Start a Fire With Air

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Introduction: Start a Fire With Air

About: I'm an Emu. As a young chick my parents use to feed me watermelon and I loved it so much everyone nick named me, you guessed it, watermelon. Now that I have moved away from home I rarely get to eat any water...

To do this we need to make a firepiston, which is a device for starting cook, camp and signal fires with air.

Firepistons seem so high tech that it's hard to believe they were not developed at MIT or Carnegie Melon under a top secret DARPA contract with unlimited funding. Since the firepiston is also given credit for Rudolf Diesel's invention of his Diesel engine it is quite surprising that the firepiston was not invented by Diesel himself or by one of his contemporaries or the likes of Ben Franklin and other European and American pyro based device inventors of the 16th, 17th and 18th centuries.

What historians note is that the firepiston was most likely invented in conjunction with the invention of the blow gun by prehistoric South East Asians since firepistons are normally found in the possession of those who use blowguns. The need to dislodge the internal partitions at each connecting joint inside a length of bamboo by ramming a rod or piston through the membrane, and in the course of doing so, rapidly compressing the air thereby setting dust particles or the membrane alight, is the reasoning behind co-invention.

I was so amazed at the technology and the science behind it that after building my own firepiston to prove to myself that the science and technology was real I could not resist sharing the science, technology and construction of my first firepiston with you by creating this instructable.

Here then is a description of how to make your own working firepiston to see first hand for yourself that the science and technology do in fact work. I left lots of room for improvement in materials, workmanship and degree of completeness for possible use in the field, if going beyond a demonstration is what you want to do.

Step 1: So How Does a Firepiston Work, Anyway?

A firepiston can set an ember to burn as a result of energy being concentrated into a smaller and smaller space by compression of air resulting in a corresponding increase in the air's temperature.

The principle of increasing temperature by method of compressing air is explained by the Adiabatic process in which the internal energy of a gas must increase when a mass of air is rapidly compressed (or the volume of space containing a mass of air is rapidly decreased). The resulting increase in internal energy results in a rise in the temperature of air sufficient to light an ember, just like the pressure produced by an ice skater's blade is sufficient to increase the internal energy of the ice, which turns ice under the blade into water.

You can envision the effect in a 2D graph (below) with pressure as the ordinate (vertical) and volume as the abscissa (horizontal) and the adiabat or curve of constant entropy as the inverse relation curve. (Black lines are the curves of constant entropy.)

Rapid compression by a factor of 25 to 1 produces sufficient internal energy to send the air temperature to 800 degrees Fahrenheit. This temperature is sufficient to ignite a piece of char cloth for use in kindling a fire.

After several tries and some fine tuning (better sealing with more lubricant) I was able to produce embers with char twine using the apparatus I constructed.

Step 2: Materials and Tools

In general you want a material that will allow a cylinder to be bored smoothly with approximately an 1/4" ID which is around 6" deep and sealed on one end. Incidentally, If you do the math then you will see that it is the ratio of the height of the uncompressed space to the height of the compressed space that determines the height of the cylinder. In other words if you want .25" of char cloth to be ignited and you need a compression ration of 32 to 1 (instead of 25 to 1) to do it then the height of the cylinder will need to be 32 times .25 or 8", plus a little extra room to insert the piston.

The piston is a rod that fits snugly inside the bore of the cylinder using a gasket or seal of some type to make it air tight. The bore and the piston must be perfectly straight and smooth to achieve and to maintain an air tight seal while it is being operated to produce an ember.

Natives might collect woods and cutting tools and keep at least one firepistons under construction in various stages of completion to be able to go from start to finish within minutes, hours or days.

To speed up some of the process required for construction requires use of a 1/4" by 6" brass nipple with an end cap filled with JB Weld and an aluminum or oak dowel to construct two test pistons. The pistons require a 1/4" OD O-Ring (or slightly larger diameter that can be filed down to fit) to act as an air tight seal. Natives would use fibers of some sort and perhaps anything from animal fat to earwax as a sealing lubricant. We can use lip balm or Petroleum Jelly.

I used a 1/4" power drill and a piece of dowel wrapped with an inch long sheet of tissue paper soaked with a solution of water and Bar Keeper's Friend (Oxalate acid) to polish the inside of the brass nipple to a mirror finish. (On the larger 3/8" nipple I'm working with now the inside of the nipple is much less smooth and straight requiring various grades of sandpaper to hone it smooth before polishing.)

I used a hack saw blade, a glass file and the threads on a bicycle wheel spoke to fashion the seat for the O-ring in both the aluminum and in the oak dowel. A 1mm bit was used to drill the hole in the char twine box. (Commercial units have a much deeper cylindrical hollow to hold more char cloth better.)

Originally I used a temporary piston stop made by using a pair of vice grips clamped around the piston shaft where the handle would be attached to the piston shaft to keep the char twine from striking the bottom of the bore. This worked but it appears that commercial makers of firepistons hollow out the end of the piston much deeper to provide greater room for more char cloth and allow the end of the piston around the hollow to serve as the piston stop, rather than using a shaft pin or the handle as the piston stop. BTW - commercial versions can run upwards of $50, but some come with all of the amenities such as char cloth and lubricant.

Step 3: Polishing the Cylinder

Do not use cylinders with a weld seam left inside but only nipples that have been bored smooth at the factory. Otherwise you will have to bore out the inside of the pipe to remove the excess material remaining after the seam was welded.

I used a 1/4" power drill and a 1/4" oak dowel with an inch wide piece of damp tissue wrapped around it for polishing. I used various grades of sandpaper for honing first since the nipple was dented or had internal high or low areas resulting from the equipment used to keep the nipple from slipping while the threads were cut.

The tissue was dampened with a solution of water and Bar Keeper's Friend (oxalate acid), inserted into the nipple and spun by the drill. The nipple can become quite hot so wear rubber or leather gloves to prevent pain and give a better grip on the brass. Also, stop frequently to add water or more solution to help keep things cool. Adjusting the width and amount of tissue wrapped around the dowel will help to optimize the fit and lower the degree of friction. The more you polish the better, but 10 minutes or less should be enough if your last job of honing was with extra fine grit sandpaper.

Step 4: Putting on the End Cap

JB Weld is used to fill in the space where the nipple does not reach the bottom of the end cap. If the space is not filled the O-Ring will expand in this space and release the air pressure too soon as well as get caught in the space.

The end cap is set down like a cup and filled halfway with "steel" and half way with "hardener." They are mixed with a matchstick or toothpick. Then the nipple is held upright and the bottom end threaded into the end cap and tightened. Once tightened the nipple and end cap are either hung by a string or stood up so the JB weld will set with a flat and horizontal surface on the inside to stop the piston and to eliminate all unintended air space.

The hard part comes next - waiting the full 16 hours for the JB Weld to set completely.

Step 5: Cut the Hollow and the Seat

On the very end of the piston a hollow is cut using a rounded or squared end drill bit. The hollow may also include 1mm or 1/16" hole, drilled in the center for a total depth of no more that 1mm or 1/16" to help hold the char cloth or twine better. Commercial versions may use a slightly deeper (3/16") hollow with no center hole and with the O-Ring set back behind it for practical use in the field.

For construction of this firepiston I just wanted to see if it the limits of the science and technology that might keep it from working. I tried several other configurations. You can experiment with all sorts of arrangements, including a double O-Ring configuration. Feel free to experiment and learn everything you can in case you ever really need to make one of these out in the field!

I cut the seat for the O-Ring next by placing the other end of the piston in a 1/4" power drill and using a hack saw blade, glass file and the threads of a bicycle wheel spoke as lathe chisels.

The O-Ring is and seat are next lubricated and the O-Ring is slid on and the O-Ring fitted to the inside diameter of the cylinder.

Step 6: Test the Fit of the Piston and O-Ring

While it should not be difficult to insert the piston and O-Ring into the nipple there should be obvious resistance from air pressure and the piston should spring back when released. If not try a little more lubricant.

If the piston can not be inserted then remove all lubricant from the shaft and O-Ring, slide the O_Ring up onto the shaft past the seat, put the piston back in the drill and spin the O-Ring on some sandpaper to reduce the outside diameter of the O-Ring a very small amount each time.

Re-lubricate and re-seat the O-Ring and try again. Repeat this process if necessary.

Step 7: Add Handles

Since I was not planning to use this in the field (just yet) but rather testing compression ratios I used vice grips as an adjustable piston stop and for the piston handle and a towel to hold the cylinder. For field use you can used pieces of wood with a hole drilled in them the size of the outside diameter of the piston and the outside diameter of the cylinder and secure them with epoxy.

Step 8: Insert Char Cloth and Test

Char cloth is cotton or denim cloth that has been placed inside a closed container, like an Altoids tin or capped nipple, with a small hole drilled in it about 1mm or 1/16" in diameter to allow gases to escape. The container is heated in a fire to drive off water and other volatile compounds. I found also that setting a piece of twine alight after inserting it in the hole and letting it burn down and then capping it just before the flame went out produced enough char twine on the very end to be set alight by compression, although for a much shorter period of time.

( Here is an instructable for making char cloth in the field for use with a firepiston...)

A piece of char cloth is inserted in the recess of the piston head and the piston is inserted into the cylinder. A rapid motion is used to drive the piston forward with great force and then withdraw immediately (but with some slight delay).

When withdrawn a small ember should be found which must be nurtured if used to set a piece of tinder alight in order to build a fire.

Do a Google search on the keyword "firepiston" and you can find hundreds of sites on the internet that discuss how to use a firepiston and find videos that show the glowing ember and how it is used to light tender and start a fire. If you have an Adobe Flash Player or add-in you may also be able to view this.

Mine works but until I put on handles I'm not going to develop an operating technique. I have learned that a slight delay after plunging rather than a sort of very rapid bounce worked much better. Experiment.

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    83 Comments

    The environmentally safe, clean burning alternative to liquid charcoal and liquid fire starters are safe waterproof fire starters. The built in O-ring keeps fuel sealed and prevents evaporation indefinitely. Waterproof Fire Starter

    Good job on an interesting uncommon project. Like another I thought that a larger diameter may make construction easier, then it dawned on me that would require extra force to compress the air. Have you looked into finding or creating a cup like piston, where the air pressure would force the cup walls against the cylinder wall making for a tighter seal? I think the oil field supply store here sell seamless brass nipples, that may make it easier to make a good bore

    2 replies

    One of the reasons I drilled the char cloth indent or hollow so shallow was to get a higher compression ratio since the longest nipple available to me off the shelf from my local plumbing store is 6". Since the piston head takes up at least 1/2" that only leaves me with 5.3125 inch height and a 0.1875 inch char cloth hollow or a 28:1 compression ratio. versus a 5.375 inch height and a 0.125 inch char cloth hollow or a 43:1 compression ratio. Commercial units use a 25:1 compression ratio with a 3/16" char cloth hollow. Experiment.

    I love my fire piston. I got mine from Wilderness Solutions, (the "Scout" model)
    and it's never failed me. It did, however, take me a long time to learn how to turn that ember into a roaring blaze. I've never had problems lighting a fire, but I was accustomed to using flint and steel, or ferrocerium rods.
    Any suggestions on natural tinder for fire pistons though? all I've ever used is char-cloth.

    1 reply

    You can start with a small piece of char cloth in your piston and use that to light a larger piece to give more time for the tinder or other fire-starter material (e.g. cotton ball saturated with Vaseline) to ignite. Then it's just the usual method of going from smaller combustibles (twigs, for instance) to larger ones to build up the fire.

    Could you just not use a push bike pump with the metal ball nozzle? They get rather hot :)

    Cool I will have to try this out,Is this the same principle that some Diesel Fuel engines start up ( the ones that do not have glow plugs ) ?

    7 replies

    Glow plugs heat up the engine when You start up a diesel. Thats all they do. Once the engine is hot, the pistons compresses the fuel and that plus the little bit of heat makes it work. I also do not know of any diesels without glow plugs, but it could be possible in hot areas. I'm a teenager thats a nerd and does nothing with trucks and I can tell you that. Sorry I did that. It just bothered me. and yes, its kind like that, but this isnt as powerful as a diesel and a lighter is easy to me compared to this. Just saying.

    cool I like to see the younger generation thinking about other things then sex drugs and rock and role. there all good ,but I am in my 40s I know about the glow plug thing probably be for you was a twinkle in your dad's eyes. ( not meant to make ya feel bad ) older farm tractor did not use glow plugs some of the old Mac trucks and military vehicles did not use glow pugs. I think the use of glow plugs came in around the 60s ,I could be wrong on that thought as well as my thought that friction created the heat to light up the diesel fuel

    by all means continue to feed your mind better things then drugs and Challenge current technology make it bettermake new ! (lol my life in some old folks home may be much better by you doing it lol)

    You are correct. Not all diesels do have glow plugs... Early diesels were just cranked over repeatedly, which created enough heat due to the compression to start the engine. However, cold weather made it hard to start the engine especially when high compression/high speed diesel engines appeared. Glow plugs were the most successful method of starting diesel engines in cold weather. Some of the methods used before are solid fuel blocks that were fitted into the cylinder head (rudementary glowplug), intake heaters (increase incoming air temp), and introducing ether into the intake. Some example of pre glow plug diesel engines are: - Field Marshall tractors (large single cylinder 2 stroke diesel) which used a solid fuel block, and then later a stogun cartridge style started which ignited fuel in the cylinder. -Stationary diesel engines, like Petter's and Lister's, which are low speed engines that didnt need glow plugs or heater - I believe that the Detroit Diesels featured the ether intake system. Hope that helps. By the way, I'm 19, but have been interested in old engines since I was born :P Old tractors that used TVO still produce the nicest smell :)

    Yes this dose to you young lad you have my honers. you have done well in your studying and investing your knowledge to better living and only 19 at this point of time. I can see much more grate things coming from your efforts in the years ahead of you ! keep it growing

    This is something I'll have to do in the future. It combines technical things with fire which is an irresistible combination. It'd make a great grill ignitor (I like to grill with real wood)

    3 replies

    I dont know if you have heard of this,not very technical,but take paper egg cartons fill with sawdust or dryer lint then pour melted wax into each section,when cooled seperate them,they will each burn about ten minutes,a little longer if useing sawdust.

    Yeah, actually knapweed and grass clippings work well for that also.  There's actually an instructable on it.

    I take a paper towel, fold it 4 times so its like 1 inch wide ( you have to tear the paper towel) and then soak most of it in wax. leave a little bit without wax so you can light it. they burn for like a candle.