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Miniature Fuel Cell To Keep Drones Aloft For Over An Hour (gizmag.com)
Zothecula writes: Drones are being utilized in everything from parcel delivery to search and rescue, but their limited flight times are restricting their ability to travel great distances or stay for extended periods of time in the field. Simply adding more batteries, however, affects flight characteristics and reduces the load the drone can carry. To help solve this problem, researchers at the Pohang University of Science and Technology (Postech) have created a miniature fuel cell they claim not only provides enough energy to keep a drone in the sky for over an hour, but may well find applications in powering everything from smartphones to cars in the not-too-distant future. Developed by Professor Gyeong Man Choi and his Ph.D. student Kun Joong Kim at Postech, the new solid oxide fuel cell is claimed by the researchers to be the first to use porous stainless steel in combination with thin-film electrolyte, all brought together using a technique known as tape casting-lamination-cofiring. Allied with electrodes of low heat capacity, this amalgamation not only results in increased performance, but also in higher long-term durability. The Postech device generates power by converting hydrogen (in this case, "Wet" H2 gas comprising 97 percent H2 and 3 percent H2O mixture) supplied as fuel gas to the anode to create electricity. It does this through the use of a solid oxide material acting as the electrolyte that allows the conduction of negative oxygen ions from the cathode to the anode. These ions diffuse through the solid oxide electrolyte to the anode where they oxidize the fuel. This reaction produces electrons, which then flow through an external circuit to provide power.
"solid oxide material" anyone?
For a lot of these applications, the noise would be prohibitive. The weight of the generator may be a problem. And if it's being used for imaging in a stationary hover, the (usually very visible) exhaust cloud from those small engines could be a show-stopper. But I'm betting that an engine/generator/fuel combo with enough output to replace what's coming out of (say) a 6S 8000mah LiPo would be much too heavy.
Don't disappoint your bird dog. Go to the range.
How the hydrogen is stored and supplied to the fuel cell is my biggest question.
The gas is infamous for requiring very high pressure and very low temperature to remain liquid, and even then has pretty low energy density (large volume, however low weight - but the heavy tank takes away that advantage). Wondering how they solve that for an application where limiting size and weight are paramount.
Efficient gas engines are heavy. Lighter gas engines used in RC applications are not at all what the kids would call fuel efficient and to generate the amount of electricity a normal quadcopter uses they'd probably go though 8 ounces of fuel in about 8 minutes which would actually be a step back in endurance, plus now you've added a whole bunch of moving parts to potentially go wrong. Plus, noise. Plus most of those RC engines are 2 stroke so pollution as well.
It's only once you're scaling your vehicle up to large drone size that a gas engine becomes reasonable, and that only if your drone is a fixed wing variety.
Over an hour is quite possible with conventional drones - there is a tradeoff between prop diameter and power usage - most quads optimise for low prop diameter for performance reasons.
http://www.rcgroups.com/forums... >2h flight.
I decided to do the arithmetic because I know that diesel locomotives do just what you described.
I looked at the ratings for a sample glow-plug engine consuming 1 fluid oz of fuel per minute, and found it can produce about 1300 watts. That's more than I expected. A fluid once of fuel weighs about an ounce, or 28 grams. So 1300 / 28 = 46.42 watt minutes per gram. We normally use watt /hours per kg for these things, so we do the arithmetic and get 774 watt hours per kilogram for the nitro engine.
Lithium ion batteries are about 200 W/h / kg. So the fuel, run through a nitro motor, DOES have more energy than a battery of equivalent weight. The fuel weight also goes away as it's burned, whereas a battery stays the same weight.
HOWEVER, the engine weighs 17 ounces (486 grams). Add to that a small alternator at let's say 10 ounces. You'd have 27 ounces of engine and alternator to burn the 12 ounces of fuel, and your total specific energy comes out about the same as the battery.
if you can get X energy from either a battery weighing 27 ounces or an engine/alternator/fuel combination weighing the same, the simpler choice of just a battery makes more sense.
If you REPLACED the electric motors with engine(s) instead, that might make sense. It does make sense when you only need one, in a plane or helicopter. For a quad, you'd need either four engines or a complicated adjustable belt-drive system. Electrics make more sense for small quads.
On a land or sea vehicle, you can carry much more fuel in relation to the engine size, and volume is as important as weight, so fuel makes more sense than batteries.
They say, "peak power density of 560mW cm2 at 550C" but don't list the room temperature of the container.
What matters is how hot it is at the oxygen transport site - which is heated by the losses (because this is high energy, insulated, and less than 100% efficient.). Some solid oxide cells can run VERY hot - like orange - no problem.
You have to insulate them anyhow, to keep them hot, so the oxygen ions will be mobile enough for them to work at all. If they're running at 550C and were designed for a 25C room environment, running them at -40C (where C and F come together and mercury freezes) requires increasing the amount of insulation by less than 13%.
It's about time somebody made them out of thin films, so they can start up quickly and are small and light. Making them tiny also shrinks the insulated container. Big win.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Am I the only one who thinks this use of the word "Drone" is unintentionally onomatopoeic!
Build a Man a Fire, and He'll Be Warm for a Day. Set a Man on Fire, and He'll Be Warm for the Rest of His Life.