PDA

View Full Version : Windscreen Dilemma



niteshdw
03-29-2007, 18:53
OK all you alcohol burners....help me out here.

Am playing with a Brasslite Turbo IID and having an issue with my windscreen design that is causing undesirable results.

Using a MSR Titan Kettle (.85L), 1/2 oz denatured alcohol. Windscreen constructed with aluminum roof flashing, one row of 1/4" holes spaced 1" apart, 1" from bottom edge, heightened to just clear the bottom of the pot handles when opened. Windscreen gap is 3/4" from pot. Perfect; windscreen fits rolled up inside my pot real neat. I like that.

Using this set-up I'm getting a whole lot of flames shooting up the sides of the pot AND shooting out the simmer slots of the stove. On the assumption that I was getting a radical burn effect caused by radiant heat from the windscreen I repeated my test opening the gap between windscreen and pot to 1 1/2". At a 1 1/2" gap I get a good efficient burn; boiling 2 cups of tap water in 7 minutes and a total burn time of 9 minutes.

All of these observations were performed in a closed garage with lights out to better visualize what was happening and no wind to screw with the flame.

Taking the whole shebang with redesigned windscreen outside in moderately gusty wind conditions the whole theory now falls apart. The wide gap (1 1/2") between windscreen and pot now does little to block the wind. Flames being whipped around like a dust devil, 1/2 oz fuel burning out in 3 minutes, no water boiling, etc.

OK back to the drawing board! New windscreen now extends to the top lip of the pot and with the new 1 1/2" gap. Radical burning is back. Uh? :-?

Been following stove/windscreen threads here with interest and note that some use tall windscreens, some half-way up the sides, some 1/2" from bottom of pot. Most, I've noted, are using a relatively small gap between pot and screen ( 1/4" ~ 1/2") with no apparent ill effects.

Would dearly love to use a design that would allow me to store inside my pot but so far have been unsuccesful. Am I stuck with a tall windscreen & even wider gap? Anybody else ever seen this radical effect with a 3/4" gap? Brasslite windscreen instructions call for a minimum 1/2" gap. I'm in spec....! Can you hear corporate America singing! :)

Solutions, comments, BS, smart-ass remarks? I'll accept all! Thanks in advance guys/gals/other.

Footslogger
03-29-2007, 19:00
Don't use a Brasslite but here is the system that works for me with a Trangia burner.

My windscreen is made out of the same material you describe but has NO holes drilled in it. Rather, it is elevated off the ground by approximately an inch or so. The top edge of the windscreen is about 1/2" above the bottom of my cookpot and there is approximately 1/4" of space between the windscreen and the outer wall of the pot.

I do not get the radical flaming you describe nor does the wind cause any dust devil like flame whipping.

'Slogger

Skidsteer
03-29-2007, 19:05
Try lowering your intake holes to about 1/4" from the bottom of the windscreen.

An additional outer screen (http://www.whiteblaze.net/forum/showthread.php?t=17529)helps in very windy conditions as well.

niteshdw
03-29-2007, 19:51
Try lowering your intake holes to about 1/4" from the bottom of the windscreen.

An additional outer screen (http://www.whiteblaze.net/forum/showthread.php?t=17529)helps in very windy conditions as well.

Skidsteer, are you suggesting that by lowering the intake holes it would help reduce wind effect? I was thinking that the adverse wind affects were coming across the TOP of the windscreen due to the wide gap. Worth a try...hell, I got plenty of flashing.

Footslogger, from your pics it looks as if the Trangia pot stand facilitates the raising of the windscreen off the ground saving the need to punch holes. The Brasslite is designed so that the windscreen must sit on the ground.

Thanks for the quick reply's guys!

Skidsteer
03-29-2007, 20:03
Skidsteer, are you suggesting that by lowering the intake holes it would help reduce wind effect?


It's possible. Your windscreen intakes currently are higher than the stove intakes which could contribute to funky air gusts. JMO. though. Worth a try, right?




I was thinking that the adverse wind affects were coming across the TOP of the windscreen due to the wide gap. Worth a try...hell, I got plenty of flashing.

That gap would be the next variable I would play with but it's important to try one mod at a time.

The third thing I would try is reducing the # of holes in the windscreen.

niteshdw
03-29-2007, 20:15
OK Skids....makes sense. Tomorrow's project; lower intake holes to 1/4" from bottom, reduce number of holes by half, play with tightening up screen/pot gap without invoking radical burning. One step at a time. Thanks! :)

Footslogger
03-29-2007, 23:04
[quote=niteshdw;346783]
Footslogger, from your pics it looks as if the Trangia pot stand facilitates the raising of the windscreen off the ground saving the need to punch holes.

=========================================

I modified the pot stand so that it would work that way. If my pot was any wider in diameter the windscreen would fall outside the margins of the potstand sections and would rest on the ground. The Trangias thrive on good air flow from below, in my experience. The Westwind potstand supports the Trangia burner off the ground so, with the windscreen slightly elevated the "draw" is excellent and the burner uses fuel very efficiently.

'Slogger

Outlaw
03-30-2007, 08:50
Just some food for thought from a different perspective. I used to use the same stove as you (switched to a Super Cat) and had good luck with it. I use a KMart grease pot, which has a wider base than the MSR kettle you are using. Is it possible that if you switch pots for one with a wider diameter that could resolve your problem? Here is a quote from Aaron's website on pot sizes:

"The Turbo II-F and Turbo II-D have a standard pot stand that is 2.5 inches (6.25 cm) in diameter. For best results with both models, a pot or cup with a minimum base diameter of 4.0 inches (10 cm) is recommended. Narrower cups may have a problem with flame spilling out the sides and into the air, wasting fuel and lengthening boil times. The flame profile may be controlled by adjusting the simmer sleeve. The maximum recommended pot base diameter is 7 inches (17.5 cm) and a maximum capacity of 1 liter for the Turbo II-F, and 2 liters for the Turbo II-D."

My homemade windscreen (utilizing roof flashing like you) has holes punched like your original design with one exception; I did not put holes all the way around, but left an area about 6" long without holes that I face into the wind. On a completely windless day, I can just prop the windscreen on a pebble or something to raise it for a little more air flow, although I have never needed to do this yet. Also, I use a +/- 1/4" gap between the pot & windscreen.

big_muddy
03-30-2007, 09:36
I also just got the Brasslite Turbo-II D . . . I made my windscreen out of the aluminum oven liners (you can get them at the grocery for about $2-4 for two. I am using the Vargo Ti-lite mug, which has a base diameter of around 4 inches. I also get some flame spillage up the sides when the stove is on full but this is because the Turbo-II likes a pot with a base diameter of at least five inches. I have not had a problem with flames shooting out the side holes unless I blow really hard down into the top hole when it is on (its pretty cool effect with flames shooting all around). My suggestion would be to get something cheep, like aluminum foil, and first test the stove with a windscreen with no holes. Then start adding holes. Also, make sure that you donít wrap the wind screen around the base of the pot. leave an inch or so room so air can also get out. My guess on the flames shooting out the sides is that some how fuel got from the inner chamber through the double wall (the D in the stove name stands for double) and is then being ignited by the hot brass.

Big M.

niteshdw
03-30-2007, 11:31
Is it possible that if you switch pots for one with a wider diameter that could resolve your problem?


Had the same thought Outlaw. As luck would have it; I was in possession of a Evernew 1.3L with a diameter of 5 3/4". The MSR Kettle measures 4 1/2". I get the same effect though. I get a radical burn effect with flames shooting out the stove simmer vents. Using the MSR Kettle I expected some flame leakage up the side of the pot due to it's small diameter and can live with that. Interestingly though there is very little flame licking up the sides of the Kettle without a windscreen or a wide gap ( 1 1/2").



My guess on the flames shooting out the sides is that some how fuel got from the inner chamber through the double wall (the D in the stove name stands for double) and is then being ignited by the hot brass.


I'm thinking the same thing Big Muddy. My take on this is that a LOT of radiant heat is being directed into the fuel chamber, boiling the fuel over into the outer wall and exiting through the simmer vents. Quite pretty actually...however fuel efficiency, etc. is the pits. :)

The effect is repeatable throughout the burn by removing the pot (radical burning eliminated), put pot back on (flames shooting out vents).

OK, experimenting with different air hole configurations gives me somewhat better wind protection, though it's hard to tell because I'm not getting the gusty conditions I had yesterday (17 ~ 24 mph gusts). The wind thingee I believe can be controlled.

My biggest concern at this point is the uncontrolled flaming out the simmer vents when using any type of windscreen with a "reasonable" screen/pot gap (1/4" ~ 1/2"). Tried adjusting stove simmer vents in small increments from fully opened to completely closed. Only effect this seems to have is to starve the fuel of oxygen.

May shoot an e-mail to Aaron later this evening and get his take on this. Don't think it's a quality issue. If there was a solder leak between the fuel chamber and outer wall then I would see this with or without a windscreen or a pot I would think.

An enigma wrapped inside a mystery. :confused:

TDale
03-30-2007, 11:45
My windscreen is made out of the same material you describe but has NO holes drilled in it. Rather, it is elevated off the ground by approximately an inch or so. The top edge of the windscreen is about 1/2" above the bottom of my cookpot and there is approximately 1/4" of space between the windscreen and the outer wall of the pot.


'Slogger

I need to get the camera out. You and I came up with almost identical designs for the trangia westwind, totally independently. Too strange.

Fiddler
03-30-2007, 12:47
Hey niteshdw - I've never used a commercial alky stove, just home-made of a few different designs. But you might try something that works with them for burning problems. With some of the designs that require a pot stand I have found that the distance from the top of the stove to the bottom of the pot can be somewhat critical. Try raising or lowering the pot in relation to the burner. Might make a difference, might not.

niteshdw
03-30-2007, 14:11
On a completely windless day, I can just prop the windscreen on a pebble or something to raise it for a little more air flow


:-? Thanks to you Outlaw the thought (it happens occasionaly) occurred to me that perhaps I needed to think outside the box. Windless day....mmmmm! I'm testing this inside a closed garage with lights off to get a visual. NO WIND! Duh! NEED MORE AIR FLOW!

Radiant heat is the problem. Have to get rid of it either through the top by opening up the gap or through the bottom either by raising it 1/4" or so or punching more or bigger holes.

Grabbed the original windscreen, one row of 1/4" holes spaced 1" apart, 1" from bottom edge & added a second row 1/2" from bottom, spaced 2" apart and staggered between the holes punched in the upper row. I gots lotsa holes now....swisscheese! Closed up the windscreen/pot gap to 1/4" ~ 1/2".

Fired it up with 1/2 oz alcohol, simmer vents fully opened, 2 cups tap water in the MSR Titan Kettle, closed garage, lights off, grabbed a stopwatch and a Miller Lite. Showtime!

NO flames shooting out simmer vents, no flames licking up 4" over the top of the pot, nothing but a nice blue flame just barely extending past the diameter of the pot and a rolling boil just shy of 8 mins with a total burn time of 10 mins. :banana

Even a blind pig finds an acron now and then!

OK...this configuration appears to work in "ideal conditions". Will test outside once the weather gods decide to give me some more hurricane force conditions.

To all....you guys are GOOD! Thanks a bunch! Should our paths ever cross on the trail I owe ya a cold one.

Fiddler
03-30-2007, 14:35
Windless day....mmmmm! I'm testing this inside a closed garage with lights off to get a visual. NO WIND! Duh! NEED MORE AIR FLOW!
Easy to get the wind. Just put a small fan blowing at the stove.

Outlaw
03-30-2007, 15:02
Glad it all worked out for you Niteshdw. You actually did all the figuring out on your own, but a tall cold one sure would be great! Hope to meet you someday on the trail.

niteshdw
03-30-2007, 15:25
You actually did all the figuring out on your own


Contrare Outlaw...you planted the seed! I just added a little water to it.

Happy Trails!:)

Outlaw
03-30-2007, 15:41
Contrare Outlaw...you planted the seed! I just added a little water to it.

Usually when I plant a seed, all I get is weeds; and, no I don't mean the smoking kind!:rolleyes:

niteshdw
03-30-2007, 16:06
Usually when I plant a seed, all I get is weeds; and, no I don't mean the smoking kind!:rolleyes:

Try a little fertilizer!:D