ORIGINAL: Antique
Tried and discarded many years ago by Briggs and Stratton for some lawnmower engines...
Perhaps the large progress made in materials in the intervening years might change things a bit. Also Briggs and Stratton was not known for innovation. ( my spell checker wants to change Stratton to castration)
edit:
Take a look at this:
http://homelandsecurity.psu.edu/disc...h_voltage.html
Research is going on. Piezoelectric transformers might make real small gas engines practical.