The idea of using flash steam in a turbine is a good idea since it would open up the possibility of using simpler valving and perhaps even utilize a batch process where you would heat a small reservoir of water (maybe a 50ml shot at a time); a temp senser could then pop a solenoid open to the turbine for a short burst and generate electricity. Then reload with condensate and start over. The vessel and tubing would have to handle serious pressures. Not something to taken lightly.

Here's an interesting aside: http://www.blastwavejet.com/rocketcar.htm

"Hot water rocket engine" that used a 2 foot metal ball filled with water, heated, then crack the valve...whoooosh!