Sterling is a whole different type of engine, but falls in the category of external combustion. A car engine, whether Otto, or diesel is an internal combustion engine (ICE). The fuel is burned inside the engine to make power. Steam and sterling use an external combustion, but totally different dynamics to turn that heat into mechanical power. Sterling's work, but never really caught on. Here is one commercial application of stirling
http://www.whispergen.com/index.cfm Pretty cool stuff, but since it's somewhat exotic, it's expensive. They don't have prices, but if memory serves me right they are as costly as my steam links, but not as serviceable by you and me.
