Gas burners

[modeng2000]

I would like any help from folk with gas burner experience please.

What is happening to my burner is much the same as what went wrong with James' burner in the 'Not enough steam' postings. The flame flashes back to the injector after a while and burns under the ceramic.

My first thoughts were that the burner assembly was getting too hot so I made sure that there was air available by making a ring of holes round the outside of the burner to provide cold air into the combustion chamber. This has made no difference, the flame still flashes back to the jet.

I have had my first successful steaming of my De Winton style boiler and was trying to see if the safety valve could cope with the maximum steaming rate and so the burner was full on. Things were looking good when the flash back happened. Even with the burner turned down somewhat, after a while the problem recurred.

These photos show the arrangement.





John

[baggo]

Is it possible you are not running the burner at a high enough gas pressure? If the pressure of the air/gas mixture under the ceramic is too low then the flame may burn back through the holes in the ceramic rather than staying on the top? Maybe a similar thing could be caused by the jet being too small? Just a couple of thoughts.

John

[modeng2000]

That is something that I had not considered John. The gas is butane and the jet size is a No. 8 and the burner is 32mm dia.

Would the flame be more inclined to flash back to the jet if the ceramic became hot right through to the underside instead of just the top surface being hot? The burner starts out performing normally then after something like 10 minutes the problem occurs.

I suppose I could run the burner outside the boiler to see if it might be an overheating problem.

John

[steam4ian]

G'day John

Firing the burner outside the boiler is a good idea, it will show if the problem is at the mixing end. You may want to put a sleeve around it the simulate the firebox.
My bet is on the flue size. At maximum rate there is a lot of hot air to get up the stack and the only thing driving it is the pressure in the firebox, this builds up pressure under the ceramic element and whoosh.
You could lengthen the mixer tube and/or put a screw in the bottom of the burner where the mixer tube enters, this will break up the gas jetstream for better mixing, the screw needs to be capable of being adjusted in and out of the stream. This trick was used on my mothers old cooker/stove when it was converted to natural gas.

Regards,
Ian

[modeng2000]

Hi Ian,

I'll try the things you suggest. A longer mixer tube seams a good idea. I did put a tube round the burner to try to simulate the firebox when I first tried the burner but it was not on for very long, just enough to see that it was burning properly.

Not too sure about the position of the extra screw but I guess creating turbulence in the gas/air mixture is the aim.

John

[ron]

Hi John
It's hard to tell for sure from your photos but I think the gas nozzle in mine is slightly further into the mixing tube at it's optimum setting.
Ron

[modeng2000]

Hi Ron,

I tried setting the nozzle for what seemed the optimum flame condition but it was not at all critical. I'll try to have another play this evening.

John

[modeng2000]

The answer to the blow back problem seems to be ensuring that the gas/air is mixed properly. I made a copper wire coil spring and formed this into a ring that fitted into the space under the ceramic burner. One obvious effect of this mod is that the burner flames are much more even across the ceramic disc.

Try as I might I could not get the flame to flash back to the jet. So it looks like another problem is solved.

John

[steam4ian]

Well done John!

Beats tapping a hole for a screw and if it didn't work just take out the spiral.

Put that in the handy hints book.

Regards,
Ian