If you burn the gas from a gas bottle, why does the flame not propagate into the bottle?

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Is it because of the exit velocity of the gas?

In: Engineering
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The flame needs both oxygen and fuel to burn. The bottle only contains gas (fuel) and the pressurized gas moving outwards prevents air from moving in the bottle and mixing with it. So, the flame only burns outside where the gas mixes with surrounding air.

From what I know it’s because of a valve that sit in the entrance to the bottle . but I may be mistaking.

Bottles are manufactured with safety mechanisms in place to prevent you from going boom. Depending on the bottle size and type, some have a check valve, also referred to as a “back flow preventer” which only allows the gas to flow in one direction and prevents flame from backing its way into the food source. Some smaller bottles simply have an orifice (opening) that’s so narrow it basically eliminates the possibility of flame from chewing its way backwards. All are the same basic principle. Hope that helps.

I think thunderf00t on youtube recently showed this in practice when explaining what happend to spaceX rocket that exploded after it landed.

basically you need 3 things to make something burn: heat, fuel and oxygen in the container you only have fuel and it’s much higher pressure than the air around it so no air can flow in to the bottle since gas always flow from high pressure to low. these bottles also have valves that only let gas out one way and not the other.

if you don’t have a valve though, and only a hole you can only have a controlled flame as long as the gaspressure inside the bottle is higher than outside, but what will happen when enough of the gas has been let out is that air can start flowing in, and let the fire spread to the gas that remains in the bottle creating a burst of flames that can be quite big if the container is big enough