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Plant-powered planes show promise

About the author

Jon is the presenter of Science in Action on the BBC World Service. He trained as a mechanical engineer (with automotive and aeronautic design) before becoming a journalist. He has worked at the BBC for over a decade and has reported from areas as diverse as war zones and technology shows.

Plane taking off over a field of yellow flowers (Copyright: Getty Images)

(Copyright: Getty Images)

'Green' biofuels are increasingly being used by airline owners to reduce harmful emissions. But are they really a viable solution for powering every craft in the skies?

To the eye, there was nothing remarkable about the aging Falcon 20 jet as it took off from Ottawa International airport in Canada at the end of October in 2012. But the twin-engined, 10-seater plane was in the process of making aviation history.

After a short flight that saw it climb to 30,000 ft (9,000m) over the capital city, the plane touched back down at the airport to secure its world first.

"Today, I flew the world’s first 100% biofuel flight," said pilot Tim Leslie on landing the National Research Council of Canada (NRC) craft. "It is truly inspiring to take this step towards an eco-friendly future."

Unlike conventional aircraft which burn kerosene – a polluting fossil fuel - Leslie’s plane was powered by fuel derived from rapeseed oil. However, it could equally have been powered by one of a number of biofuels made from algae, flax, coconut husks or even from used cooking-oil.

These kinds of fuels are considered to be eco-friendly and “green” because the plants from which they are derived absorb CO2 from the atmosphere as they grow and release it when they burn, with no net addition of greenhouse gases to the atmosphere. As a result, they are viewed by many as one of the main ways the aviation industry can reduce its carbon footprint.

That’s important when you realize that aviation currently accounts for around 2% of all greenhouse gas emissions, according to the Intergovernmental Panel on Climate Change, although the effects are disproportionate to other types of pollution.

“In terms of climate impact it’s somewhat higher than that,” says Steven Barrett, assistant professor of astronautics and aeronautics at the Massachusetts Institute of Technology (MIT), and the director of the Laboratory for Aviation and the Environment. “Estimates vary from 5 to 10%, because of the altitude at which aircraft fly. Emissions from planes have a different impact than they would on the ground.”

For example, the contrails from a jet – those white streaks you sometimes see trailing a plane – are known to cause high-altitude cirrus clouds, which compound global warming.

Dropping in

It is generally agreed, that these effects will only get worse if nothing is done because air travel is growing….quickly.  In fact, between now and 2030, the number of passengers and number of fights is likely to more than double, according to the UN International Civil Aviation Organization.  

Airline manufacturers and carriers are all too well aware of these effects and are working to try to mitigate them.

“We feel it’s our responsibility to deal with our segment in a very aggressive way,” Dr John Tracy, chief technology officer (CTO) at Boeing, recently told me. “Probably 75% of the research and development dollars we invest in the commercial airplane side goes towards improving our environmental footprint.”

Long term,  new aircraft shapes could help, while even further into the future are the prospects of electric, hydrogen or even solar powered aircraft. However, these kinds of development are years – even decades – away. In the short term biofuels are looked on as a potential savior as most commercial passenger jets can use them with little to no modification, and because they seem to offer significant benefits.

For example, newly released figures collected by a plane trailing the Canadian Falcon 20 suggested that there was a 50% reduction in aerosol emissions compared to conventional fuel. Previous studies with the rapeseed fuel also show that there is a 25% reduction in particles and up to 49% reduction in soot – or black carbon - emissions compared to conventional fuel. Additionally, the NRC research also claims to show increased engine efficiency.

“We are pleased with these positive results. The flight went smoothly and the data collected enables us to better understand the impact of biofuel on the environment,” said John R McDougall, president of the NRC, which partnered with a number of firms – including biofuel suppliers - for the trial.

The NRC test is the latest in a series of demonstration flights aimed at proving the worth of biofuels.  In 2008, Virgin Atlantic was the first to fly a plane on a blend of biofuel and regular jet fuel. Since then, the number of trials has increased year on year, withat least 15 airlines and several aircraft manufacturers performing flight tests with various blends containing up to 50% biofuel. And, in 2011, KLM became the first airline to test it in regular commercial flights between Amsterdam and Paris.

All of these tests – including trans-Atlantic flights - have shown that biofuel works well, improves efficiency and, crucially, can be “dropped in” to existing fuel infrastructure at airports.

With so many apparent advantages, you might expect that every airline is beginning to draw up a plan to use these fuels. But you would be wrong.

Sound barrier

Biofuels are not without problems, leading the chief scientist of environmental group Greenpeace to label the first flight by Virgin as "high-altitude greenwash".

One of his main criticisms is that in some cases biofuels can lead to deforestation and a large increase in greenhouse gas emissions. It is a view backed up by a recent report from MIT, which cautioned that the entire life cycle of a fuel has to be assessed before it can be called ‘green’.

The 2011 analysis of 14 fuel sources, including conventional petroleum-based jet fuel, showed that emissions from burning biofuels varied hugely depending on the type of land used to grow the fuel-crops. For example, biofuels made with palm oil from a plantation made by clearing rainforest emitted 55 times more carbon dioxide (over its life cycle) than oil from a previously cleared area. The comparison with conventional fuels can look very different too. Crops grown in an unsustainable manner can actually create fuels that emit 10 times more CO2 than fossil-fuel based fuel.

“The situation is more complex than just looking to biofuels,” says Prof Barrett. “There are many types of biofuel, there are many different kinds of biomass which can be used to create biofuel, and there are many different ways of taking that biomass and converting it, and all of those things have different properties in terms of how much they cost and how efficient they are. We need to get more sophisticated about determining which ones make environmental sense.”

Other big challenges for biofuels include whether land used for growing the necessary crops is taking land away from growing food, and also just the sheer size of the land area that would be needed to cultivate enough biomass to feed the growing aviation industry.

As a result, scientists increasingly advocate the use of crops that grow in areas that would not normally support agriculture – such as salicornia, a salt loving plant – or the use of algae, which could potentially be grown in massive vertical vats or ponds. However, there is still a long way to go before these crops are grown on anything like the scale needed to support aviation.

But people like Boeing’s Dr Tracey believe it will happen.

“We are convinced that sustainable biofuels can provide a way to reduce the CO2 by between 60 and 80% on an airplane,” he told me.  “We really do believe that by 2030, 30% of all airplane fuel could be provided by sustainable biofuels.”

And if you’re still concerned about flying in a plane powered by plants, his message is: don’t be. Although they are produced from a variety of sources, any fuel that finds its way into a plane is tightly controlled and regulated.

“There are 12 different parameters that you have to measure with exact precision to get certified to be a jet fuel,” he says. “We’ve flown on commercial flights, we’ve flown F18s over the speed of sound, C17s, Apache helicopters, you name it, it’s been flown. So this is not a technology question on whether these fuels will work or be safe. This is only a question of scale-up of production.”

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