Internal combustion engines, like the one in your car, generate power by burning a fuel source (usually gasoline) and converting that heat into mechanical energy, usually by heating a gas or liquid and causing it to expand, using the pressure to move the pistons outward. But it turns out that the process is fairly energy-inefficient, resulting in most of the heat (about 70 percent) being lost to the atmosphere (that's why the hood of your car gets hot and the exhaust gas that comes out your tailpipe is, likewise, hot). But what if we could capture some of that waste heat and use it for energy? That would make cars more energy efficient.
It turns out that heat can be converted directly into electricity using devices called thermoelectric generators. The U.S. Department of Energy recently challenged researchers to use the wasted heat energy to make automobiles 10 percent more fuel efficient, and the researchers are coming through.
It turns out that if you wrap the exhaust pipe of a Chevrolet Suburban with thermoelectric generators, it will add about one mile-per-gallon (or about five percent) to the vehicle's overall fuel efficiency. It doesn't sound like much, but I'm sure most Suburban owners would love to get better mileage. And, it turns out, the improvement would be greater in smaller, more efficient vehicles.
Additional work with putting thermoelectric generators in other parts of the car could increase the efficiency further. While the devices don't generate enough energy to power the vehicle (or even just its air conditioner) yet, they can power electronic devices such as the radio or GPS. And if used in hybrids, the electricity generated could be used to more efficiently recharge the vehicle's battery.
If the DoE's goal of 10 percent improvement is met, it would reduce fuel demand in the U.S. alone by more than 100 million gallons per year, not to mention the amount of carbon that would be kept out of the atmosphere. Prototypes of the devices will be tested by GM and BMW over the next couple of years. Other manufacturers are also working on the technology.