MEMS-Based Turbine Chip for Portable Power
30 September 2006
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| One component of the micro gas-turbine. Source: MIT |
MIT researchers are developing a gas-turbine engine the size of a quarter. The MIT micro-electro-mechanical systems (MEMS)-based micro turbine is a 1 cm diameter by 3 mm thick silicon heat engine designed to produce 10-20 W of electric power.
The resulting device could run 10 times longer than a battery of the same weight, with the potential to power laptops, cell phones, radios and other electronic devices.
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| Cross-sectional drawing of earlier version of the MEMS turbine. |
The microengine is made of six stacked and bonded silicon wafers. Each wafer is a single crystal with its atoms perfectly aligned, so it is extremely strong. To achieve the necessary components, the wafers are individually prepared using an advanced etching process to eat away selected material. When the wafers are piled up, the surfaces and the spaces in between produce the needed features and functions.
Inside a tiny combustion chamber, fuel and air quickly mix and burn. Turbine blades, made of low-defect, high-strength microfabricated materials, spin at 20,000 revolutions per second—100 times faster than those in jet engines. A mini-generator produces 10 watts of power. A little compressor raises the pressure of air in preparation for combustion. And cooling (always a challenge in hot microdevices) appears manageable by sending the compression air around the outside of the combustor.
The team is now attempting to integrate the different components into a single functioning device.
This research was funded by the U.S. Army Research Laboratory.
(A hat-tip to Garrett!)
Resources:
One wonders if a tiny catalyst will be incorporated to reduce emissions. I'm only half-joking. In enclosed spaces, running these for some time might be stinky, especially if the military fuels it with their JP8/9 (sic) kerosene.
Posted by: Ron Fischer | 30 September 2006 at 12:41 PM
Methanol or butane seem to be the more likely fuels.
The output is good, but the efficiency... if the turbine achieves 20 W output but is only 10% efficient, it would emit 180 W of waste heat. This is going to be an issue, both for environmental management and safety.
Posted by: Engineer-Poet | 30 September 2006 at 02:46 PM
This is very cool technology, but I'm not sure I see the connection with sustainable mobility.
Posted by: Nick | 30 September 2006 at 03:53 PM
This is great. I mean this is truely excelent. My girlfriend uses a power wheelchair, which can run for 2-3 days on one full charge. The batteries are 24V and 40AH. which makes 1/2 KWH. This generator could charge her chair in 20-50 hours, or basicly her depleation rate, and could be safe to run indoors on say propane.
Posted by: Michael McMillan | 30 September 2006 at 04:24 PM
ALL COMMENTERS ABOVE, take a look at the Resources: link provided.
_Other uses would be prosthetics, free roaming robots (Terminators?), and current/future military equipment. One specific use would be the US Army FCS systems slated for ~2020. They may include powered armor suits akin to those in the game HALO. JP-8 fuel would have to work there, unless others are developed/used. As for waste heat/heat signature, high efficiency thermovoltaics or thermoelectrics would help. Getting >30% of the energy from the exhaust may be possible.
Posted by: allen Z | 30 September 2006 at 06:02 PM
H2 was used as the demonstration project's fuel for its combustion properties.
Posted by: allen Z | 30 September 2006 at 06:06 PM
What happens to fuel cell at 50 to 60% efficiency? Seems like the smaller the application, the less efficient gas turbine will be, while PEM fuel cell maintains its efficiency regardless of size.
Welcome back, Allen Z :)
If fuel cell is used at 50-60% efficiency, then there wouldn't be enough heat to worry about thermoelectric recycling.
Posted by: Roger Pham | 30 September 2006 at 08:05 PM
Roger Pham,
One downside to fuel cells is the need for a H2 source. It may be H2 itself (which presents a logistical problem), or a H2 carrier like CH4 or C2H6O (but requires a reformer). With H2 carriers, what do you do with the C left over? There is energy lost if the carbon is not exploited in some fashion. Here is one example of a carbon fuel cell:
_
http://en.wikipedia.org/wiki/Molten_Carbonate_Fuel_Cell
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It runs quite hot (400-600C) which limits its use for armor suits (unless aerogels become cheaper and easier to manufacture), but not for vehicles. A 10 ton 6x6 can use it (with extensive cell thermal insulation and recycling) to power electric motors, at ~50% better than today's diesels. A warship can use it with steam cogeneration to have efficiencies akin to combined cycle gas + steam turbines (>59%), with 80%+ possible.
Posted by: allen Z | 01 October 2006 at 04:48 AM
Turbines get more efficient the smaller they get but ya that wouldnt be very effiecent alone it would need a cogenerator to use and defuse the heat it gives off. Otherwise the thing is gona have a glowing hot ir sig and no way the mil wants that.
Also they are developing small fuel cells that run DIRECTLY off military grades of fuel. AND they are developing new military feuls as well.
Posted by: wintermane | 01 October 2006 at 07:13 AM
I mean WOW a turbine in our pockets, and I thought it was cool when i worked on an F15 flightline. I doesn't seem to efficient but what a neat idea. I've seen these around before with other micro machines. It isn't that is great for all current(forgive the pun) battery used, but it does give more options. As for sustainability, I would rather see methanol, butanol, ethanol... whatever, that lead, acid, mercury... etc. from batteries used up and put in landfills.
Posted by: Andy | 01 October 2006 at 08:53 AM
Actually, in reference to all the questions concerning efficiency, it is claimed that the target efficiency will nearly be met (as efficient as a large electric company turbine generator).
Posted by: Patrick | 01 October 2006 at 03:21 PM
Btw, mike the image links are broken.
Posted by: rexis | 01 October 2006 at 06:51 PM
how is it possible to make a usable Stirling Engine this small?
Posted by: rexis | 01 October 2006 at 09:08 PM
Andy:
Lead is not really chemically reactive and in state of batteries does not pose real environmental problem. Moreover, lead-acid batteries are among record-breacing recyclers, for car batteries recycling rate is around 90%. Mercury have not been used in batteries for a long time. The last toxic battery (and it is really big s#%^t) adopted was Ni-Cadmium, with cadmium being the problem. Luckily, Ni-Mh batteries have almost the same properties and use and intensively pushing Ni-Cd out of market. For all new batteries under development non-toxicity is number one priority.
Posted by: Andrey | 01 October 2006 at 10:44 PM
Wow, a nifty little device. When it works. That might be useful for something. Someday. Maybe. They hope.
Geez, how many qualifiers make this more "Popular Science" than "Science"? Again, a neat device, but will it replace batteries?
Definitely not. A single turbine will have pathetic efficiency, and the thermal losses from such a hot device with a short thermal path to the environment will be outrageous. Unless they wrap it in thermal insulation to the tune of at least a hundred times its volume.
Sorry, no free lunch here. Come back for the power and efficiency numbers when they actually have a working prototype. My guess is 100 mW at 2%, even with lots and lots of thermal insulation.
[q->t to email]
Posted by: Adam | 03 October 2006 at 12:03 PM
Patrick, I think you are WAY off on efficiency. Their 2003 paper points to simple cycle (what they hope to have running by yearend) SFC of around 0.7 grams of H2 fuel per watt-hr of output electricity. Since 0.7 grams of H2 contains about 23 w-hr of energy, this represents about 4% efficiency.
If they can eventually design and build a MEMS turbine with recuperation, they believe they can reduce SFC to about 0.35 g/w-hr or about 8% efficiency. Microtubines achieve 25% efficiency. Large utility combined cycle plants achieve 60% efficiency, but the turbine part alone is closer to 35%.
8% would be impressive for such a small device, but hardly competitive with large utility generators.
Posted by: doggydogworld | 04 October 2006 at 02:30 PM