Turbofan manufacturers continue ‘green’ efforts

 - August 27, 2010, 4:50 AM

Turbofan manufacturers are developing cleaner, quieter and more environmentally friendly engines that will meet current and future regulatory requirements. That fact should come as no surprise, since they have been doing this all along as the natural byproduct of efforts to build more fuel-efficient and quieter turbofans for a market that demands nothing less. And they were doing so long before government agencies and environmental watchdog groups began taking such an interest in aircraft propulsion.

"We've been reducing emissions and increasing turbine efficiency for twenty-five years," said Walter Di Bartolomeo, v-p of engineering for Pratt & Whitney Canada.

These days, there is the additional motivation provided by a flurry of regulations coming from government agencies in the U.S. and abroad, from the EU Emissions Trading Scheme to the so-called cap-and-trade proposal in the U.S. Not to mention aircraft noise level restrictions set by the FAA, ICAO and thousands of local municipalities. And there are public groups such as the Government Accountability Project, which has criticized the FAA for "inattention to greenhouse emissions," warning of the "harmful effects on the future of U.S. aviation if action is not taken."

As a result, manufacturers are spending billions of dollars on research and development projects to create more reliable and efficient engines that will reduce both GHG (greenhouse gas) emissions and noise. The technology advances include every thing from improved fan, core and exhaust-nozzle designs to composite materials.

This summer, GE Aviation was one of many engine manufacturers that received an award from the FAA as part of the agency's continuous lower energy, emissions and noise (Cleen) program. Cleen is designed to accelerate the development and maturation of aircraft and engine technologies that reduce noise and emissions and improve fuel burn. The award will allow GE and the FAA to share in the investment of up to $66 million over a five-year period.

GE sees the money going toward its Taps II combustor, open-rotor technology and flight management and air traffic management systems.

The Taps II lean-burn/low emissions combustor is at the center of GE's eCore hot section, and the company began testing it in June 2009. It will be at the heart of partner CFM International's Leap-X engine for single-aisle aircraft as well as the company's next generation of regional and business jet engines.

CFM started running phase one of the eCore demonstrator on schedule last year, and phase two was completed this year. Testing of the eCore demonstrator two with the 10-stage compressor and two-stage turbine is scheduled to begin next year. "This is a core that 'wants' to run," said a CFM spokeswoman. She added that the result will be an engine that produces a ground noise footprint 75 percent smaller than a comparable current-production engine, keeping noise within the confines of the airport.

GE expects the new core will provide up to 16 percent better fuel efficiency than the best it has in service today.

General Electric's new GEnx engine program will produce a turbofan for widebody aircraft and features the latest in carbon-fiber composite materials in both the fan blades and fan case. Their use in the fan case alone will reduce the engine weight by 300 pounds. With such improvements as a 23:1 pressure ratio, pre-mix nested fuel nozzles, four fewer stages and 30 percent fewer parts, the engine is expected to produce emissions 95 percent below current requirements and 15 percent better fuel consumption.

GE began experimenting with the open rotor, or unducted fan, design in the 1980s, when the price of fuel was climbing. Like other open-rotor programs, it was put on a back bench when the price of fuel fell. But with growing emphasis on fuel efficiency and greenness, these programs have seen a revival in recent years.

By applying advanced data acquisition systems and computational design tools, GE now believes it has improved the design to reduce fuel consumption by 26 percent (compared with current turbofans) and address the problem of noise inherent with the open rotor. The program also has GE engineers and designers evaluating the open rotor for the Leap-X engine.

GE and CFM are calling Leap-X the "power of the future." Test results are matching what GE said are "aggressive" targets set by CFM. Endurance testing on the full-scale Leap-X RTM demonstrator, a Snecma proprietary technology, began this summer and certification is expected in 2014.

The fan and casing will be built of composite materials. The fan's larger, 3-D woven transfer molding blades will allow much greater efficiency than the CFM56, and the engine will weigh some 500 pounds less than a comparable powerplant with metal fans and casing. It will run on 15 percent less fuel and emit 16 percent less CO2 compared with today's most fuel-efficient CFM56. 

Meanwhile, testing continues on the GE Honda HF120 turbofan that powers the new HondaJet.

Features include advanced airfoils, materials and coatings; a high- temperature, reverse-flow com bus tor configuration; single-stage air-blast fuel nozzles; titanium impellor in the compressor; two-stage, low-pressure turbine; and counter-rotating high-pressure and low-pressure shaft system.

Cost of ownership is key, according to Honda, which is aiming for 5,000 hours between major overhauls.

Honeywell Investing Heavily

Honeywell's HTF7000 fleet recently surpassed 700,000 total hours, and the company continues to make improvements in the line. The HTF7500 that will power Embraer's new Legacy 450 and Legacy 500 has completed design review and core testing. Engine tests began this summer and certification is expected next year.

And as Gulfstream ramps up for production of its G250, Honeywell is increasing deliveries of its new HTF7250G to the Savannah, Ga.-based OEM.

Honeywell will also incorporate technology from its Saber 1 engine improvement program into HTF7000 production engines, and those same improvements will appear in the new HTF7250G and HTF7500. Certification tests are under way for the updated HTF7000.

According to Honeywell v-p of propulsion systems Ron Rich, the Saber 1 technology will meet all ICAO standards, with a 25-percent reduction in NOx (nitrogen oxides) emissions.

The company has also launched Saber 2, which is expected to reduce NOx emissions by another 25 percent. The new Tech 7000 technology demonstrator makes use of a fleet of HTF7000s to develop Saber 2 as well as make other improvements "in a relevant environment." Full component-level testing has already begun and combustion systems are running. "We'll move toward engine testing near the end of 2010 or early 2011," said Rich.

The improvements will include the fan, compressor and turbines. Among the goals for Saber 2 are better power-to-weight ratio, a smaller core to reduce engine weight, and a higher pressure ratio for improved fuel burn.

MTU Plans Green Lead with Geared Turbofan

German engine manufacturer MTU Aero Engines has been making much of a geared turbofan, with its Claire (clean air engine) technology leading the way. The aim is to cut CO2 emissions by 20 percent by 2035, and at the Paris Air Show last year MTU was exhibiting a geared turbofan mockup.

The first steps are being taken under the umbrella of the European Commission's Clean Sky joint technology initiative. MTU is investing some $27 million in the project and industry partners such as Avio and Volvo Aero are adding another $40 million. 

The Claire project will use an existing geared turbofan, focusing on the high-pressure compressor and high-speed low-pressure turbine. Designers expect to reduce the length and weight of the turbine, while improving efficiency by way of the new low-pressure turbine, first-stage concept. The initial target is a 15-percent reduction in fuel burn.

The second step is to combine a two-stage counter-rotating fan with the geared concept, targeting a fuel burn reduction of 20 percent by 2025. The third is implementation of an intercooled recuperative aero-engine concept in which exhaust nozzle heat is used to increase the temperature of the air entering the compressor.

MTU is also a partner in Pratt & Whitney's PW1000G program. The engine from that program is expected to power the Mitsubishi regional jet and Bombardier's C Series regional jet.

Pratt & Whitney 'Changes Everything'

At the Farnborough airshow in July, Pratt & Whitney was promoting its PurePower engine core, saying, "This changes everything." According to Bob Sala, v-p of the next generation product family, "This advanced core contains many key technologies contributing to the lower engine operating cost of the PW1000G." Current tests are confirming expectations.

The PurePower PW1000G features gearing that allows the fan to operate at lower speeds than the low-pressure compressor and turbine. The combination of the gear system and advanced core, reported P&W, "delivers double-digit improvements in fuel efficiency and emissions with a 50-percent reduction in noise over today's engines." Entry into service is scheduled for 2013.

P&W is in the midst of a five-year program during which it expects to spend approximately $1.5 billion in research and development. 

The engine manufacturer claims to be the leader in developing low-emission technology, primarily through its Talon (technology affordable low Nox) combustion design. According to Pratt & Whitney Canada, it makes the PW307 "the greenest engine in its market," with an emissions reduction of 33 percent relative to ICAO standards. 

The Talon 2 combustor technology also meets Zurich 5 requirements for avoiding emissions surcharges. It also surpasses ICAO environmental standards by more than 35 percent for CO2 and by more than 50 percent for NOx emissions, unburned hydrocarbons and smoke.

Rolls-Royce E3E Core at the Center

Rolls-Royce announced in July that it has successfully run the latest E3E (efficiency, environment, economy) core engine as part of its two-shaft research. The program is intended to develop future powerplants for business jets and single-aisle airliners.

The latest core-build produced "excellent results" during 40 hours of run trials at Stuttgart University's altitude test facility, exceeding the flight-envelope requirements, accord ing to the company.

Rolls-Royce said E3E is developing "leading-edge technologies" that increase engine temperature, pressure ratio and component efficiencies, combined with a 25-percent increase in thrust-to-weight ratio.

Other goals include a 15-percent reduction in fuel burn as well as CO2 emissions, along with a 60-percent reduction in NOx emissions.

Specific technologies used ​on the E3E core include a two-stage shroudless high-pressure turbine; tip clearance control system with advanced ceramic abradable linings; lean-burn combustion; blisked high-pressure compressor air system for bearing-load management; and improved cooling using car bon oil seal and brush-seal air sealing technologies.

The nine-stage blisked high-pressure compressor has thus far demonstrated a 22:1 pressure ratio.

More cores are to be tested over the next two years and the program calls for 1,200 cycles of max-takeoff-power endurance testing.

Snecma Continues Silvercrest Development

Despite still lacking a launch customer, Snecma of France continues to develop its Silvercrest business jet engine.

The plan is to build the powerplant in versions developing between 6,500 and 12,000 pounds of thrust to power large-cabin business jets and single-aisle bizliners such as the A319. In addition to better performance in climb and cruise, the Silvercrest is expected to be "environmentally friendly, with low levels of both noise and [GHG] emissions."

Snecma believes the direct-flow engine, 74 inches long, will yield lower emissions. In fact, the company expects emissions will be 50 percent lower than ICAO CAEP6 standards. In addition, fuel consumption is expected to be 15 percent better than other engines in that class.

Williams International Plays It Close

Williams International, which traditionally plays its research and development cards close to the vest, says it has been improving engine efficiency by about one percent per year on the FJ44 since the FJ44-1A went into production in 1998.

"Our engines have a good combination of low NOx and low CO2," said v-p of business development Matt Huff. "And all our engines fall into the zero emissions surcharges category for the Zurich model."

The FJ44-4 was certified in February for Cessna's new CJ4, and the FJ44-3AP is in the certification process, earmarked for Hawker Beechcraft's Premier II, the Nextant re-engined Diamond/Beechjet 400 and the PiperJet single. 

Also going through certification is the FJ33-5, intended for the Cirrus Vision and Diamond D-Jet.

While engine manufacturers are rapidly developing new technology in search of leaner, cleaner and quieter turbofans, hardware is not the only focus in the quest to provide power that is more efficient for customers and more environmentally friendly for government agencies and public watchdog groups.

Alternative fuels are also under examination, as are changes to the processes that control air traffic aloft and on the ground.

Since none of these is the elusive silver bullet, the solution will likely be a combination of all of them–new engine technology; alternative fuels to produce energy values similar to those of fossil-based jet fuel; shorter ground-hold times; idle approaches from 10,000 feet; and more aerodynamically efficient aircraft designs.

The real answer, says Honeywell chief technology officer Bob Smith, "is a collective effort by the entire aviation industry."