Skip to comments.Powering Your Car with Waste Heat
Posted on 05/27/2011 12:06:51 PM PDT by Red Badger
New thermoelectric materials will be tested in BMW, Ford, and Chevrolet vehicles by the end of summer.
At least two-thirds of the energy in gasoline used in cars and trucks is wasted as heat. Thermoelectrics, semiconductor materials that convert heat into electricity, could capture this waste heat, reducing the fuel needs of the vehicle and improving fuel economy by at least 5 percent. But the low efficiency and high cost of existing thermoelectric materials has kept such devices from becoming practical in vehicles.
Now researchers are assembling the first prototype thermoelectric generators for tests in commercial cars and SUVs. The devices are a culmination of several advances made independently at thermoelectric device-maker BSST in Irwindale, California, and at General Motors Global R&D in Warren, Michigan. Both companies plan to install and test their prototypes by the end of the summerBSST in BMW and Ford cars, and GM in a Chevrolet SUV.
BSST is using new materials. Bismuth telluride, a common thermoelectric, contains expensive tellurium and works at temperatures of only up to 250 °C, whereas thermoelectric generators can reach 500 °C. So BSST is using another family of thermoelectricsblends of hafnium and zirconiumthat work well at high temperatures. This has increased the generator efficiency by about 40 percent.
At GM, researchers are assembling a final prototype based on a promising new class of thermoelectrics called skutterudites, which are cheaper than tellurides and perform better at high temperatures. The company's computer models show that in its Chevrolet Suburban test vehicle, this device could generate 350 watts, improving fuel economy by 3 percent.
Fabricating skutterudites, which are cobalt arsenide compounds that are doped with rare earth elements such as ytterbium, is a time-consuming, complicated process, and incorporating them into devices is difficult, says GM scientist Gregory Meisner. The crucial challenge is making good electrical and thermal contacts. The large temperature gradient across the device puts mechanical stress on the contact-thermoelectric interface. Plus, joining the different materials introduces resistance that heats up the contact, degrading the device. "By a suitable choice of materials, you can affect resistance," he says. "The challenge is in arriving at the right formula for materialsboth the semiconductor thermoelectric and the contact."
Power from heat: A thermoelectric generator that converts waste heat from a cars exhaust system into electricity could improve fuel economy. Credit: General Motors
Thermoelectric Waste Heat Recovery Ping!.................
The crucial challenge is making good electrical and thermal contacts.
Seems to me like the cooling system would be the best place to do this. Either that, or embed high-temperature heat pipes right into the engine block, and put the thermocouples on the outside of the engine.
If this can get perfected and mass produced it could provide more energy per square inch than regular solar cells because solar cells only work with a small amount of em spectrum, where all you would need is a black panel to absorb all light and heat up with this device under it.
Who knew skutterudites are cheaper than tellurides?
Anyone here own a newer 2010 or 2011 model prius ?
Don’t like ?
If ya have a minute......:o)
Mercury contacts maybe?..............
The people in Telluride won’t like this.................
The problem being that thermocouples are very inefficient -- less than 10% of the heat gets converted to electricity.
The article touts a 40% increase in efficiency with the new materials, but when you're only starting out at 5-7% the improved efficiency is still quite low.
Seems like this would work well with a turbo. You could remove the heat, use it as energy, and scavenge the now cool gasses to run the turbo which would allow you to use a smaller displacement engine to produce the same amount of power.
I prefer superchargers over turbos..............
Yeah, let’s hang an extra 1000lbs of this crap on our vehicles instead of drilling here for our own oil.
This makes much more sense than windmills, solar panels, and ethanol.
I just hope there is little, it any, government funding. which will lead the program down a dead end path.
Well, THAT certainly sounds Sustainable and Green.
Well, I've been to Telluride and it certainly was expensive.
You mean a SoSumi Patent?...............;^)
When you say cooling system, do you mean as a source or a sink of the thermal energy?
High temperatures are crucial; from the temperatures mentioned they must be going for the exhaust system, where the most waste heat is available at high temperature. This suggests the exhaust system would be the best source.
If they need a sink, I think they’d try to use ambient air for simplicity. Ambient air’s advantage is that it’s cooler than the cooling system (duh!); its disadvantage is that it’s hard to get waste heat into ambient air compared to putting it into the liquid-based cooling system, which itself uses a fairly large liquid-to-air heat exchanger. In fact, if the existing engine cooling system took on the additional waste heat load of the thermoelectric generator, it would have to be made somewhat larger.
Due to thermodynamic considerations, the total (cooling+exhaust) heat rejection has to be at least twice the power output of the engine, in the steady state. Off the top of my head, I don’t have figures on how much of this waste heat the cooling system needs to dissipate; it must be in the tens of kilowatts under most conditions. Also, it would be nice to know exactly how this amount compares to the amount heat given off in the exhaust, which I think is the larger quantity.
Just some idle speculations here.
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