system
Given the following post, respond as if you're commenting on Reddit:
human
Can flammable liquids/gases just "combust" in high temperature environments or do they require a spark or some sort of ignition/catalyst?

We touched on the combustion of organic molecules in my org chem class and I was just curious if a flammable substance is placed in a controlled environment and the temperature increases, will it eventually just ignite?
What would happen to initiate this on the molecular level (like is there a mechanism)?
gpt
A diesel engine operates by this principle. A fuel-air mixture is compressed until its temperature and pressure become great enough for it to ignite. What happens on a molecular level is that in order for any reaction to proceed, there is a certain energy barrier that must be overcome, and once the temperature is high enough, the molecules have enough kinetic energy to overcome that barrier.