Get Set for the Next Generation!

One theme dominates the thinking of every aeroengine manufacturer worth the name nowadays – aviation sustainability. And sustainability depends on an extremely challenging target coming ever closer. In fact it is only 25 years away. In October 2022, to prevent the aviation industry from effectively becoming an environmental pariah, member states of the International Civil Aviation Organization (ICAO) agreed to a long-term aspirational goal (LTAG) of net zero emissions from aviation by 2050. Net zero means the amount of greenhouse gases (GHG) removed from the atmosphere is equal to that emitted by that activity. A near-term milestone of reducing carbon emissions by five per cent by 2030 has also been formalised.

The International Air Transport Association (IATA) predicts that the airline industry will serve 4.7 billion passengers in 2024. This will probably more than double to ten billion travellers by 2050. The carbon consequently emitted could make aviation one of the planet’s prime polluters. With the clamour for air traffic caps growing ever louder, the need for more fuel-efficient engines is urgent. And the world’s leading manufacturers – CFM International, Pratt & Whitney, GE and Rolls-Royce – are determined to deliver these next-generation turbofans sooner rather than later.

REVOLUTIONARY RISE

The CFM International RISE (Revolutionary Innovation for Sustainable Engines) Technology Demonstration programme was launched in June 2021. RISE’s ambitious goals include reducing fuel consumption and carbon emissions by more than 20 per cent compared to today’s most efficient engines. It will be compatible with 100 per cent sustainable aviation fuel (SAF), capable of hybrid-electric operation, and possibly permit running on hydrogen. The defining feature of RISE is its open rotor or fan which means the total absence of a pod around the fan blades. The woven carbon composite fan blades will be up to 156 inches in diameter, thus sweeping backward a far greater volume of air than present engines. They will bring a huge increase in the bypass ratio, perhaps to over 70:1. Engines with higher bypass ratios are more efficient because when less air passes through the core less fuel burns.

Another key feature of RISE is the extensive use of ceramic matrix composites (CMC) in the engine’s hot section. Made of silicon carbide, ceramic fibres and ceramic resin, CMCs are more heat resistant and twice as strong as metal, yet weigh just a third. In general, the hotter the combustion, the more efficient the fuel burn. But even the strongest metal alloys start to soften at temperatures above 1,100 degrees Celsius. Since CMCs can withstand higher temperatures, they need less than half as much cooling airflow as conventional metal parts. NASA’s HyTEC project, which is an integral part of the RISE programme, aims to develop a compact core that will potentially reduce fuel burn by 10 per cent compared to current engines. HyTEC’s hybrid-electric capability means the core will also be augmented by electrical power to further reduce fuel use and carbon emissions. In April 2024, Mohamed Ali, Vice President and General Manager of Engineering for GE Aerospace said about RISE, “We are at a stage of the programme in which we’re doing real testing on real hardware and making real progress.”

POWER MONSTER – THE GE9X

Apart from CFM International – its 50-50 joint venture with Safran Aircraft Engines (SAE) – GE Aerospace is working on its own next-generation engine, the GE9X. It is custom-built for the long-awaited Boeing 777X, now expected to enter commercial service in early 2026. The GE9X holds a Guinness World Record and is officially known as “the most powerful commercial aircraft jet engine (test performance)”, clocking an astounding 1,34,300 pounds on test. It is also GE’s most efficient engine per pound of thrust. Thanks to its advanced suite of technologies, the GE9X will deliver up to 10 per cent greater fuel efficiency than its predecessor, the GE90, with emissions of nitrogen oxides (NOx) 55 per cent below current regulatory requirements.

The GE9X fan has just 16 fan blades against 22 in the GE90. The large fan with fewer blades to impede airflow gives the GE9X another mark of efficiency – a bypass ratio of 10:1, which is among the highest for a commercial engine. The GE9X engine also has fewer parts, making it lighter and allowing the low-pressure system to function more efficiently.

PRATT & WHITNEY’S PROMISE

Pratt & Whitney continues to grapple with problems plaguing its PW1000G geared turbofan (GTF) that powers the Airbus A320neo family. The most significant issue is a rare manufacturing flaw – a powder metal defect that could lead to the cracking of some engine components of the high-pressure turbine (HPT) blades. The HPT issue became public in July 2023 and the current assessment is that till 2026 Pratt may have to withdraw a total of 600 to 700 engines from A320neo jets for lengthy quality inspections.

It will take a slew of highly efficient, next-generation engines burning 100 per cent SAF, to deliver around 80 per cent of the net zero solution by 2050

However, determined to overcome these hiccups, and promising a much brighter future, the company is focusing on the improved GTF Advantage version of its turbofan for the A320neo. This will deliver an additional one per cent in fuel efficiency compared with the current GTF, increasing to 17 per cent its performance margin over earlier engines like the IAE V2500.

Under a separate project called SWITCH, P&W is developing a hybrid-electric propulsion system for the GTF. It is also pursuing two concepts to address different types of emissions from engine combustors, using water reclamation and steam injection in a hydrogen engine that could cut NOx emissions by 80 per cent.

ROLLS-ROYCE – THE LARGEST FAN

Rolls-Royce which has mainly focused on powering widebody aircraft, is now banking on its UltraFan technology demonstrator to enter other market segments.

Rolls-Royce UltraFan contains several new technologies that will deliver greater fuel efficiency, lower emissions and enhanced sustainability

Rolls-Royce plans to introduce a family of two-shaft and three-shaft, direct-drive and geared propulsion systems, ranging in thrust from 25,000 to 1,10,000 pounds, for both narrowbody and widebody airliners that could enter service in the 2030s. It is also working on so-called micro hybridisation – integrating an electric starter generator with a smaller engine. This involves using electrical power during some phases of flight to supplement other improvements in energy efficiency.

In November 2023, Rolls-Royce ran the UltraFan at maximum thrust of 85,000 pounds – the highest power yet achieved by a gear-driven turbofan. This figure is about 5,000 pounds higher than the thrust level for which the engine was designed. Part of the test was conducted using 100 per cent SAF. The UltraFan is projected to improve fuel efficiency by 10 per cent over the Rolls-Royce Trent XWB when burning conventional fuel. It is designed with a 140-inch fan, six inches wider than the fan on the GE9X, the largest turbofan currently flying.

The UltraFan also has a 50-megawatt power gearbox, a composite fan system, hybrid ceramic bearings, and CMCs. It contains several new technologies that will deliver greater fuel efficiency, which in turn means lower emissions and enhanced sustainability.

ALTERNATIVE ENERGY

SAF is an alternative fuel to fossil fuels that can greatly reduce emissions from air travel. It is produced from non-petroleum feedstocks like agricultural waste, municipal solid waste, waste oil and fats, green waste, and non-food crops. It can also be made synthetically by capturing carbon directly from the air. According to IATA, only 13 per cent of the net zero target is expected to be met from new technology engines, including electric and hydrogen powered ones, while as much as 65 per cent must come from SAF. That is why an important feature of every next-generation engine is 100 per cent SAF compatibility. And wherever possible efforts are being made to incorporate electricity and hydrogen functionality as well.

In May 2024, the International Aerospace Environmental Group (IAEG) formed a new work group to study the impact of 100 per cent SAF on airplane and engine systems and evaluate technical issues. GE Aerospace will join Airbus, Boeing, Dassault Aviation, Safran, and other companies in coordinating 100 per cent SAF testing results. Work Group 13, as it is called, will periodically share its findings with ASTM International, a standards-setting organisation, in a larger effort to develop new specifications for the use of 100 per cent SAF. This initiative is significant because burning SAF is essential to get the maximum gain from nextgeneration engines. In fact, the main hurdle in the path of using 100 per cent SAF is not technological. It is the limited current production of SAF and the steep ramp up required to attain the projected 449 billion litres the airline industry will need globally by 2050.

There is also intense activity in the field of battery-driven electric aircraft. However, range is a major limitation because one litre of lithium-ion battery pack stores 20 times less energy than one litre of jet fuel. Hybrid-electric aircraft are probably more practical as they enjoy the best of both worlds. In a hybridelectric configuration, the aircraft uses a combination of energy sources – jet fuel and electricity – either in tandem or alternately. This optimises the overall energy efficiency and reduces fuel consumption.

Further into the future, hydrogen is the most exciting energy source with the potential to completely rid the aviation industry of its “high polluter” tag. With a specific energy-per-unit mass three times higher than jet fuel, and if generated using renewable energy, hydrogen emits no CO₂. However, it occupies four times the storage volume for the same energy output. For this and other reasons, there are formidable design, performance, safety and regulatory challenges to overcome before hydrogen-powered commercial flight can become a reality.

WANTED – CLEAN SHEETS!

With all major turbofan makers harnessing their best and brightest brains and investing billions in sustainable aviation the next few years are expected to bring dramatic breakthroughs in cleaner jet propulsion technology. It will take a slew of highly efficient, next-generation engines burning 100 per cent SAF, to deliver around 80 per cent of the net zero solution by 2050. Electricity and hydrogen propulsion may take some decades to make a significant impact.

Ultimately, engine makers can do only so much. To attain the commanding heights of fuel efficiency, aircraft manufacturers need to be on the same page. Currently Airbus and Boeing cannot build aircraft fast enough to satisfy their eager customers and reduce their huge backlogs. But if they bask in this glory, and are content to churn out the same planes for many more years, the airline industry will definitely miss out. There is welcome evidence that plane makers and engine manufacturers are coming closer. For instance, both the Airbus A350 and Boeing 777X will have custom-built engines meant to maximise their capacity, fuel efficiency and range.

However there is no news yet of firm plans to build all-new narrowbody planes. Last year, Rolls-Royce chief technology officer Grazia Vittadini summed up the imperative for Airbus and Boeing to go for clean-sheet designs in order to fully reap the benefits of next-generation engine technology: “Dear airframers, give me an aircraft and you will have your engines.”