The Evolution of a Winter Stove - Part 1
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Maia
(maia) - MLife

Locale: Rocky Mountains
The Evolution of a Winter Stove - Part 1 on 07/03/2013 00:54:27 MDT Print View

Companion forum thread to:

The Evolution of a Winter Stove - Part 1

Stuart R
(Scunnered) - F

Locale: Scotland
Re: The Evolution of a Winter Stove - Part 1 on 07/03/2013 06:53:10 MDT Print View

WOW - that looks like a serious investment in equipment!

I'm sure that you have been thru the same make-a-prototype/test-on-a-trip/refine-prototype cycles that I have, but in different circumstances. The one thing I have deliberately made different is the needle valve position. Why? With a really light stove that does not use the canister as a heatsink, the stove itself can get really hot with extended use. That means any o-ring in the valve can be subjected to high temperatures. Viton can handle fairly high temp, but I did not want to get even close to it's limit. So, I have the needle valve at the canister connector, but not the usual crude needle valve that comes with most remote stoves - one with a much finer thread that is actually designed to control liquid. Even so, a very low simmer is tricky with liquid feed, but there is an easy solution - use the canister upright for simmering! The gas flow is low, so there is very little evaporative cooling and little propane gets used. When more heat is required, invert the canister again. I use a narrow bore fuel tube, so there is very little volume of liquid within it. The other thing I prefer about the valve at the canister is that there is no fumbling under a pot of near boiling contents to make adjustments.

Not claiming that my solution is any better at all, just that different experiences can lead to different conclusions!

Peter S
(prse) - MLife

Locale: Denmark
Exciting on 07/03/2013 07:29:14 MDT Print View

And very interesting. Looking forward to seeing the end result.

Eric Blumensaadt
(Danepacker) - MLife

Locale: Mojave Desert
Still not convinced on 07/03/2013 12:02:45 MDT Print View

I'm still not convinced that using a canister stove in winter - inverted or otherwise - is a good idea.

For now I'll stick with my MSR Dragonfly multi (liquid) fuel stove and TD Sidewinder/Inferno wood stove for winter.

But maybe Roger's ensuing quest will result in a break through design beyond Coleman's engineering.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: The Evolution of a Winter Stove - Part 1 on 07/03/2013 14:51:09 MDT Print View

Great article - love all the details of how things work - looking forward to parts 2 and 3

If the valve isn't right close to the Lindal valve, then you'll lose a lot of fuel whenever you unscrew it. Maybe part 2 or 3 will resolve that.

Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: The Evolution of a Winter Stove - Part 1 on 07/03/2013 14:53:01 MDT Print View

Roger,

You are such a tease, and set up us up for the sequels. You must be reading too many mystery novels. Looking forward to the next installment anyway.

Mike Cecot-Scherer
(mikescherer) - F - M
CO on 07/03/2013 15:25:35 MDT Print View

Hi Roger,

Enjoyed your Part1 of the winter stove quest but have found a rather serious mistake in your referenced carbon monoxide article.

Carbon monoxide in camping stoves is caused by exhaust getting into the intake by recirculation currents. The exhaust is obviously very low in oxygen so it causes incomplete combustion despite the stove manufacturer's lean mixture. I got this information from a Professional Engineer that specialized in forensic reconstruction of combustion events (usually for use in lawsuits). BTW a Professional Engineer in the US is a multi-disiplinary engineer whose passed quite a gauntlet to be certified. He QUITE disagrees with the cold pot quenching theory of CO production.

You can easily test this:
1) put an empty pot on the stove, let it get red hot and see if the CO stops
2) deliberately cause some recirculation with an obstruction and see if the CO goes up

This explanation also appears to be completely consistent with less CO generation with raised pots.

Exhaust recirculation also can be seen to be a factor in hanging stove or lantern CO creation as both types form an exhaust pool at the roof from which some can easily get back down to the intake. It also conjures a nightmare scenario where someone operates a stove in their tent beneath a gas lantern - CO in knock-you-out-and-kill-you doses could be quickly produced.

Best,
Mike Cecot-Scherer

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: The Evolution of a Winter Stove - Part 1 on 07/03/2013 15:31:58 MDT Print View

Hi Jerry

> If the valve isn't right close to the Lindal valve, then you'll lose a lot of fuel
> whenever you unscrew it. Maybe part 2 or 3 will resolve that.
A good point, but ...
First of all, if the hose is much thinner than average, the volume of fuel in it is low.
If you put a filler cord inside the hose to displace some of that fuel, the loss is even less.
And if you think ahead a wee bit, you can turn the stove off at the canister 10 seconds before you are finished, in which case there may be no loss at all. This soon becomes automatic.

Yep, more soon in Parts 2 & 3. Part 2 has already been submitted, and Part 3 is close.

Cheers

Edited by rcaffin on 07/03/2013 16:23:35 MDT.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: The Evolution of a Winter Stove - Part 1 on 07/03/2013 15:43:38 MDT Print View

Hi Stuart

> With a really light stove that does not use the canister as a heatsink, the stove
> itself can get really hot with extended use. That means any o-ring in the valve can
> be subjected to high temperatures. Viton can handle fairly high temp, but I did not
> want to get even close to it's limit.

Safety First!!!

Yes, but just how hot the stove gets does depend on what sort of stove it is and how it is used. Lots of testing needed, and done.

I suspect that if you put several inverted canister stoves next to each other under one vast pot or BBQ plate and ran them for half an hour that way, they might very well get much too hot. I know one such case where the tank on an MSR white gas stove actually blew up, causing severe injury. There were two of them side by side. But this is an unlikely scenario for UL walkers, and is easily avoided.

Under actual field use conditions almost none of my experimental stoves ever got too hot, as far as I can remember. The vortex burner stoves were a bit of an exception: they do get hot and they need to have the O-rings a long way away from the flame. One of those is shown in the second photo, bottom right. It was nice, but hard to make.

Cheers

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: CO on 07/03/2013 16:12:42 MDT Print View

Hi Mike

> Carbon monoxide in camping stoves is caused by exhaust getting into the intake by recirculation currents.
I have to disagree with you here. Carbon monoxide results from incomplete combustion: that's basic chemistry.

For there to be incomplete combustion one of two conditions have to apply: flame quenching or insufficient oxygen. In the case of a small camping stove being run in open air or with adequate ventilation, I find it hard to imagine that 'inadequate oxygen' could apply.

> He QUITE disagrees with the cold pot quenching theory of CO production.
Tough. He needs to learn some basic chemistry.

> I got this information from a Professional Engineer that specialized in forensic
> reconstruction of combustion events (usually for use in lawsuits).
Sigh. Meaningless, and valueless.

My wife was on a jury once in a lawsuit about an injury. Both sides had qualified/certified engineers as technical witnesses. The two engineers testified radically differently: one had calculated that the forces involved were X (within OSHA limits) while the other had calculated that they were about double that (well outside OSHA limits). They could not both be right.

Later on I sat down and did the full analysis myself and I could see what each guy had done, and why one of the QUALIFIED engineers was wrong. 'Experts' have been wrong before.

> You can easily test this:
> 1) put an empty pot on the stove, let it get red hot and see if the CO stops
I have done that test many times, with continuous measurement. Yes, when the cold metal in the flame gets red hot the CO production often drops to ~0. Except when the stove is something like a Reactor, for which there is no hope.

> Exhaust recirculation also can be seen to be a factor in hanging stove or lantern
> CO creation as both types form an exhaust pool at the roof from which some can
> easily get back down to the intake.
Abstract theory, and using a false premise.
Practice is that the hot air circulates, and can be seen to drift out of the tent door. (Steam goes with it - makes a good photo with a flash.) If the tent was sealed and there was no wind at all, then you would have a real danger. But under such conditions who seals a tent up?

Sorry, but your theory does not apply to small camping stoves being used in bad weather.

Yours
Roger Caffin (BSc Hons, MSc, PhD, consultant research scientist)

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: The Evolution of a Winter Stove - Part 1 on 07/03/2013 16:57:02 MDT Print View

I noticed that your hose was much smaller than the other hoses.

I know what you mean about flexibility - my old MSR Whisperlite hose is so stiff it's a little difficult to get the fuel bottle and burner with pot on it postioned properly.

Stephen Parks
(sdparks) - M

Locale: Southwest
Injection molding, etc. on 07/03/2013 17:14:36 MDT Print View

Hi Roger. In case you haven't already become aware of them in the course of your efforts, check out the services offered by protolabs.com. They have two services: firstcut, which is a direct CAD to CNC machining service, and protomold, which uses the same automated programming/machining service to make injection molds that they use to mold your parts. For most applications, they will make the mold from aluminum, but they recently started making stainless molds for higher temp plastics like Ultem and PEEK, which they now offer. They promote their service for lower volume injection molding, say up to 1,000 or 10,000 parts (how big do you think your stove market is?), but if you wear the mold out they will make another at no charge. The prices are reasonable as far as injection molding goes, and the turnaround time is excellent; "parts in one week". They have online tools such as online quotes and mold flow analysis if needed. Having the entire process handled start to finish by one outfit has its advantages. They are in the US, which may not be convenient for you, but you won't have to worry about your IP. You can also request their "Injection Molding for Dummies" booklet, as well as some physical design aids that illustrate best practice and their various finishes. Best,

-Stephen

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Injection molding, etc. on 07/03/2013 18:26:40 MDT Print View

Hi Stephen

Thanks! I will look them up immediately.
(Do you have any connection with them?)

Cheers

Stephen Parks
(sdparks) - M

Locale: Southwest
Re: Re: Injection molding, etc. on 07/03/2013 20:53:14 MDT Print View

I have used them for their rapid machining service several times, but I have never had any injection molded parts made with them. Actually, I haven't had any injection molded parts made from anyone except for some high pressure electrical bulkheads, but that is complicated stuff. Most of the equipment I design does not lend itself toward IM. But I think it would be fun to work on.

One thing protolabs does not do is dimensionally inspect your finished parts. Their rapid machined parts are provided "as is", which is usually within +/-.005". They gave a presentation at my company recently, and it seems like some refinement of the molds is possible if needed, but I don't have any personal experience with that. I can send you some contact info separately if you would like.

Now, given that you have a CNC center on hand that can make small parts efficiently, and given the setup costs for IM (and the fact that you are considering those costs), you must have some very intricate parts or are planning on some significant production volume. I'm very interested to see your future articles!

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Injection molding, etc. on 07/04/2013 00:35:51 MDT Print View

Hi Stephen

I trawled through their web site with great interest. However, I suspect that they won't be able to help me. They make no mention of being able to handle threaded parts, and my design uses quite a few threads.

Technical digression to explain: to extract a threaded part from a mold you have to actually unscrew the bit forming the thread. This applies especially to female threads, and there are at least four of those. That's complex, both for the mold itself and for the gear surrounding the mold in the press.
Pity!

Cheers

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: CO on 07/04/2013 00:56:18 MDT Print View

Is there enough air circulation in a tent? Obviously not if you seal it up, but what about with the door open?

Steam Out Tent Door 1621

Here we have an illustration of what I was talking about: steam wafting out the door while I am cooking dinner. Well, yes, it was sub-zero overnight. Combine this view of where the exhaust air is going with the windshield wrapped around the stove to make a little bit of a chimney, and maybe the amount of recirculating air getting back into the air inlets could be predicted to be rather low?

Cheers

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: CO on 07/04/2013 01:02:03 MDT Print View

"Well, yes, it was sub-zero overnight."

C or F degrees?

--B.G.--

Tad Englund
(bestbuilder) - F - MLife

Locale: Pacific Northwest
Re: The Evolution of a Winter Stove - Part 1 on 07/04/2013 01:46:08 MDT Print View

Great work Roger.
Today I was digging around my gear closet and saw my supply of Powermax canisters and wondered what type of stove I would purchase for winter when they ran out. I haven't seen a suitable replacement as of yet, until know....
Keep working on this, you seem to be working through all the issues, I hope it all goes well.
Tad

Stephen Parks
(sdparks) - M

Locale: Southwest
Re: Re: Re: Re: Injection molding, etc. on 07/04/2013 06:51:39 MDT Print View

That is probably why so many plastic designs use self-tapping screws in smooth-bore holes. Cheap, easy, and won't loosen from vibration. But sometimes you need a real thread form. It can be tapped later, but that still isn't as nice as a molded thread, which isn't as nice as a molded-in insert.

Eric Blumensaadt
(Danepacker) - MLife

Locale: Mojave Desert
Fuel mix/type on 07/04/2013 13:27:35 MDT Print View

Roger,

Is it possible (apart from propane & it's attendant container weight) that ther is a different fuel suitable for cartridges or at least a better mix for cold weather?

Failing that could lightweight fuel container technology be devised to handle 100% propane? The ultimate goal would be refillable canisters form a BBQ propane tank.

Mike Cecot-Scherer
(mikescherer) - F - M
Re: CO on 07/04/2013 14:53:41 MDT Print View

Hi Roger,

It's hard to know what way to write this. I was pretty sure I said that carbon monoxide results from incomplete combustion CAUSED by the fuel-to-oxygen ratios being shifted to too rich by low oxygen exhaust mixing into a stove's intake. You seem to be disagreeing with this most basic first-order stoichiometric chemistry in favor of a second-order effect flame quenching argument. Let me first point out that these two effects would not be mutually exclusive and one would therefore expect that there would be times when one predominates (see below for a tragic real-life example).

Exhaust recirculation is a a primary cause of carbon monoxide generation in many accidents – people die all the time from this. Cars don't produce CO until they're run in a closed space and the exhaust goes back into the intake. Ice fishing hut heaters work great until the occupant wants to stop loosing that last bit of precious heat and closes the vents - making the exhaust go into the intake. HVAC engineers have learned to be very very careful with exhaust.

Flame quenching is a second order effect. Congratulations on finding it. But I must point out that you have no actual data as to where CO is generated and destroyed in the flame. For all you know the reason that CO production drops with raised pots is exactly because recirculation currents are effectively stopped. Or goes up when the pot is lowered because of strengthened recirculation. A recirculation explanation seems to fit your data quite well.

I know recirculation can cause CO generation because I have made CO with a camp stove or two in just this way. And I've found that wind screens are a terrific way to cause these recirculation currents. Put them on: significant CO generated. Take them off: low to no CO. Isolate the intake from the exhaust and then put on a windscreen: again, low to no CO (all done with a pot of water on the burner). Seems pretty convincing.

Pooling of warm stove exhaust at the top of a tent is easy to verify. That pool may or may not mix well depending on conditions. Just saying it mixes well is not an argument. If you hang a gas lantern high in a closed-up tent and let it run for a while you will see CO production. Probably not a heck of a lot, I've seen 70-100ppm, but definitely not the "theoretical" amount one would find with a false premise and quite enough to give thinking people pause (and to make one worry what might happen if someone, for instance, ran a stove below the lantern).

Your pooh-poohing the advice of a VERY experienced combustion engineer is entirely unsupported and not at all the kind of attitude that the buying public wants to see in their would-be stove designers.

And then there's your "faulty expert" example which brings no information to the table (unless, perhaps, you were intending irony). Nobody knows how many experts that lawyer had to interview to find one that said what he wanted to hear. Doesn't matter either.

I can tell you this: that combustion engineer I referred to and I were asked by a lawyer to figure out why two people died in their tent. They were found in their sleeping bags, pink skinned, their faces laying in vomit - obvious carbon monoxide victims. Their tent was zipped shut but there was a non-closable vent right at the top. They had mis-assembled their lantern (very easy to understand if you saw it) so that the exhaust was being forced down toward the intake which resulted in a plume that registered 500-1000ppm CO. That's a monstrous amount of CO - enough to actually knock someone out. Their tent did not/could not ventilate enough. And we were shocked to find that a wind - which one would have expected to aid ventilation - could actually block outflow. So don't be so nonchalant about adequate ventilation. What happened next? Nothing. The lantern company had gone bankrupt. The wives and children of the victims got nothing.

Looking at the whole outdoor stove configuration, it's kind of preposterous that it normally works so well. I mean, here's an open flame blasting away within a few inches of the intake which is sucking air for all it's worth. The flames and exhaust mostly go up and out - no question - but it's hardly a failsafe design.

Mike,
(just Mike)

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: CO on 07/04/2013 15:28:37 MDT Print View

You're saying that CO is produced when the intake air has a reduced Oxygen level?

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Fuel mix/type on 07/04/2013 15:48:10 MDT Print View

Hi Eric

Yes, 100% propane would be much better, but the pressure is much higher and you have a safety issue with the Powermax-style Aluminium containers. This problem is not insurmountable, as you can buy such canisters with 100% propane in Europe. I forget the brand right now, but they are allied to Primus. I have tried to get some, but they can't be bothered shipping them to either Australia or the USA. DoT regulations etc etc. SNARK!

I suspect that they have simply made the containers with a heavier wall thickness. That should be enough to get the higher tensile strength to handle the pressure.

Cheers

Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: Re: Re: CO on 07/04/2013 15:48:52 MDT Print View

CO is produced when there is incomplete combustion of any hydrocarbon fuel. Perfect air/fuel mixture produces no CO, but this is almost impossible to do. With a backpacking stove there are too many uncontrollable variables.

In a car, perfect combustion would be an air/fuel ratio of 16:1, but that would create excessive HC and NOx emissions. So car manufactures compromise with 14.7:1 ratio and use exhaust gas recycling and catalytic converters with oxygen sensors to provide constant feedback and adjustments to keep all emissions within "acceptable levels." There is no free lunch :)

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Re: CO on 07/04/2013 16:02:01 MDT Print View

So in a car if you have something less than 14.7:1 air to fuel it will start producing CO?

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: CO on 07/04/2013 16:16:35 MDT Print View

Hi Mike

A couple of things. First, I have followed the literature on flame chemistry and combustion engineering for some time now, and I do understand the basic chemistry and thermodynamics. Second, I have also followed the literature on CO deaths in small enclosures, including tents and huts for some time.

Can one kill oneself by using a stove in a moderately (or even partly) sealed enclosure such as a tent? Oh yes, absolutely, and people have done just that on a number of occasions, around the world. We have had that happen here in Oz in a snow cave, with heavy snow fall blocking vents, wet snow stopping air flow, and a well-known white gas stove. The four bodies were found in and out of sleeping bags, with the stove set up, valve open and tank empty.

> They had mis-assembled their lantern
User error. Unfortunate of course, but the responsibility rests with the user. A bit like driving a car at 100 mph on a wet road.

> a plume that registered 500-1000ppm CO. That's a monstrous amount of CO
True, I agree. MSR seem happy to sell the Reactor stove which emits (by my measurements) around 2,000 ppm. User responsibility to take the necessary precautions.

On to techie details.

> Flame quenching is a second order effect.
I am not sure what you mean by 'second order' here. I don't think the term means anything. What I am sure of is that flame quenching does happen in practice, as I have run enough enough experiments under controlled conditiosn to verify this. That is, I have put cold steel and titanium in and out of a flame and monitored the effect on the CO levels. It happens.

> A recirculation explanation seems to fit your data quite well.
We will have to disagree on this. It does not fit the data at all. See next.

> but it's hardly a failsafe design.
Nothing in this world is failsafe. However, experimental data from actual measurement shows that one can have a stove emitting under 10 ppm of CO in the exhaust stream, sometimes as low as 2-3 ppm. If the hazard from recirculation was that severe, you would not get that result. the recirculation theory fails the experimental data. So I don't think it is all that preposterous.

> the kind of attitude that the buying public wants to see in their would-be stove designers
Me, I go for experimental results over theory every time. Sure, the theory is valuable in helping you design something and understand what may be going on, but only real measured data tells you whether you got the theory right! I have the data.

Cheers

Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: Re: Re: Re: Re: CO on 07/04/2013 16:17:07 MDT Print View

Less than 16:1 produces CO. Cars use catalytic converts to reduce the CO because the A/F ratio is under 16:1. At 16:1 the combustion temperature is too high, which creates too much NOx. Lower combustion temperatures are critical for NOx reduction. By recycling exhaust gases into the combustion chamber we can reduce combustion temperatures, which even at 14.7:1 would be excessive.

Also at 16:1 too much HC is produced.

So cars run at 14.7:1 because we are concerned about HC and NOx too. Too much NOx is very bad for our atmosphere. Here is what my 200,000 mile SUV currently produces out the tailpipe:

CO2 = 15%
O2 = 0%
HC = 1 ppm
CO = .01%
NOx = 5 ppm

ppm = parts per million

Allowable emissions in Calif for my year vehicle are:
HC = 98 ppm
CO = .55%
NOx = 978 ppm

There is no standard for CO2.

Edit: this is response to Jerry's question.

Edited by ngatel on 07/04/2013 16:19:25 MDT.

Michael Gillenwater
(mwgillenwater) - M

Locale: Seattle area
Re: The Evolution of a Winter Stove - Part 1 on 07/04/2013 20:43:44 MDT Print View

Roger,

I'm excited to see your series on this coming out. As I have posted before, I am eager to see someone better optimize a design for a winter canister stove. Keep it coming and I want to be an early customer.

Tanner M
(Tan68)
Re: Re: CO on 07/04/2013 22:45:25 MDT Print View

Are you suggesting that the base of a pot could create a circulation pattern that could lead exhaust to the intake ?

I wonder how much exhaust would have to enter the mix chamber for appreciable amounts of CO to be created.

There was an article a little while back that explained how the bottom of a pot could work together with the burner to create a roiling effect. This particular stove created very little CO and is actually designed to create this effect. The description just seems like a good illustration of what I believe is your point.

You might have to jump to 'Fire Maple FMS-300T' at: http://www.backpackinglight.com/cgi-bin/backpackinglight/2013_developments_canister_stoves.html#.UdZKUsUXJv8

I don't get the idea you exclude flame quenching as a source. I guess that is a secondary effect because it happens after combustion and exhaust gas recirculation is a primary effect because it happens to/during combustion. I don't think you call it 'second-order' in an attempt to minimize its contribution.

If I put cold metal in the flame and that cold metal is a pot, I could contribute CO generation to quenching but that doesn't mean some exhaust gas didn't recirculate. I could isolate the intake to remove the possibility and test one variable at a time. I suppose if I just put cold bar stock into the flame there wouldn't be much likelihood of exhaust gas being redirected... I guess it would still be a good practice to isolate the intake.

Mike Cecot-Scherer
> I know recirculation can cause CO generation because I have made CO with a camp stove or two in just this way. And I've found that wind screens are a terrific way to cause these recirculation currents. Put them on: significant CO generated. Take them off: low to no CO. Isolate the intake from the exhaust and then put on a windscreen: again, low to no CO (all done with a pot of water on the burner). Seems pretty convincing.

Stuart R
(Scunnered) - F

Locale: Scotland
Re: Re: CO on 07/05/2013 08:56:34 MDT Print View

> carbon monoxide results from incomplete combustion CAUSED by the fuel-to-oxygen ratios being shifted to too rich by low oxygen exhaust mixing into a stove's intake.

In a stove the fuel-to-air ratio of the pre-mixed gas is rich in any case, without any exhaust recirculation. Complete combustion relies on secondary air mixing with the flame.

> But I must point out that you have no actual data as to where CO is generated and destroyed in the flame.
The light blue part of the flame is where all the CO is generated and the dark blue upper part of the flame is where this residual CO burns in the secondary air.

> I know recirculation can cause CO generation because I have made CO with a camp stove or two in just this way. And I've found that wind screens are a terrific way to cause these recirculation currents. Put them on: significant CO generated. Take them off: low to no CO.

Yes, if you restrict the availability of secondary air (or quench the flame) then you will get CO. Wrapping a windscreen tightly around a stove, or using it in a sealed up tent are both good ways to restrict the availability of secondary air.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: CO on 07/05/2013 09:05:02 MDT Print View

Is CO only an issue if you run stove in closed tent, room, snow cave, or whatever?

If it's raining, I run stove under one side of tent right next to door which I leave open. And I just boil water so I don't run it long. I don't think I have to worry.

If you're creating CO does that mean you're not running the stove efficiently? Or does making stove more efficient tend to result in CO? Or are the two independent?

Damien Tougas
(dtougas) - BPL Staff - F

Locale: Gaspé Peninsula
Needle valve after pre-heat loop on 07/05/2013 10:53:03 MDT Print View

Very cool, I am looking forward to the rest of the articles!

Having the needle valve after the pre-heat loop, is there any danger of excessive pressure building up in the fuel line due to the high volume of expansion that happens when the fuel vaporizes?

Mike Cecot-Scherer
(mikescherer) - F - M
Re: Re: Re: CO on 07/05/2013 11:17:35 MDT Print View

Hi Tanner,

Exactly! a circulation pattern (not necessarily symmetrical or uniform) that brings exhaust back to the intake.

My understanding is that combustion engineers will always shoot for a slightly lean mix (including secondary air entrainment) as a safety feature even though it decreases the efficiency due to the heating of extra gas. Lean flame becomes surprisingly inefficient.

I definitely don't want to be seen as trying to exclude flame quenching as a source of CO. I refer to recirculation as primary because it messes with the most basic part of the combustion reaction - the fuel/air mix, because it's the dominant effect in many accidents, and it's able to create incredibly high CO concentrations for long periods of time.

That roiling pot/stove combo is very interesting. Seems like they made the circulation strong enough that it entrained fresh air and isolated the intake - very cool! A nice example of the fractal nature of reality - loosely speaking, a bad thing that becomes good after a certain point.

After thinking about it I think I can offer a couple of characteristics that should be not-unusual for recirculation caused CO in some stoves:
— uneven CO distribution around a centered pot that has maximums in-line with the intake ports.
— a burner that fires more upward than outward might show high CO because of what I'm going to call "flame bounce" off the pot; essentially driving exhaust downward. Stoves with more outward directed burners should be more resistant to recirculation. A Pocket Rocket might fit this.

Best,
Mike

Edited by mikescherer on 07/05/2013 11:29:19 MDT.

Mike Cecot-Scherer
(mikescherer) - F - M
Re: Re: Re: CO on 07/05/2013 11:26:15 MDT Print View

Hi jerry,
Yes, exactly. But the reduced oxygen I'm referring to is the percentage of oxygen, not the absolute up or down variation from altitude. Altitude is another thing. Maybe Roger can explain some of the ins and outs in his next article.
Best,
Mike

Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: Re: CO on 07/05/2013 11:42:35 MDT Print View

Roger's testing under controlled conditions show that some stoves emit more CO than others. If I remember correctly, MSR Pocket Rocket among the worst and Snow Peak GigaPower among the best. With proper ventilation you can safely cook in a vestibule. The problem with CO poisoning is that it is a silent silent killer. You are dead before you know there is a problem.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: CO on 07/05/2013 11:43:49 MDT Print View

Yeah, Roger hates Pocket Rockets : )

Mike Cecot-Scherer
(mikescherer) - F - M
Re: Re: CO on 07/05/2013 12:04:24 MDT Print View

Hi Jerry,

The vast majority of stove users have found no issues with CO in well ventilated areas. Your description of how you use your stove sounds pretty safe. It seems to match the protocol of the Rainier Guides. You could always check things with a little CO monitor...

If the burning device causes concentrations of CO over 500ppm it could literally knock a person out so my personal opinion is that there is no safe way to use such a product.

(BTW I should probably mention here, given what's been written here in BPL, I have a production MRS Reactor, love it, and mine produces no CO.)

That said, I believe that hikers and climbers that are struggling to acclimate to higher altitude are probably routinely being impaired by low levels of CO and, in the case of sealed-in stove users, by lowered oxygen in their tent. My 2¢.

Best,
Mike

Edited by mikescherer on 07/05/2013 14:09:08 MDT.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Enclosed areas. on 07/05/2013 13:01:06 MDT Print View

Jerry: Being in an enclosed area has several effects.

For the stove: if you're in such a tightly sealed environment (unventilated tent, snow cave without vent holes or in which vent holes have been covered by snowfall) that the percentage of O2 falls and CO2 rises, then the stove will see less oxygen in the pre-mix air and hence the flame will be richer in fuel (i.e. prone to make more CO) - the effect Mike is discussing, although he is also arguing for smaller-scale recirculation within a windscreen, for instance.

For you: not only may the stove be making more CO per minute, but all the CO (and CO2) being generated is being retained in your breathing space and increasing in concentration the longer you run your stove.

Usage pattern makes a difference. If, in a very-tight house, someone bakes a batch of cookies, they end up with a batch of cookies. If, however, they attempt to heat their very-tight house by running an unvented stove continuously, they can end up dead. Similarly, your brief usage of a stove, near the entrance, just to boil water is well within my personal safety limits. While running a stove in an attempt to heat up a sealed tent or a snow cave is a bad idea. If the area is sealed enough to retain heat, it is inadequately ventilated to run combustion equipment.

All stoves make CO. Some make a little, some make a lot. If you use it in a way that you are venting that poisonous gas away, fine. If you are in an environment in which the stove's heat or water vapor effluent (two things you can detect) are being retained, you need more ventilation.

Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: Enclosed areas. on 07/05/2013 14:33:57 MDT Print View

Jerry,

We have a furnace in our camper with a vent to the outside, so we can keep the camper closed up when using it. But most often we use a catalytic heater because it uses about 75% less propane and no electricity. When using the catalytic heater, the camper must be vented otherwise the heater will deplete the oxygen, which then cause more CO. Some catalytic heaters have oxygen depletion sensors that will turn the heater off. Most of these heaters with the depletion sensors don't work above 7,000 feet.

That is my blue-collar explanation since I am not a scientist. Sort of my translation of what David Thomas said :)

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Some simple facts on 07/05/2013 16:38:34 MDT Print View

Let's have some measured facts here.

Measurements show many stoves emit quite low levels of CO (<30 ppm). This is incompatible with the recirculation theory.

Measurements show that a stove emitting a very low level of CO can be made to emit a whole lot more by inserting cold steel into the upper part of the flame and quenching the combustion process. Removing the steel from the flame drops the CO level back.

Measurements show that a simple windscreen placed 3/4 of the way around a stove does not increase the CO emitted. A totally enclosing windscreen might bve very different - don't do that.

Measurements show negligable amounts of CO in a tent when using a good stove in a ventilated vestibule. (Actually, very often the readings are down around 2 - 3 ppm, in the 'noise'.)

Basic physics/chemistry also says that an incomplete combustion process gives off less heat than complete combustion.

Cheers

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Needle valve after pre-heat loop on 07/05/2013 16:48:19 MDT Print View

Hi Damien

> Having the needle valve after the pre-heat loop, is there any danger of excessive
> pressure building up in the fuel line due to the high volume of expansion that
> happens when the fuel vaporizes?

Nope. If the pressure in the line near the needle valve gets higher than the pressure in the canister, it will simply stop the fuel coming from the canister. Actually, that happens all the time in any remote canister stove: fuel oscillates back and forth.

If you take the fuel in the region of the needle valve and heat it to 1,000 C, you might think that could raise the pressure. Nope: it will still push back into the canister and recompress fuel vapour back into liquid.

On the other hand ... if you heat the canister to 100 C, you can expect instant transmogrification. See http://www.backpackinglight.com/cgi-bin/backpackinglight/exploding_gas_canisters_the_hazard_of_overheating.html

Cheers

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: CO on 07/05/2013 17:05:48 MDT Print View

Hi Nick

> MSR Pocket Rocket among the worst and Snow Peak GigaPower among the best.
Well, the PR was not good. The full data is at http://www.backpackinglight.com/cgi-bin/backpackinglight/stoves_tents_carbon_monoxide_pt_3.html but a few stoves extracted are:

Optimus Crux: 300/260 (low/high, ppm)
MSR Pocket Rocket: 240/140
Coleman Xtreme: 5/5
Snow Peak GST-100: 5/21
FMS-116T: 10-50/50-100 (The FMS stoves are from later testing)
FMS-300T: 20/3

The variable results with the FMS-116T are due to some solid Titanium in the flame: while that metal is 'cool' the CO emission is high, but it drops as the metal heats up. (No recirculation was harmed during the testing.)

As far as the Reactor goes - we tested a preproduction model and found >1,000 ppm emission at low power. Boosting the air inflow (with a compressed air line!) reduced the emissions enormously. We sent these results in to MSR and they withdrew the Reactor from the market weeks before its release as a result of our report.

Several months later MSR reissued the Reactor with modifications to improve the air flow. It still tested very high (350 ppm at low power), but obviously not as bad. We reported on this at http://www.backpackinglight.com/cgi-bin/backpackinglight/co_series_supplement_1_msr_reactor.html Yes, we still have all the correspondance with MSR over this.

If you only use a Reactor at full power the CO emissions are lower. It was not designed for low power or cooking, but may be useful outdoors for melting snow.

Cheers

Edited by rcaffin on 07/05/2013 17:11:36 MDT.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Re: Enclosed areas. on 07/05/2013 18:49:57 MDT Print View

>"since I am not a scientist."

I'm not a scientist either. Scientists do things like entangle more photons than any human ever had before or find an exception to the Heisenberg Uncertainty Principle. Both of which my BIL has done. Engineers clean up toxic waste sites, build snowball cannons and backyard zip lines for their kids, and bring portable hot tubs on backpacking trips. All of which I've done.

Engineers (generally) don't publish in Science or Nature.

Scientists (generally) don't use pipe wrenches and voltmeters. Nor are they satisfied with one significant figure.

Scientists discover things no one ever knew before. Engineers get paid better.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Enclosed areas. on 07/05/2013 21:40:19 MDT Print View

> Scientists discover things no one ever knew before. Engineers get paid better.
Sulk.
Snark.

Sigh
PS: I own about 6+ voltmeters...

Edited by rcaffin on 07/06/2013 16:40:58 MDT.

peter vacco
(fluff@inreach.com) - M

Locale: no. california
Re: Re: Re: Re: Enclosed areas. on 07/06/2013 18:35:03 MDT Print View

" I go for experimental results over theory every time. "
yes. quite correct. i have read that the laws of thermodynamics owe more to James Watt's engine, than his engine will ever owe to the laws of thermodynamics. (it was a horrible thing efficiency wise).
also somewhere along those lines, is, "if it looks good on paper, but doesn't work in real life .. you've got it written down wrong."
---
anybody hanker'n to produce something in quantity might be well advised to read/study/come-to-Believe, Rajan Suri's principles of Quick Response Manufacturing.
they are a godsend of common sense, that is a good leap forward from what is openly obvious.
(and to boot, you'll make a better product with less scrap)
---
if ever the little voice in your head shuts off, and you are still alive, there is a fine chance you have CO poisoned yourself.
(tuck that tidbit of information away. you may need it someday.)
---
great article. we can all see how as a product evolves, several generations of equipment may be purchased and quickly discarded as knowledge matures during a manic development cycle.
---
peter gives not a squat of snot about CO coming off a pot.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Wallet-limiting career choices. on 07/06/2013 18:53:47 MDT Print View

> Sulk.
> Snark.

In my major, we'd say, "Chemical Engineers just want to be chemists. Chemists just want to be physicists. Physicists just want to be mathematicians. Mathematicians just want to be philosophers. Philosophers just want to be God. Unfortunately (for the rest of them), the pay scale is the other way around."

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Wallet-limiting career choices. on 07/06/2013 21:12:40 MDT Print View

Hi David

Where'd you put the programmers?

Cheers

Jason Brinkman
(jbrinkmanboi) - MLife

Locale: Idaho
What's that got to do with...? on 07/07/2013 02:11:30 MDT Print View

What do programmers have to do with the price of tea in China?! :)

For that matter, what do exhaust recirculation patterns, carbon monoxide pools, snow caves, or faulty lanterns have to do with Roger's new stove?

If someone were to try hard enough, they could probably off themselves with their titanium spork, but the prudent user has predictably few problems. I'll give you that canister stoves (or mis-assembled lanterns) are slightly more risky than sporks, but with rare (albeit notable) exception, the average user survives more times that not.

Oh, and I am definitely intrigued by the cliffhanger, Roger... Let's see that baby!

Edited by jbrinkmanboi on 07/07/2013 02:36:28 MDT.

Jason Brinkman
(jbrinkmanboi) - MLife

Locale: Idaho
Manufacturing on 07/07/2013 02:13:53 MDT Print View

BTW, I've learned more than a couple things about prototyping and manufacturing from the responses here - good stuff! I like the notion of molded-in threaded inserts the most!

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Re: Wallet-limiting career choices. on 07/07/2013 08:25:09 MDT Print View

>"Where'd you put the programmers?"

Roger: that's what the physicists and mathematicians end up doing to pay the rent, IME.

Stuart R
(Scunnered) - F

Locale: Scotland
Re: Re: Re: Wallet-limiting career choices. on 07/07/2013 14:03:23 MDT Print View

Too true!

Then: BSc Applied Physics and Semiconductor Electronics

Now: writing code for things like the Dodge Viper engine management

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Manufacturing on 07/07/2013 16:14:11 MDT Print View

Hi Jason

> the notion of molded-in threaded inserts
You can also mold a plain hole and later press in a small brass or steel thread-insert. This usually lasts longer than self-tapping.

Cheers

Tad Englund
(bestbuilder) - F - MLife

Locale: Pacific Northwest
Re: Manufacturing on 07/08/2013 17:29:44 MDT Print View

Jason, I thought you fell off the end of the earth- good to see you are still alive.