British Military No.12 burner woes

Rather than transferring that design to thicker stock, I thought I'd try another approach, and took one of these spare burner plates from a British Army Military No.3 stove

Burner plates from Mil. No.3

In a thread discussing the complex form of the original No.12 burner plate and the purpose of the small 'legs' on the underside ...

I was inclined to agree with David when I read that, but George (Kerophile) had tried a 'plain' burner plate without such slots ...

Kerophile's experiment

In his post, George said that proper combustion was achieved when the 'plain' plate was raised half to one inch above the burner.

I wondered how would it be to hammer a more pronounced 'dish' in a plain plate and adjust it's height above the jet to be lower.

So, I set to work with a ball-pein hammer and bent and machined the 'legs' of the No.3 burner plate to produce the following result









How did it perform? Well, at full power, combustion was excellent and gloriously noisy!



Part-throttle, it did well too ...



Anxiously, I screwed home the control valve to a simmer ... perfect!



Back to full throttle ...



... and a triumphant tea test!



John

 

Wow! That burner plate is a color I've not seen before - yellow. That is definitely a hot burn. Bravo!


sam

 

Well, I and the stove have had a chance to cool down and a frank appraisal of that burn is called for.

Sam's hit the nail on the head, the burner plate got exceptionally hot - too hot in fact. Spectacular pyrotechnics resulted, but it's the plate and not the bottom of the pot that's taking most of the heat, shielding the base of the pot from the flames, so that boiling a kettle of water was distinctly laboured for such a (potentially) powerful stove.

Though no further evidence was needed, the plate was getting hot enough for the the steel to oxidise, with flakes of oxide peeling off in the blast!

More experimentation is called for, probably by trimming the edge of the plate to make the disc of lesser diameter. Whether that will upset the combustion I don't know.

John

 

Nice work, John! I don't know if you have the specs on the original #12 flame plate, but I'll try to get some measurements and post them here later today in case that might help. I'm enjoying your voyage on this greatly.
Cheers,
Gary

 

Maybe making a copy in stainless steel would be the answer? Just a thought, I've never tried this myself! But the heat output of your stove is flabbertastic!

Regards,

Wim

 

John:

Have you considered drilling a pattern or holes in your new flame spreader, like the original. That would allow the flames to get to the pot bottom, and perhaps cool the flame spreader a bit.

Paul

 

Here's a thought that's just smacked me between the eyes, for this exercise, and generally. The flame is just the visible manifestation of the burn. But when, as we often do, debate effeciency and so on I wonder whether viewing what's happening in the infrared might provide additional infomation, particularly when it comes to amount of heat being transfered to the pot vs being lost up the sides?

Anyone got an IR scope or binos?

Cheers, Graham.

 

Ok. Here're some specs. The round part of the plate is 39.5mm in diameter. It dishes down from the rim 5.5-6mm or so. The punched slots are 2mm x 2mm. If you put the punches on a flat surface and measure from the surface to the bottom of the dish, it's about 1-1.5mm.

Hope this helps.

Cheers,
Gary

 

Thanks Gary, Wim, Paul and Graham for taking an interest in this and for your helpful and thought-provoking suggestions. Infra-red heat output, Graham!!! I'd never thought of that, and it would be fascinating to 'see' the form it takes with a suitable scope. In terms of what was necessary to boil a kettle though, whatever radiation energy was coming out of that burner was distinctly unimpressive in terms of the all-important Kerophile Tea Test!

Apologies, but I got home from work tonight and before cranking up the laptop (and therefore having the benefit of your thoughts), I dived straight into revising the flame plate and this was the outcome ...





On the burner, here was the result at full power. Still excellent combustion but now more visible flame





Part-throttle ...



... and simmer



Back up to full power ...



... and with a kettle of water on board



Didn't take at all long to get a head of steam



I've still got the oxide-flaking phenomenon, but not so pronounced, and will indeed be looking out for a suitable thickness of stainless steel plate, Wim, to craft a copy to that pattern.

I expect a 'pierced' plate (drilled holes or slots) would work, but I elected to cut out those 'scallops' from the circumference of the plate (using the edge of a 6-inch grinding wheel and trimming with a Dremel grindstone) to get some flames to spill out.

John

 

Hi John,

Good progress

Here's my observation comparing the burn pattern to my stove. If taking pics in the dark like yours, with my No.12 using the standard issue flame spreader I would normally see the burner skirt getting to a reasonably bright cherry red on full power, and maintaining a reasonable glow to quite low power. This indicates to me that there is more lateral flame spread than you are currently achieving. Maybe this is something to do with the underside tabs creating some sort of disruption? I think yours is nearly there but on mine I'm more aware of the flames shooting out almost sideways, hitting the skirt and then being diverted upwards. Presumably this also creates an excellent heat feedback for ongoing vapourisation given that this is supposed to be a Diesel powered stove. Hope this helps.

One of the major reasons I rate the No.12 as a practical cooker is that it has a wider flame pattern compared to most stoves and actually, whilst powerful, creates less of a concentrated hot spot problem on the pan resulting in food being less likely to stick.

Cheers, Graham.

 

Thanks Graham for yet more excellent comment, which again I consider is right on the mark. What you say about the vapourisation of diesel is something that had crossed my mind, though for now I'm happy to stick with kero.

I know from our chat at 2009's CCS gathering at Newark that you are a huge fan of the No.12 for what it confers on the 'gourmet' camp and back-yard cook, which I flatter myself to be too!

You'll remember perhaps that my main camp cooker at Newark was a No.12 with a regulated Optimus silent burner grafted on, so I'm entirely in agreement about its qualities, which discounting the burner itself for a moment, I'd cite as:-

- stainless steel construction throughout and non-ferrous metal where it's not stainless, so physically tough and won't degrade by being left outdoors

- excellent windshielding that can nevertheless be dropped flat to allow a large-diameter pan (more often than not a wok in my case) to be accommodated.

- stainless steel, welded tank of a decent capacity, that can take the pressure (and reflected heat from the large-diameter pans!) without popping a seam

- controllability, thanks to the regulating burner as standard

- add the point that Graham's made for the No.12 pattern burner and that's the wide spread of heat on the pan base, which I got to some extent from the silent burner I'd fitted, rather than the roarer burner I'd tried

- arguable this last point (given David Shouksmith and Ross's well-documented experience of trying to unscrew the pump tube) but the removable pump tube is (potentially if you can actually unscrew the thing) a servicing asset, in terms of access to the NRV

Negatives? None really, but one or two issues have cropped up on quality control - Gary (Bernie Dawg) had a fuel pick-up tube to re-weld I recall and Bill (Paramethrol) I think it was, had a burner spring a leak. Oh yeah, the noise! Not a negative for some, but I'm sure Bernie Dawg's on the case to offer a quiet and refined alternative!

Again reminiscing on Newark, I unintentionally put the stove to a really stern test by using a Coleman oven on it in searing (for Britain) ambient temperatures. I'd used the Coleman without incident all week but probably pushed it a bit too far on my last day by inadvertently pressurising the tank too much and getting the oven temp up to canelloni-burning levels (it was a canelloni bake I burnt).

It was too much for the soldering of the pump tube cap arrangement, which sprang a leak and the stove depressurised in a subdued and non-fiery fashion, leaking air and not fuel. In that sense, it was idiot-proof and the idiot in question lived to cook on it another day, with the tube easily re-soldered.

You'll gather I'm a fan of the No.12 stove too, but dismayed by the hefty prices these things have been going for on ebay for some time now. £179 was clocked up on an example just recently, though it looked like a bidding war between two people more than a true reflection of its intrinsic value.

I'll probably back off from tinkering with the burner for a while now, since I've restored it to useable condition.

I've a pot-rest to construct though, since the one I've been using has been borrowed from my other stove, and I think I'll restore a pump knob retaining loop, which seems to have parted company with the stove at some point.

For some the loop is a dubious asset and a hindrance when pumping, but I don't find it so and like to have it because without it the pump shaft tends to stick out a bit (even with the tank depressurised) and get in the way when closing the lid.

John

 

Hey John, Don't give away years. Last year was 2010

 

Doh! Been inhaling too many unburnt paraffin fumes with all this burner plate testing.

John

 

The stove was low on fuel when I took those pics. Three-quarter full now, the tank pressurised just that little bit more ...





Mmm, judging by those spark trails, I guess there's some diesel residue still to be dislodged from those burner tubes!

John

 

I got round to fabricating a pump knob retaining 'loop' in brass. I brazed it in place, the solder originally used just can't take the strain!




The burner got a finishing touch too ...

BD cap

John