Materials:

• Compression Igniter (Hollow Cylinder and Piston)
• Combustable Material (Piece of Tissue Paper or Cotton)

Demo:

A piece of combustable material is placed at the bottom of a cylinder. When the piston is rapidly pushed down into the cylinder, the air inside is compressed so quickly that there is very little time for thermal energy to leave the cylinder. As a result, the temperature of the air becomes so high that it is able to ignite the combustable material.

Explanation:

Compression Igniter is designed to demonstrate the principle of adiabatic compression, which is a fundamental process in a diesel engine. In this demonstration, a small amount of combustible material (such as cotton, tissue paper, or magician’s “flash paper”) is ignited inside a replaceable, thick-wall glass tube. This is achieved by rapidly pressing down a piston into the glass tube, which causes the temperature inside the tube to rise quickly due to the compression of air. This rapid compression of the air inside the cylinder causes the temperature to rise, igniting the combustible material. The reason for this phenomenon is that the compression of air inside the hollow cylinder is an adiabatic compression, because the compression is so rapid that there is no time for heat energy to leave or enter the cylinder.

Adiabatic compression is an adiabatic process in which the thermodynamic system never exchanges heat with the outside world, that is, a process in which dQ =0. According to the first law of thermodynamics, in an adiabatic process, the work done externally by the system is equal to the reduction in internal energy. According to the second law of thermodynamics, in a reversible adiabatic process, the entropy of the system does not change. Simply put, from the energy point of view, there is no heat transfer between the adiabatic container and the outside world, and the compressed volume is to do work on the gas, so the increase in gas energy is the increase in internal energy, then the temperature must rise.