A new step by the Obama Administration toward limiting heat-trapping emissions from airplanes could get a lift from cutting-edge technologies such as non-stick coatings that stop bug guts from clinging to jet wings.
Biofuels, lighter engines, aerodynamic designs, 3D printing of aircraft parts, and, yes, even bug-proof coatings could boost fuel efficiency, which in turn reduces pollutants.
The U.S. Environmental Protection Agency on Wednesday found that aircraft’s greenhouse gas emissions pose a threat to human health by contributing to global warming. This “endangerment” finding allows the agency to develop a proposal to limit emissions from planes as it has done with cars, trucks and power plants. Such a standard would likely take more than a year to finalize.
As more people take to the skies, global aviation is expanding and its carbon emissions are projected to triple by 2050. Already, airplanes account for 2 percent of all human-induced carbon emissions and 12 percent from transportation sources. They also emit pollutants that add to the smog and soot shrouding many cities.
Could technology fix this? While some ideas sound nifty, such as the solar-powered Solar Impulse 2 and NASA’s battery-powered plane, they’re not likely to slash emissions from commercial planes in the near future. These five approaches hold more potential:
1. Fuels made from cooking oil, sugar cane, and biomass.
Though costlier than conventional jet fuel, some biofuels emit less pollution. A biofuel blend cut soot emissions at least 50 percent in NASA testing last year in the California desert.
In a new study, researchers found a way to convert ketones from sugarcane into heavier compounds that could potentially be used as aviation fuel. They said this fuel could cut greenhouse gas emissions up to 80 percent compared with traditional jet fuel.
Co-author Alexis Bell, an engineering professor at the University of California, Berkeley, says commercialization of the new technology, funded by oil giant BP, is dependent on its costs. “A large investment is required to make a bio-refinery,” he says, adding a U.S. mandate for reduced emissions could spur such spending.
Alaska Airlines is stepping ahead. Consistently ranked first among U.S. domestic airlines for fuel efficiency, it flew 75 commercial flights using a biofuel from cooking oil in 2011 and aims to use a biofuel blend on all flights from at least one airport by 2020. Later this year, it plans the first commercial flight using an alcohol-to-jet fuel and next year, a demonstration flight will use an alternative fuel from forest residue.
2. Engines feature lighter materials, added gear.
Aircraft manufacturers are using more fuel-efficient engines in new commercial jets. In June, Boeing began production of the 737 MAX and expects initial test flights next year. The single-aisle planes use CFM International’s new LEAP 1-B engine which has a light-weight carbon fiber fan and is up to 15 percent more fuel efficient than current models.
Not to be outdone, Airbus is making the single-aisle A320neo jet with either a CFM engine or a new Pratt & Whitney one that has an extra gear. (Learn why adding a gear saves fuel.) Airbus says it has already tested the jet with both engines and plans to begin deliveries late this year. The jet uses 20 percent less fuel per passenger seat because of the engine and other features, Airbus says.
3. Newer shapes and smaller vertical tail.
Researchers are testing new shapes. In a project funded by NASA, engineers at the Massachusetts Institute of Technology are exploring whether a wider, double fuselage—the tube-like central body—can improve fuel efficiency. Their concept, known as the “double bubble,” could incorporate engines into the fuselage so the wings could be made of thinner, lighter materials.
Gray dots indicate tufts for flow visualization.
Red dashes show location of active flow control actuators.
Exit nozzles for active flow control actuators
Heat exchanger for active flow control air supply
Another idea: a smaller vertical tail. In April, the Boeing ecoDemonstrator 757 made six round-trip flights from Seattle to test the feasibility of reducing a plane’s tail size. It had 31 tiny devices or “sweeping jet actuators” blow air on the tail to create the same side force during takeoff and landing that a larger tail does.
"The ability to reduce the size of the vertical tail would reduce weight and drag and decrease fuel consumption and emissions,” NASA engineer Mike Alexander said in discussing the test flights. NASA’s wind-tunnel tests of the technology in 2013 suggested the tail’s size could be reduced 17 percent, cutting fuel usage by as much as 0.5 percent.
4. Non-stick coatings could repel bug guts.
Other fuel savings could result from non-stick coatings designed to slough insect residue off jet wings. Test flights by Boeing’s ecoDemonstrator 757 found a coating that reduced the number of bugs and residue by 40 percent compared with a control surface.
Bug guts are no small problem. “We learned when a bug hits and its body ruptures the blood starts undergoing some chemical changes to make it stickier,” NASA senior materials scientist Mia Siochi said in announcing the test results. When bugs accumulate on the wings, she said, they cause drag.
5. 3-D printing lightens plane parts.
A Northwestern University case study, published in May, found 3D printing could make plane parts lighter and cut fuel use. Team leader Eric Masanet doesn’t expect such printing of crucial jet parts, such as the wings and engine, anytime soon, but he sees potential in other parts such as brackets, hinges, and buckles.
“There are enough parts that, when replaced, could reduce the weight of the aircraft by 4 to 7 percent,” Masanet said in a press release, adding the result could be a cut in fuel consumption of up to 6.4 percent. Before that happens, though, he said scientists will need to improve 3D printing technology.
Environmental groups say a strict U.S. limit on plane emissions could help spur ingenuity and set a model for the rest of the world. The aviation industry prefers a global standard. (Learn more about the tussle over setting a limit.)
“You boost technological innovation” by setting fuel efficiency standards, says Benjamin Longstreth of the Natural Resources Defense Council, one of five environmental groups that sued the EPA to rein in aircraft emissions “We’ve seen that happen with automobiles, and the same should happen with airplanes.”