This article is part of our special report Greening aviation.
The aviation industry has little choice but to turn to biofuels to help meet its commitments to reducing carbon emissions in the decades ahead, argues Alan H. Epstein, an engineer who is vice president for technology and environment at Pratt & Whitney.
Alan H. Epstein is the vice president for technology and environment at Pratt & Whitney, a US-based manufacturer of aircraft engines. The following is an excerpt of an interview with EurActiv’s Timothy Spence.
To improve efficiency, aircraft manufacturers have made steady improvements in aerodynamics and using lighter materials. Your business is propulsion – what are you doing to make engines more efficient?
Some of us think that most of the reduction in fuel burn in airplanes actually come from better engines. The engines have improved since the dawn of the jet age by about 1% a year, on average. And some people say that’s not very much, but then I would say: what don’t you understand about compound interest? And so the latest engines from Pratt & Whitney – which is the geared turbofan – are actually about 16% better than the ones that are flying today. So that’s a big step, but it took us 20 years to get there.
Road transport is the largest contributor of greenhouse gases, but the growth of aviation emissions exceeds all other sectors. Is there a point in the future where you see that changing, that growth declining and if so, how do you do it?
Let me amend your statement. The biggest percentage growth has been in aviation, the biggest growth is still ground transport. …
Air transportation is more efficient in terms of CO2 than driving a large SUV or even a small car. It’s more efficient than a diesel locomotive. It’s not more efficient than the TGV in France – run mostly by nuclear energy – but it’s the most efficient way of getting long distances and you could say, why is that? It’s a big airplane, it’s 100 tonnes, it’s travelling eight-tenths the speed of sound.
The answer is there’s a trick, and the trick is for all vehicles – cars, buses, trains and airplanes – once you get above 80 km per hour, 90% of the energy or more goes to pushing the air aside, so it’s all air drag. And the trick with an airplane is, you go up high enough in altitude where there is almost no air, so there’s not much drag, so that’s why they’re such an efficient way of moving people.
That’s the peculiarity of air transportation. Efficiency is … economic return to the airline, so they have every incentive to absolutely minimise the amount of fuel burn and CO2 produced.
One of the big changes in aviation is biofuels, and it is at a very maiden stage. Is an airplane able – without any modification to the engine – is an airplane either able to use a fossil fuel or a biofuel without changes?
Simple answer: yes. It think it was a mark of collective genius between the fuel people, the aviation people, the engine people, the airplane people to make the idea of a drop-in fuel a reality. A drop-in fuel is a fuel that I can put any place in the supply chain – in the big tanks at airports, in the tanker trucks – and the airplane and the engine don’t care at all.
And then we did something more clever, I thought, although it seems trivial in retrospect. Instead of saying that you can use this new fuel, all we did was modify the definition of fuel so that all the airplanes in existence, all the engines in existence which reference some arcane specification don’t have to be changed. [Instead,] we’ve changed the definition of that specification. So we did it first with cold liquid fuel in the middle of this last decade – and that was for energy independence – and now we’ve done it for the first biofuel, which is defined by how you make it not what’s in it. … The engines are agnostic to what the source of the biomass is.
It’s possible to mix traditional kerosene with biofuels, and it makes no difference to safety?
The requirement now is that you can’t have more than 50% biofuel mix. The reason is we’re extraordinarily conservative when it comes something like flight safety. For 100 years of aviation, all the fuels have been fossil-fuel based … as we gain more experience, you would expect to relax that [50-50] specification.
Certainly we have run tests with much higher concentrations of biofuels …
… and there is no difference in performance and safety?
Safety is unquestionably the same. Few people realise how variable jet fuels is – how variable petroleum is around the world. You drive your car in South America, it’s actually different than in Europe and a different fuel than in North Asia versus South Asia, and jet fuel is much the same.
So at the moment, the biofuel we’ve tested is actually a slightly better fuel, and if you could guarantee to me that all my engines would burn this biofuel, I could actually reduce the fuel consumption a little. At the moment I haven’t figured out how to do this, with this undefined mixture, where I land in Los Angeles and it’s all biofuel, I land in Tokyo and it’s all fossil fuel, I land in Frankfurt and it’s a 50-50 blend. We haven’t figured out how to do that.
Certainly biofuel is in no way inferior to conventional fuel.
Does this translate into a greater efficiency and a reduction in emissions?
For pure biofuels there is a reduction in particulates – smoke – which are regulated and is important. There doesn’t seem to be a difference in oxides of nitrogen. And fuel efficiency is an open question, because of the wide variety of fossil fuels [used in the blend]. …
There is increasing concern here in Europe about the origin of biofuels. Is that something that concerns you as you produce engines that can burn these types of fuels?
It used to until we defined biofuels to mean sustainable biofuels. … So when we talk about biofuels now, we mean sustainable. And sustainable at the very minimum means it doesn’t interfere with food and food prices, and it doesn’t interfere with water.
What about land impact?
Things get very complicated, and I’ll leave it to the experts as to how land use and land-use policy is affected. But certainly no one in their right mind would say, if you went and ploughed under rain forest and used it to produce fuel, that that would be a sustainable fuel. It certainly isn’t.
One of the concerns in the industry is the supply, and there are government policies in the US and Europe that in effect subsidise biofuel production –
– but not for airplanes.
– for ground transport. Is there competition between the fuels for the people on the ground and people in the air?
Is that affecting the ability switch to a cleaner jet fuel?
The fundamental point is airplanes don’t have an option. Airplanes need biofuel, maybe biofuel doesn’t need airplanes. Cars, we can electrify. Electricity we can make from renewable sources or nuclear sources, we don’t have to burn fossil fuels.
Airplanes need a liquid hydrocarbon fuel. In the past this liquid hydrocarbon has been a fossil fuel. … Solar energy – you can’t cover an airplane with solar cells and get it to fly very far or very fast. You can do a one-up demonstration, but on the planet Earth you can’t fly passenger airplanes with solar cells.
But I can solar power the airplane by collecting solar energy and turning that into a liquid hydrocarbon where the carbon comes from the atmosphere. That’s exactly what a plant does. I could use a big industrial plant and harvest the CO2 from a coal-fired power plant, and I could even take nuclear energy and synthesise a hydrocarbon from it. Mother Nature, though, does most of the work for us with plants.
The challenge is there is very little biofuel now. So how do you make more biofuel in a sustainable way? I think it’s through technology. But it’s biological technology, not airplane and engine technology. …
How much land does it take to grow enough fuel for one flight – say from Washington to Brussels?
The answer is a lot. You get a couple hundred gallons per acre a year. A very large airplane might have 20,000 to 40,000 gallons of fuel, so if you just took current land, you’d need most of Europe to grow biofuels for Europe – just for aviation. …
Aviation has committed to carbon-neutral growth after 2020. And if we start to grow again at 4 to 5% a year, the new equipment like the Pratt & Whitney geared turbofans [engines] will give you 1 or 2% a year – the average of aviation has been about 2% per year reduction in fuel burn – but the only way you can cover 4 or 5% is to go to a low-carbon fuel.
There is no other option for aviation to stop the growth in CO2 than to go to a low-carbon fuel. We’re the most organised, focused group on the planet due to a) safety and b) the economic returns, so we’re going to do it.
Most of the fuel in Europe and North America is concentrated in very few places, so it’s an ideal way to start up a new industry where you don’t have to worry about side distribution channels.
Europe has a commitment to 10% biofuels in ground transport by 2020. If you scoop that away from ground transport and dedicate that to aviation, does that make a big difference?
Yes, it solves the aviation problem … but it’s a different fuel …
… it’s a different fuel and refining process. But does it give you what you need?
The short answer is just about yes.
Is there any conflict between the industries – the auto and the aviation industry – over biofuels? Or with policymakers in the EU, where you say: ‘look, rethink where you are putting your biofuels’?
I’m a naïve American, so I have no idea how you pressure anybody in the EU.
Education, however, is sometimes helpful. In the United States, the Department of Energy has decided that the future of ground transportation is electrification. There were other options, fuel cells for example. As Europe becomes greener for power generation, it makes more sense to think about electrification [for transportation]. In Europe, the automobile trips are shorter, the cars are smaller, so electrification may make even more sense than it does larger parts of North America.
In terms of the global environment, you could say it doesn’t matter if I’m saving a million tonnes of CO2, it doesn’t matter whether it’s from aviation or the ground as long as it’s a sustainable biofuel.
What percentage of flights today are using biofuels?
It’s miniscule. For example, Lufthansa had a regularly scheduled Frankfurt to Hamburg run … and they basically scrambled to get as much biofuel as they could.
There is very little biofuel now, and it is very expensive. But it has only really been a year since it has been legal to use it on commercial flights.
The next biofuel mark will be a new kind of biofuel that we are working to certify … that’s called alcohol-to-jet [ATJ]. And this doesn’t mean we are taking the vodka from the world’s martinis and using it to power airlines, although that’s perhaps feasible in some sense. It’s cellulosic – plant waste, the corn stalks left over, the stuff you throw away now can be processed into biofuel, and that’s a way to vastly increase the supply and the economic return to the farmers is – you sell the corn, you sell the corn stalks. So within a next couple or three years, I expect those biofuels to be certified.
This 1% improvement in efficiency that you’ve seen in commercial aviation for 60 years, does that continue, does it drop off or does it go up?
Efficiency in converting energy in the fuel, of pushing the airplane. We’re now about 40% efficient – taking the theoretical energy in the fuel and using it to push the airplane. The first jet engine was 10%. The law of thermodynamics, which I won’t burden you with, defines a limit to how efficient things are and it’s not 100% – it’s about 80%.
We’re now at 40%, so we’re now halfway to the goal. So there’s enough headroom ahead of us in the next 40 or 50 years of jet travel as we’ve had in the last 50 years in terms in improvement.