January 25, 2013 – Vol.17 No. 45

BOEING'S ELECTRICAL PROBLEM.
by Bruce Mulliken, Green Energy News

With a fascination of aeroplanes and a dedication to energy efficiency, I watch the still-unfolding story of the battery problems on Boeing's 787. Burning and smoldering batteries aboard two Dreamliners led to the global groundings of the aircraft. The 787 was designed to save 20 percent on fuel compared with similarly-sized aircraft. The lithium-ion batteries were incorporated in the aircraft to save a few dozen pounds in weight, about equivalent to a couple of checked bags.

According to the latest reports the batteries in question experienced a short circuit in a least one cell, as well as a thermal runaway of the batteries. In that situation one cell gets too hot, causing the neighboring cell to overheat, etc, etc. Overheating, can cause cell cases to melt, exposing the cell innards to the air, and then combust. No one knows at this point which happened first, the short circuit or the thermal runaway. (It's hard to tell since at least one of the batteries was consumed in flame and destroyed. I'm guessing there was a manufacturing defect in one of the cells in each of the two batteries under investigation.)

The 787 is a ground-breaking airplane in many ways from its light-weight, mostly carbon-fiber construction, to its fuel saving and unconventional electrical-hydraulic-mechanical systems for which those batteries play only a minor role.

If you read the mainstream press, journalists, apparently refusing to do any research, are making it sound as if the lithium-ion batteries somehow power all the electric systems on the whole airplane. This is not the case. For those who fail to analyze, the first clue is in the photos of the one burnt-out battery. That battery and its twin on the airplane, are each about the size of a car battery. The 787 is considerably larger and significantly more complex than the average car. Those two dinky batteries obviously can't power all the electrical components on board.

According to really easy-to-find Boeing documents on the Web, the batteries do little more than power-up one of the two starter motors on the airplane's auxiliary power unit or APU. (All large aircraft have an APU) The APU is a rather powerful gas turbine generator mounted in the aft end of the jet, just behind the lavatories. Running on jet fuel, just like the main engines, the APU on the 787 provides gobs of electric power to run many systems on the aircraft, such as air conditioning and lighting while on the ground, as well as provide enough electric power to start up the main engines. As essentially a smallish jet engine, the APU's exhaust is ducted out of the tail of the Dreamliner. Some say that the APU exhaust adds a little forward thrust to the airplane cutting fuel consumption a bit. The APU on the 787 can also be run in flight to provide additional electric power should a main engine fail.

The 787, however, does use lots of electric power since, in the quest for fuel efficiency, Boeing uses electric motor driven hydraulic pumps to replace pumps driven in other aircraft by air pressure (bleed -air) from the plane's engines and their APUs. Those electric/hydraulic pumps on the 787 do most of the work on the airplane like move control surfaces, raise and lower the landing gear, etc. All those systems are definately not lithium-ion battery powered.

Aside from starting the APU, it seems feasible that the batteries could also do some relatively small tasks like provide backup power to the airplane's computer systems while on the ground and parked for long periods of time away from the gate. It seems feasible, as well, that the batteries could provide emergency back-up power to computers in flight should other systems fail. Essentially, though, the batteries do the same thing as the one battery under the hood of your car: Start the engine, in this case the APU. The APU in turn, provides power to the starter motors for the propulsion engines. Shore power, or power from the grid, can also be used to start the APU and the jet engines if need be.

Now matter how badly the situation is reported, Boeing has a considerable problem on its hands. The fix may not be just swapping the lithium-ion batteries for something like the more common and time-tested like nickel cadmium (NiCad) batteries. Electrical systems on the 787, are likely "tuned" to the electric output and unique charging systems for the lithium-ion batteries, just like your laptop or smart phone is tuned to its lithium-ion battery. With another battery chemistry those systems might have to be changed and reengineered on all 50 Dreamliners already in service as well as those in production. Further, to add mountains of paper work and cost to the switch, the airplane would have to be recertified as airworthy by the FAA with any new battery type installed. All the while 50 airplanes remain out of service losing revenues for the operating airlines: They're probably not happy about this.

You can bet Boeing will work very hard to make those lithium-ion batteries work.

Bad lithium-ion batteries on the Dreamliner could have negative repercussions throughout the clean energy industry which is staking much of its future on the light and power dense electrochemistry, particularly for use in hybrid and all-electric cars.

 

Links:

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

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