(Cologne) – Long-haul flights only transport around ten percent of all passengers annually, but due to the long distances and flight times, they generate around 40 percent of the CO2 emissions from aviation. “Small changes in flight altitude, flight speed and the choice of energy source can significantly reduce the climate impact of air traffic,” says a report from the German Aerospace Center (DLR).
Comparison of fuels
The scientists in the “KuuL” (climate-friendly ultra-efficient long-haul flight) project compared the fuels kerosene, sustainably produced, CO2-neutral synthetic fuels (Sustainable Aviation Fuels, SAF) and liquid hydrogen (LH2). They also linked a reduction in flight altitudes and flight speeds to the respective energy source, drew up plans for modified aircraft and used them to simulate 3.000 long-haul flights per year over an operating period of 23 years.
Reduce climate impact with hydrogent
“Our studies show that simply switching from kerosene to SAF reduces the climate impact by around 25 percent without the need for new aircraft,” explains project leader Martin Hepperle from the DLR Institute of Aerodynamics and Flow Technology. If you look at CO2 emissions alone, they would be reduced by one hundred percent if SAF were produced in a CO2-neutral manner.
If kerosene were replaced, this would lead to a reduction in the climate impact. Airplanes flying lower and slower require reduced wing sweep. © DLR (CC BY-NC-ND 3.0)
By using SAF, the effect of so-called non-CO2 effects can also be reduced. Since the combustion of synthetic fuels leads to fewer soot particle emissions, SAF produces less pronounced contrails. However, the climate impact cannot be reduced to zero simply by changing energy sources.
However, further savings in terms of climate impact are possible by switching to hydrogen, as nitrogen oxide emissions from aviation would also be reduced. “But here too we have to produce the hydrogen sustainably,” explains Hepperle. “If you reduce the maximum flight altitude in addition to changing fuel, a reduction of up to 70 percent can be achieved,” says Hepperle.
However, an adjustment to the shape of the aircraft and flight speed is then required, which, according to the report, requires “the development of new aircraft”. “A long-term compromise must be found between energy requirements, economic efficiency and climate impact.”
LH2 tank volume as a challenge
While aircraft powered by kerosene and SAF with the same fuel systems would result in very similar designs, aircraft using liquid hydrogen as fuel differ significantly from conventional aircraft. “Above all, the tank volume as well as integration and safety represent a particular challenge for long-haul aircraft,” explains the scientist.
However, “contrary to the researchers’ expectations,” it turns out that hydrogen can also be an option for long-haul routes. An LH2 aircraft requires slightly more energy than one with SAF. “But if you take into account the approximately 30 percent lower primary energy requirement for the production of LH2 compared to SAF, there is potential for this technology path.” Final forecasts as to whether SAF or LH2 would be more climate-friendly and economical on long-haul routes in the long term would, however, be based on the “ “Major technological challenges” in the use of LH2 make it difficult.
In addition to the Institute of Aerodynamics and Flow Technology, the DLR Institutes of System Architectures in Aviation, Air Transport, Propulsion Technology and Atmospheric Physics were involved in the DLR KuuL project. In a follow-up project, the existing uncertainties in the models will be further reduced.
The number of passengers is increasing again
The need for research remains high: long-haul flights at German airports experienced large increases in the first three quarters of this year. The number of passengers increased by 36 percent compared to the same period last year. Domestic German traffic grew by 27,3 percent, European flights by 17,2 percent. The airport association ADV published these figures last week.
However, the ADV naturally pursues other interests. The association criticized the fact that with these growth figures, Germany was “at the bottom of the major European aviation markets”.
Photos
Reducing the climate impact by adjusting the flight altitude, flight speed and choice of energy source leads to increasing operating costs. © DLR (CC BY-NC-ND 3.0)
