Behind the GE9X engine’s advanced technologies

Ohio doesn’t get many sandstorms. But an hour east of Cincinnati, on an otherwise sunny day, a dust devil is brewing. Atop a towering scaffold, a row of hoses pumps out dense clouds of powder and grit. They are instantly sucked, like a horizontal volcano, into the spinning fan blades of a jet engine a few feet away. This is GE Aerospace’s test site in Peebles, Ohio, where the company unleashes havoc on prototype engines to make sure they can stand up to the rigors of flight. On this day, the crew is simulating the challenges the new GE9X engine might encounter while powering a Boeing 777X airliner down a runway in a far-off desert.

Aerospace manufacturers call these conditions “hot and harsh,” and they’ll get to experience the real thing this month as industry leaders converge on the United Arab Emirates for the biennial Dubai Airshow. The country is the base for two of the world’s largest airlines, Emirates and Etihad Airways; together with Qatar Airways, they are responsible for more than half the orders for the 777X, the GE9X’s exclusive platform. And just this week, Emirates doubled down on the engine, placing an order for 202 additional GE9X engines, bringing its total order to 460 units.

Surrounded by deserts, Dubai is an epicenter for the sandstorms GE Aerospace engineers have been inflicting on the GE9X. In thousands of hours of tests, they’ve also blasted the engine with grapefruit-size ice balls and torrents of water — re-creating the atmosphere’s most unforgiving environments.

After undergoing a rigorous development program, the GE9X engine has emerged as GE Aerospace’s most advanced certified commercial engine to date. It holds the world record for highest thrust — 134,300 pounds — a feat made possible by its unprecedented size: At 11 feet in diameter, it’s big enough for LeBron James to dunk inside without brushing the ceiling.

But the engine was also designed for reduced emissions, not just for brawn. Building on the proven architecture of the GE90 engine, the GE9X team has adapted key innovations from newer product lines to deliver the most efficient wide-body engine in its thrust class, with up to 10 percent lower specific fuel consumption than its predecessor, the GE90-115B.

“Around here, we talk about ‘standing on the shoulders of giants.’ GE9X is a great example,” says Alisha Kalb, the program’s systems engineering leader. “We were developing this engine before we even knew it. We’ve been maturing the technologies — in test and fielded engines — for decades.”

As an example, Kalb points to their use of ceramic matrix composites (CMCs). Made of silicon carbide, ceramic fibers, and ceramic resin, CMCs are twice as strong as metal at a third the weight. They’re also more heat-resistant — a crucial benefit in the core of the engine, where fuel is ignited at temperatures high enough to melt wrought iron. The hotter the combustion, the more efficient the fuel burn, but even the strongest metal alloys start to soften when the thermometer tops 2,000 degrees Fahrenheit. Because CMCs can withstand higher temperatures, they need less than half as much cooling airflow as conventional parts, so that air can be burned to produce additional thrust.

The first production engine from a GE Aerospace venture to incorporate CMCs was the LEAP engine, made by CFM International, a 50-50 joint venture between GE Aerospace and Safran Aircraft Engines. The LEAP engine had a single CMC component part number. The GE9X engine contains five CMC components. “We learned a lot about CMCs on the LEAP,” Kalb says. “We started small, got experience with manufacturing and scalability, and then grew the technology on the GE9X.”

The engine gets an additional efficiency boost from some key design updates. “Advanced aerodynamics has been a point of pride for us in the GE Aerospace and CFM programs,” Kalb says. “We’ve continued to improve the aerodynamics on the GE9X.”

Based on high-tech analysis, the team revamped the airfoils in the compressor, a series of rows of rotating blades that accelerate and squeeze the incoming air. The higher the air pressure, the faster and more efficiently the air burns, and the stronger the thrust it produces. Thanks to the team’s redesign, the GE9X’s pressure ratio — the measure of how much the compressor increases the air pressure — reaches a high of 60:1, while the GE90 engine has a 42:1 pressure ratio.

Along with streamlined components in the core, the fan’s long, thin carbon-fiber blades maximize airflow through the engine. Because the blades are designed to be more efficient, the GE9X engine needs only 16, down from 22 in the GE90.

With fewer blade surfaces to hinder airflow into the engine and a larger fan, the GE9X achieves another mark of efficiency: a high bypass ratio. Modern airliner engines channel most of the airflow around the core rather than through it. Driven by the fan, this air creates thrust when it exits out the back of the engine. The ratio of the masses of each stream — the air that skirts around the core and the air that moves through it — is called the bypass ratio. Engines with higher bypass ratios are more efficient, because when less air moves through the core, less fuel burns. The GE9X has one of the highest bypass ratios for a commercial engine, at 10:1, meaning that for every unit of air that goes through the combustion chamber, 10 units bypass it.

In addition to being GE Aerospace’s most efficient jet engine per pounds of thrust, the GE9X also reduces non-CO₂ emissions. To reduce the emission of nitrogen oxides (NO_x), by-products of fuel combustion, the team turned to a technology GE Aerospace has been maturing since the early 2000s: the Twin Annular Premixing Swirler (TAPS). First implemented in the GEnx, TAPS premixes air with fuel before, rather than during, combustion. Exiting the compressor, airflow is directed through two high-energy swirlers to induce turbulence. The whirlpooling air then blends with fuel at the ideal proportions. As a result, the GE9X engine’s third generation of TAPS has NOx emissions that are nearly 55% better than any engine in its class and less than half the latest regulatory limits.

Kalb and her colleagues have refined these technologies by putting the GE9X engine through its paces in thousands of endurance and flight tests — over 12,000 hours’ worth, more than any other GE Aerospace commercial aircraft engine has undergone before entry into service. After many cycles of iteration and analysis, the team has been able to make improvements that will help ensure reliability right out of the gate.

“In my 20 years at GE Aerospace, I’ve learned to test early, test often, and pursue every result all the way to the root cause,” Kalb says. “It’s never easy. But I think of these learnings as gifts. If we learn something and make the engine better, that’s a win.”

This story first appeared on GE Reports.