Andy Dingley wrote:

BMW are experimenting with using the waste heat from an IC engine to
produce steam which drives a motor attached to the main engine.

http://www.gizmag.co.uk/go/4936/

Looking at the pics ( which aren't very clear & I haven't spent very
long looking) it seems they're using the heat from the catalytic
converter as a superheater.

My understanding was that a catalytic converter increased fuel
consumption by about 10%, whilst the heat generated in catalysing CO
into CO2 was sufficient to make it a fire hazard in dry grass. So now
the Germans have added on a steam engine which recovers 10% of the
efficiency.

I saw Maggie Thatcher (ex industrial chemist) on TV ranting about
catalytic converters, the only time I heard her speak sense. A more
cost-effective method of reducing emissions was the lean-burn engine,
which was both more efficient and less polluting that an un-catted
engine. I believe Rover had done much development on the lean-burn
technology, but that seems to have been scuttled after BMW's brief
period at the helm.