Free-Piston Engines Are Ultra-Efficient, Could Replace Gas and Diesel

As we move toward battery and hydrogen cell breakthroughs that could wean us off our addiction to oil, here's at least one engine design from yesteryear that ought to be examined a bit more. The free-piston engine, first invented in 1920, is cheap to build and roughly twice as efficient as current gas engines. Unlike… » 10/03/08 12:30am 10/03/08 12:30am