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Jet Engine on a Chip
Posted by
michael
on Tue Oct 19, 2004 01:53 PM
from the go-go-gadget-jet-engine dept.
from the go-go-gadget-jet-engine dept.
Roland Piquepaille writes "Today, our handheld devices are powered by batteries, which are heavy and inconvenient. Fuel cells are just arriving on the market as a replacement. But there is a new contender: micro gas turbine engines under development at the MIT. Engineers there shrunk jet engines to the size of a coat button. And their blades which span an area smaller than a dime can spin a million times per minute and produce enough electricity to power your PDA or your cell phone. While there are still a few hurdles to overcome, these micro turbine engines should be operational in two or three years, with commercial products available four years from now. These micro jet engines also have the potential to free soldiers or travelers from carrying heavy batteries. The engineers even think their engines on a chip could be used in poor countries to bring electricity there. This summary gives you the essential details about a technology which promises to free us to carry extra fuel instead of batteries."
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Fear... (Score:4, Funny)
Engineers there shrunk jet engines to the size of a coat button
Naturally the Department of Homeland Security will declare that people with 4 or more buttons on their coat are 'terrorists'
Re:Fear... (Score:5, Funny)
Parent
Re:Terrorist apparel (Score:4, Funny)
Parent
Cool, but misleading title (Score:5, Interesting)
2. Saying that a Gas Turbine == a Jet Engine is a bit misleading. It's a bit like saying "Scientists have shrunk an electric motor to 4 nanmometers", then before you even finish thinking about all the MEMS devices, you read "Scientists have produced a 4 nanometer electric genertor for use in making power for MEMS devices." Still very cool, but not the same thing.
Re:Cool, but misleading title (Score:5, Interesting)
Gas turbines seem to only become highly fuel efficient when the heat of their exhaust gas is captured by a secondary system, like a steam recovery boiler. http://www.ornl.gov/info/ornlreview/v33_1_00/turb
Parent
Re:Cool, but misleading title (Score:5, Informative)
That used to be true, but the current breed of Gas Turbines are amazingly efficient. From wikipedia [wikipedia.org]:
They can be particularly efficient -- up to 60 percent -- when waste heat from the gas turbine is recovered by a conventional steam turbine in a combined cycle.
The primary issue in obtaining high efficiencies is in (as you stated) efficiently recycling the waste heat. I can only assume that the inventors would be attempting to shrink the secondary cycle along with the gas turbine. The physics really aren't all that different, so it should just be a matter of materials.
Also from the wikipedia link above:
Typical micro turbine efficiencies are 20 to 35 percent. When in a combined heat and power system, overall efficiencies of greater than 90 percent may be achieved.
Parent
Two lessons for you: (Score:5, Informative)
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Re:Cool, but misleading title (Score:5, Informative)
Actually, in terms of the overall thermodynamic efficiency, they aren't all that great. 40% efficiency is *very* good for a Brayton cycle (i.e. turbine engine) system, but is fairly easily done with a large-scale steam system. Microturbines tend to run around 25%, which means that (a) you need a fairly big recuperator to run efficiently (which doesn't seem to be part of the MIT design), and (b) you need to be able to reject a lot of waste heat (so running your laptop on one of these means you'll be blowed 200+ watts out the back).
Not that gas turbines are without their advantages. Their specific power (weight per kW) is very good, so for the same amount of power the engine is very light compared to most other engine types (which is why they use them in aircraft). They also start and stop quickly compared to steam turbine systems. And they can be nicely combined with other systems like a steam system to make a combined cycle, the whole system can be fairly efficient.
But, by themselves, they aren't all that efficient.
Parent
Re:Cool, but misleading title (Score:5, Interesting)
You are correct. However, much of the fluid mechanics of very small microturbines is rather well understood, so the basic goal isn't unreasonable. And usually the answer to viscosity is speed---small turbines generally spin very, very fast.
(Disclaimer, I work for a company that makes very small turbines [creare.com].)
Parent
size and efficiency (Score:5, Interesting)
You will also notice that (in general) the smaller the gas turbine, the less efficient.
I have been to multiple talks on these engines, I used to work for one of the industry colaborators on the project as an aerodynamicist. These engines are no exception to that rule. The turbine on these engines hardly extracts enough work to run the compresser when you are running the combuster just below the melting point of the engine.
Also (addressing the summary, not the parent post), these things have been "2-3 years away" for at least 6 years.
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exaust (Score:5, Funny)
What about the exaust?
I can't wait to get kicked out of a snooty coffee shop because my dual core G5 laptop was asphyxiating the customers . . .
Re:exaust (Score:4, Informative)
Well, your cell phone only needs about a watt, a PDA about 2-10 watts, and your laptop about 20-100 watts. If you consider that cars produce kilowatts of constant power output, you should realize that the amount of exhaust shouldn't be anywhere close to what your car puts out.
In addition, these turbines will probably use something a smidge cleaner than gasoline. Even kerosine is better, but ethanol would probably rank the cleanest.
Speaking of kerosine, these turbines shouldn't even be as back as burning a kerosine lamp.
Parent
Re:exaust (Score:3, Interesting)
What about hydrogen? I know that's kind of a played-out concept but look at the possibilities. You could have your own electrolyser at home and bottle your own hydrogen, then slap it into your laptop and go. You could generate the electricity off the grid, or whatever. Output is water vapor, which is pretty harmless as long as it's exhausted outs
Storage (Score:5, Informative)
Parent
You also planning to use this excuse in elevators? (Score:5, Funny)
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Or at dinner... (Score:5, Funny)
A guy goes to dinner with his girlfriend's family, and finds he is a bit windy about the arse. Anyway, he is sitting down at table, and the family dog is lying down behind his chair, so he figures he'll try a little experiment. So, he shifts his weight to his left cheek, and squeezes out a fairly quiet fart.
The mother looks up at the noise, and says "Baron!" (this being the dog's name). Encouraged, the guy lets out another one, quite a bit louder this time.
Again, the mother looks up, and exclaims "Baron!" in a more urgent tone.
By now the guy figures he's got carte blanche for whatever trouser stunts he wants to pull, so he let's rip with all his might, and lets one go that sounds like the curtains are being ripped in half!
At this, the mother stands up, panic-stricken, and shouts "Baron! Get away from that man before he shits all over you!"
Parent
Re:exaust (Score:3, Insightful)
Why not use a small tank of compressed gas (i.e., nitrogen) to drive the turbine? For small portable power, the inefficiency inherent in compressing the gas in the first place isn't that big of a deal.
Roland Piquepaille! (Score:3, Interesting)
MOD PARENT UP (Score:3, Interesting)
Re:MOD PARENT UP (Score:5, Interesting)
I dunno, I found this article very interesting.
Also, did you actually read some of the other stories on his blog? Mongolian monks and fish? Hydrogen Economy? Phoning Home from the Bottom of the Ocean?
I actually found that blog to be quite interesting and unlike most, he took the time to post illustrations. I say: Good job Slashdot! That was indeed a "News for Nerds" article.
Parent
Re:MOD PARENT UP (Score:5, Insightful)
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Re:MOD PARENT UP (Score:4, Insightful)
He's driving traffic to his blog to increase ad revenue and his reputation (he's now working as a professional blogging consultant [smartmobs.com]), and slashdot are helping big-time. If there's money changing hands, or it's a favour for a friend, then fine - but the slashdot guys really ought to tell us.
Parent
Roland Piquepaille (Score:4, Interesting)
http://science.slashdot.org/search.pl?query=Rolan
Re:Roland Piquepaille (Score:4, Insightful)
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Business Plan (Score:5, Insightful)
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Vaporware (Score:4, Insightful)
no kidding dept. (Score:5, Funny)
Ya think?
gas powered calculator (Score:5, Funny)
So, wow, my silly dreams could become reality!
Runs on Fart Gas? (Score:3, Funny)
Re:Somebody want to geek out for me? (Score:4, Informative)
The sun is a mass of incandescent gas... ^H^H oops sorry... wrong comment.
Here's the lowdown on fart gas content, for those interested in such things:
(source: Facts on Farts [heptune.com])
What is fart gas made of?
The composition of fart gas is highly variable.
Most of the air we swallow, especially the oxygen component, is absorbed by the body before the gas gets into the intestines. By the time the air reaches the large intestine, most of what is left is nitrogen. Chemical reactions between stomach acid and intestinal fluids may produce carbon dioxide, which is also a component of air and a product of bacterial action. Bacteria also produce hydrogen and methane.
But the relative proportions of these gases that emerge from our anal opening depend on several factors: what we ate, how much air we swallowed, what kinds of bacteria we have in our intestines, and how long we hold in the fart.
The longer a fart is held in, the larger the proportion of inert nitrogen it contains, because the other gases tend to be absorbed into the bloodstream through the walls of the intestine.
A nervous person who swallows a lot of air and who moves stuff through his digestive system rapidly may have a lot of oxygen in his farts, because his body didn't have time to absorb the oxygen.
According to Dr. James L. A. Roth, the author of Gastrointestinal Gas (Ch. 17 in Gastroenterology, v. 4, 1976) most people (2/3 of adults) pass farts that contain no methane. If both parents are methane producers, their children have a 95% chance of being producers as well. The reason for this is apparently unknown. Some researchers suspect a genetic influence, whereas others think the ability is due to environmental factors. However, all methane in any farts comes from bacterial action and not from human cells.
Parent
Good Laptop Power Source for Travelers? (Score:4, Insightful)
You: "Oh, it's just some gasoline for my laptop."
Sure...this technology will be a GREAT laptop power source for travelers...
Geese (Score:5, Funny)
Conspicuous omission (Score:5, Insightful)
This matters a lot, because small turbines suffer much more from viscous flow losses and heat-transfer losses than large ones. If a 50 W microturbine is 10% efficient, its waste heat will amount to 450 watts; if it is 5% efficient, the waste heat will be 950 watts! This could easily lead to them being banned from commercial aircraft, because the extra heat load and oxygen consumption would drive A/C loading too high (not to mention the discomfort of adjacent passengers).
Energy = energy, danger = danger (Score:5, Insightful)
We don't really want to carry larger and larger packages of energy on our person. As it is, we are seeing accidents like this one [zwire.com] due to today's ordinary lithium-ion batteries. And I recently got a recall notice from Verizon about the kind of batteries used in my cell phone, so this isn't an isolated incident.
When someone tosses a 9V battery in their pocket and it gets shorted out by a coin, they are startled, yell, and pick the hot coin out of their pocket.
When a cell phone battery acts up, Shelley Kaehr got a handful of battery acid and set fire to the floor.
Multiply that by "a few heavy handfuls" and you start to get the possibility of really serious personal injury.
What we need are breakthroughs on the power consumption side, not ever-increasing power supplies
Obvious joke (Score:5, Funny)
"WHAT?"
"I said, what is that"
"MY NEW JET-POWERED MP3 PLAYER"
"cool , what are you playing?"
"I'M NOT SURE"
Can we PLEASE STOP linking to this guy's blog??? (Score:5, Informative)
In all seriousness, why does
Yes, this is probably off-topic (as in "not about tiny turbines") but it is still relevant. At least give us the option to ignore him.
Roland... (Score:5, Insightful)
here [technologyreview.com]
Re:Roland... (Score:5, Interesting)
Parent
Roland (Score:5, Insightful)
For as much as I love Slashdot, there exists little recourse for people who want their input on the site to be heard, even when its on as large a scale as the current hatred of Roland posts.
1 million rpm? (Score:5, Interesting)
A better TR article blasts "hydrogen hype" [technologyreview.com] but in fact H2 would be about the best fuel for these little buzzers:
- a fuel spill will dissapate very rapidly
- the byproduct, in answer to the questions posted re pollution is just water.
A set of bearings however will be an awsome thing to handle the gyroscopic reaction torques as you wave your jet powered cellphone about. You turn the corner, the phone does not. I don't have my old physics books handy but the linear velocity of a point on the tip of a blade isand is changing direction 180 degrees about 2000000 times a minute. The F=MA to pull this constant direction change will be staggering unless M is damn near zero.And aren't you just all breathless, when the "batteries die", to take your cellphone to the out-of-work airline mechanic who got re-trained at a watch factory ?
Re:1 million rpm? (Score:4, Informative)
Assuming the (very rough) idea of the blades as a solid disc, a 10 mm turbine blade (which is what is suggested for a 20 W turbine, running at 100krpm, from other experimental papers I've seen) comes out as follows:
I =
Density of silicon nitride, a commonly mentioned blade material, is 3.28 g/cc.
Volume of a solid disc 10 mm blade, assuming it is 1 mm in thickness (a value pulled from some of the experimental papers), would be pi*r^2*h, giving us pi*25*10^-6*1*10^-3, or 2.5*10^-8 m^3.
2.5*10^-8 m^3 is 2.5*10^-2 cm^3, yielding a mass of 3.28*2.5*10^-2, or 8.2*10^-2 grams, which is 8.2*10^-5 kg.
Thus, moment of inertia is
The correct equation for energy is
So, at 100krpm (2*pi*100000/60 rads/s), the turbine I'm thinking of is carrying:
Even if its spinning at 1 million RPM, we get:
TNT explodes with an energy of 2.175*10^6 J/kg, meaning that the turbine disintegrating at 1 million would yield something roughly equivalent to 0.025 grams of TNT. Not exactly a big explosion.
Yes, it is spinning very, very fast, but it is also very very small and very very light. These counterbalance the speed.
Parent
See same story from 1997 (Score:5, Informative)
They've been working on this since 1993, and in 1997 they said they'd have it working in three years. In 2004, they say they'll have it working in three years.
It doesn't work yet. They can fabricate the individual parts, but it doesn't really generate power.
It's not an unreasonable idea, but if this was going to work, there should already be little gas turbine powerplants a few inches long, machined out of metal by standard techniques. The smallest turbines available [bairdtech.com] weight around 1.5Kg, and are used for model aircraft, and they don't have to run for very long. There's a "microturbine" industry, but they mean 10KW units taller than a man.
Little turbines are hard. Automotive turbines and light-plane turbines have been attempted many times, but have never been cost-effective.
Re:See same story from 1997 (Score:5, Funny)
Parent
The potential problem with these things... (Score:4, Informative)
That's why you don't see very many working concepts of small aircraft (the kind that fit in the palm of your hand) with what most people recognize as wings. They're usually equipped with small flat-plate type wings, or a ribbon-like system like on a cuttlefish.
And the reason that many folks that do happen to understand the physics don't try and do things at such small scales is that the problem is difficult. Not impossible, but difficult.
As a person with a background in fluid mechanics, I don't see how the approach in the article will ever work well or efficiently. It might work, but it's not using the kind of principles that you need. (The whole point of my post is that you can't scale a device down without adjusting or remaking how it does what it does. The physics change.)
Re:What about pollution? (Score:5, Insightful)
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Re:What about pollution? (Score:4, Funny)
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Re:What about pollution? (Score:5, Funny)
I'd be more worried about having blades rotating a million times a minute right next to my genitals!
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Re:What about pollution? (Score:5, Insightful)
Compare with traditional rechargable batteries.
First, there is the one-time environmental cost of manufacturing the batteries. Making a battery requires fuel for mining equipment, transporting the materials, running the manufacturing equipment, and producing the electrolyte.
Second, there is the energy required to charge the battery. This energy comes from the power grid. Ultimately, it comes from burning fossil fuels in power plants. This energy must be transmitted via wires to an electrical outlet, turned into DC by a rectifier, and finally, used to charge the battery.
In other words, here's the energy path for the turbine:
Fossil fuel ---> Combustion ---> Turn turbine ---> Generate DC power
And for the rechargable batteries:
Fossil fuel ---> Combustion ---> Turn turbine ---> Generate AC current ---> Transform to high voltage ---> Transmit down wires ---> Transform back to low voltage ---> Rectify to DC power
Which do you think is more efficient?
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Re:What about pollution? (Score:5, Insightful)
The important question is actually, which one weighs more? Which one is cheaper to use? Seriously, who cares about the environmental effects. We have millions and millions of big engines in the form of cars, a few hundred thousand small gas turbines aren't going to matter much.
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Re:What about start procedure ? (Score:3, Interesting)
Using the generator as a starter motor is probably the absolute best way to go. This is probably coming on automobiles, too; we'll end up with a combination AC motor/alternator-generator for starting and charging. This will be driven by everything and I mean everything on the car going electric. No more vacuum lines, no more hydraulic system. The system will be higher-voltage (automobiles are about to go 48V, even in the US) and that will reduce the gauge of wire necessary for the electrical system, furthe