Non consistent simmering problem

Discussion in 'Stove Forum' started by okerol, Mar 30, 2023.

  1. okerol Turkey

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    Hi Everyone,
    I'm wondering why a liquid fuel stove (BRS12 or BRS12A) running exceptionally well on full throttle, runs inconsistently when simmering.
    The tank pressure is around 50 PSI, the stove is preheated well. When I lower the BTU output, the flame either roars blue for a while then slows down to yellow and sometimes extinguishes and cathes fire again then roars again with blue flames. When I open the valve, the stove roars consistent and throws a considerable amount of blue flames. I am sure this is not because of liquid fuel spray from the jet otherwise there would be a flare up. This is simply due to the lack of gasoline vapor pression to withdraw enough oxygen (Bernouilli principle).
    The generator is made of steel. In the generator tube there is 2mm diameter wire similar to bicycle brake inner wire. It starts from the valve orifice and elongates past the 90 degrees downturn.
    I don't have any idea of the mechanics of this strange phenomenon. I expect that less fuel would result less BTU but this oscillation is not something that I want.
     
  2. itchy

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    What you describe is relatively common for camp stoves where there is a single valve between the fuel tank and the generator. There are good safety reasons why the valve it there instead of between the generator and the burner, but you probably know that. Most liquid fuel stoves known for being good at simmering have a shut off valve at the fuel tank and a valve for regulating the flame between the generator and the burner -- or they somehow accomplish both in another manner (eg. some Coleman stoves).

    There has been a fair amount of discussion over the years about this, and similar stuff, and there are probably several factors at play.

    Someone probably has some better ideas, or can explain it much better, but here is how I see it -- and it is not an original idea on my part. In your stove, the rate of flow of fuel into the generator is going to be dependent on pressure in the tank, how "open" the valve is, AND, importantly, back pressure from the vapor in the generator in your stove. At full blast, the vapor pressure within the generator will likely limit how much raw fuel flows into the generator and on to the burner. But for lower outputs it becomes "touchy" to get just the right amount of fuel since the vapor pressure within the generator will vary somewhat -- as the amount of fuel first decreases pressure may first drop, but this in turn will cause an increase in raw fuel which first absorbs heat, cooling the generator, perhaps with another drop in pressure but then it vaporizes the pressure will rise again and that dampens fuel flow momentarily, in the mean time the temperature of the generator has probably gone down and up again, and the cycle repeats (perhaps). All this up and down nonsense makes it difficult to get just the right setting when you first turn down the flame. When there is a valve between the generator and the burner there will be less disruptive feedback since the vapor pressure within the generator can remain high and constant.

    Keep experimenting as you are doing, but it is my experience that simmering on camp stoves requires a fair amount of attention and fiddling. I'll turn the burner down but then watch it closely and adjust it back up a bit after some time -- still, best to just keep checking it.
     
  3. Jim Lukowski United States

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    I don't have a BRS stove, but 50 PSI seems excessive for one. Have you tried to see how it behaves with lower pressure, like half of that?
     
  4. okerol Turkey

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    I would like to thank you first. Your detailed explanations as well as your suggestions have raised an idea that may well be a possible cause for that.
    Firstly let me answer the shortest one: Yes, beforehand I was using the orignal pump and 10 or 15 strokes were sufficent to start running however the problem was there. I have converted my stove to be pressurized with a bicycle pump and I have tried pressures up to 70 PSI or more. The pressure release valve has never opened. But I don't give it as advice since it is risky. I know that disposable butane canister's pressures are that much and their walls are thinner therefore I have tried to pressure my tank without fuel first.
    The long answer is that when I open the throttle fully, the tank itself may behave like a condensator in an electronic circuit. The high volume may regulate the pressure inside the generator. However when I shut down the valve for simmering, this time the pressure has no way to escape other than the jet and the valve. When two valves are used (like some early Coleman's) you fully open the valve near the tank which "connects that capacitor" enabling the pressure regulation and adjust the flame strength with the second one. Since according to "Ohm's law in electric engineering", stable pressure at the input port of the second valve will result in a steady gas flow.
    Once the problem has been understood, the remedal action is nothing but a procedure. Thank you again :) I will only look for two valve designs so far.
     
  5. okerol Turkey

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    You can also check my topic "BRS12A" that explains my R&D steps and suggestions. These may trigger an idea that may serve you, I hope.