Hi,

I can understand the frustration you must be having. I am not sure I can help you, but I do own 2 111 Triple Fuel stoves, and one of them is new, unused.

Neither 111s have any holes on the tube leading down to the jet--the tube over which the domes are placed. The used one (I do not plan to light the unused one) so far gave me only one occasion of underburning

I prime it normally with alcohol, and sometimes I can light it from above the dome even while the priming flame is still on, and it will ignite and operate normally. I experienced only one occasion of underburning so far. Maybe I have been lucky: underburning has been an extreme rarity.

I doubt, however, that the burner tube lacking extra holes causes underburning.

My new, unused 111 has a silver colored outer dome, and it appears to have been made with a few corners cut--suggesting of the later manufacture. Its burner body is made of copper, and the outer dome did not make the full contact with the bottom as it arrived. The rough manufacture left the portion of the burner body raised up, when the stamping machine pushed the "fitting lips" out. It had at least 2 mm of gap between the lower enge of the outer cap and the burner body.

I can only guess one possibility for underburning: if the outer cap is not making the full contact with the burner body, due to the irregularity of the "fitting lips," flame may be introduced back into the underside of the outer cap through the gap under the lower edge. This might ignite the air fuel mixture and cause underburning.

Does your outer cap sit squarely on the burner body and create no gap between its lower edge and the burner body? My unused 111 wobbled quite a bit on the fulcrum of the "fitting lips." I could see the sign of rough manufacture at the fitting lips' insufficient angle to allow the flange of the outer cap to seat squarely on the burner body.

I can imagine that, if I ever decide to fire up the new one, this condition may cause underburning. So this is what I did. By placing a flathead screw driver around the raised edge of the fitting lip, I gently tapped the screwdriver's handle with a small hammer carefully. This flattened the rough cut, and helped the outer cap make a better contact with the burner body.

As for the material of the 111s--as a reference--the used 111's outer cap is made of brass, and the burner body is also of brass. The cap makes the full and even contact at the bottom, unlike that of the new, unused 111's.

Both stoves have inner domes of the same design and dimension: three groups of three holes, of the same diameter and height. Maybe you could block the holes by packing aluminium foil underside of the inner cap and fire up the stove: this should show what the holes were designed to do.

I have checked the dimension of the underside of the two burners, and I could not see much difference at all: the gap between the top of the jet to the lower lip of the tube are almost the same.

I hope you would find the cause of underburning.

Hi Ross,

Have you tried your Loke in the wild yet? I just found one new(!) in a camping equipment shop in New Zealand - absolutely irresistable.

The globetrotter is a classic, like my primus 2241 and 2243 (You can still get the gas for the Primus though)

Rik

Frustrated Yes I know what you are talking about.
I worked on a burner for about 3 days trying to work out what the problem was.
The nearest things I pin pointed it to be was.
1) The distance between the inner and outer spreaders.
2) The hight of the tube in the center of the burner in relation with distance away from the jet.
I believe underburn is caused from one or the two of these.
I have never been able to get back onto this problem.
I posted my findings and what I tried, at this site going back about 6 monthes ago or more.
I also have inner burner rings that has the 3 sets of 3 holes in it, and it gives no problems at all, but when I try them on a perticular burner it will under burn each time. Also it does not matter if this ring has the holes in it or not on this burner it always under burns. Unless I light from the outer burner ring after the preheat meto has gone out.
Best of luck with this
Albert

I've taken to always lighting the silents at the outer burner dome after burn-off of the spirit. This is easy with an adjustable, but with a standard silent you do get a little puff of vapor between the pumping and the ignition, unless you have three hands helping. But love that kero smell anyway.
This solves the underburning problem, and another as well: on some silents it's just plain hard to get ignition with the preheat meths, quite aside from the underburning issue. More distance from the point of ignition than with a roarer, by quite a margin.

As I understand the Valor patent, the holes in the inner cap are to allow recirculation of the products of combustion back through the holes in the vertical bunsen tube behind the flame front to extinguish underburning if it starts. In fact I have a silent burner which shows this behaviour - it will spontaneously recover from underburning...

If the inner cap is not properly seated in a silent, the flames on that side of the outer cap may stand out from the cap - presumably because the additional constriction increases the flow speed. Maybe packing under the inner cap with foil might raise the flow rate and suppress underburning.

Thanks to b2m, Albert, Ed and Murray!

I've read your advices and done another experiment, using tin foil inside and around the inner cap.
Well, initially it started out quite nicely, and I got the impression that the vapour ignited slightly further out from the holes in the outer cap. Good, I thought! This means that the foil has reduced the volume between the caps. But alas, after 2-3 minutes with proper behaviour, where I also was able to reduce and increase the flame, the roar was suddenly there...

I pumped it well, primed it well and was sure to light it from above (after the priming flame had gone out). Oh yes, throughtout it all, I've used kero... I've never tried it with white gas.
There was no wind, and no external reasons for it to suddenly start underburn. The only reason I can think of might be the temperature of the burner assy. Both the outer and the inner caps are firmly seated onto the burner "floor". The only difference cap-wise between this burner and my "good one" is that where the cap of the good is screwed onto the floor with 2 small screws, the cap of the bad is seated in a way of a "bayonet lock" in which the 2 lips go into a fitting slot; a hole through the burner floor. Could there be a leak of flame back into the chamber between the caps through these?
From what b2m states in his post it seem that our 111Ts are quite similar. The fact that he has an unused burner with this setup inclines that my stove not necessarily is (as I feared) an odd collection of parts from various stoves that a soldier from the Norw. Defence has remantled at random (in other words: the 3x3 holes in the inner cap are supposed to be there...).
I've previously read the reports from Alberts experiments, with emphasis on the tube. I've got the impression that my tube is at a slight angle to the rest of the burner, and hence the jet, as well as there is a slight difference in length compared to my good burner.

In a couple of days I'll get back to my stoves, and will try some more experiments...
I'm willing to try all "non-destructive" actions before I get the drill and do the Valour trick...!

Regards
Eivind

As far as I understand it, flame should be confined to the outside of the cap by a combination of the speed of the gas/air mixture through the perforations in the outer cap being faster than the flame speed and possibly the perforations being smaller than the extinction diameter so that a flame front moving upstream is cooled by the lower temperature cap.
I have seen underburning caused by an ill-fitting cap where gas issuing under the outer cap ignited and flashed back, so flame leaking back under the cap at the bayonet fitting seems a possibility if the diameter of the cap is slightly too large.
The other possibility seems to me to be what Albert mentioned - the height of the Bunsen tube above the jet which I think determines the amount of pre-mixed air. Maybe if the mixture is too lean it might start to burn under the cap as the temperature of the burner rose, which sounds like what you are seeing, so maybe extending the length of the tube with a liner would make a difference. Underburning sometimes starts with a loud pop which might be due to the vapor/air mixture exploding when it reaches a high enough temperature. You've already eliminated a faulty jet that could spray vapour outside of the tube where it could ignite- which I guess is what happens in a breeze.
I don't understand the influence of the spacing between the caps at all - steady state flow should give the same speed of flow through the perforations regardless - unless the effect is somehow related to recirculation between the caps.

I've been following this thread and have finally got around to having alook at the only two silent burners that I own. They are both on the same stove but they are not the same. The stove is an Optimus 155 Marine stove which has had a good deal of use over the years under canvas both in sail and tent. Presumably one of these burners is the original fitting ie No. 207 & the other the replacement burner introduced for these stoves, the No. 9007. I know one is a replacement as I can remember Peter Benscher at City Hardware telling me so when I bought it about 12 years ago, but I can't, for the life in me, remember which is which (Anybody out there know?) However that doesn't really matter at this time.
I took the outer and inner caps off both burners and looked to see if either, neither or both had the holes in the tube wall and one does and one doesn't. Up to press neither burner has been especially prone to U/B-ing but both have done so at one time or another. I might add at this point that I generally preheat with spirit in the burner pans rather than use the quicklighters (Instruments of the Devil) which are both temperamental, and brutal gobblers of pressure, especially if you want to light both burners at the same time. Experience has taught me, like others, to let the spirit burn out then light the burner from above. Looking at the burner without the holes in the tube, I reckoned that if what Ed W. said about U/B occurring between inner and outer domes is right, then why not take the inner dome away. On the face of things, without holes in the tube the inner dome appears to serve no useful purpose - with only the holes in the top of it and no other designed holes it would seem that vapour would either bypass the inner dome altogether or go in through the top holes & out under its lower edge. I couldn't see any good reason for it being there so I took it out, replaced the outer dome, flashed-up the burner and it ran sweet as a nut for twenty minutes until I got fed-up of watching it.
When I tried the same thing with the other burner (the one with 4 holes in tube wall) it didn't like it at all and burned very badly with little blue flame and an unsteady, flaring & unpleasant-looking yellow/white flame
Out of curiosity I tried to make the well behaved sans inner dome burner U/B by:
a) lifting the edge of the outer dome whilst burner running - this caused U/B but it stopped as soon as I let the dome sit properly again,
b) introducing a flame ( a match in a pair of pliers) into the lower end of the tube, just above the nipple - this caused U/B but it seemed reluctant to get started although when it did the burner had to be shut off. I did this a couple of times to make sure it wasn't a fluke.
In conclusion, if you haven't already tried it without the inner dome, give it a go, and if it doesn't help, well, puzzle on. (Different burner? Different stove?!)


Both burners with both domes running normally.


Burner(L) no holes in tube


Burner(R) with holes in tube


Burner(L) no holes & no inner dome


Burner(R) with holes & no inner dome

And Yes, I know the stove needs cleaning!



Ian

The 207 has the conventional brazed tubes, the 9007 looks like it is machined from a single block.

The 207 I have has holes, the 9007 I can't check at the moment. Interesting result...

HI.

Just a thought.

I was thinking about the underburning problem while I was fiddlign with a kero coil stove.

I do remember that at least for myself. Underburning occurs most often (90+% of the time) with dense fuels such as kero, deisel, lamp oil, heating oil e.t.c. are utilized.

I've seen it on Optuimus 99 hunters (8r clones) utilizing gassoline. However that was when the valve was 99% shut. Which is understandable.

I agree that there has never been a 100% solution to the underburning problem. Perhaps a multiple stream (smaller hole) jet.

However that's another story best left for another thread.

yt

Northernflame

Thank you all who have been responding to my questions regarding my underburning problem!

I have all the time assumed that "the good" and "the bad" burners were of the same type (except for the tube holes), but it appears that they differ a bit when it comes to tube length and jet - tube distance.

The measurements are:
The tube length of my good one is 2.9cm, whereas the bad one measures 2.6.
The distance from the jet to the bottom of the tube: Good one: 0.9cm, bad one: 0.4cm.
The distance from the tube top to the seat of the inner dome is 0.95cm for the good and 0.9 for the bad burner.

Well, the metrics tell me that extending the tube (on my bad burner) down towards the jet, to get a richer mixture and thus reduce the possibility for underburning, is not a way to go... Sad really, I think Murray's reasoning on this is sound and might very well lead to a cure.

I also tried to fire my stove without the inner dome as Ian suggested, but except for the flames seeming less controlled, the underburning started as early as with my previous attempts...

Not leaving a stone unturned I tried changing the jet again to a new multifuel jet from a new Optimus repair kit, but with the same result. I even tried the alcohol jet... Shouldn't have... Messy bonfire, even though the burner was well primed...

I've so far only used kerosene on my stoves, but now I decided to try Northernflame's hint. I went to the local gas station, bought a 4-litre can of Statoil Miljøbensin (equivalent of "White gas" I'm told), and this time I had some results!
Not only did the flame keep blue and outside the outer dome as it should. After about 10mins of proper operation I forced it to underburn by reducing the flames a lot. This time it was actually possible to reverse it to normal burning by letting it cool for some seconds.
So far so good! I now know that my "bad" stove is willing to perform provided it gets the right fuel...

However, a stove designed for kerosene to underburn is still a faulty stove. As the stove burned merrily with white gas I made one more observation that can give a clue to the cause:
My other silents burn with a uniform blue flame all around the dome, but this had a part (20-30%) of the dome where the flames were uneasy and flickering, whereas the rest burnt well.
The tube as I think i've mentioned before has a slight, hardly noticable angle compared to the jet and the dome.
The area with improper flames coinside with the side that the tube is tilting "away from"... The tube is also sticking slightly higher up from the inner dome on this side, than on the other.

I think that if I managed to tilt the tube back to centre and grind the tube/dome level difference away, it might possibly work with kerosine as well.

Regards
Eivind

I took a couple of pictures of the burners, but as I'm currently using a Linux-machine, I'm not sure how to upload them. They'll come later.

I don't think I could have lasted top side of six weeks without resorting to the drill. 10/10 for dogged determination, Eivind. If, as Murray states, the holes in the tube work towards killing u/b as soon as it starts and, as I stated, there doesn't seem to be any need for the inner dome unless there are holes in the tube, I'd be looking to make a sleeve which would fit nice and tight (possibly a shrink fit) on the top end of the burner tube, then put it (the sleeve) to one side for possible later use. The I'd get to work with the drill, starting with small holes (you can always make them bigger, but it's hard to make them smaller) and see how the burner performs. If it seems necessary enlarge the holes. It may solve the problem. It may not. but if it doesn't you can fit the sleeve which you previously prepared & you are back to square one again. I should try and straighten-up the tube first as it may be a factor in all this - who knows?

Ian

Howdy,
I cleaned and started the Primus #5 that arrive today. It has a silent burner. The behavior of the stove got me thinking.

When it is pumped up beyond light pressure, the burner begins to produce the unburned gas escaping from under. Apparently, the burner is not able to burn all the kerosene vapor coming out of the jet. It may have to do with the design of the burner caps, I am not sure.

When Primus #5 is pumped up beyond the light-medium pressure while it is burning blue, then, underburning takes place. I can see that the excess gas is not able to go through the tube, and is finding its way around the burner dish.

I have Buflam #2 that produces half blue and half yellow flame. I can pump this one up till my arm falls off, and it will not underburn: it just burns half and half. Its burner can process all the vapor though the tube. Interesting that each stove has its quirks and personality.

I have a question: when your 111 underburned, did you pump up the fuel tank lightly or high? Your 111 might be having trouble processing all the vapor through the burner tube.

Although my workig 111T does not underburn, it cannot produce blue flame with kerosene. It does extremely well with white gas, however. I haven't tried with alcohol, for I do not see why I should use alcohol in 111T. It is supposed to be triple-fuel capable, but not at the moment.

Maybe some one could throw in a clue: does 111T need a separate jet for kerosene, or is it designed to use the same jet for both white gas and kerosene?

Your last question first: To my knowledge there are only 2 jets for the 111T; the M-jet (multifuel; white gas and kerosene) and the A-jet (alcohol). In my recently aquired 111 spare set these jets are stamped with those letters. On the jets that came on my stoves by the way, there are no such letter markings, but by the look of it, they are very similar to the M-jet in size.

I'm pretty sure that my 111 manages to process all the vapour through the tube and burner dome. The reason for that is that when I tried the A-jet I could see no unburned vapour escaping from under the tube. All went through the burner dome, producing a very high flame with only hints of blue in the bottom.

When it comes to pumping I believe that for all my tests I pumped the tank to a "good pressure", as I assumed that a lower tank pressure would make it easier for the flame front to migrate back through the holes in the burner dome...

Alcohol? I agree with you, haven't tried it as I never saw the point. Kerosene is cheaper and gives a higher BTU as far as I know...

The behaviour of your Primus #5 is strange. Does the burner tube stick up higher than the inner dome, possible leading to the restriction, or is it on the same level?

Regards
Eivind

Eivind I went all though this proceder about 1 year ago. I posted my findings here as well.
From what I can recall, I found the main problem to be the clearence between the inner and outer spreaders (or rings).
I also noted a differance between the hight of the burner tube. I also bent the tube to lign up the jet in center of the tube.
My good stove when working I could not make it under burn by lighting it at the jet. Where as with the bad stove it would under burn from this point readerly.
I spent 3 or more days on this and had to get onto my work load building up on me.
Good luck with this If I can help please contact me off this site.
Albert

I thought one jet was supposed to take care of both white gas and kerosene. Too bad my 111 is not doing well with kero.

As for #5, the tube portion that rises above the top of the inner cap is not significant. I guess I will just live with it. It still boils, but slowly...

However, I installed #5's inner cap on Buflam #2, and surprise! Buflam now burns pretty blue. Now I know why Buflam is not burning blue: it needs an orthocentric cap.

Buflam's inner cap has the center hole punched somewhat off center, so that one half is too narrow, while the other half is wide enough (Albert previously observed on the gap between the caps). That apparently explains the incomplete combustion on the unfortunate side of the flame half. Buflam's own inner cap is too small for Primus, so it could not be put on Primus for comparison.

After this, I noticed that Buflam's burner tube rose above the height of the inner cap by about 3mm. I thought it could afford lower height, so I filed down 1mm. There was no improvement on the flame, so I left it as is.

White gas? Now I'm completely baffled. Does anyone have any plausible explanation of Northernflame's observation that underburning occurs most often with denser fuels?