The comment on Volvo's Environmental Concept Car seems to be correct; unfortunately, I'm also having a tough time finding information on it. It was back from 1992/1993, so I'm sure we could do better these days, what with new research being done on micro power turbines (often used for onsite cogeneration of electricity for buildings, etc.). I think that a properly outfitted turbine (with regenerator and possibly intercooling and reheat) would be much more efficient than an Otto or Diesel cycle engine, and would certainly be more reliable. Cost, however, is another story. Maybe this is another case where the "law" of supply and demand would apply, though. For more on turbine efficiency, see: