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Eaton’s fuel inerting and fuel gauging technologies

In recent years, Eaton has emerged as a leading developer of fuel inerting and fuel gauging technologies for the aerospace industry. These technologies, while still in the early stages of their evolution, are already leading to improvements in a number of performance areas for customers, says Eaton - such as enhanced aircraft safety, weight savings and improved reliability.

Eaton’s ascendancy in fuel systems technologies can be attributed, in part, to the company’s deep and diverse engineering expertise. Eaton’s global engineering team has developed a suite of analytical and systems integration tools and processes that have been instrumental in advancing technologies for fuel inerting and fuel gauging. Tools include sophisticated modelling software, hardware-in-the-loop emulators and computational fluid dynamics, to name just a few.

“Eaton is able to execute complex design and development programmes using people and resources based in the United Kingdom, India and the United States,” says Jay Iyengar, vice president of engineering and technology for Eaton’s Aerospace Group. “Our tools and processes enable collaboration among our integrated development teams on projects in a virtual environment, which has proven to be a productive and efficient approach for our customers. We believe it’s somewhat unique in systems integration.”

Technology roadmap leads to new fuel systems capabilities

Eaton’s experience in aerospace fuel systems spans more than 60 years and has produced an extensive portfolio of components and technologies that can be found on virtually all major commercial, military and business aircraft programmes.

After identifying the aerospace business as a key growth segment more than a decade ago, Eaton pursued a series of strategic acquisitions to build up its core market strengths and to add cutting-edge speciality engineering capabilities to its aerospace design team.  

With all the right players and skill sets in place, Eaton began to focus on complete fuel systems in addition to advanced components based on customer feedback and market direction. Around five years ago, Eaton launched a strategic plan to identify and fill gaps in its fuel systems capabilities. Companies acquired by Eaton had already begun developing fuel inerting and fuel gauging hardware and components, which gave it a strong head start in adding these technologies to its product line-up.

“Our strategic plan was a technology roadmap designed to help us close product and performance gaps and expand our presence in the fuel systems market,” Iyengar notes. “We focused on technologies that would enable us to offer systems solutions to customers and broaden our market base. We also want to help our customers reduce aircraft weight, improve fuel efficiency and increase reliability and safety. Our continued growth as a fuel systems provider has been the result of listening to customers and understanding their needs, as well as understanding the market.”

Eaton’s fuel tank inerting system enhances aircraft safety by injecting inert gas into fuel tanks to significantly reduce the potential for ignition sources. In 2011, Eaton successfully completed the industry’s first civil multi-tank inerting gas distribution system certification process for the 787 Dreamliner. That achievement was followed by two more major contract wins based on Eaton’s dual expertise in fuel inerting system design and certification — the Learjet 85 business jet and the KC-390 military transport aircraft.

Eaton also holds a patent for an aircraft fuel gauging system using a digital probe. Eaton’s fuel gauging technology, which is currently in development for a Part 25 aircraft programme, improves the accuracy of fuel-level readings and reduces system weight by up to 40 per cent when compared to traditional analogue systems.

“We’re excited about the rapid progress we’ve made filling product gaps in our fuel systems portfolio and moving innovative new technologies from the development phase to the market,” says Einar Johnson, vice president of customer solutions and services for Eaton’s Aerospace Group. “We want to be a lifecycle partner with our customers, which means much more than simply providing them with a product or service. We look at the big picture in our development programmes to address issues that will help our customers improve aircraft performance and control cost over the long term. Our teams work closely with customers to address their needs in our development programmes.”

Advanced fuel inerting technology for the KC-390

Eaton’s in-depth knowledge of aircraft fuel and vent systems is an essential background for fuel tank inerting, where interactions between inert gas deposit locations and the fuel tank vent system are critical for safe aircraft operation.

Eaton developed onboard inert gas generating systems (OBIGGS) for commercial aircraft with bleed or cabin air-supplied inerting systems. In 2011, Eaton was selected by Embraer to supply fuel system components for the next-generation KC-390 military transport aircraft. In early 2012, Embraer announced that Eaton also would supply the aircraft’s OBIGGS.

“One of the factors in Eaton’s selection was the flexibility we demonstrated in working with Embraer to provide technical solutions for the KC-390,” comments Matt Jones, engineering manager for Eaton’s Fuel and Motion Control Division in Titchfield, England, and systems integration manager for the KC-390 OBIGGS development team. “For example, one key feature of OBIGGS is getting enough engine bleed air pressure to run air separation modules to separate nitrogen from oxygen. We assisted Embraer in determining how much engine air pressure could be available for inerting. We were also able to gain insights from Eaton’s Vehicle Group about technologies that boost pressure from the engine, and we performed trade studies to explore different options. All of our work led to the right solution for the KC-390.”

Another strength Eaton brought to the table was its successful combination of capabilities to develop both the nitrogen generation and inert gas distribution subsystems for OBIGGS.

Initial civil fuel inerting systems focused on only one part of the aircraft fuel tanks — the centre fuel tank in the fuselage. The introduction of composite-winged civilian aircraft presented a new challenge to the industry to develop an inerting system specifically for wing tanks that could achieve FAA certification. The challenge for Eaton on the KC-390 programme was proving that every single bay in the wings could be inerted. By integrating the venting and fuel systems, Eaton designed a complete interaction to deliver a single solution for wing-tank inerting.

“We developed a number of processes and tools internally, such as system thermal and ASM models, to use as a basis for integrating the KC-390 inert gas distribution system,” Jones says. “The key to the inerting system is to prevent the development of ‘hot spots’ or big pockets of oxygen content in wings. To produce faster analytic results, we developed a very successful 1-D modelling tool using our 3-D model as a basis.

“Our customers have recognised the critical role that tool development plays in designing more sophisticated inerting systems, and we continue to refine these tools to produce even better modelling capabilities,” Jones comments.

Eaton’s mastery of computational fluid dynamics has also been an advantage in developing advanced fuel inerting technology. For recent aircraft certification programmes, Eaton has used the tool to analyse the mixing of nitrogen-enriched air inside aircraft fuel tanks. Initially, results were verified with a fifth-scale model of an aircraft fuel tank fitted with oxygen sensors.

Eaton expanded its computational fluid dynamics capability and verification by using a 737 wing tank for a larger-scale test. The rig was again fitted with oxygen sensors to verify results of tank-mixing analyses. Eaton’s tank-mixing analysis tools successfully supported Boeing through the 787 flight test and certification programme.

The experience from computational fluid dynamics analysis and testing has enabled Eaton to accurately characterise mixing characteristics of different compartments around the aircraft. Validated models are then integrated with the nitrogen-enriched air generation system, distribution system, flammability model and vent system to provide a powerful tool for analysing the complete inerting system as well as the interaction of its subsystems.

Digital solution revolutionises fuel gauging technology

In addition to superior accuracy, Eaton’s digital fuel gauging technology enhances aircraft safety, reliability, fuel efficiency and weight savings, and also reduces carbon emissions.

More precise fuel quantity readings reduce the need to carry large volumes of extra fuel to cover for the inaccuracies of analogue systems. Less fuel means less weight, which in turn improves fuel efficiency, lowers fuel costs and reduces carbon emissions.

Federal regulations determine the minimum amount of fuel an aircraft must carry to provide margin for unexpected events that could alter its course. Determining the amount of fuel needed for the aircraft to be flown safely to an alternate destination is yet another reason why accurate fuel measurement is critical.

Digital signals can also improve aircraft turnaround times by transmitting more accurate fuel-tank level readings to ground crews that help them prepare to automatically fuel aircraft based on preset quantities.

Historically, aircraft operators have struggled with reliability issues related to analogue technology. The wiring in analogue systems is susceptible to electrical magnetic interference, a problem eliminated by digital technology. In addition, analogue technology has a tendency to drift due to low-energy signals caused by shielding, distance and continuity issues, which can generate inaccurate readings for pilots and ground crews. Complex wiring and monitoring electronics also make analogue systems heavier, more expensive and potentially less reliable.

As the FAA places strict limits on the amount of electrical current allowed in fuel tanks, digital technology has been designed to operate at intrinsically safe levels, even when failure scenarios are considered.

Eaton has designed a fuel gauging system that is up to 40 per cent lighter than similar analog systems and provides aircraft operators with improved water detection capabilities and reduced maintenance requirements. Eaton’s digital technology uses a capacitance-to-digital signal converter and stores digital data for calibration and measurement conversion. Digital values are communicated to a fuel gauging computer via a data bus.

A typical fuel gauging system relies on multiple sensors, or probes, throughout wing fuel tanks. The goal of fuel gauging system designers is to use probes as economically as possible to minimise aircraft weight while providing accurate fuel readings for flight and ground crews. To optimise probe placement, Eaton developed a tool that enables engineers to study a large range of angles of an aircraft in flight to learn how fuel moves around and affects readings. Modelling the aircraft’s wing shape, Eaton’s probe-placement tool helps the design team find optimum positions throughout each wing for 20 to 25 digital probes.

“We have to work closely with customers because they may have competing requirements for wing access points,” explains Dominic Ashton, engineering manager for Eaton’s Fuel and Motion Control Division in Irvine, California, and systems integration manager for the Part 25 aircraft programme development team. “We’ve largely automated the process as much as possible for a quick turnaround so customers can review probe placements and provide feedback to our team.”

Eaton’s design team also provides hardware-in-the-loop fuel and probe emulators so customers can “fly” virtual prototypes of fuel gauging systems. The availability of emulators helps customers reduce programme risk at the overall aircraft development level and gain confidence in product performance.

“Fuel inerting and digital fuel gauging are great examples of solutions Eaton has developed to meet specific customer needs and respond to growing market demand,” Iyengar concludes. “Our solutions also give our military and commercial customers a number of cost-effective options to modernise ageing fleets and help them comply with new industry standards and requirements. The technology roadmap we developed five years ago for fuel systems continues to lead Eaton in positive new directions that benefit our customers.”

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