What is always necessary in the combustion process?

In the combustion process, oxygen is always necessary because it is the key element that supports the chemical reaction between the fuel and the oxidizing agent. During combustion, hydrocarbon fuels react with oxygen to produce heat, light, water, and carbon dioxide. Without oxygen, the fuel cannot ignite or sustain a flame, making it an essential component for combustion to occur.

While fuel and thermal energy are also important in the process—fuel provides the substance that burns and thermal energy can help initiate combustion—oxygen is the critical variable that must be present to facilitate the reaction. Carbon dioxide, on the other hand, is a byproduct of combustion, resulting from the reaction but not a requirement for it. Therefore, it is clear that oxygen is the fundamental necessity for the combustion process to take place.