We built the engines using parts from my garage and from Home Depot. The last engine also included two borosilicate glass-graphite piston cylinders generously donated by Airpot. The Riverton Science Department hooked us up with real-time pressure and rotation sensors. The end result was an engine that could run on a candle and a faster one that ran off of a propane stove; we measured the thermodynamic cycle of the second engine, creating and experimental PV diagram.
My partner-in-crime Sawyer just facebooked:
Hey! You went to ISEF a while ago, didn't you? Any advice on choosing a project?
Sure! In my unhumble opinion, engineering is the way to go.
Pick something fun or cool, because then you'll spend time on it and make it great. Also, pick something that you can build. I have way better experience with that than doing pure science or math, at least in the context of a science fair. (Science fairs are really science/math/engineering fairs; I like the engineering part best.) If you do pure math or science, then you'll need a mentor. Many entrants in those categories, even at Utah-level fairs, partner with university professors; needless to say, it's very hard to compete if you're going it alone. Building stuff is different; you need a lot less arcane knowledge. I wrote some of the programs I'm most proud of before I had any formal CS training; my friend Nathan built a car -- from scratch -- that does 0-60 in under four seconds -- before he went to Stanford and took introductory mechanical engineering. If you're excited about it, if you persevere, and if you're willing to use Wikipedia a lot, you can learn as you go and build really cool stuff.
I also recommend building something physical. You can enter a computer science project, but you'll have plenty of chances to code. In my experience, the clubs, groups, and other orgs you'll be part of in college never have enough programmers. Web developers are especially in demand -- you'll spend lots of time sitting in front of a screen hacking apps into existence. Science fairs are your chance to design, machine, tinker with, and generally build stuff, and get recognition for it. Companies sponsor you. Teachers love it and are often very helpful. It's a very good deal, and one you really don't get once you're out of school. I can't overstate how great an experience my project was. Find something interesting and build it. You'll rock the science fairs and get more out of it than you can imagine.
(Tom and I at Sandia National Labs. One of our judges invited us to come see his project there: harvesting solar energy with Stirling engines. The dish focuses sunlight onto the hot end of a 25KW engine. The other side is cooled with a radiator.)