New Kovea Hydra

Discussion in 'Stove Forum' started by Madbasser, Nov 13, 2014.

  1. hikin_jim

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    @presscall, rain is forecast for tomorrow and Friday, so it may not be until this weekend that I get a chance to take out the stove again. I'm sure that a taller windscreen will help... but will it be enough? That I don't know. And yes the Hydra seems far more susceptible to wind currents than any stove I know -- at least for the one particular circumstance where pot and windscreen are both in place, as I have been emplacing them. I am quite curious to see what might happen:
    1. If I open up the windscreen a bit more in terms of its circumfernce.
    2. If I use a smaller sized pot.
    3. If I use a taller windscreen.
    Any one of the above may be able to disrupt the odd coincidence that causes the flame to yellow.

    @Jeopardy, now that's a good question about flame levels. I believe it does yellow at all levels of flame, but I haven't specifically tested for that. I will do so soonest. As for canister gas, no, I haven't even touched that yet. I was so dumbfounded that the stove could be as sensitive to wind as it appears to be -- and in the one particular circumstance only (pot and windscreen both in place). With the windscreen in place but no pot, there is no yellowing. With the pot in place with no windscreen, there is no yellowing. Very strange. However, I would be remiss to pass judgment on a stove without having tried one of its principle fuels. I shall try canister gas this weekend.

    HJ
     
  2. hikin_jim

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    Gentlemen,

    I believe I've more or less sussed out what is going on here with the Kovea Hydra. First, it is very sensitive to wind, and in particular to updrafts (as best as I can put together) coming up from under the burner.

    Take a look at this photo:
    IMG_3734b.JPG

    The Hydra is a fairly tall stove. The Hydra comes with 5.5" (14 cm) high windscreen. The pot sticks up well above the edge of the windscreen. The wind rushing in, hits the side of the pot. Some of the wind flows over the pot, no problem. However, some flows down the side of the pot into the area of the burner.

    IMG_4028b.JPG
    The wind plunging down into the gap between the windscreen and the pot sidewall strikes the aluminum base plate and is deflected toward the burner intakes. The wind currents hitting the intake ports disrupts the intake of air which in turn disrupts the fuel-air mixing process, causing the yellowing of the flame. @presscall I think you may be on to something with your discussion of the mixture becoming too rich. Somehow the vortices in the wind disrupts smooth air intake and fuel mixing.

    Now, interestingly, per suggestion of @Jeopardy, I tried the same with canister gas instead of petrol (MSR Super Fuel to be specific). No yellowing. The flame was still disrupted in the same pattern visually as before, but no yellowing.

    I suspect that the aperture of the jet is optimized for petrol and the fuel/air ratio needs to be just so. When the air intake is disrupted, the mixture becomes too rich, and yellowing occurs. Canister gas will normally have a larger jet aperture than for petrol, but in the case of the Hydra, only one jet is used -- the one presumably optimized for petrol. So the mix is a bit lean with canister gas. If the air intake is decreased, it doesn't hurt anything to richen up a lean mixture. At least that's what I think is going on.

    Whether I've got the mechanism precisely right or not is irrelevant. The relevant datum is that the flame yellows severely with a short windscreen when using petrol as fuel.

    Now I've mentioned the height of the wind screen several times already, and for good reason: use a taller windscreen, and the problem essentially disappears. With a windscreen that extended to within a couple of cm of the top of the pot, I got good results. With a windscreen that extended a cm or two above the pot, the Hydra acted almost as though there were no wind at all.

    IMG_4026.JPG
    Here, my Hydra is ensconced within a 9.5" (23 cm) tall windscreen. I got very good results with this set up.

    My conclusions are as follows:
    1. The Hydra is very wind sensitive, particularly to down drafts coming down between the pot sidewall and the windscreen.
    2. The wind screen that comes with the stove is grossly inadequate. In these tests, I used a 2.6 L pot which is hardly an unusual size for a stove of this type. I would think a large stove of this class should handle pots that range in size from 1 L to perhaps 5 L. My 2.6 L pot would fall in the center of that range, so I think my results are truly reflective of the nature of the stove.
    3. It is **essential** that the Hydra be protected from wind. One's windscreen needs to extend to within a cm or two of the top of the pot. A taller windscreen doesn't hurt anything and may indeed improve performance. I think an 8" (20 cm) windscreen should generally provide sufficient coverage, but I haven't tested that exhaustively.

    Here's a video where I'm fiddling with the wind screen. You'll see me open up the windscreen deliberately several times, and you'll see the flame respond by yellowing. Note however that when the wind screen is fully employed, that that the flame does quite well.


    And again I apologize for the video quality. A tripod is on order but has not arrived yet.

    HJ
     
  3. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @hikin_jim
    Excellent Jim!
    I always find your discourses on stoves and their use in the field profoundly satisfying and this exploration of the Hydra has been no exception.
    Thank you.

    John
     
  4. hikin_jim

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    Well, thank you, @presscall.

    I'm now in a bit of a quandary as to how to rate the stove. I really thought it was no good when I first encountered the yellow flame problem, but, as you know, after I thought about what was happening, I realized you just had to get the right sized windscreen. However, one could still be vulnerable in high, gusting winds. I'm not sure, and unfortunately it's beyond my power to conjure up a wind storm on demand. (It's probably better that way; I can get awfully cranky sometimes) :lol:

    I think under normal conditions it's a perfectly usable stove. I suppose I could recommend it but with two caveats:
    1. You **must** shield the stove from wind; the supplied windscreen is inadequate. A windscreen of a minimum 20 cm in height is needed.
    2. In strong, gusty winds, there is the possibility that the flame may become inefficient, at least momentarily.

    The second point is putting it nicely. I think I would have to explain what I mean a bit more. I would also post one or more videos of what could happen if one could not shield the stove properly from wind.

    Many thanks for your input and encouragement. Always fun to have (I think) figured out what's going on with a stove.

    HJ
     
  5. hikin_jim

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    @presscall @Jeopardy and whomsoever may have interest:

    Well, God only knows what mother nature can throw at one, but I *think* my theory that you really need a taller windscreen is vindicated. It was a bit windy today, so I went over to Crystal Cove State Park and shot the below video. It was shot with my iPhone, so the sound volume is somewhat lacking. However, if one were to turn up one's speakers, I believe the lack of volume can be compensated for.


    HJ
     
  6. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    The weather was very obliging!

    Convincing demonstration certainly Jim. Apart from the benefit in getting the Kovea to run right, a windshield protecting a pot is no bad thing in reducing the wind-chill effect and preventing prolonged boiling time.

    John
     
  7. hikin_jim

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    @presscall
    I very much agree. There's every reason to use a windscreen and little reason not to use one. They focus the heat, and on remote set ups, they keep the fuel supply properly separated from the flame. Oh, and yes, they block wind too. ;)

    Were anyone interested, my completed review has been published on SectionHiker.com:
    https://sectionhiker.com/the-kovea-hydra-backpacking-stove/

    I finally got a tripod for my iPhone, so there's a somewhat improved video available.

    HJ
     
  8. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Thanks for the link to the review @hikin_jim

    It's a very fine review indeed, comprehensive, critical where justified (crucial issue of instructions that can be misinterpreted for example) and picking out the many positives for the stove.

    Excellent piece, excellent research and analysis to complete it.

    John
     
    Last edited: Nov 28, 2016
  9. HunterStovie

    HunterStovie United States Subscriber

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    @hikin_jim
    Do you think a heat exchanger pot would help with the wind sensitivity of the stove since the exchanger acts like a windscreen? Although I would never purchase a Hydra I did enjoy your review, thanks.

    Mike
     
  10. hikin_jim

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    Thank you, @presscall; you're very kind. The review was quite a bit more work than I would have thought going in. I do hope I've rendered the "sense of the stove", that is that I have given enough information that one could then decide whether or not a given stove were suitable for their needs. That's my hope at least. :)

    @HunterStovie, let me answer you regarding heat exchangers and wind as follows: Take a look at the first video in this blog post, and then compare it to the second. I think you'll see that a heat exchanger is not a critical factor in windproofness for a stove.

    HJ
     
  11. shagratork

    shagratork United Kingdom Moderator, R.I.P. Subscriber

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    @hikin_jim
    Thanks for posting a link to your review.
    It is very detailed and also very enjoyable.
    I appreciate the research and thought put into the process and also the many hours it must have taken you.
     
  12. hikin_jim

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    Hello, @shagratork,

    Thank you. I was greatly aided by @presscall and @Jeopardy who allowed me to bounce ideas off of them and who gave me some good insights.

    HJ
     
  13. HunterStovie

    HunterStovie United States Subscriber

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    @hikin_jim
    I was not suggesting that a heat exchanger type pot by itself would help, only that it might prove beneficial with the shorter windscreen as long as the additional height didn't place the pot above the top of the windscreen. Just a thought and something I would try if I found myself in a similar situation and had the equipment to test a what if theory. Like I said above I would never buy a Hydra, but the information might prove useful to others under a different scenarios than this one.

    Mike
     
  14. hikin_jim

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    @HunterStovie,

    Yeah, the heat exchanger might at least off set the loss of heat due to wind, at least in light breezes. And that's a good point about the heat exchanger raising the pot still higher. Ultimately, I think getting the right size windscreen is the best bet. Barring that, perhaps cooking behind a log or in the lee of a large rock.

    HJ