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787 No-Bleed Systems: Saving Fuel and Enhancing Operational Efficiencies

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787 No-Bleed Systems: Saving Fuel and Enhancing Operational Efficiencies 787 No-Bleed Systems: Saving Fuel and Enhancing Operational Efficiencies by Mike Sinnett, Director, 787 Systems The Boeing 787 Dreamliner features a unique systems architecture that offers numerous advantages to operators. The new airplane’s use of electrical systems reduces fuel usage and increases operational efficiency. The primary differentiating factor in the systems reasons Behind the Move to ■ Expanded range and reduced fuel consumption architecture of the 787 is its emphasis on a More eleCtriC airplane due to lower overall weight. electrical systems, which replace most of the ■ Reduced maintenance costs and improved pneumatic systems found on traditional com­ Recent advances in technology have allowed reliability because the architecture uses fewer mercial airplanes. Boeing to incorporate a new no­bleed systems parts than previous systems. One of the advantages of the no­bleed electri­ architecture in the 787 that eliminates the The 787’s no­bleed systems architecture cal systems architecture is the greater efficiency traditional pneumatic system and bleed manifold will allow the airplane’s engines to produce thrust gained in terms of reduced fuel burn — the and converts the power source of most functions more efficiently — all of the high­speed air pro­ 787 systems architecture accounts for predicted formerly powered by bleed air to electric power (for duced by the engines goes to thrust. Pneumatic fuel savings of about 3 percent. The 787 also example, the air­conditioning packs and wing anti­ systems that divert high­speed air from the engines offers operators operational efficiencies due to ice systems). The no­bleed systems architecture rob conventional airplanes of some thrust and the advantages of electrical systems compared offers operators a number of benefits, including: increase the engine’s fuel consumption. to pneumatic systems in terms of weight and ■ Improved fuel consumption, due to a more Boeing believes that using electrical power is reduced lifecycle costs. efficient secondary power extraction, transfer, more efficient than engine­generated pneumatic This article explores the 787’s no­bleed and usage. power, and expects the new architecture to extract systems architecture and explains how the ■ Reduced maintenance costs, due to elimination as much as 35 percent less power from the engines. airplane’s efficiencies are realized. of the maintenance­intensive bleed system. Conventional pneumatic systems generally develop ■ Improved reliability due to the use of modern more power than is needed in most conditions, power electronics and fewer components in causing excess energy to be dumped overboard. the engine installation. 06 AERO QUARTERLY QTR_04 | 07 787 NO-BLEED SYSTEMS ARCHITECTURE Figure 1 The 787’s no-bleed systems architecture replaces the traditional pneumatic system and the bleed manifold with a high-power electrical system that, in addition to the traditional electrical system functions, supports a majority of the airplane functions that were traditionally performed via bleed air. RAT P G P M SG HX P Engine M SG Battery ECS M XFR CTAI P M M SG APU NGS SG P P M M CTAI ECS XFR M SG HX P Engine M SG HX Heat Exchanger XFR Trans / Rectifier SG Starter Generator RAT Ram Air Turbine P Hydraulic Pump M Motor CTAI Cowl Thermal Anti-Ice ElectrIcal Electrical POWER IS MORE Hydraulic effICIent than Pneumatics ENGINE-Generated Fuel PNEUmatIC POWER. Ram Air 07 WWW.BOEING.COM/COMMERCIAL/AEROMAGAZINE COMPARISON OF BLEED AND NO–BLEED ENGINE BUILDUP Figure 2 A comparison of typical engine buildups of a no-bleed engine (left) and the traditional bleed engine. The ducting used to pass the pressurized air valves. There is no need to regulate down the hydrauliC systeM around the airplane employs check valves and supplied com pressed air. Instead, the compressed pre­coolers, and is itself made of titanium, which air is produced by adjustable speed motor com­ The hydraulic system in the 787 no­bleed archi­ adds hundreds of pounds of weight to the airplane. pressors at the required pressure without significant tec­­ture is similar to the one in the traditional The electric system is also inherently easier energy waste. That results in significant improve­ architecture. There are three independent sys­ to monitor and control, and produces only enough ments in engine fuel consumption. tems — left, center, and right — that collec tively power as needed. The power, which comes off the support primary flight control actuators, landing generators at variable frequencies, is conditioned gear actuation, nose gear steering, thrust engines in the electronics bay before being distributed to reversers, and leading/trailing edge flaps. the appropriate systems. The primary power source for the left and right In the traditional architecture, the engines provide systems are engine­driven pumps mounted on the majority of secondary airplane systems power the engine gearbox. In addition, the left and right 787 no-Bleed systeMs arChiteCture needs in pneumatic form; in the no­bleed archi tec­ systems are each powered by an electric­motor­ ture, the engines provide the majority of airplane driven hydraulic pump for peak demands and for The 787 no­bleed systems architecture is shown systems power needs in electrical form via ground operations. schematically in figure 1. On the 787, bleed air is shaft­driven generators. The traditional airplane The key difference between the traditional only used for engine cowl ice protection and pres­ pneumatic bleed system architecture results in and 787 hydraulic system is the power source surization of hydraulic reservoirs. The electri fied less than optimum engine efficiency. Eliminating for the center system. In the traditional architec­ functions are wing deicing protection, engine start­ the pneumatic bleed results in a more efficient ture, the center system is powered by two large ing, driving the high­capacity hydraulic pumps, and engine operation due to reduced overall airplane air­turbine­driven hydraulic pumps, which operate powering the cabin environmental control system. level power requirements — the airplane does not at approximately 50 gallons per minute (gpm) at In this architecture, the power sources for the draw as much horsepower off the engine in cruise, 3,000 pounds per square inch (psi) to meet peak electrical system are engine­driven and auxiliary­ so it doesn’t burn as much fuel. The corresponding hydraulic demands for landing gear actuation, power­unit (APU)­driven generators, while the power predicted improvement in fuel consumption, at high lift actuation and primary flight control during sources for the hydraulic system are engine­driven cruise conditions, is in the range of 1 to 2 percent. takeoff and landing. During the remainder of the and electric­motor­driven hydraulic pumps. The Moreover, the no­bleed architecture allows flight, two small (approximately 6 gpm) electric­ engine­driven hydraulic power sources in the significant simplification in engine buildup due driven hydraulic pumps power the center system. no­bleed architecture are similar to those in the to the elimination of the pneumatic system In the 787 no­bleed architecture, the center traditional architecture. and associated pre­coolers, control valves, and hydraulic system is powered by two large (approxi­ In the no­bleed architecture, electrically driven required pneumatic ducting. Figure 2 compares mately 30 gpm at 5,000 psi) electric­motor­driven compressors provide the cabin pressurization typical engine buildups of no­bleed engine and hydraulic pumps. One of the pumps runs through­ function, with fresh air brought onboard via the traditional bleed engine. out the entire flight and the other pump runs only dedicated cabin air inlets. This approach is during takeoff and landing. The higher pressure significantly more efficient than the traditional of the 787’s hydraulic system enables the airplane bleed system because it avoids excessive energy to use smaller hydraulic components, saving both extraction from engines with the associated space and weight. energy waste by pre­coolers and modulating 08 AERO QUARTERLY QTR_04 | 07 Figure 3 The 787’s electrical system uses a remote distribution system that saves weight and is expected to reduce maintenance costs. TRADITIONAL 787 External Power E/E Bay 2 x 115 Vac, 90 kVA Forward E/E Bay External Power 115 VacFeeder 115 Vac 230 VacFeeder Generator Generator 1 x 120 kVA 2 x 250 kVA Aft E/E Bay External Power 115 Vacor 2 x 115 Vac, 90 kVA Loads 28 Vdc Wire Loads Remote Power APU Generator APU Generator Distribution Unit 2 x 225 kVA Centralized Distribution: Remote Distribution: Circuit Breakers, Relays, Solid­State Power Controllers and Contactors and Contactors eleCtriCal systeM simplest and the most efficient generation method supplied by four auto­transformer­rectifier units because it does not include the complex constant that convert 235 VAC power to ±270 VDC. The The 787 uses an electrical system that is a hybrid speed drive, which is the key component of an ±270 VDC system supports a handful of large­ voltage system consisting of the following voltage integrated drive generator (IDG). As a result, the rated adjust able speed motors required for the types: 235 volts alternating current (VAC), 115 generators are expected to be more reliable, require no­bleed architecture. These include cabin VAC, 28 volts direct current (VDC), and ±270 VDC. less maintenance, and have lower spare costs pressurization compressor motors, ram air fan The 115 VAC and 28 VDC voltage types are tradi­ than the traditional IDGs. motors, the nitrogen­generation­system compressor tional, while the 235 VAC and the ±270 VDC The electrical system features two electrical/ used for fuel­tank inerting, and large hydraulic voltage types are the consequence of the no­bleed electronics (E/E) bays, one forward and one aft, pump motors. electrical architecture that results in a greatly as well as a number of remote power distribution The system, as shown in figure 3, features two expanded electrical system generating twice as units (RPDU) for supporting airplane electrical forward 115 VAC external power receptacles to much electricity as previous Boeing airplane models.
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