Can you introduce the principle of oxygen index test in detail?

When a material is combusted, the oxygen concentration required for its combustion is an important parameter. The oxygen index test is one of the test methods used to evaluate the combustion performance of materials, which measures the minimum oxygen concentration for materials to burn in a mixture of oxygen and nitrogen. The following is the principle of the oxygen index test.

In the oxygen index test, the sample is placed in a vertical combustion chamber with a burner underneath. A burner ignites the lower end of the sample, and then injects a mixture of oxygen and nitrogen of varying concentrations into the combustion chamber. Testers record how samples burn at each concentration of the mixture to determine the minimum concentration of oxygen required for the material to burn. This minimum oxygen concentration is called the oxygen index.

The higher the oxygen index, the higher the oxygen concentration required for the material to burn and therefore the better its combustion performance. For example, a material with an oxygen index of 60% requires a higher concentration of oxygen than a material with an oxygen index of 30%, and therefore burns better.

The principle of the oxygen index test is based on the fact that oxygen is an essential gas in the combustion process. Combustion of materials requires oxygen and fuel (eg wood, plastic, etc.). If the oxygen concentration falls below a certain threshold, combustion cannot continue because the fuel cannot be fully oxidized. Therefore, the oxygen index test is a method of evaluating the combustion performance of a material by measuring the minimum oxygen concentration required by it.