1. A ‘primitive’ fire starting tool,
The FIRE PISTON
A ‘primitive’ fire starting tool,
and a neat demonstration of the fundamental physics of why the Diesel Engine works.

2. Description
A simple, strongly made, tube with one end closed off, a close fitting plunger with a seal and a small amount of tinder.
The tinder is placed in the tube and the plunger inserted a small way into the open end.
When the plunger is pushed rapidly and firmly to the bottom of the tube the trapped air gets very hot and ignites the tinder.
The glowing tinder is quickly taken out and used to get a fire going.

3. History
Said to have been found being used by forest tribes in Borneo, Indonesia and Malaysia by European explorers in the 1750’s.
Taken back to Europe and America as a scientific curiosity.
It briefly became one of the most common methods of fire starting in America and Europe, because it was more reliable than flint and steel.
Real flint, as found in a field, and steel produces a very weak spark. Modern ‘flints’ are a special alloy that makes a very big hot spark.
By the mid 1800’s the Safety Match was invented and improved to the point where it completely took over the job of fire starting.
No one knows when it was invented. However the area where it was first found is famous for the use of the Blow Dart. A guess is that whilst making a Blow Gun from Bamboo someone stumbled upon the effect. This is best explained by the fact that the technique for making a Blow Gun Tube is to take a large bamboo and clear out the pith. But at every leaf node there is a hard wooden diaphragm that has to be removed. Lacking suitable drills the traditional tribal method is to knock them out with another thinner bamboo, or an iron rod. We can only suppose that one day this set fire to the pith dust on the end of the rod and an idea was born.

4. Physics
When a gas is squeezed it gets hot in direct proportion to the pressure rise and trapped volume.
Heat is an effect caused by atoms vibrating. Pressure is a force caused by the atoms or molecules ‘bouncing’ off each other as they vibrate. When a gas is compressed the molecules are forced into in a smaller space and ‘bounce’ off each other more frequently to give higher pressure. More ‘bounces’ make them vibrate faster, so the temperature increases. (‘absolute zero’ temperature is when the atoms stop vibrating, at -273 deg. C)
Adiabatic Gas Law:
T1 = initial temperature, deg. Kelvin
Rc = Compression Ratio
k = ratio of specific heats for air, 1.4
Final temp. T2 = T1·Rc^((k-1)/k), deg. Kelvin (deg. C+273.2)
If this is done rapidly the heat does not have time to conduct or radiate away and the temperature of the gas can get very high.
If the air in the Fire Piston is very quickly compressed by a factor of about 20:1 then the air can briefly get to well over 400 degrees Centigrade. This is more than enough to light the tinder.
All Diesel Engines rely upon this effect to ignite the fuel injected into the cylinders.

5. Demonstration
This example of a Fire Piston was made to demonstrate the effect.
It uses a clear polycarbonate tube, and a plunger with modern O Ring seals so that you can see the flame being generated in the ‘fuel’.
We are using cotton wool as ‘fuel’ because it flares up and can be seen easily.
Anything that catches light easily and then afterwards smoulders reliably for a short time can be used to start a fire with it.
Some varieties of dried Fungus can be used. More commonly ‘Char Cloth’ is used (cotton or linen cloth packed into an air tight container and ‘cooked’ until blackened but not burned through – a bit like charcoal)

6. Video
Click in the box to view a video of a fire piston

7. Traditional Fire Pistons
Can be made from many materials. These are examples in Bamboo, Buffalo Horn, Hardwood and Antler.
The plunger is traditionally furnished with a tightly wound waxed or greased cotton or linen thread seal near the bottom.
19th Century examples could be wooden, brass or even made of lead.