So specifically I’m interested in gas vs diesel, but I would love to learn further about the specific property that determines this. It’s obvious that an explosion occurs when pressure builds up, and when gas ignites, it propels outwards and expands, but why isn’t diesel like that? Why isn’t every flammable gas explosive in nature?
In: Chemistry
All fuels are potentially explosive if you put enough vapor in a small enough chamber. The question is whether the vapors are warm enough to ignite. Gasoline has a flash point of -40C/-40F. This means as long as gasoline is above -40C/-40F it’ll ignite if you have an ignition source. Hell, if you have gasoline vapors and an ignition source in close proximity you can probably get it going by accident. Diesel on the the other hand has a flash point of >52C/125F. This means diesel vapors won’t ignite until they’re over that temperature. Try lighting a cup of room temperature diesel with a lighter. It won’t work.
In the case of an engine this temperature requirement is easily met by the cylinder itself which is why diesel is still capable of being used in an engine. In open air? You won’t get temperatures that high so trying to ignite the vapors won’t actually work. Gasoline? It’s heavier than air and probably above its flash point so it’ll pool around the floor and then ignite if you even look at it funny.
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