Boosting gas mileage by turning engine heat into electricity

July 22, 2015, American Chemical Society
Engine

Automakers are looking for ways to improve their fleets' average fuel efficiency, and scientists may have a new way to help them. In a report in the journal ACS Applied Materials & Interfaces, one team reports the development of a material that could convert engine heat that's otherwise wasted into electrical energy to help keep a car running—and reduce the need for fuels. It could also have applications in aerospace, manufacturing and other sectors.

In 2012, the Obama administration announced standards that would require U.S. vehicles to average 54.5 miles per gallon by 2025. Improving gas mileage could help reduce greenhouse gas emissions and global dependence on . One approach scientists are exploring to help address these issues involves capturing waste heat from engines and other power systems and turning it into electricity. Many compounds can do this but are heavy, costly, toxic or only operate at high temperatures. Ian A. Kinloch, Robert Freer and colleagues sought new alternatives.

The researchers started with a material called strontium titanium dioxide and added a small amount of graphene, a stable material with excellent conductive properties. The resulting composite was able to capture and convert heat into electric current efficiently over a broad temperature range.

Explore further: Natural gas versus diesel: Examining the climate impacts of natural gas trucks

More information: ACS Appl. Mater. Interfaces, Article ASAP. DOI: 10.1021/acsami.5b03522

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adam_russell_9615
5 / 5 (1) Jul 22, 2015
Hey why not convert atmospheric heat into electricity?
winthrom
5 / 5 (1) Jul 22, 2015
Seems like a good idea for hybrid cars. Recharge the battery with electricity derived from the fuel burning motor's heat. Simply feed it through the same system used for regenerative braking.

Atmospheric heat...
We could do that by creating a large differential in temperature between the heat source and the heat sink. In a car, that exists already because a fuel burning engine makes a lot of heat. To do this in the atmosphere, we would need to take advantage of the temperature change from hot to cold as we go up in altitude. The numbers are: 3.5F° or 1.95C°/1,000 ft. The Empire State Building is 1,250 ft from ground floor to roof (spire not included). Thus 4.4F° differential is all you get. Probably not enough for making electricity.
an_engineer
5 / 5 (1) Jul 22, 2015
Hey why not convert atmospheric heat into electricity?

Because you need a temperature difference to produce energy. What is your sink going to be? Like nathj72 said, the Carnot efficiency is pretty terrible for small temperature differences, and thermoelectrics are particularly terrible, getting just a fraction of Carnot efficiency. They're good if you have high grade heat, like waste heat from an engine, and you want to make some marginal improvements in efficiency. The auto industry has been looking at thermoelectrics for years, but I'm not sure anything has actually been commercialized.
jimbo92107
5 / 5 (3) Jul 22, 2015
What...that's your article? Where's the rest of it?
Eikka
4 / 5 (4) Jul 22, 2015
standards that would require U.S. vehicles to average 54.5 miles per gallon by 2025.


Seems completely ridiculous.

It's one thing to have some cars that do 54.5 miles to the gallon, by being small and powerless or battery powered and generally useless - and a complete other thing to have ALL cars average that.

How on earth would you get a pickup truck do 54 MPG with half a ton of stuff on the back?

TechnoCreed
5 / 5 (1) Jul 22, 2015
@Eikka
54.5 mpg by 2025 is an average for the passenger vehicle fleet, but for a pickup like the F-150 it will be 30.2 mpg. http://www.econom...ightness
Shabs42
5 / 5 (2) Jul 22, 2015
standards that would require U.S. vehicles to average 54.5 miles per gallon by 2025.


Seems completely ridiculous.

It's one thing to have some cars that do 54.5 miles to the gallon, by being small and powerless or battery powered and generally useless - and a complete other thing to have ALL cars average that.

How on earth would you get a pickup truck do 54 MPG with half a ton of stuff on the back?



The article is poorly worded, but when it says cars must average 54.5, they mean all cars must average that amount on aggregate, not each individual car. Going off memory, it's the average of all cars sold, so if you sell 20 compacts that average 60 mpg, you can afford to sell a few pickups that get 25-30.
Eikka
not rated yet Jul 23, 2015
so if you sell 20 compacts that average 60 mpg, you can afford to sell a few pickups that get 25-30.


That's was my understanding of "average" as well.

However, it assumes that most people will buy these hyper-mileage cars. 45-50 MPG is pretty much the point where regular cars stop and small econoboxes start, because the laws of physics don't let you improve mileage arbitrarily.

Engine efficiencies are already at diminishing returns, so the only way to improve mileage significantly is by making the cars smaller.

A family of five won't buy a Honda Fit or a Nissan Leaf unless those are literally the only cars they can buy, which would require some heavy handed and invasive regulations.

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