Hi Mate,
How about a presentation/demostration in producing & using bio-diesel.
http://en.wikipedia.org/wiki/Biodiesel
It's fairly easy to setup a process to produce it & fairly easy to test it (model engines).
Making Biodiesel...
http://www.schnews.org.uk/diyguide/h...ebiodiesel.htm
The above link gives you an idea of what is needed, but you can scale it down for test purposes.
That said, you can just use chip fat that is filtered well + mixed with 25%ish standard diesel. This would be very easy to demonstrate.