Planes are dirty – real dirty. In fact, according to a recent report by the Center for Biological Diversity, by 2050, carbon emissions by commercial aircraft will triple, generating 43 gigatonnes of carbon dioxide and other greenhouse gasses. This number represents 4% of the remaining carbon budget, or the amount of carbon we an release into the atmosphere before catastrophic global warming hits. It is more than the entire country of Belgium will produce during the same time frame.
The aviation industry, especially in the US, has so far been able to skirt around getting regulations stamped on it. The industry as a whole has always argued that it exists on very small margins and that putting new emissions standards in place would cripple it. But with fuel prices at the lowest they’ve been in recent memory, and airlines posting record profits – United made $1.13B in 2014 – that argument is now falling short.
EDIT: A person on the Tek22 Facebook page made a comment that planes are much cleaner than cars. I decided to add the following section to explain why that is not the case:
How Clean (or Dirty) are Planes?
Planes use Jet-A aviation fuel for turbine engines (turbo props and turbofans). According to a US Energy Information Administration report from 2013, Jet-A produces 156.3 pounds of CO2 emissions per million BTUs of energy produced. Comparing that to gasoline at 157.2 pounds per million BTUs, you can see they are about the same.
The FAA produced the following chart showing how many BTUs it takes to move a person one mile (a passenger-mile).
A passenger-mile in a car took 3,193 BTUs in 2012 vs. 2,654 for aircraft. When you add it all up, moving someone by plane from point A to point B in an airplane puts out about 83% of the emissions that doing so in a car does. So aviation is better than driving, but still is a big contributor.
With passenger departures continuing to increase, the airline industry is coming under pressure to go green. Here are a few ways it can make it happen.
More Efficient Conventional Airliners
One has to look no farther than the Boeing 787 Dreamliner to see that the airline industry is beginning to design more efficient aircraft. Its engines are 20% more efficient than those on the 767, and, combined with its light-weight, carbon-fiber/composite construction, the aircraft as a whole reduces carbon emissions by as much as 30% versus other similar class planes. Well-publicized battery issues aside, the Dreamliner is a major step forward in airline technology. Boeing’s chief competitor, Airbus, is also delving into the world of composites. Its Airbus 350XWB, like the 787, will be made up of about 50% composite materials, and claims a 25% improvement in fuel consumption. Still, with soaring (no pun intended) demand, simply making conventional aircraft more efficient won’t be enough.
Oslo is Going Biofuel
The second largest airport in Scandinavia just became the first to make biofuel available to all its customers. Offering a mix consisting of processed used cooking oil, camelina oil, and conventional fuel, the airport is the first large international airport to provide an alternative to Jet-A, or kerosene. According to the airport, Lufthansa, SAS and KLM have already signed agreements to use the fuel. BP will provide the biofuel, supplying the airport with 330,000 gallons. That may sound like a lot, but it would fill up only four Airbus A380s. But it is a very important step. Biofuel presents much lower carbon emissions than pure fossil fuel, and once a production pipeline gets in place, its cost will fall and demand will rise. Hopefully more airports follow Oslo’s path.
Put Your Prius in the Garage – Try Out a Hybrid Aircraft
In July, an Airbus test pilot flew the all-electric E-Fan aircraft across the English Channel. Powered by dual 60 kw ducted fan motors, the small aircraft may enter service as a general aviation training aircraft in 2017, with a four seat version planned for 2019. But a lot of work has to be done before electric flight is really viable for commercial flight. The main issue is that battery technology isn’t quite there. The E-Fan has only 55 minutes of powered flight time at full power. At its maximum speed of 100 knots, that won’t get you very far. Still, the plane provides a beginning. For commercial travel, Airbus is looking to its hybrid E-Thrust technology until batteries become viable for all-electric aircraft. The concept would be to use a combination of jet engines and electric ducted fan engines. The jets and electric engines would both be used on takeoff and climb, but then the jet would be throttled back for cruise flight, only providing electrical power to the fans and to recharge batteries. On descent, all engines would be “turned off” and the airflow through the ducted fans would recharge batteries even more. There are a lot of advantages to hybrid aircraft, and they go far beyond fuel efficiency. First, electric motors are far, far less prone to failure than jet engines. If the jets go out on a hybrid, the electric engines provide a welcome safety mechanism that can get the aircraft to the nearest airport. Additionally, a significant number of fatalities in aircraft accidents are caused by fire – fire is caused by fuel. Hybrids will need to carry less fuel, which lowers the fire risk.
Alternative Energy Aircraft: Solar and Hydrogen Fuel Cell
Last year, the all-solar aircraft, Solar Impulse 2, attempted to travel around the world solely using solar power. Some issues with its batteries (there are those pesky batteries again) forced a pause in the endeavor, but the plan is to complete repairs and continue the journey in 2016. The aircraft is very light, fragile, and does not travel very quickly. As such, I don’t believe we’ll see pure solar powered airliners anytime soon, if at all. However, solar power definitely has a place in commercial aviation – primarily for hybrid aircraft. Anything that can add power to batteries is a good thing – and aircraft have large surface areas that can be covered with photovoltaic cells. Additionally, since aircraft travel above most weather and much of the atmosphere, the solar efficiency is substantially better than ground based cells.
Another technology that is gaining momentum is the hydrogen fuel cell. A fuel cell burns hydrogen to produce power and emits only water vapor as exhaust. The first piloted fuel cell aircraft has take flight: the Antares DLR H2. While still really a test bed, it is capable of flying for about five hours and nearly 500 miles. The technology is nothing new – it’s been used in some cars, trucks and buses for some time – but only recently has it made its way to aviation. Fuel cells haven’t made the splash in the automotive industry that many had hoped, but that’s primarily due to the massive changes in infrastructure required. With relatively few airports, taking it to scale in aviation is more feasible.
Advantages of Electric Engines
There are a number of benefits using electric engines over jet engines. One an economic benefit in the form of maintenance. Turbofan engines – the “jets” on modern airliners – have to go through an overhaul after anywhere between 3,000 and 10,000 hours of use, depending on the model of the engine. While much simpler than piston engines, there are still moving parts in the form of fuel pumps, hydraulics and more that must be broken down and maintained. One of the reasons we are seeing fewer four engine airliners is a combination of maintenance costs and efficiencies. Electric engines have a coil and power leads. They are very simple mechanisms and putting more electrical engines on an aircraft doesn’t carry the same penalties that putting on multiple jet engines does. This brings another benefit in the form of airfoil efficiency.
NASA is testing a concept called distributed electrical propulsion – shown in the image above. The project is called Sceptor. The agency has taken a wing with 18 electric engines distributed across it, mounted it to a test truck and driven it at high speed across the dry lake beds at Edwards Air Force Base in California. When a propeller turns, it forces air out behind it. This is what propels an aircraft forward. That “extra wind” creates additional lift across the wing. On today’s planes, that area of “extra wind” is present on only a small portion of the wing. On Sceptor, the entire wing gets to take advantage. This makes the wing much more efficient. Additionally, it provides more lift at low speeds, as when landing or taking off. This means that wings can be designed for more efficient high speed performance, sacrificing low speed characteristics because the engines help make up for it. When aircraft can go hybrid/electric, it will dramatically change their wing designs and overall efficiency in ways that go well beyond just what the obvious gains from hybrid technology.
On top of all of that, electric engines produce very little noise. Currently, noise restrictions at many airports cause inefficiencies in scheduling and operations. Anyone who has flown out of John Wayne Airport in Southern California has experienced this first hand during its special noise abatement take off procedure. This procedure tends to both alarm unfamiliar passengers, as well as use extra fuel.
Will Aviation Go Green?
I believe the aviation industry will eventually get more efficient and will adapt new technologies that both cost and pollute less. Biofuel probably represents the easiest way to get airliners moving green since it represents solely an infrastructure change – and a relatively easy one at that. But beyond that it will be a slow roll. The top 40 airliners in service today represent more than 20,000 aircraft. For reference, the list price of a 767-300 freighter is about $200M. Even if the average price of those 20,000 aircraft is only a quarter of that, those aircraft represent more than a trillion dollar investment. They aren’t simply going to go away just so the airlines will go green. They will have to be phased out over time as their useful lives run out. Additionally, the number of airliners is expected to double in the next twenty years. The big question will be whether alternative technology in place to replace the aging aircraft and fill those new orders. I hope the answer is yes – the industry needs it.
Photo credits: Airbus, Oslo Airport, NASA, Boeing, Solar Impulse, DLR