Some many years ago I was doing some research on an old engine from like the 1930s. It's only fuel was burning wood or straw or what ever. What is was was, a Stirling Engine. The first use of this type of engine I saw was for pumping water to the upper floors of a house. Now , this technology uses almost anything thing that can cause a difference in temperature. Before I get confused, here is a link to a page that will give you more information. This type of engine is in use now in Australia and New Zealand as a source of power in the outback. I have considered one for use as a back up power supply here at home for when the power goes out.

Anyway, no reason that the principal could not be used in a car, some day.

Check out this link and follow the links from there.
http://www.airsport-corp.com/stirlinginfo.html

Also this link.
http://www.airsport-corp.com/stirling.html