History has many good ideas that for whatever reason were relegated to obscurity.
Remember the Sarich Orbital Engine? It was petrol but initially touted to be cheap to manufacture, light, and fuel efficient. In the end it did not go well 
How about the Pritchard steam car? I met Ted Pritchard around 2004 and his tale about how he was led along to do tweaks on his own capital, and finally done over by lowball licensing offers, put him in bankruptcy. His description of his car engine reminded me of an automotive thermoblock - seconds to startup and off you went.
