Why fire doesn't burn back to gas tank (stove and welding)

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Discussion Overview

The discussion centers around the question of why fire does not propagate back to a gas tank in scenarios involving natural gas stoves and potentially welding applications. Participants explore the conditions under which flames interact with gas streams and the physical principles involved.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the coherence of the initial post, asking for clarification on the type of tank and the relevance of gasoline to welding.
  • Another participant specifies that the discussion pertains to natural gas stoves and suggests that the absence of oxygen in the gas tank may prevent the fire from burning back.
  • A later reply explains that in a Bunsen burner, the flame remains at the top of the tube due to flame speed, which is slower in certain conditions, and that if the gas flow is too low, the flame can indeed travel down the tube.
  • Another participant adds that in a tank, the air above the fuel is saturated with fuel vapor, which may inhibit flame propagation, noting that flames cannot proceed if the temperature is lowered through certain materials.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms preventing flame propagation, with some agreeing on the role of oxygen and flame speed, while others introduce additional factors like fuel vapor saturation. The discussion remains unresolved with multiple competing explanations.

Contextual Notes

Participants mention specific conditions such as flame speed and the saturation of air with fuel vapor, but do not fully resolve the implications of these factors on flame propagation.

lemd
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Hi,

Why the fire doesn't burn back to gas tank as there is a continuous stream of fuel from the fire to fuel tank?

Thanks
 
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I find your post incoherent. Can you be a lot more specific in what you are talking about. What KIND of tank and what does gasoline have to do with welding? Why is there an open stream of fuel? What are you talking about? Be specific. Be descriptive.
 
Thanks,

I am just curious about normal natural gas stove, as there is a countinous stream of natural gas from the tank to the stove, and there is fire, why doesn't the fire burn back through that fuel stream into the gas tank? Is it because there is no oxygen in the tank?
 
Correct. There is no oxygen in the pipes.

However it's worth looking at a Bunsen burner. The gas and air combine at the bottom just above the jet but the flame is normally at the top of the tube. So in this case there is a short length of tube with both gas and air in it. So why doesn't the flame shoot down the burner tube to the jet? I believe this is down to the flame speed. If you have a long thin length of flammable material a flame will normally propagate along it at a certain speed called the flame speed. The flame speed is quite low for a natural gas in a Bunsen Burner tube (it's much slower in a regular wax candle and much higher in something like Detonating cord!). If the material is also moving at the same speed as the flame the flame appears stationary. So in the case of the Bunsen burner if you turn the gas flow rate down too low (eg below the flame speed) the flame can indeed burn down the tube to the jet.
 
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In a tank, the air above the fuel is saturated with fuel vapour. A flame may not be propagated in fuel saturated air. This is the situation with gasoline, too rich or too lean and it will not ignite.

If the temperature of the flame is lowered such as when passing through a metal gauze or say steel or copper wool, then the flame cannot proceed.
 
Many thanks for the clarifications
 

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