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I'm troubleshooting a problem with a brand-new propane gas grill that is experiencing flameouts and making puffing/popping sounds. I'm asking here because I want to understand the basic chemistry that would cause this problem.

The problem is demonstrated in this video.

I've already been through all the expected troubleshooting steps:

  • Replaced the gas regulator
  • Replaced the burner
  • Tried three different propane tanks

The grill was purchased about 3 weeks ago. The valve/regulator assembly was replaced last week, and the burner was replaced yesterday, so both parts are essentially new and unused.

It's hard to tell from the video if the puff causes the flameout or the flameout occurs first, followed by accumulation and detonation of a small amount of unburned propane.

I would like to understand the chemistry principles that govern the combustion of propane in a grill, and what design flaw(s) could cause this behavior.

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  • $\begingroup$ Very important question about that video: Did you intentionally adjust the color balance in any way? $\endgroup$ – Lighthart May 13 '16 at 16:45
  • $\begingroup$ No. It's from an iPhone 4s camera and color was not adjusted. On my photography-calibrated monitor it looks like a faithful representation of what I saw. $\endgroup$ – Jim Garrison May 13 '16 at 17:07
  • $\begingroup$ It seems to me that the flame is more green than it normally should be. $\endgroup$ – Ivan Neretin May 13 '16 at 18:08
  • $\begingroup$ I would blame that on bad grill design, since you replaced critical parts and the problem persists. It seems like incomplete propane burning. Unburned gas accumulates below the top lid and when a fresh air blow comes it ignites. The unburned gas might also be accumulating below the lid to a point when it finally "overflows", reaches the air around the grill and sputters. You should perhaps consider getting your money back to purchase another grill model. $\endgroup$ – Carlos Gouveia Jun 12 '16 at 18:39
  • $\begingroup$ Does this behave in the same manner whether the flame is at it's highest or lowest settings? $\endgroup$ – airhuff Mar 9 '17 at 22:14
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The brilliance of the orange in flares suggests suggests incomplete combustion of a carbon residue. This can happen with a poor oxygen mix, but the blue in the core of the flame indicates that mix is fine.

Also, on the base of the grill there is some charred residue.

Based on the color, and the residues I expect somewhere in the flow you have some carbon deposits that are occasionally getting dislodged, causing the sputtering.

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  • $\begingroup$ This would be a possibility, but the grill is brand new (used 4 times) and the valve/regulator and burner have respectively 2 and 0 total usage counts. There is no possibility of carbon deposits anywhere in the gas system. I'll update the question. $\endgroup$ – Jim Garrison May 13 '16 at 17:30
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This looks to me like there was a piece of something (plastic film, maybe?) loosely pinned inside the propane feed line, that periodically would flap over and block the flow of gas to the burner.

Reasoning:

  • The simultaneous disappearance of the flames across the entire width of the burner implies a total cutoff of upstream feed pressure.

  • The relatively sharp and short aspect of the noise accompanying each flameout supports the supposition of a mechanical blockage upstream, and the "PHWAFFPH" character of the sound implies a soft material (no metallic clank or ping) and is quite reminiscent of an empty plastic grocery bag catching a stiff wind.

  • The irregular and very long (fluid mechanically speaking) time interval between instances of the flameout is strongly suggestive of some sort of discrete interruption of the gas flow, rather than an oscillatory flow disruption downstream of a static constriction.

  • The reduced severity of the problem at lower gas flow rates is consistent with this hypothesis, since a lower gas flow rate would result in a lower pressure drop at the flap as it starts to occlude the flow, and thus less of a driving force for pushing the flap fully across the feed line.

  • Recovery of the gas flow after only a brief flameout is also consistent with a flexible material causing the blockage, since a stiff material would probably not be able to rebound after closing off the flow, but instead be held in place by the pressure coming from the gas cylinder.

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  • $\begingroup$ Interesting deduction chain but (1) everything in the pipeline from cylinder to burner was replaced with no change, and (2) the same cylinder on a new grill of a different brand exhibited no problems. I still favor a design problem. $\endgroup$ – Jim Garrison Mar 12 '17 at 5:20
  • $\begingroup$ @JimGarrison Everything, including the length of line between the regulator and the burner? $\endgroup$ – hBy2Py Mar 12 '17 at 11:31
  • $\begingroup$ Yes, absolutely everything. $\endgroup$ – Jim Garrison Mar 12 '17 at 14:54
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    $\begingroup$ @JimGarrison Well then. What were you thinking, going and buying a possessed grill?! $\endgroup$ – hBy2Py Mar 12 '17 at 22:56
  • $\begingroup$ @JimGarrison What about the gas flow control valve/knob, was it replaced too? $\endgroup$ – hBy2Py Mar 13 '17 at 3:57

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