Air traffic – Aviation climate balance: the strips have to go away

Flying transport aircraft with a bright blue sky flies at great altitude, often white stripes form behind the machines, which can be seen for a long time. The condensed strips resulting can exist at heights of eight to twelve kilometers for several hours. Over time, they form high clouds, which are referred to as condensed stripes. These consist of tiny ice crystals and are particularly effective.

CO₂ According to a popular point of view, the main factor is also the main factor for the proportion of people in climate change. But that is not the case- as already resulted in an extensive international study by Manchester Metropolitan University with the participation of the German Aerospace (DLR). In principle, global aviation has a share of 3.5 percent in human -made climate warming. But only a third of the climate effect of air traffic is based on CO₂-Missions. Two thirds are eliminated on so-called non-co₂-Effects. These include ozone, aerosols, nitrogen oxides and condensed strips. These-and the developing condensed stripes have the largest share. It follows: If you want to reduce the climate -damaging effect of air traffic, you have the biggest lever for condensed strips.

Cold plus humidity

How do condensed strips arise? A combination of low temperatures and high humidity is necessary for this, the so-called Schmidt Appleman criterion. The temperature must be between minus 35 and 55 degrees Celsius. At the same time, the air must not be too dry, otherwise the cover strips will quickly resolve. If kerosene burns in jet engines, 1.23 kilograms of water vapor, 3.15 kilograms CO are created per kilogram of fuel₂ – and myriad tiny soot particles. If they leave the engine, quickly clump and form condensation germs for small, hypothermic drops of water. These freeze to ice crystals. Behind the aircraft form condensation strips and are pulled into the width by the vertebrae.

The DLR has been researching possible solutions internationally for years. Basically, condensed strips and thus their climate -damaging effects on two ways can be significantly reduced.

One solution is to optimize the flight routes, so that the machines fly as much as possible under environmental conditions that do not even make the development of condensed strips possible. This is not only theory, it also works in practice. DLR and the Maastricht Upper Area Control Center (MUAC) have jointly demonstrated that long -lasting condensed strips can be avoided by comparatively small changes in the flight altitude. Corresponding test flights took place during Corona pandemic, in which air traffic was drastically restricted worldwide. This offered ideal conditions for analyzes in the upper airspace over the Benelux countries and northwestern Germany.

If the weather reports predicted durable condensed strips, the machines on the test flights were redirected by around 600 meters up or down. On other days with these conditions, the aircraft flew without intervention into the altitude. The results were monitored, made comparable and documented by satellite. In fact, the attempts showed a significant reduction in the formation of the condensation through the flight height adjustment.

Change of flight height is worthwhile

Questions are still open: climbing flights are often necessary to change the flight altitude. As a result, the plane consumes a little more kerosene and generates more CO₂. The disadvantage of this should be less than the advantage due to the reduced condensed strip formation. It must also be certain that the change in flight heights and routes is not limited to the security or capacity of airspace. These questions are clarified, among other things, in the research project D-cult. The abbreviation stands for the demonstrator climate and environmentally friendly air transport. Among other things, the DLR, the German Weather Service, the German Air Trailout, Airlines and IT service providers are working on this.

Condens stripes are made up of tiny ice crystals and are particularly high in climate.

The airline Etihad already showed on October 23, 2023 that flights can also be carried out in everyday operation, in which flight altitude and route are optimized with regard to condensation formation. On this day, Flight Ey20 of the airline led from London to Abu Dhabi. In cooperation with the British company Satavia, airline employees had identified regions in the atmosphere in which the formation of condensed strips was expected and the flight route adapted accordingly. Result of the flight: Due to the slightly changed route, additional consumption of 100 kilograms of kerosene was created. According to the airline, this corresponds to 0.48 tons of CO₂. In this flight, 64 tons of CO became arithmetical₂ saved.

The other approach to reducing the condensed strips is to reduce the soot particles in kerosene. The less soot is, the less ice is formed in the exhaust gas beam and the smaller the condensed strips are. Kerosene is made from crude oil. In addition to various hydrocarbons such as paraffins or cycloparaffins, kerosene contains ring -shaped hydrocarbons. Experts also speak of aromatics. These “cause more soot particles in its burning as short-chain hydrocarbons,” as Patrick Le Cllercq from the DLR Institute for Combustion Technology in Stuttgart explains. If it were possible to produce kerosene without ring -shaped hydrocarbons, the formation of soot particles in the exhaust gas of aircraft could be significantly reduced.

That is exactly what is feasible. And it doesn’t just work in theory. Such kerosene already exists. It is referred to as Sustainable Aviation Fuel (SAF) and made from regenerative sources. This does not require any oil. SAF has a lower co₂-Fußprint as the conventionally generated kerosene.

Less soot due to fellow metabolism

SAF can be produced in different ways. In many cases it is produced from waste, in others from plants. In the latest methods, SAF is made from renewable energies, for example, using wind power “green” hydrogen-and referred to as e-fuel. “All of these sustainable fuels have in common that they can be produced without cyclical hydrocarbons, so -called aromatics,” explains Patrick Le Clercq. »Less aromatics in fuel means less soot in emissions and thus fewer ice crystals in the condensed strips. This reduces sustainable fuels the two largest climate warming effects of aviation, condensed strips and the CO₂-Footprint.”

Already in 2018, the DLR carried out flight attempts on this topic together with the U.S. world dream authority NASA. On the one hand, an Airbus was refueled with conventional kerosene, on the other hand with a 50-50 mix of kerosene and safe. The experiments were continued by the DLR and finally a test aircraft with 100 percent SAF was refueled. The reference served as a reference with a 100 percent conventional kerosene. As with the attempts before, a measuring aircraft followed. The results of these flights were recently published. They show a smaller output of soot particles and a 56 percent lower number of ice crystals in condensed strips. This led to a reduction in the climate effect of condensed strips by 26 percent, as the DLR calculated in global climate model simulations.

Duty to add 2030 from 2030

The next step would now be to use SAF on a large scale in commercial air traffic. So far, the new fuels may only be used mixed with kerosene. It can be up to 50 percent. However, such quantities are not yet available on the market. This should change in the future and the SAF share in flights in Europe gradually increase. From 2030, an admixture of five percent SAF is required by law. It should be 63 percent in 2050.

Condensid strips can be reduced by SAF. If the flight routes are then optimized, plus the already lower CO₂-Fußprint of the SAF comes and the lower CO₂-Empire due to technical progress in the form, for example, the introduction of modern engines, the climate warming effect of aviation is already significantly reduced. This should create a bridge until electric drives on extreme short-haul and green hydrogen or e-fuel are available for the drive in sufficient quantities.