Airbus is taking a down-to-earth approach for its latest study into aviation’s non-CO2 impacts, unveiling plans to replicate the conditions found at cruise altitudes and generate contrails at ground level.
Running until June 2028, the EU-funded project, called PACIFIC, sees Airbus head a consortium that includes engine supplier Rolls-Royce, German aerospace research centre DLR, fuel supplier Neste, and universities in Finland, Germany and the UK.
PACIFIC is designed to improve modelling and prediction capabilities to better assess contrail formation.
Typically found in the upper troposphere at altitudes of 32,000-42,000ft, contrails are increasingly considered to have a warming effect on the atmosphere that is more short-lived, but potentially greater than, that of CO2.
Recent studies – including the Airbus-backed VOLCAN and ECLIF3 projects – have suggested that sustainable aviation fuel (SAF) can cut contrail production by up to 25% due to lower emissions of soot particles.
While more data is needed to validate those potential benefits researchers face a challenge to replicate the results obtained through flight testing.
“The repeatability and predictability are not there,” said Mark Bentall, Airbus head of research and technology programmes, speaking during the manufacturer’s Summit event in Toulouse on 25 March.
The accuracy of weather forecasts is a particular problem, with contrails only forming in ice super-saturated regions.
“It is very difficult to predict the weather. We have to schedule multiple aircraft, and then we don’t produce contrails and then we go home,” he says.
Airbus and its partners in the three-year study will assess how the composition of different fuels and the combustion process affects soot emissions and contrail formation.
“You can easily measure emissions on the ground – it is much easier than in flight – but it is harder to replicate the temperature, pressure and humidity conditions you find at altitude,” says Thomas Viguier, Airbus innovation and technology specialist.
To do that, Airbus will use a cold chamber – described by Bentall, half-jokingly, as a “big fridge” – supplied by project partner the University of Helsinki.
This will be located to the rear of one Rolls-Royce Trent XWB engine on an A350 test aircraft and will cool the exhaust stream and “set the conditions so the water vapour emitted will freeze and generate ice crystals”, says Viguier.
“To actually create a contrail on the ground is something we have not done before,” adds Bentall, who hopes this will create a “repeatable test”.
Before it can begin tests with the ‘big fridge’, though, the project will need to select the exact fuels to test.
Starting with 10 different fuels, including Jet A-1, the team will run a series of combustion tests, both in the laboratory and on test rigs, to evaluate the soot particles produced by each and how different engine power levels affect that.
It will then select three fuels to take forward to the ground-test phase, examining how different fuel compositions and engine settings influence contrail formation and properties.
Separately, Airbus is to collaborate with major Canadian aerospace academic and research organisations to measure non-CO2 emissions from different fuel types.
Called CRYSTAL, the project includes ground- and flight-test campaigns at the airframer’s Mirabel site in Quebec using a Pratt & Whitney PW1500G-powered A220 test aircraft.
Ground tests are due to start in the third quarter of this year, with flight tests following in 2027.
