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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