Early findings from the first study of the effects of using 100 percent sustainable aviation fuel (SAF) in both engines of a commercial jet have provided promising early results, Airbus said Monday in a statement detailing work on an A350 powered by Rolls-Royce Trent XWB turbofans. Known as ECLIF3, the study into inflight emissions and associated ground tests began earlier this year and recently resumed. It involves Airbus, Rolls-Royce, German research center DLR, and SAF producer Neste. 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 toward the end of next year or in 2023.
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 percent SAF and experienced “no operational issues.”
In-flight emission tests using 100 percent SAF and a HEFA/jet-A-1 fuel blend resumed this month, while the team also performed ground-based emissions testing to quantify the benefits of SAF for local air quality. 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, said Airbus.
Meanwhile, SAF has lower density but higher energy content per kilogram of fuel compared with 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. The team continues its detailed analysis of the preliminary results of the studies.
“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 program to be successful is to fly an aircraft in real conditions,” said Airbus's new energy program manager, Steven Le Moing. “In-flight testing of the A350 offers the advantage of characterizing direct and indirect engine emissions, including particulates from behind an aircraft at high altitude.”
Engineers equipped the DLR Falcon chaser aircraft with multiple probes to measure emissions at cruise level down to a distance of 100 meters 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-CO2 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.”
DLR performed the ECLIF1 campaign in 2015, investigating alternative fuels with its Falcon and A320 ATRA research aircraft. The 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. The research showed the advantages of reduced emissions of fuel mixtures up to 50 percent SAF and paved the way for the 100 percent SAF test flights for ECLIF3.