Reverse flame?

[Michael Moroney]

Let's say I have a sealed but vented chamber filled with natural gas or propane
or something (no air/oxygen in it). Also in the chamber is a Bunsen burner.
I connect the Bunsen burner to a tank of oxygen or air. At the same time I
turn on the oxygen/air I start an electric spark at the burner so oxygen doesn't
build up and cause an explosion.

Do I get a flame? It will be oxygen "burning" in an atmosphere of methane or
propane. Would such a flame be normal or unusual/strange in some way?

Also assume methane/propane is resupplied in excess and pressure relieved
so ignore build up of combustion products.

[Libor Striz]

It was a favourite experiment of my high school teacher of
inorganic chemistry.
It was not a burner, just a simple tube.

Burner may need adjustment due different gas ratio and viscosity.

The flame may need to compare side by side to tell the difference.

I do not remember anymore, perhaps there was different/reversed
flame zoning.

[Martin Brown]

Post by Michael Moroney
Let's say I have a sealed but vented chamber filled with natural gas or propane
or something (no air/oxygen in it). Also in the chamber is a Bunsen burner.
I connect the Bunsen burner to a tank of oxygen or air. At the same time I
turn on the oxygen/air I start an electric spark at the burner so oxygen doesn't
build up and cause an explosion.
Do I get a flame? It will be oxygen "burning" in an atmosphere of methane or
propane. Would such a flame be normal or unusual/strange in some way?

Inside out when compared to a flame of propane burning in air.
Where the oxygen rich part is at the fringes of the flame.

A Bunsen burner when placed in a propane atmosphere and supplied with
air via the tube would be the most entertaining demo.

Post by Michael Moroney
Also assume methane/propane is resupplied in excess and pressure relieved
so ignore build up of combustion products.

A variant of this was typically done as a school or university open day
demo with a long fairly wide glass pipe filled with natural gas and when
full of gas lit at the far end to consume the excess. Then so long as
the gas flows continuously you then have your pure gas reducing
atmosphere and a pipe fed with compressed air can be introduced and lit.

I have never seen it done with a Bunsen burner which would be more fun
because then you could vary the fuel air mix.

The finale was to switch off the gas supply and leave both ends open
until the mix reaches an explosive critical point and the by then blue
flame runs back down the tube making a tremendous howling noise. On a
bad day it can explode showering the room with glass.

A bit like the NO and CS2 howling demon flash trick.

Diffusion limited fires in microgravity are also unexpectedly
interesting in their complex behaviour with no easy way for the hot air
reaction products to move away from the flame without gravity to help.

https://www.smithsonianmag.com/science-nature/zero-g-fire-pulses-jellyfish-space-station-180952454/