Apparently the Patent expired in March 2002 & nobody stumped up the $$$ to renew it.
There has been some discussion on the following Forum in recent times;
Engine & fuel engineering - Smokey's Adiabatic Engine
Had a test run in an old Holden that a friend had built a system for- used a carburettor from a small chainsaw of about 50cc. Car would cruise quite happily at up to 60mph and coped with small hills etc quite well. Only weak area was acceleration if you wanted to pass another car . Fuel consumption tests indicated that around 55/60 mpg would have been achievable. Normal consumption for this car would be around 25 mpg under similar conditions. Have no idea of any ill effects there may have been long term as he never kept it on the car ( It was his Family car and his wife was not too keen on his experimentation )
Jac Mac