Companion forum thread to:

Stoves, Tents and Carbon Monoxide - Deadly or not? Supplement 2: Primus Express and EtaExpress

It seems that even top brand manufacturers like Primus do not always bother to test the CO output of their products. It's hard to believe that if they were testing they would allow a product this bad to go into production. I thought MSR's Reactor was dodgy but this is just ridiculous - bordering on criminal. It's just not good enough for them to say "only use it in a well ventilated space" they know very well where camping stoves are going to get used and they should design accordingly. It's not like it's an impossible task, they got it right with the EtaPower!

Double posting deleted.

Edited by andydolman on 07/02/2008 18:30:32 MDT.

Roger,
I have been considering buying one of the Primus pots with the attached heat exchanger to go on my Snow Peak Ti GigaPower. Do you feel that the heat exchanger would raise the CO2 output by cooling the flame.

Does the pot (wide, Narrow, heat exchanger attached) used have any measurable effect on CO2 output?

Thanks

Hi Brian

> I have been considering buying one of the Primus pots with the attached heat exchanger to go on my Snow Peak Ti GigaPower. Do you feel that the heat exchanger would raise the CO2 output by cooling the flame.
Very good question. I don't have experimental data to answer this directly, but herewith my thoughts.

The Snow Peak stoves have very low CO emission. One of the reasons is that the flame-spread goes out sideways, so the flame has largely completed the combustion cycle by the time the gases reach the pot sitting on top of the standard pot supports. The way the flames spread out also mean that extra air can reach the flames very easily.

The Primus EtaExpress stove has a focused flame, going straight up, and this leads to the stove having a poorer CO emission level by itself. Extra air cannot reach the core of the flame before it hits the pot.

If the Primus EtaExpress pot was put on top of the standard Snow Peak pot supports the result *should* be OK. The flame should have largely completed the combustion cycle. Lowering the pot downwards would be another matter - not good of course.

A serious question to ask yourself is whether the small heating efficiency you might gain with the Primus pot justifies the extra weight of the pot. The Primus pot is quite heavy and rather narrow. If you compare it with something like an MSR Titan pot, I question the gain. Check the review of the Titan pots at:
http://www.backpackinglight.com/cgi-bin/backpackinglight/msr_titan_pots_spotlite_review.html
This does quote the weights of the two pots in that set as:
"a 1 litre pot at 81 grams (2.86 oz) and a 1.5 litre pot at 115 grams (4.06 oz)"



As you can see here, I use these pots myself. I have found that the larger of the two pots heats significantly faster that the kettle, which is sitting beside the stove. I now use just the pot.

> Does the pot (wide, Narrow, heat exchanger attached) used have any measurable effect on CO2 output?
Not in my experience, unless you are using a very narrow pot and the flames are excaping up the side at a great rate. Not a preferred scenario anyhow.

Cheers
Roger

Hi Roger,

>The second problem is the size of the air holes around the jet: they are only 5.5 mm diameter. The holes in many canister stoves are 6.0 mm. The effect of smaller holes is to limit the amount of oxygen being entrained by the jet of gas inside. Tests on a Trekka stove showed that increasing the size of the holes reduced the amount of CO being produced.

On my Xtreme I measured the air intake holes which are 5 mm diameter, and this is from your CO review of the Xtreme stove. "Owing to a good burner design coupled with a good burner to pot clearance it has very low CO emission levels at all power levels" This does not fit in with your statement above.

>The third problem is the internal diameter (ID) of the tube going from the jet to the burner head. It is 10 mm outside diameter and about 7.5 mm ID. This very small ID also limits the amount of air entrained. Note in connection with these last two points that the measurements of CO production were taken at about 200 m (600 ft) above sea level where the air pressure is 'high'. I do not know what level of CO might be emitted at 3,000 m (7,000 ft) where the air pressure is lower: certainly emissions will be greater.

Again my Xtreme stove mixing tube measured 10mm ID reducing to 8mm ID near the burner head. This again does not fit in with your statement above.

Would it be possible for your opinion on why the two stoves are so different in CO levels, I think there is more in it than the hight of the pot.

As I do not have the resources to purchase all stoves that I would like to look at, could you please tell me if the ETA burner has a deflector plate in it.

Thanks

Tony

Sorry accidental double post

Edited by tbeasley on 07/10/2008 19:01:05 MDT.

Hi Tony

Yeah, it gets very complex. I am amazed by the Xtreme, but I note that it has a wide burner head. This means the flames can get a LOT more air to mix with to reduce the CO level, after the gas mix comes out of the burner head.

The size of the jet matters too. I haven't measured the jet on the Xtreme yet, but I suspect that it may be smallish. This would make the gas velocity out of the jet high, which would help drag in more air despite the small holes and narrow tube. With a typical small-head burner that would make the gas come out of the burner head too fast, but the larger diameter means the gas velocity is reduced to sufficiently below the flame velocity. Even so, I can see incipient signs of flame-lift-off at high power.

But there is even more to consider. Look at the Xtreme and the Snow Peak stoves. The flames come out sideways from these (well, sort of), and this means the flame takes longer to hit the bottom of the pot than with something like Pocket Rocket or the Primus EtaExpress stove. The PR and PEE shoot the flame straight up to hit the pot quickly. The greater flame path of the Xtreme and SP stoves means the combustion cycle can complete before the flame is quenched.

Can I support this claim? Yes: look at the CO level vs Clearance graph for the PEE stove by itself (in the article). Raising the pot or increasing the clearance by 5 or 10 mm can halve the CO level. Just that little extra flame path length makes the difference. Similar results obtain with the special EtaExpress pot.

However, if you put the burner head too far below the pot you start to lose peak power, and the stove vendors love to claim macho heating power, even at a cost of raising the CO emission level.

Everything is a trade-off.

Cheers
Roger

Edited by rcaffin on 07/10/2008 21:16:23 MDT.

I wonder if this is a problem with the oft rumored MSR non-pressurized "capillary stove" they are trying to build for the military (and us). The capillary stove will burn diesel fuel and J4 aircraft fuel - "supposably". But will the capillary ceramic block get easily contaminated and lower efficiency??

A non-pressurized capillary stove sounds great but I also wonder how hot it can get and how efficient it can be.

As of now I'm happy cherry picking JeetBoil's 1.5 Liter pot to use with all my stoves from ESBIT/FIRELITE tabs to canister to white gas.(I have no JetBoil stove.) The pot is definitely worth the extra weight on long trips for fuel savings. Windscreens are a must for efficiency. I use MSR's aluminum roll up windscreen.