Clemson University physicist Terry Tritt aimed to built a system which could capture and convert the hot of engines into energy with the help of thermoelectric device. He said that more than 60% of the automotive combustion cycle’s output has been wasted. Therefore, if these energy could be captured, it must be a good thing for environment.

He also claims that with the current thermoelectric technology-whose efficiencies range from 7-8%, over 1.5 billion gallons of diesel could be saved each year if applied to heavy trucks only in U.S.

[source]
http://www.sciencedaily.com/releases/2007/10/071003154956.htm