Remember that all Projects must include: Research on the theory of the science and/or engineering, a literature review, and original science research and/or engineering design

Building Models
Stirling Engines Design Article with Templates
Also see Addendum to above

Youtube video on building a Stirling Engine
ASR Stirling Engine
Wikipedia explanation Research Paper on Stirling Engines

Tea Cup Stirling Engine

Electric Engines
Did you like the electric motor project?
Check out the links, there are many different types of electric motors and you can continue your investigations.
Animations: All Types of Electric Motors
Hit and Miss Engines
Jet Engines  Build a Model Jet engine and send a model plane zooming through the sky GE Beginners SiteIon Engine Propulsion
Fuel Cells These guys sell prototyping needs:
Horizon fuels. And we have a lot of equipment in the lab.
Fuel Cell Cars
Wirmhurst Engine Uses static electricity. See Wirmhurst engine