With the root cause of the Boeing 787 battery fire still unclear, one leading battery expert suggested this week that the need for an active cooling system on Dreamliners is even more important.
"This is a step in the right direction," Elton Cairns, a professor of chemical and biomolecular engineering at the University of California Berkeley, said of Boeing’s reported intention to put more space between the battery’s cells. "But it’s not clear that it’s sufficient."
Cairns told Design News that an active cooling system -- particularly one that uses a liquid coolant to draw heat away from the battery pack -- is especially important, given the fact that the failure mechanism in the JAL Boeing 787 fire in January is not fully understood yet. A liquid cooling system -- like the kind used in the Chevy Volt battery pack -- would be more likely to isolate heat and prevent it from passing from cell to cell, he said.
"The battery did catch fire and you don’t want that to happen under any circumstances," Cairns said of the 787 incident. "We know for sure that the thermal management system needs to be changed, even if there was an externally caused short circuit."
Cairns is a well-known expert in the battery community, having designed fuel cells for the Gemini space program, and having served at General Electric Research Laboratory, General Motors Research Laboratory, Argonne National Laboratory, and Lawrence Berkeley National Laboratory.
Click on the image below for a close-up look of the Dreamliner and some of the problems that have plagued it.
Boeing began assessing the idea for a "middle-of-the-market" airplane in 2002.
(Source: Boeing Co.)
According to numerous news reports, Boeing plans to fix its 787 battery by employing additional spacing between the battery’s eight cells to allow for more effective cooling. Boeing reportedly will also use a more fire-resistant container, add sensors for monitoring cell temperatures, and equip the 787 with the ability to vent smoke to the outside. Venting would require that Boeing cut and reinforce holes in the jet’s carbon fiber skin, according to a report in The Wall Street Journal.
After more than a month of intense study of the January battery fire, Boeing is confident that its engineers know the way to fix the faulty lithium-ion battery packs that grounded the 787 Dreamliner fleet in January. The company is now awaiting approval from the Federal Aviation Administration (FAA) to test the new battery design. “Ever since the fleet was grounded, our team has been working around the clock,” Boeing Co. spokesman Marc Birtel told Design News. "We brought in experts from outside, as well as within the company, to validate our ideas, and that culminated in our proposal to the FAA."
If the FAA approves the fix, Boeing would still have to demonstrate, through lab tests and flight tests, that the repairs are satisfactory. Afterwards, the aircraft could return to service. Still, approval may not be a slam dunk. Transportation Secretary Ray LaHood has said he wants to personally conduct a thorough review of the 787 battery situation. Satisfying LaHood would be critical, since the US Department of Transportation oversees the FAA.
The incident that provoked the grounding of the 787s occurred on January 7, 2013, at Boston’s Logan Airport. While the aircraft was parked at a gate, a mechanic found smoke and flames coming from the lithium-ion auxiliary power unit battery located in the aft electronic equipment bay. One firefighter sustained a minor injury while dousing the blaze.
Since that time, the National Transportation Safety Board (NTSB) has not found the root cause of the fire. In February, investigators determined that data from the flight recorder, combined with thermal and mechanical damage, pointed to short circuiting in one of the battery’s eight cells, leading to a thermal runaway condition. Temperatures inside the battery case were believed to have exceeded 500F. As of a March 7 press conference, however, NTSB had still not nailed down the cause of the short circuiting.
Cairns told Design News that the biggest safety concern is the low density of air at high altitudes. There, he said, it might be more difficult to draw heat away from the battery.
"A much safer solution would be to have a liquid-based thermal management system," he said. "You don’t want the battery to get too cold and you don’t want it to get too hot." A liquid-based cooling system would not be affected by the density of the surrounding air, he added.
Birtel of Boeing told Design News that the company will provide more details about the fix if it is approved by the FAA. For now, he said, Boeing is working with GS Yuasa Corp., manufacturer of the lithium-ion battery, to implement the improvements. "We see this as a permanent fix and the best fix for the airplane," Birtel told us.