3 ms·
It's worth noting that hydrogen is orders of magnitude more energy-dense, by mass, than lithium-ion batteries. As a benchmark: the DJI Phantom weighs roughly 1
by teraflop 8y ago
It's worth noting that hydrogen is orders of magnitude more energy-dense, by mass, than lithium-ion batteries.
As a benchmark: the DJI Phantom weighs roughly 1kg, and its battery can store about 80kJ of electrical energy. I found a NASA study [1] which estimated that the energy released when a li-ion battery combusts is roughly 2x the usable energy capacity. So let's say that a battery fire would release 160kJ of energy.
In contrast, a balloon capable of lifting a 1kg drone would need about 830 liters of hydrogen, with a mass of 75 grams. That amount of hydrogen, if burned in room-temperature air, would release about 9MJ -- roughly 50x as much energy as a battery failure.
(Of course, most of the hydrogen would burn itself up quickly and harmlessly, assuming the balloon isn't flying near any flammable objects.)
[1]: https://www.fire.tc.faa.gov/pdf/TC-15-40.pdf https://www.fire.tc.faa.gov/pdf/TC-15-40.pdf
- caf 8y ago9MJ is roughly 2kg of TNT. I'm not so sure that kind of energy release would be entirely harmless.
- learc83 8y agoA kg of gasoline is about 40MJ. The speed at which the energy is released is the important factor, not the total energy.
- caf 8y agoSure, and the speed at which a cloud of hydrogen-oxygen will release energy after ignition is very rapid indeed.
- learc83 8y agoThe theoretical maximum detonation velocity of a hydrogen /oxygen mixture is significantly less than TNT. You're also not going to get anywhere near the theoretical maximum detonation velocity if it ignites because of a leak. My point is comparing hydrogen to TNT is very misleading.
- learc83 8y agoAlso worth nothing that a single kilogram of gasoline would release 4 times as much energy as the hypothetical hydrogen balloon.