This tiny combustion cannon is one of my all time favorite projects. I made the one displayed to the left when I was 15. All the parts besides a few screws and the barrel are from a standard BBQ lighter. The clear chamber (which is made from the butane gas reservoir of the lighter) allows a view of the spark and flame as the cannon ignites. The trigger from the lighter is quite suited for use on the cannon as well, and the piezoelectric igniter normally used to spark a stream of butane is wired to ignite a combustible mixture within the chamber.
The cannon is made to fire airsoft pellets, and could do so quite powerfully when I could get it to work. At the time I could rarely make it fire properly using typical combustion cannon fuels; hairspray, propane, etc. I had such difficulty because in a combustion reaction between a flammable gas and the oxygen in the air, there is a very small window of ratios between the gas and the oxygen that the mixture will be flammable. Too much or too little gas added and the cannon will not be capable of firing. In a cannon so small, it is very difficult to measure out so little fuel to add to the chamber to create the proper mixture. I eventually gave up and moved on to other projects, not rediscovering the cannon until about year ago.
I stumbled on the device while cleaning out my workshop and became determined to make it function properly. It was a dozen different fuel tests later before I considered isopropyl alcohol. Unlike more commonly used cannon fuels, alcohol is a liquid at room temperature. The vapor is flammable in a way similar to gasoline, and a +90% solution just so happens to create a flammable mixture when open to the air at room temperature. Against what might seem like common sense, gasoline and most other chemicals with flammable vapors will over saturate the air with vapor if left alone in a closed container, and create a fuel to air ratio that is not combustible. It is only with careful regulation that such fuels are capable of burning in an engine.
Having realized that alcohol was capable of the proper vapor mixture on its own made things easy. A little alcohol on the end of a cotton swab quickly passed around the inside of the chamber turned out to be all that was needed to allow the cannon to fire every time. Having now discovered a consistent method of firing, I could finally present a functioning video project to you reading this article. In the following video I detail the steps used to create my second BBQ lighter mini cannon:
Many lighters have a divider in the gas reservoir that makes them very difficult to use for this project. Should you encounter trouble finding a suitable reservoir, the one used in the video is from a ‘grill zone flexible lighter’. Another lighter that will work well is the Scripto Aim ‘N Flame II Lighter, which is carried by Home Depot.
Remember, this mini cannon is capable of firing pellets just as hard as a real airsoft gun, and should not be used without safety glasses.