Will planes ever be sustainable? New study probes the science of eco-fuels

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Go by private jet is not the greenest thing to do. But while planes are huge emitters of CO2, there is also a lot of work behind the scenes to change that.

The most promising is Sustainable Aviation Fuel (SAF). While airline fuel made from renewable sources is still in its infancy, everyone from European aircraft manufacturer Airbus to Shell is working to make it a reality. But, like Delta Air Lines points out, all the SAFs produced in 2020 would only be enough to power Delta’s fleet for one day – and that’s just one airline.

But two new studies published this week in Earth & Environment Communications show how beneficial FAS could be. The results could help green the dirty and dirty airline industry.

What’s up – Both studies were carried out by the German Aerospace Center (acronym DLR in German), the German equivalent of NASA. The first showed that SAF-powered planes produce less soot and less ice crystals in the atmosphere, which means less warming from artificially produced drag clouds.

The second showed that scientists may have overestimated the amount of sunlight reflected back into space by these artificial cirrus clouds. This means that more sunlight is passing through than we thought, and therefore there is less potential for cooling contrails.

Together, the two studies show that the SAF could have a significant impact on the total warming of air transport.

Contrails emit aerosols into the atmosphere, which greener fuels can solve. Andreas M. / 500px / 500px / Getty Images

Here’s the background – It seems unlikely that people will stop stealing. Even during the slowest flight day At the height of the pandemic lockdown, the Transportation Security Administration still screened more than 87,000 passengers in the United States alone. On Sunday, June 13, the TSA screened more than 2 million passengers in a single day for the first time since before COVID.

But while there are active movements for encourage people to fly less, like the inspired Greta Thunberg flygskam or “the shame of the flight” which may have led to a decline in air travel in Sweden and elsewhere, there are several million more who are jumping on the plane for the first time in developing economies around the world.

ICAO expects passenger and freight transport by air will double by 2036 so without much flygskam, we will need another solution. It’s probably sustainable aviation fuel, and thanks to this new study, it’s even more promising.

Aircraft engines spew 3.16 kg of carbon dioxide and 1.23 kg of water vapor for every kilogram of fuel consumed. Although the planes fly high, the temperatures are very low and this water turns into ice crystals. Under the right conditions, these trails can stay for hours, which can keep warm air trapped in the atmosphere and attract more sunlight to create even more heat.

fhm / Moment Unreleased / Getty Images

How they did it – According to the DLR study, unlike CO2 emissions, trail cirrus clouds dissipate within hours. This means that removing them could have an immediate cooling effect on the climate.

The researchers took an Airbus A320 aircraft and used five different types of fuel mixtures to determine the effect of the fuel type (including SAF) on the drag produced by the aircraft.

  • Two traditional Jet A1 aviation fuel blends were used, as well as three other blends of Jet A1 with synthetic or bio-based alternative jet fuel.
  • The A320 flew at constant speed and altitude in closed research airspace in Germany and used a fighter jet to measure the results.
  • The team showed significant reductions in soot emissions and an increase in the size of ice crystals, which as a result showed a smaller total number of crystals.

“The initial concentrations of the number of ice in contrails are a key parameter in determining the extinction of light by contrails and their impact on climate,” the authors write.

And after – Trails with a lower initial ice count have a shorter atmospheric lifespan, which directly contributes to reduced energy disposal in the atmosphere and reduced warming.

In other words, the mixture of more sustainable aviation fuel into commercial jet fuel has an immediate regional and global effect on the warming caused by contrails.

This, combined with the results of the second DLR study that the cooling effects of these artificial cirrus clouds due to the reflection of sunlight in space were previously overestimated, shows how much these drag clouds can make an impact – and if switching to SAF blends can get rid of them faster, we’ll both help the planet and improve our views of the beautiful blue sky.

Summary of study 1: Drag cirrus clouds account for most of the climate impact of aviation. Yet the links between the composition of jet fuel, the microphysics of contrails and climate impact remain unresolved. Here we present unique observations from two DLR-NASA aircraft campaigns that measured the exhaust and drag characteristics of an Airbus A320 burning either standard jet fuels or durable, low-carbon aviation fuel blends. aromatic. Our results show that soot particles can regulate the number of trailing cirrus ice crystals for current emission levels. We provide experimental evidence that burning sustainable low-aromatics aviation fuel can result in a 50-70% reduction in soot concentrations and ice counts and an increase in ice crystal size. Reducing the number of ice trails results in less energy deposition in the atmosphere and less warming. Significant reductions in the climate impact of aviation could therefore be achieved through the widespread adoption of low aromatic fuels and regulations aimed at lowering the maximum content of aromatic fuels.

Summary of study 2: Fully accounting for the climate impact of aviation requires a process-level understanding of the impact of aircraft soot particle emissions on ice cloud formation. Assessment of this impact using global climate models remains elusive and direct observations are lacking. Here we use a high-resolution cirrus column model to study how the soot particles emitted by airplanes, released after sublimation of ice crystals at the end of the life of contrails and contrails cirrus clouds , disrupt the formation of cirrus clouds. By combining cloud simulations with a description based on measurements of soot-induced ice formation, we find that only a small fraction (

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