1969 GM
The "state of the art" show at the GM Technical Center -- called "Progress of Power" -- included 26 special vehicles which were exhibited or demonstrated, many for the first time. These had a variety of unconventional power plants, including turbine, steam, electric and hybrid systems along with experimental piston engines with reduced air pollutant characteristics.
https://www.gmheritagecenter.com/fea...rimentals.html