Waste Heat Steam Engine

[WisdomWarlord]

I've got a 50cc 4 stroke air cooled gasoline engine and I'm wondering if a waste heat steam engine (using the heat from the cylinder head and exhaust pipe to make all the steam) is practical for the following goals:

Drive a 150w dc generator and weight 12 lbs or less, not counting the water needed.

I learned a lot about waste heat boilers in the Navy, so I could easily refresh that knowledge by reviewing the training materials I've kept all these years, if the project it possible and reasonable. I'd like something self-contained since it will be used on a recumbent trike. Space to install is isn't a concern, the trike is huge.

Thanks