cent blend of SAF and conventional jet fuel, but both companies support the drive to certify 100 per cent SAF use.

In April, the A350 flew three flights over the Mediterranean Sea pursued by a DLR Falcon chaser 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 per cent SAF and no operational issues were experienced.

In-flight emission tests using 100 per cent 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 to 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.”