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Author Topic: Optimizer 250 / Gassing / Tenting Over Nozzle  (Read 11308 times)

TheSnowDO

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #15 on: January 15, 2018, 07:40:05 AM »

I've set the air flow controls to specs as per recommendations on this site but if I told you I had a solid grasp of what the restrictor plates in the air-box do...... I'd be lying to you. I understand what the restrictor plate on the intake of the fan DOES, but not really sure the end results and I also don't have a strong grasp of impacts of different rates of air flow directed by the restrictors in the air box or overall flow has on gassing or efficiency of burn.  Can someone explain the effects of each of the restrictors in the air-box and the restrictor on the fan?

Don't have any way to measure the moisture content.

The wood certainly could have a higher than optimal moisture content.  I know it's drier than any wood I've put into it since I've been using it.
---- Building a wood shed with racks on wheels and THAT has been a priority.  Hoping to have racks full (Hopefully 2 seasons) before this coming June.

I would say.... almost half the wood I have stacked is split and still have issues with tenting / doming over the nozzle.


**** Really interested in what the restrictor plates do!!****
Do they changes direction of airflow?
How do they affect gassing and rate of burn??



Also pretty sure the fact that my house is so poorly insulated resulting in very long burns by the 250 prematurely expends the coals necessary to trigger gassing especially over the nozzle.

My experience has been that she is more reliable when I have at least 4-6" of coals (with low ash content) in the bottom of the burn box!!

I'll be VERY INTERESTED to see how she runs with a full compliment of well seasoned wood.
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hondaracer2oo4

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #16 on: January 15, 2018, 08:14:20 AM »

Others with optimizers can talk to exactly the flow path of the air. My suggestion about the air settings would be to mark or write down what you are currently at so that you have a baseline to compare to and return to if needed. After thst I would open the reaction chamber door so you can observe your nozzle gassing and then expierement with how different settings affect your flame from the nozzle and affect your coal bed in the area of the nozzle.

Your wood may be drier than you have ever used but you stated that you have always struggled with running issues so just being drier than thst probably isn’t the best comparison. From what you described about when your wood was cut and split I see your moisture content being in the 40% area which is very difficult to burn in a gasser without a deep coal bed and small splits.

You didn’t say how big your splits are? Can you describe how you load the stove with wood?

Heating demands do your heat loads vary greatly from user to user. The only way to know how many btu and hour your house is using is to Time how long it takes for the boiler to go from high set temp to low set temp when idling. Best to do this 2-3 times during the day st a given outside temp. Then you can average the time and calculate th btu per hour.
« Last Edit: January 15, 2018, 08:16:20 AM by hondaracer2oo4 »
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jreimer

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #17 on: January 15, 2018, 08:51:27 AM »

Ok, I'll give it a go.  Others will probably have differing opinions so YMMV, but this is what I have found.

The restrictor plate on the fan acts as kind of a global restrictor to limit the total air introduced into the system.  I run mine quite closed down to 1/4" to 3/8".  Any more open than that and I struggle with tuning it properly as that fan just creates too much air flow and pressure to gasify consistently. 

The top primary plate limits the air flow into the firebox which will determine your rate of primary burn.  With dry small splits it's surprising how little air is needed to keep things burning and coaling properly.  I am burning very dry wood that has been inside the shed as well as some structured lumber cutoffs, so I have mine closed nearly all the way.  It's a round plate covering a larger rectangular hole so the airflow is still there. I found it's very easy to add too much air into the primary firebox and blow the coals out of the nozzle and create a big hole and bridge.  With a gassifier you need to be running an oxygen starved environment in the firebox to create the flammable gasses for the secondary chamber.  Of course that also requires dry wood or the moisture will create too much steam in the primary firebox and kill the temperatures required for the secondary burn.  If you are just blasting the flames into the secondary chamber using the air force of the firebox airflow, you're just running a gasser like a conventional and it won't work correctly.  You'll get good gasification for the first bit before the wood starts to burn fully, then it will stop gassifying as all the gasses are being burned in the primary chamber, it will burn a hole above the nozzle and start bridging.  I think too much oxygen in the primary chamber burns all of the coals and wood around the nozzle fully as the air is going from the primary to secondary chambers.

The lower plate restricts the secondary airflow into the reaction chamber.  I have this set to 5 turns out.  This one doesn't seem quite as picky to maintain gasification, but 5 turns for me is plenty to supply enough oxygen for the secondary burn.  Any more and it just increases the stack temperature and blows coals up the tubes.

Keep your nozzle clean.  Maintain a small coal bed, but not so much coal and ashes that the wood sits too high and creates a potential channel to burn out over the nozzle.  Anything more than 2-3" and you're creating the opportunity for the wood to tent over the nozzle and not fall down so it's touching the nozzle and refractory because it's being supported on the sides by the ashes and charcoal.  Stir the coals up once a day to bring the charcoal chunks up so they can burn so it doesn't get too deep.  I clean the ashes out every week.

Long burns are actually ideal with gassers if they are tuned correctly.  If it's gassing well at the beginning of the burn but stops after 10-15 minutes, I suspect the problem is too much air as the wood starts to burn too much in the primary chamber and it wants to burn like a conventional.  I have mine tuned well and turned down to a slow enough burn that I am seeing stack temps of only 250 degrees with a good secondary burn and the nozzle glowing cherry red.  It can burn this way for hours at a time and maintain gasification.  Our natural inclination is to think that more air = hotter, cleaner burn = good.  The light came on for me when I realized and accepted the fact that it's really counter-intuitive that you want to starve the fire of air to limit the rate of burn and make it burn cleanly.  The nozzle is too small and restrictive to support a full burn in the firebox like you want from a conventional. 

What does a typical burn cycle look like? 
When does it gasify and when does it not? 
What is your differential set to?
How often does it cycle?

It still sounds like your wood might be too high in moisture content.  Can you post or PM me some pics what your coal and ash bed looks like as well as the "tenting" to see if that can help with further troubleshooting?  Can you send pics of your logs and splits?
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hondaracer2oo4

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #18 on: January 15, 2018, 02:50:52 PM »

 :post:
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karlk

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #19 on: January 15, 2018, 03:06:07 PM »

Thats a great explanation
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coolidge

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #20 on: January 15, 2018, 06:11:40 PM »

I find a secondary burn like this, with just about no air, gets me the most efficiency.


https://www.youtube.com/watch?v=IZNOW4raTaQ
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tinfoilhat2020

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #21 on: January 15, 2018, 11:26:33 PM »

grady is that how your 250 is running again now? same secondary air settings? that video u link said 2014...was that when ur 250 was in service the 1st time?
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coolidge

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #22 on: January 16, 2018, 03:15:18 AM »

Yes that is an old video, it's not running exactly like that now, but not far from it.
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jrider

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #23 on: January 16, 2018, 06:56:22 AM »

I'm in my 7th season with mine and I must be one of the lucky ones.  No matter what I put in it for wood (except for a load of wet wood) it burns it up great.  A lot of what I burn is junk that I produce in processing 130-140 cords of wood to sell.  It's all partial rotten, knarly knotty pieces - some of which can be pretty darn big, short cutoffs, sweet gum I don't want to split, or just pine that I can't sell.  I will add 2 pieces of info here that may or may not help but as already stated a box full of large rounds doesn't do so well.  If I have a big piece of gum - one that barely fits in the door and is 24"-30" in length, I need to pack small wood around it.  Also, as already stated, my unit seems to do best with 2"-3" of coals. 
Even though the wood I put in mine is mostly "uglies" it generally is well seasoned. 
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TheSnowDO

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #24 on: January 16, 2018, 08:09:31 AM »

 :post:

Great Post jreimer!!!

I've done what you suggested and so far it seems to have worked.
Will follow it over the course of the day/week and see how she does!!

The flame into the secondary does not seem as forceful and yet is seems to be a more sustained pure blue flame and the nozzle is cherry red.

Fairly certain that my wood has more than 23% moisture which some have said on her is near ideal!!

Been working on the Wood Shed and rolling rack system.  This year I should have 2 years of wood in by June and give it some time to cure.  Can't wait to see what she does with that.

Have hesitated to split the stuff I can handle wrangling into the box because I was afraid to create too much surface area to burn thereby burning thru the wood in the primary too fast.

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TheSnowDO

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #25 on: January 16, 2018, 09:44:25 AM »

Pics
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jreimer

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #26 on: January 16, 2018, 10:05:37 AM »

That's great news!  Don't be afraid to turn the air down in the primary to keep the wood cooking down to coals instead of burning up in flames in the firebox.  Keep us posted with how it performs over the next few days. 

I have found that ideally anything over 6-7" diameter should be split once.  Anything bigger than that is questionable to fully dry in a year or two.  If it isn't dry enough it won't form the nice coal bed you want in a gasser. 

The 250 is quite forgiving and very efficient if your wood is dry enough.  I have found that you actually can run really small stuff in a 250 due to it's wide range of adjustments.  I can burn full loads of small structured lumber cutoffs which was historically considered a no-no in a gasser by turning the primary air WAY down to just a trickle.  For bigger stuff you can turn the air up a bit.  Now that I understand it, I love the tuneability of the 250.
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Shindaiwa 488
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jreimer

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #27 on: January 16, 2018, 10:15:29 AM »

Nice pics!  That's a big bed of coals!  You shouldn't have any trouble burning cleanly with that bed.  I would even try to reduce the coal bed somewhat to make sure the nozzle doesn't get too restricted. 

I would consider splitting those bigger logs once to get better internal drying and good surface contact with the coal bed.  Nice shed and rack system!
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coolidge

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #28 on: January 17, 2018, 02:07:12 PM »

I used to split all my wood to 3-4" splits so I could pack them in there good.
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TheSnowDO

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Re: Optimizer 250 / Gassing / Tenting Over Nozzle
« Reply #29 on: January 18, 2018, 07:12:57 AM »

I have always been concerned about creating too much surface area to burn which would in turn decrease my burn times and efficiency but the more I think about it and after reading the responses to this post, it dawns on me that I am not "BURNING" wood so much as a I am "CHARRING" wood to create the actual fuel which is the by-product of the charring process.

I will be seasoning my wood better and splitting the bigger stuff for next year.

I will also be playing with the airflow settings, with the thought process of facilitating a low oxygen smoldering ( CHARRING )scenario in the PRIMARY with the goal of creating fuel for the SECONDARY and a sufficient base of coals to trigger ignition.

Adjusting the airflow already seems to have made a difference in the tenting or bridging.  Has not eliminated it but, I think my primary issue right now is the moisture content of the wood.

Will be very interested to see how she reacts to a more well seasoned fuel source.
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