The Fire Syringe – an explosive demonstration of physics principles
This Fire Syringe is great for demonstrating adiabatic compression (rapid compression that raises air temperature) in diesel engines, Ideal Gas Laws, the laws of thermodynamics, and the resourcefulness of ancient people. As air compresses, the temperature increases and combustible material bursts into flames.
What is a Fire Syringe and how does it work?
A fire syringe is a piston-and-cylinder device with a thick-walled transparent cylinder fitted with a metal piston which can travel within a short distance of the bottom of the cylinder. It is used to demonstrate compression ignition.
Compression ignition is demonstrated by placing a small piece of cotton at the bottom of the fire syringe and then plunging the piston forcefully down into the cylinder. The cotton will burst into flame due to the rapid rise in temperature which accompanies the sudden reduction in volume (and increase in pressure) of the air beneath the piston.
The energy provided by the arm muscles working to compress the air is transferred into the much reduced volume of the air during compression and manifests itself as heat energy sufficient to ignite the tinder.
Compression ignition is the principle underlying the operation of a Diesel engine.
Here’s how to work the Fire Syringe:
To operate the Fire Syringe, push down quickly on the handle (piston). You will see with increased compression, the gas reduces its volume, and causes the temperature to rise so suddenly that a small bit of cotton fibers burst into flames. In essence, you witness the science of combustion by adiabatic heating.
- Pull out the syringe and place a small piece of cotton at the bottom of the tube, approx 5mm.
- Gently re-insert syringe so it just enters the mouth of the piston chamber.
- Place unit base on flat, stable 3. surface and push syringe straight down with force and speed.
- You will see a flash of fire which will last as long as there is oxygen present in the tube.
You need to have just the right amount of cotton in the apparatus to have success. Experiment with larger and smaller pieces to find the right amount before using with students.
Pull the cotton apart a bit to allow air to circulate through the material to help with ignition.
If the seal on the o-rings is not tight enough, the air will not be adequately compressed. Adjust so that o-rings form a tight seal to compress the air.
The chamber must be opened and cleaned between demonstrations because the oxygen in the tube is consumed during ignition. The chamber should be clean and dry to have success.
This kit includes:
• 2 extra butadiene-acrylonitrile rubber O-rings
Check out operation of the Fire Syringe in the video below.