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.
Hope Boeing contributed to the correct political campaign! Then Ray Lahood may well approve. Seems the SC "right to work" move may also affect their approval for the fix.
I know, should not be a political thing but a design decision. But just wanted to throw out some reality of the bureaucracy climate.
I like your point. Driving and flying with Li batteries are not the same animal! I might be very disappointed to see my expensive car burn up. Not so much if my plane burned up (but then my wife would be rich from the life insurance).
I work in the aircraft industry as an elec. eng. for helicopters and (to quote GM's advert. slogan) what is "Tried, Tested and True" are the ubiquitous lead acid batteries. Intuitively, I've felt that the choice of going to Li-ion in the air wasn't worth the weight/E-density savings. Heck, even transporting Li-ion batteries as air-cargo is a huge issue! Appears to me that weight savings can be made in MANY other places than the main battery source....right? What happens in the situation where the aircraft reverts to battery power only...high currents to run all basic systems when you need them the most and everyone is feeling good because Boeing vented battery smoke to the outside?? What? That's part of the proposed fix? Wow...! I believe that the use of Li-ion batteries in the auto industry is sound. One can always stop the car, get out and watch her burn if the battery pack heads south; not so for aircraft. "Tried, tested and true" should be the slogan for designing aircraft, not "let's try, let's test, let's push certification, oh-oh it's not true".
Many times what we think might be better is not better. The fact that the speak around Li-ion technology is: fire, smoke, explosions, unstable, thermal runaway, advanced cooling, etc. should make designers think twice. Li-ion batteries in space...is a trade off where weight to push 'er into space is critical and energy usage while in space is carefully managed.
To me, it's a no brainer. When we can make lap-tops work reliably without lap fire incidents, then perhpas Li-ion technology can move to the air.
I'll bet Nissan is watching this Boeing incident with great interest. In Florida, I'm hearing the 100 mile range of the Leaf is more like 70 miles due primarily due to the inefficient air cooled batteries - and of course the use of air conditioning.
This is just one more reason I'm glad I chose a Volt 2 years ago . . .
Boeing used Lithium systems to reduce weight...liquid cooling just increases weight and the Law of Diminishing Returns suggests that changing the battery system may be the only solution and that involves recertification....a long process.
Internal shorts in cells. Again, in Duracell, zinc dendrites (analagous to stalactites) growing within the cell pierce the separator and create a soft short which becomes gradually worse until the cell dies. There are indications that some researchers are working on reducing dendrite growth in lithium systems. Was dendrite growth the problem in the 787 system?
I think lithium ion batteries should be used only with air cooling and only in ground. While flying, the conventional acid lead batteries can be used alternatively. Why ?During flying some moving energy of the engines can be used energy source, and there is no need big batteries while flying. Water cooling can bring some complex failure initialization in mean time and water must be capsulated very well, if the water face with low atmospheric pressure it can easliy vaporuised and this can generate contamination, dirtiness and aging problems. Air cooling can always be problem in high altitudes, because there is no enough air.
You've been all over this story, Chuck, and it seems like it will continue for awhile. Great coverage. I agree that it seems to be a liquid vs. air debate. Perhaps some of the latest research I've covered about lithium-ion battery design could be helpful in terms of what best way to design the battery so this doesn't happen again. I guess it's a little too late to start from scratch, though, so Boeing will have to fix the problem based on what it's already done.
Thermal runaway occurs at 120 -200 deg. Celsius, is a strong exoterm reaction which can not stop until all active material is consumed. Actually is the liquid electrolyte which starts decompose. The only commercial available technology able to transfer more than100 watt/ cm2 is the heat pipe. Boeing should have experience with this technology. It was extensive in the spacecraft technology to cool the sunside of a spaceship (transfer the heat from the hot to the cool side). More than that the heat can be transferred to a heat exchanger outside the battery walls (trough the firewalls). Another system should be also included to cool down the cells at bellow 20 degrees Celsius where the liquid electrolyte ions stop to move (available for the military technology). This approach is possible to be implemented with special designed hot pipes at reduced volumes. The space for the cooling pipes (integrated into cooling plates between the cells) is the same as with the current (empty space between the cells) Boeing solution. Yes, Walter can be dangerous, if water comes in contact with battery electrodes the battery will explode.
Liquid cooling is not my favorite solution. The thermal energy developed during lithium ion battery charge discharge cycles should be just moved away from the source. To obtain an efficient thermal energy transport the use of heat pipes will bring much more benefit. In case of battery thermal runaway the water system will be a big, big problem.
I don't know how much it would cost to add liquid cooling, Cabe. In today's electric cars and plug-in hybrids, packaging is said to be about 50% of the cost of the entire battery package. How much that differs between passive and active cooling situations, I don't know. Whatever the cost, though, the production volumes for a 787 are ridiculously small compared to those of a production car, so the cost wouldn't be multiplied by hundreds of thousands of units.
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