Which of the following is NOT one of the four fundamentals of combustion?

In the context of combustion, the four fundamentals are typically considered to be fuel, oxygen, heat, and the correct mixture of these elements. Temperature, as an essential component, is crucial because it relates to how heat influences the combustion process. The mixture refers to the appropriate ratio of fuel to air (oxygen), which is necessary for efficient combustion. Time is also a significant factor because combustion does not occur instantaneously; there needs to be sufficient time for the chemical reaction to take place.

Pressure, on the other hand, is not commonly listed as one of the four fundamentals of combustion. While pressure can influence burning, especially in specific systems like engines or gas turbines, it is not classified alongside the basic requirements needed for combustion to occur. In standard combustion processes, the essential elements focus more on chemical interaction rather than mechanical influences like pressure. Thus, identifying pressure as something that is NOT one of the four fundamentals is correct, as it does not represent a fundamental necessity like the others do.