"How Backpacking Stoves Work"

Hi there,



Here's an interesting page on "How Backpacking Stoves Work". Talks about some very interesting areas, like Flame Chemistry, Flame Color, Flame Structure, Jet Sizing, etc.


Here's the table of contents:

Flame Chemistry
Flame Color/Chemiluminescence
Hottest Part of Flame
Dynamics of Various Stove Types
Open Jet Alcohol Stove
Pressurized Jet Alcohol Stove
Open Flame Alcohol Stove
Open Vented/Chimney Alcohol Stove
Pressurized Petrol Stove
Canister Stove
Wick Stove/Candle
Wood Gas Stove
Carbide Lamp
Fundamentals behind Flames and Flame Structure
Laminar Flow vs. Turbulent Flow
Laminar flow
Turbulent flow
Premixed vs. Diffusion Flames (non-premixed)
Flame Quenching
Jet Sizing
Generator Tubes
Flame Stabilization
Recirculation Holding
Bluff Body Recirculation
Sudden Expansion
Opposed Jet
Swirl
Spacing of Multiple Jets
Acoustic Field Coupling
Air Temperature

 

Good site. Zenstoves.net is one of my "go to" sites.

Another good site is http://www.bushwalking.org.au/FAQ/FAQ_StovesTech.htm

HJ

 

How backpacking stoves work:

1. Fill with fuel
2. Pressureize fount
3. Apply preheat fuel if appropriate
4. Light match
5. Apply match to preheat fuel, or;
6. Open valve to admit fuel to burner, apply lighted match to burner
7. Add pressure to fount if necessary.
8. Cook meal.

Simple soluation for complex issue.

lance

 

Lance: There is a difference between "how they work and how to work them". Mike...

 

I know you are right, and i forgot that part.

9. Flame derived from the burning of some type of fuel (usually hydrocarbons) under pressure passing through a tiny oriface in a nozzle ignited by some sort of heat producing device resulting in a flame which is both intense and very hot.

"The least common human commodity is common sense" - Mark Twain - 1880's

lance

Why make it more complicated than necessary??????

 

Pope Urban VIII in 1632 to Galileo Galilei on the subject of Galileo's "heretical" sun-centered universe:
"Why make it more complicated than necessary??????"

Some things never change.

Nice link, Sam. Thanks!

Cheers,
Gary

 

Thanks for your comments, so far, guys. Whether simple or not, it's still valid conversation. I'm all about keeping things simple. However, for the sake of stove design, safety, and/or optimization, I like getting into the nitty, gritty details. It's the researcher coming out of me, sorry for the intricate detail that follows!...

Well, I guess I put the link up so that we could have a lively conversation about topics in the linked document. One of the pieces I was interested in was flame quenching. We boil a lot of water here and it appears that one small factor could improve boil time (am I splitting hairs here???) just by adjusting kettle distance from the flame...

Flame Quenching

Flames and hot gasses generally lose heat if they come in contact with the cooler walls of the stove or pot. The surfaces act as a "third body" and drain energy from recombination. Solid surfaces also provide a means for breaking the chain of flame propagation. Free radicals tend to diffuse toward the surfaces of these solid bodies where they can be retained for longer periods and can recombine more easily than in the gas phase.

...

Flame quenching is an important factor in incomplete combustion and carbon monoxide production. In most cases, the less contact flames have with a pot, the greater the amount of complete combustion. Therefore, smaller diameter pots and positioning pots higher above the flame source should aid in combustion. Pot position can become complex as, complete combustion isn't the most important aspect of stove performance. Keeping a pot in contact with the flames may actually transfer more heat into the pot that a more efficient combustion position. There are also questions about pot stability, wind protection and integral aspects of the pot as part of the stove system itself (particularly with alcohol stoves).



If we are talking about boiling a litre of water in a kettle, then according to these statements, the optimal position of the kettle is just above the tips of the flames. In my limited experience, some of the stoves we own have pot rests that 'sit the kettle' below the optimal range, where the bulk of the blue flame is clearly in contact with the "third body". So this begs the question, and maybe even an argument: Does the water boil quicker or slower at certain heights above the flame? Common sense says that if you raise it high enough, it will never boil. Conversely, if you set the kettle on the burner, the flame could go out or will disturb the flame.

I would have to comment on a couple of things here:
1) Some stoves produce yellow tips on the burning blue flame and when a kettle is placed on the stove, the yellow tips go away - so the kettle actually increases combustion efficiency. Am I wrong here?
2) 'Smaller diameter pots' require more time to boil as opposed to larger diameter pots. But then, larger diameter pots can produce greater thermal feedback, which could cause stove heat problems.

If we are talking about CO emissions. They say that if the kettle is in the blue flames, then more CO is produced. If a kettle is elevated further above the flame, then less CO is produced. Smaller diameter pot produces less CO too. According to a document here at CCS, this is confirmed/compared in two charts, one shows the CO emissions of a few stoves and the other shows the emissions when the kettle is raised. But now we are consuming more fuel or aren't we? (On a side note regarding the CCS document: It's interesting to see that the only liquid fuel stove within safe parameters, after 10 minutes, in the chart is the venerable SVEA 123 within a Sigg Tourist Cook kit - the pot is quite elevated and heat appears to be directed and contained within the design of the cook kit itself, thus optimizing combustion. But does water boil quicker in a Sigg Tourist or on the SVEA pot stand? Hmmmmm.) As for the CO problem, I do all my cooking outside as the instructions say and I have a really nice sleeping bag. I don't want to end up like Andrée, Strindberg, Fraenkel, as the legend goes.



OK, so another point to cover could be the Jet Sizing chart. These are approximate ranges with a link to some examples. Seems like the range for Kerosene ought to start a lot lower, like at 0.20mm where some modern stoves are set. On CCS, 0.23mm is quoted a lot, perhaps due to actual measurement of the aperture and prickers. Again, in my limited experience, kerosene aperture size depends on the stove and the burner size. In reviewing a few CCS documents, the range looks to start at around 0.20mm on up to 0.32mm and maybe even larger. Now that sounds more like a range to me than stating a single number or average, as it appears in the Jet Size table. Not looking to be critical only more precise.

Well, for the sake of conversation, these are my opinions (humble at best) and maybe even a poke at zen stoves? Can you tell I don't have anything better to do? Been ill with walking pneumonia...

Have a good day!

sam

 

Hi Sam

Its all good stuff, and makes good reading. Brain food for the stovie enthusiast.

 

Hi Sam

I hope you get well real soon!

Flame quenching is a new idea for me and I'm trying to get my head around it. I tend to view the fuel/air mix as a fluid. The pot on the stove performs two things, imo. It slows down the flow of the fuel/air mix away from the burner. It also concentrates the heat of combustion in a more confined area.

So...... I'm thinking that the confined area and slower fluid flow create a hotter "burn zone" which more completely burns the fuel. Thus, a reduction in yellow flames and a bluer overall flame pattern underneath the kettle. The time gained in the slower fluid flow enables additional oxygen to combine with the the rich mix (indicated by the yellow flames) so that the yellow becomes blue.

Just my thoughts and no science to support it. I'm not sure the flame quenching plays that much of a role, but I'm open to more on that idea.

I never use a stove in a tent, so CO is not something that concerns me overmuch. The horrific burns caused by melting/burning nylon tent material concerns me a great deal more.

Cheers,
Gary

PS - The flickering avatar is completely awesome.

 

Hi Gary,

You've described what I was thinking to a 'T'. I would have to agree that the kettle has to support the combustion process, especially highly thermally conductive copper kettles, since they'll gain heat quickly and retain it. Thanks for the thought.

On another note, I went ahead and did some really informal tests. I wanted to test the elevated pot theory to see if there were any differences in boil times. The results don't seem to show huge differences but there are differences in boil times.

I used a SVEA 123, Coleman Fuel, and Sigg Tourist Clone. The test was to boil 1 litre of water in the Sigg Tourist Clone pot:

1) in the Sigg Tourist Clone setup
2) on the SVEA 123 windscreen pot rests
3) elevated above the SVEA 123 an extra 20mm.

Garage temperature: 28°F.

Here is my SVEA 123 ready to go into action with the flame spreader in place.



Precise measurement of 1-litre, room temperature (~65°F) water. Fresh water used for each successive test.


So the first setup is the Sigg Tourist Clone with SVEA 123 installed. I made sure the stove was at maximum burn before putting the litre of water on to boil. I waited for operating temperature in all cases.



Here is the pot getting ready to boil in the Clone...






Here is the same Clone pot on the SVEA 123 pot rests...





Now, to elevate the same Clone pot I used a cooking grate that raised the pot exactly 20mm above the SVEA pot rests, using high-precision laboratory equipment underneath the grate riser brackets...




Here are the boil times for the very rigorous test (one run). I made sure the water came to a rolling boil.

1) Sigg Tourist Clone with SVEA 123 - 8:15
2) Clone pot on SVEA 123 pot rests - 7:50
3) Clone pot elevated 20 mm above SVEA 123 - 7:35.

So there is a difference, not much to make conclusive statement, but some differences. I wasn't expecting No. 1 to be last and was expecting No. 2 to be first. There is some truth to the quenching theory, maybe. More tests are in order.

I also have a CO meter that I'll do tests with too, but not right now, not feeling too good. I'll do more after I quit coughing.

sam

 

Interesting. I would have thought that the Sigg Tourist (clone) set up would have funneled the heat so efficiently that it would have overcome the pot height issue. Fascinating that it was so slow.

How close are the clone's measurements to a real Sigg Tourist set up?

HJ

 

I agree on the slow issue. It should have been the fastest to boil. I'll make sure with another iteration of tests.

As for the measurements, I have no idea. Never have afforded a real Sigg. Bought this set for $5 at a sporting goods store on clearance a while back.

Thanks for your comments,
sam

 

I am not sure that the speed of a "boil test" directly correlates to the efficiency of the burn.

i.e. what if the stove that boiled fastest consumed a far greater amount of fuel per degree centigrade rise?

I use an Edelweiss cook set with a Primus 71 on occasion. I believe that the aluminum case acts as a heat sink which reduces tank pressure during operation. The trade off for a slower burn is that the wind screen probably helps increase thermal conductivity to the pot.

NHRA top fuel dragsters can do the quarter mile in seconds flat, but at what expense to fuel economy? For those concerned about weight, why waste a drop of fuel?

I think that we need a talented(Obsessive Compulsive)member with lab equipment to drain their tank and dose it with a measured fuel load. Drain the tank after and calculate the *C/cc temp/fuel ratio.

Till then, remember that there are some things in life that are done best long and slow.

Best to all and Happy New Year,

AR

 

Hi AR,

Thanks for the provoking thoughts. I guess I'll have to think about your comments as I write here. You raise some good questions that make me think about this in a little more detail. Efficiency seems to be the name of the game. Getting more with less.

I would propose that the above tests, in a crude way, show that a stove can burn more efficiently if the pot is raised a bit, as is referenced in other more scientific articles. I was just testing their results.

As far as boil times are concerned, I tend to believe these are about efficiency as well as throughput. If you take a modern day MSR or NOVA burner, you'll boil up a pot of water with less fuel and _less time_ than most, if not all, of the old brassies and suit case stoves - maybe.

As for the boil tests I did, I was trying to show that raising that pot makes no difference. I was also trying to show that using a heat capturing cook kit would make a difference. My results show the opposite. It appears that raising the pot a bit uses the fuel more efficiently, giving us a more complete combustion process, thus producing more heat (results of my test are not conclusive). On none of these tests, did I change the configuration or burn rate of the SVEA 123 stove, only the configuration of accessories. So, if the boil time is shorter, didn't I use less fuel to do that?

Also, in a casual perusal of forum posts here at CCS, external articles, and in backpacking books, I find, in most cases, boil time is what is reported and if I'm not mistaken, shorter times are better. Whether it is an old brassie or a new modern, lower boil time, and indirectly higher efficiency, seems to be what we are trying to achieve. I seem to recall some silent caps that were home manufactured recently that reduced the boil time for a litre of water down to about 5 minutes as opposed to 7 minutes on the same stove. This seems to hint of efficiency. It could also be using the same amount of fuel in less time, OR it could mean less fuel and less time. This also seems to hint of modifying the stove like modifying the car's motor by putting headers on it, but all in the name of getting more power out of the car. You're right, maybe some OCD scientist could come in and measure the fuel consumption over a large number of tests and apply the result to a standard deviation formula and give us the numbers. I'm not really into that, I'm more about being a backyard mechanic and playing around with this stuff and by playing around with it, understanding stoves a little bit more.

As for the NHRA example, I love it. Great throughput example and I grew up being a grease monkey in my dad's shop building and racing cars. We were always thinking of ways to squeeze out more horsepower from those engines. Anyway, I digress, as I recall, the NHRA dragsters burn about 15 gallons of fuel in one quarter mile run, with a throughput of about 8000 horse power, which is quite an achievement, where 40 years prior, horsepower was nowhere near these numbers. Advances in technology and going to the extremes has brought this about. I guess my point here is that the NHRA and NASCAR engineers have contributed by developing technology that increases throughput and efficiency that has been applied to the consumer market, as in high-efficiency vehicles or more powerful, yet gas-saving engines.

Sometimes we have to go to the extremes to get our answers.

AR, thank you for the thought provoking comments. It gave me much to think about. Hopefully, this wasn't too dry to drudge through.

Have a good day,
sam

 

Greetings, All,

Yes, the carbon monoxide issue has been kicked around, and tested extensively, since the 1970's. After Backpacking Magazine published their landmark study, in the wonderful "Backpacking Equipment Buyer's Guide", in 1978, which contained the great article on CO, several stove makers raised the pot supports on their stoves, in order to lower CO levels to the safe point. Among them, was MSR. I must admit that their wonderful X-GK stove suffered greatly from having it's pot supports raised, and that stove, once modified, was NEVER able to perform up to it's originally published specs!! BUT, MSR continued to cite those very same original specs, even though they had, virtually, castrated their wonderful X-GK by raising it's pot supports!!!

SO, is raising the pot supports a "good thing"? I'd say, for most folks, that it's not worth the effort and loss of performance that is involved. But, hey, that's just one man's opinion, and your mileage may vary. For what it's worth..... Take care, and God Bless!

Every Good Wish,
Doc (very dubious of stoves who's designs have been changed with input from LAWYERS!! )

 

I agree. I like using them just the way they are! The SVEA 123 is just right. Not too hot. Not too cold. Trevor has it right, "The design is old but the Svea 123 is still one of the best!"

Dang lawyers!

sam

 

Idaho,

Glad you found my stance thought provoking. I also grew up getting "a little grease under my fingernails".

As for the racing, you are absolutely correct. We learn so much by pushing the edge of the envelope. Case in point the "space race".

Those awesome 8000 Horse Power engines get their peak HP at their peak efficiency. More fuel does not necessarily equal more power. Should be able to apply that concept to all equipment. Efficiency = output/input.

Concerning the fuel consumption on the stove, weight could be the easiest way to determine consumption. Weight full and then after boil test. If I only had a scale(already got the OCD).

Happy New Year,

AR

 

When you fig'r i'm fun'n you, let me know???

lance

 

Sam et al,

Boil time is highly correlated to efficiency, but the correlation is not 100%. I've seen test results published* that indicate that if you turn down a stove from its max output that you will get more efficiency (i.e. more water boiled per a given quantity of fuel).

However, if the stove is burning at the same rate in the same conditions and a tweak of some sort reduces boil time, then clearly greater efficiency has been acheieved.

HJ

* http://www.trailspace.com/articles/2007/01/17/integrated-canister-stove-showdown.html

 

HJ, nice link. That Reactor is something else - 3 to 4 minutes, not bad. It uses a little more fuel, about a fourth more, but for half the boil time! 6 minutes down to 3. That's awesome. Truly they've made the Reactor quite efficient. Now, here's the kicker, I'm sure the kit contributes a lot to this efficiency too. It seems to have great boil times whether or not there is wind. So, a combination of efficient burner and a well-engineered kit provide a great combination and great boil times, at least among the stoves tested.

As for the turning the stove down to get more efficiency, I'm _guessing_ that the stove is probably tuned for a specific delivery of fuel supply and not for maximum pressure. This may be due to design of the air intake, air/fuel mixture, or some factor like that. Interesting.

Thanks for the read and feed,
sam