The most important thing that drives all future civil aerospace engine design is engine efficiency, which has a direct impact on specific fuel consumption, operating costs, and environmental issues. New propulsion means for autonomous systems is another area of interest to the civil aviation world. All top engine makers are unveiling new technologies to burn less fuel, cut CO2 emissions and produce less noise. As they enhance engine efficiencies, they are simultaneously exploring electric and hybrid propulsion systems. Airbus announced in September 2020 it would seek to produce a hydrogen-powered plane by 2035. Considering that a large number of drones and Urban Air Mobility (UAM) are beginning to fly over populated areas, the aero-acoustics of these engines will also be a design focus. The benefits of research and technology in propulsion will shorten the engine development cycle, reduce engine weight, increase engine performance, reduce engine fuel consumption, enhance reliability, reduce emissions and noise, increase component life and reduce maintenance requirements. The engines being the most important, and most expensive, aircraft part, their development will shape the airline industry’s green transition. The four leading engine manufacturers are taking different approaches as they work on newer models.
Leap-powered A320neos. Image Source: Airbus
CFM International, a joint venture between GE Aviation and Safran, was behind the best-selling aircraft engine of all time, the CFM56, and now the high-bypass turbofan LEAP (Leading Edge Aviation Propulsion) engine. LEAP has been flying. It also has components from Ceramic matrix composites (CMC) and has 3D-printed fuel nozzles. LEAP is the second-most ordered jet engine behind the 44-year-old CFM56, which achieved 35,500 orders. CFM intended to produce 2,000 engines in 2023.
In June 2021 CFM announced its potential successor which is being hyped as “the future of flight”. The CFM’s new RISE (Revolutionary Innovation for Sustainable Engines) program will produce the next-generation CFM engine by the mid-2030s. The program targets are to reduce fuel consumption and carbon emissions by more than 20 percent while also being 100 percent compatible with both Sustainable Aviation Fuel (SAF) and hydrogen. Safran CEO Olivier Andriès promised that the venture would prove to be “a real game-changer”. The RISE program would be the first-of-its-kind open-fan architecture that will yield the greatest benefit. It will help optimize engine operation across each segment of the flight.
PW1000G. Image Source: Pratt & Whitney
Pratt & Whitney
Pratt & Whitney is best known for the PW1000G, which powers the Airbus A220 and the A320neo family. Its six variants collectively form the GTF family. Pratt & Whitney has now invested $10 billion into its geared turbofan technology. The GTF engine fans rotate much slower than the compressor and turbine, which gives them a 12:1 bypass ratio, which is the highest in the industry. The geared turbofan design results in “double-digit reductions in fuel efficiency, noise, and emissions”. Pratt & Whitney views the GTF’s new designs with even higher bypass ratios as “the architecture of the future”. Pratt & Whitney is also working on a hybrid-electric turboprop demonstrator on the De Havilland Canada’s Dash 8-100. It is expected to begin flight tests in 2024. The regional markets will be the first to benefit from lower-carbon technologies like all-electric, hybrid-electric, and hydrogen-powered propulsion. The same will later percolate to larger aircraft.
GE9X Engine. Image Source: GE Aerospace Blog
GE Aviation also has its stand-alone large turbofan engines. The GE90 which powers the Boeing 777 family, was the world’s largest jet engine when it entered service in 1995. It introduced the composite fan blades. The engine was also the first to use FAA-approved 3-D printed parts. The GE90 and newer technologies were ported to the GEnx, which is around 15 percent more fuel-efficient. The GEnx powers the Boeing 787 and 747-8, and is one of the fastest-selling high-thrust jet engines in the company’s history.
The GE9X is GE’s latest engine developed specifically for the Boeing 777X. In size, the GE9X is wider than the body of a Boeing 737 and more powerful than America’s first manned space rocket. The engine has the world record for the highest thrust, at 134,300 pounds. The reduced fan blade thickness improves aerodynamic efficiency, while its lower fan radius ratio maximizes air flow and minimizes drag. Combined with fewer fan blades than many others, only 16 compared to 38 of CF6, GE9X boasts the most efficient fan that increases performance and decreases fuel burn. GE9X incorporates more than 65 CMC components, the most of any commercial aircraft engine to date. These CMC components weigh a third of conventional parts, and yet are twice as strong for greater durability. Leveraging additive manufacturing, GE9X combined more than 300 engine parts into just seven 3D-printed components, resulting in less weight. The engine is ten percent more fuel efficient than the GE90. FAA Certification was awarded on September 25, 2020, and the aero-engine completed dust ingestion testing by November 2021. According to Boeing, the GE9X-powered 777X is expected to enter service by 2023. In February 2022, Qatar Airways announced a new order for GE9X engines as part of its global launch order of up to 50 Boeing 777-8 freighters. The 777-8 Freighter is powered exclusively by the GE9X engine. At the same time, Singapore Airlines added 22 GE9X engine orders to its earlier 40 orders for its Boeing 777Xs. In July 2022, Lufthansa announced the purchase of GE9X-powered Boeing 777-8 Freighters to upgrade its cargo fleet. The engine order includes 14 GE9X engines. The company had much earlier recorded some 700 orders and commitments valued at $28 billion at the list price.
GE is also working on the MESTANG (More Electric Systems and Technologies for Aircraft in the Next Generation) technology. Other technologies include composite fan blades, heat-resistant light metal alloys, advanced cooling methods, and additive manufacturing.
GE Aviation has invested $4.3 billion in facilities in the U.S. and another $1.1 billion abroad to meet production goals. As per GE, its new engine facilities will have America’s first fully-integrated supply chain to mass-produce components from advanced materials. GE is introducing several highly proprietary technologies that are upping our manufacturing capabilities in the United States.
The Rolls-Royce UltraFan demonstrator. Image Source: Rolls-Royce
Rolls-Royce has been famous for its high-bypass Trent turbofans that power many Airbus and Boeing large airliners. Their forthcoming engines feature new architectures and innovative technological improvements to deliver 2-shaft and 3-shaft engine solutions for future aircraft applications. They have announced that they are working on building the world’s largest jet engine. Called the UltraFan demonstrator, the engine with the largest fan diameter ever, 140 inches, is under assembly at the company’s facility in Derby, UK. Its power gearbox has reached 87,000 horsepower, which is a new record. The first run of the first demonstrator engine, UF001, on 100 percent sustainable Aviation Fuel (SAF) is expected later this year. It will offer 25 percent fuel efficiency over earlier Trent models. In the long run, the engine will have the potential to power the very wide-body jets of the 2030s.
Flow paths inside a jet engine. Image Credit: Paul Palies
Propulsion Technology New Approach
The past three generations of gas turbine engines have incorporated increased turbine inlet temperature, increased compressor pressure ratio, increased bypass ratio, improved fan and nacelle performance, reduction of noise and emissions, and improved reliability. The new engine technologies will involve engine-airframe integration, new and improved materials, and material-processing techniques, advances in turbo-machine technology, progress in combustion technology, and vastly improved utilisation of Computational Fluid Dynamics (CFD) in engine design procedures. The carbon-fibre blades allowed high-bypass jet engines that allowed the development of efficient long-haul jets like the Boeing 777 and the Boeing 787 Dreamliner that could use just two engines rather than four. Novel technologies such as “smart engines” and the use of magnetic bearings will change the course of engine development. Additive manufacturing offers lighter, cheaper, and quick-to-manufacture parts which will cut assembly costs and time, simplify maintenance and save on fuel.
Concept for a hybrid-electric plane. Image Source: Massachusetts Institute of Technology
Greener Engine Approach
Cutting emissions and noise abatement has been possible through technological innovations. Newer models of the two most widely used aircraft today – the Boeing 737 and the Airbus A320, not only carry more passengers but also burn 23 percent less fuel, through much better fuel burn efficiency. Lightweight low-pressure turbofans using composite fan blades, high-efficiency low-pressure turbine, advanced engine externals and installations including novel noise attenuation, advancing high-speed turbine design, aggressive mid-turbine inter-duct; and even a low emission combustion chamber for the next-generation rotary-craft engine. CMC has one-third the weight of steel but can withstand temperatures as high as 2,400 degrees Fahrenheit, beyond the melting point of many advanced metallic super-alloys, thus improving the engine’s thermal efficiency. 3D-printed components, hybrid-electric systems, and advanced heat-transfer circuits are other breakthrough technologies.
Solar Powered Aircraft. Image Source: NASA
Aircraft and Engine Design Features
Ultra-high bypass turbofans, open rotor engines, use of alternative fuels, and relocating engines on the body of the aircraft such that engine noise is deflected upwards are some design considerations. Blended wing-body as in the X-48B aircraft prototype and advanced electrical power technologies are being experimented with. Improvement in performance can be achieved by moving from a component-based design to a fully integrated design by including wing, tail, belly fairing, pylon, engine, and high-lift devices into the solution. Electric engines using lithium polymer batteries and solar-powered manned aircraft designed to fly both day and night without the need for fuel are already under development. Massachusetts Institute of Technology is also being evaluated and developed by NASA using the unmanned ‘Pathfinder’ aircraft.
Multi-Fuel Hybrid Engine Concept. Image Source: Science Direct
Heat Recovery Concept
Two new engine concepts currently under investigation include the ‘Combined Brayton Cycle Aero Engine’ and ‘Multi-Fuel Hybrid Engine’. Currently, over 50 percent of the energy gets ejected as waste heat. A heat exchanger integrated into a turbofan core can convert recovered heat into useful power which can be used for onboard systems or to power an electrically driven fan to produce auxiliary thrust. A dual combustion chamber, wherein the high temperature generated in the first stage, allows ignition-less combustion in the interstage, thus reducing CO and NOx emissions. Cryogenic bleed air cooling can enhance the engine’s thermodynamic efficiency.
Pulse Detonation Engine . Image Source: Semantic Scholar
Other New Innovations
The US Department of Defence’s Adaptive Versatile Engine Technology (ADVENT) and Adaptive Engine Technology Development (AETD) programs and the GE Adaptive Cycle Engine (ACE) are areas of action. Unlike traditional fixed airflow engines, variable cycle engines automatically alternate between a high-thrust mode for maximum power and a high-efficiency mode for optimum fuel savings. Incorporating heat-resistant materials and additive manufactured components in the Pulse Detonation Engine (PDE), gives it the potential to radically increase thermal efficiency. These adaptive features also have an additional stream of cooling air to improve fuel efficiency and dissipate the aircraft heat load. Such engines will increase aircraft engine thrust by up to 20 percent, improve fuel consumption by 25 percent and extend the range by more than 30 percent.
Smart engines use computer technology and the microelectronics revolution and allow full-authority electronic digital controls on aircraft engines. There are active controls at the component or sub-component level within the compressor, gas turbines, and bearings. They incorporate real-time feedback. Magnetic bearings are being used to reduce friction and lubrication requirements. Real-time diagnostics cut servicing time revolutionising flight efficiency and profitability. Drones and robots combined with improved imaging technology, are increasingly being used for aircraft/engine maintenance. The big data revolution and information technology allow maintenance companies to amass the correct parts and technicians to make any repairs as soon as an aircraft lands. Electric motors are increasingly being used to drive motors and reduce hydraulic and pneumatic systems. On-board power storage has also grown significantly. Additive manufacturing is increasingly being used. Airbus/Rolls-Royce hybrid electric with the gas-turbine engine will allow peak power for take-off and climb, while for the descent, the engine is shut down and the electric fans recover. Research is on plasma jet engines that will use electricity to generate electromagnetic fields instead of fuel by compressing and exciting argon gas into a plasma similar to that inside a fusion reactor. New technologies will bring change, challenge, and opportunity.
Header Image Source: Rolls-Royce
The Article by the author was first written for SP’s Aviation but has since been updated.