Fire pistons offer a novel way of producing flames using compressed air. Their plunger is quickly pushed into an air-tight tube, compressing and heating up its contents until tinder burns in its end chamber cylinder.
Copper tubing capped at one end, solder and a small hacksaw are necessary. You may also want to consider using rubber O-rings and petroleum jelly as gaskets to seal off the copper tube ends.
Compression
By applying the principle that compression significantly raises temperatures of gases, this device uses a hollow cylinder with a piston attached at one end; when compressed air rapidly fills it to temperatures high enough to ignite char cloth or other forms of tinder.
Fire pistons are an invaluable tool for backpackers and survivalists, yet anyone who enjoys spending time outdoors can build one easily. Fire pistons also serve as great emergency tools as they produce heat quickly without needing fuel sources.
STEM Learning’s video on the fire piston’s workings provides a great visual illustration for energy transfer, kinetic theory and Charles’ Law; making it an invaluable teaching resource.
Tinder
When piston rods are quickly thrust into a hollow cylinder, air gets compressed and its temperature increases rapidly – sparking off an ignition in the end of each piston rod and sparking off an ignition source at once. This same principle was originally employed by Southeast Asian and Pacific Island populations before eventually finding use as diesel engines.
The piston must fit tightly inside its cylinder in order to maximize compression pressure, and is typically coated in petroleum jelly or grease to reduce friction. Tinder must be properly placed within the end of the piston and possess low combustion temperatures – char cloth is often preferred, although Chaga conks (Inonotus obliquus) also work well as sources.
When using a fire piston, be sure to withdraw it as soon as you insert it to avoid extinguishing the coal. High humidity may make ignition more challenging but repeated attempts should eventually produce an ember.
Air
If the cylinder and piston do not match, energy can be lost through air leakage during compression, necessitating additional energy costs to compensate. A “gasket” composed of wound thread, leather or animal fat may be included to ensure an airtight seal and maximize efficiency.
The piston rod is typically constructed out of brass; other metals also work. To ensure optimal results, it should be machined for precision fit with the tube, while its end should be sanded smooth to prevent frictional problems. Furthermore, hollowing out your piston so a ferrocerium sparking rod can fit inside is key to its success.
Fill the tinder material into the piston’s notch at its base, using petroleum jelly as a lubricant so it slides easily into its cylinder (commonly referred to as an “O-ring gasket”). Carrying a fire piston as part of your survival kit or bug out bag as an additional means of ignition should other methods fail; particularly useful if the tinder can easily be ignited such as by using char cloth.
Heat
Fire pistons generate vast quantities of heat through rapid adiabatic compression of air, which is then used to ignite small pieces of tinder at the end of their piston cylinder and demonstrate the transference of energy and Charles’ Law.
An effective fire piston can be constructed using readily available materials found both in the wilderness and home environments. All you need is a hollow cylinder sealed at one end, an o-ring piston designed to create an airtight seal when placed into the cylinder, and some tinder for ignition upon compression.
Lubricate the O-ring with any oil-based products such as chapstick, lard or petroleum jelly to create an airtight seal. Cut a strip from char cloth square and insert it inside the bowl shaped end of your piston for additional airtight sealing.
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