Climate change, and the need to reduce pollution and improve air quality, are driving much of the innovation in the aviation industry. This was never clearer than at the Paris Air Show 2019, when the world's top manufacturers of planes and engines met to make a promise: They would reduce their carbon emissions drastically – to half their levels from 2005 – by the year 2050.
Those goals, set by the Air Transport Action Group, or ATAG, are as ambitious as they are necessary. Without them, aviation, which currently produces about two percent of the carbon dioxide in the world, could one day end up accounting for nearly 20 percent of global CO2 emissions – even with the normal improvements in fuel economy that the industry has historically delivered.
The conclusion is clear: The aviation industry has an imperative to innovate. At Raytheon Technologies, engineers are working diligently and creatively to bend the emissions curve downward and deliver on the promise of Paris through several paths, including: improved engine performance with better fuel economy, the development of hybrid electric propulsion, engines that can burn cleaner alternative fuels such as sustainable aviation fuels and hydrogen, and improving the operational efficiency of the fleet by optimizing flight trajectories.
Improving engine fuel economy
While it’s important to improve fuel economy in every form of flight, let’s be clear: Large engines are where we can make the greatest impact. About 80 percent of emissions comes from long-range flights, or those that travel more than 1,000 miles.
One way we’ve already revolutionized large engines is the development of the GTF, or Geared Turbofan engine. Its novel construction allows the fan and the turbine that drives it to spin at their different optimal speeds. That feature has already produced a 16 percent improvement in fuel economy and a 50 percent reduction in regulated emissions.
But there is much more we can do. The GTF we fielded in 2016 was only the first generation. Future GTF engines will derive even more fuel economy improvements from this novel engine architecture. Another area of focus is to enable higher gas temperatures in the turbine section, making the engine more efficient. That will require the use of novel high temperature materials, advanced coatings and advanced cooling strategies.
Hybrid electric airplanes
The aviation industry is also looking to adopt what has already been a great success story for automotive manufacturers: the hybrid engine.
Hybrid electric technologies hold great promise to deliver the fuel economy we will need for the next large commercial engine program. It’s likely by 2035 or sooner that we’ll see the first continental flight powered by a hybrid electric engine, as well as fleets of air taxis in cities around the world, running entirely on electric engines to shuttle people from one part of town to another.
At Raytheon Technologies, we’re aiming to increase the fuel efficiency of conventional gas turbine engines by feeding them supplemental power from electric motors and operating both in smart, optimized combinations throughout different parts of the flight envelope.
Pratt & Whitney, a Raytheon Technologies business, is focusing on the engine design as the propulsion system provider with support from Collins Aerospace, also a Raytheon Technologies business, on the motors, generators and power electronics. The Raytheon Technologies Research Center is supporting this effort.
Our work in hybrid electric technologies extends to partnerships with our government customers and academia. Pratt & Whitney, for example, was recently awarded a contract from NASA to collaborate with Penn State University, Georgia Tech and Howard University on the design of a gas turbine engine that could power hybrid electric single-aisle, medium- and short-haul aircraft. Our contributions to that project will include advanced modeling and simulation, as well as experiments on turbines that would serve as key components optimized for hybrid electric engines.
What’s especially exciting about hybrid electric technologies is that they’re a force multiplier to our work in fuel economy. Hybrid electric engines would allow us to optimize how those advanced jet engines are operated, further improving their efficiency and driving down fuel burn.
Cleaner alternate fuels
Sustainable aviation fuel, or SAF, is an alternative to fossil fuels. SAF includes biofuels, which are made from agricultural products that absorb carbon dioxide before they're harvested. On a net basis, these fuels have the potential to reduce CO2 emissions by up to 80%.
Other SAF would include e-fuels, where renewable energy from wind, solar or nuclear power is used to create hydrogen, which is then turned into jet fuel through chemical processes. Today, SAF makes up less than 0.1% of global jet fuel consumption. Building the capabilities to use SAF at scale in aviation could cancel out the net growth in emissions.
Today, most light commercial engines are cleared to run on a 50-50 blend of sustainable fuels and conventional Jet A fuel. Pratt & Whitney is working to certify unblended sustainable fuels for use on its engines. The business has more than 15 years of experience in testing engines on sustainable aviation fuels and will be ready when unblended biofuels are certified for use.
The effort to adopt SAF in aviation goes well beyond the industry; it will require energy companies to build the necessary production infrastructure and governments around the world to encourage that development.
Another alternative fuel that has drawn significant attention is hydrogen, which produces no carbon emissions when it is burned. Aircraft manufacturers have started laying out plans for hydrogen-fueled aircraft to enter service in the next 10 to 20 years. And historically, we’ve already shown it’s possible; Pratt & Whitney built an engine that ran on hydrogen in the 1950s.
But we have much work to do. Making it so aircraft can use hydrogen optimally would require significant modifications in airframes, for example – hydrogen has very low volumetric energy density and can’t be stored in the same way as conventional jet fuel – but none of those modifications is beyond our capability.
Making hydrogen work as aircraft fuel will require collaboration between airframers and propulsion providers, and, much like SAF, it will require new infrastructure efforts by energy companies and governments around the world.
Improving fleet operational efficiency
There are important opportunities to improve the fuel economy of aircraft by optimizing air traffic and flight operations. This will allow for flight trajectories to follow near-optimal routes, at near-optimal altitudes and speeds during all phases of flight, which will reduce delays, fuel consumption and emissions.
There are also opportunities to reduce fuel consumption at the airport surface through improved taxi and ramp operations. Taking full advantage of these opportunities requires more intelligence in the aircraft avionics, new automation in air traffic management systems, advanced air-ground datalink communications, more accurate and timely weather information, as well as improved systems and capabilities at airlines’ operations centers.
Collins Aerospace has been upgrading avionics to enable navigation systems to harness information for optimal aircraft trajectory planning, flight path optimization, flight planning, use of enhanced flight vision systems and weather radar for more efficient operations.
Raytheon Intelligence & Space, a Raytheon Technologies business, has been fielding and upgrading state-of-the-art air traffic management systems as part of the FAA Next Generation Air Transportation System portfolio to deliver trajectory-based operations capabilities and to bring more efficiency to the way controllers manage air traffic.
Collectively, Collins Aerospace and Raytheon Intelligence & Space have been providing and modernizing datalink and enterprise network solutions to support airlines and the FAA. They have also been key players in providing weather information capabilities, including weather sensors and integrated weather processing systems. Together, and depending on the specific airspace environment, traffic conditions, and the capabilities of the aircraft fleet, operational improvements could lead to reductions in aircraft CO2 emissions by up to 10%.
Industry groups such as ATAG, as well as the International Civil Aviation Organization have set very ambitious targets for sustainable aviation and have identified what is referred to as a “basket of measures” to achieve those goals. As an industry member, Raytheon Technologies reaffirmed its support for the ATAG target in 2020.
It’s important to realize that there are no silver bullets in the fight against climate change. None of the approaches highlighted above will by themselves accomplish the sustainability goals that so many in the aviation industry committed to at that 2019 meeting in Paris. Making it so that aircraft in 2050 produce only half the carbon emissions they did in 2005 will be a tough journey that will require significant partnership and collaboration among the aviation industry, the energy industry and governments across the globe.
But it is far from impossible. In fact, major airlines for Europe and America have committed to full carbon neutrality by 2050. Engineers at Raytheon Technologies are ready and motivated to solve the challenges and create the technologies that will introduce a new era of sustainable aviation.