  A potato cannon was designed to accommodate several different experimental
propellants and have a transparent barrel so the movement of the projectile
could be recorded on high-speed video (at 2000 frames per second). Both
combustion chamber and barrel were made of polyvinyl chloride (PVC). Five
experimental propellants were tested: propane (C3H8), acetylene (C2H2), ethanol
(C2H6O), methanol (CH4O), and butane (C4H10). The amount of each experimental
propellant was calculated to approximate a stoichometric mixture and
considering the Upper Flammability Limit (UFL) and the Lower Flammability Limit
(LFL), which in turn were affected by the volume of the combustion chamber.
Cylindrical projectiles were cut from raw potatoes so that there was an
airtight fit, and each weighed 50 (+/- 0.5) grams. For each trial, position as
a function of time was determined via frame by frame analysis. Five trials were
taken for each experimental propellant and the results analyzed to compute
velocity and acceleration as functions of time. Additional quantities including
force on the potato and the pressure applied to the potato were also computed.
For each experimental propellant, average velocity vs. barrel position curves
were plotted. The most effective experimental propellant was defined as the one
which accelerated the potato to the highest muzzle velocity. The experimental
propellant acetylene performed the best on average (138.1 m/s), followed by
methanol (48.2 m/s), butane (34.6 m/s), ethanol (33.3 m/s), and propane (27.9
m/s), respectively.
