[Stoves] Model II iCan -- update

Ron Larson rongretlarson at comcast.net
Tue Jun 7 09:59:45 PDT 2011


Jock

   Three reasons I can't promise to do the requested testing -although I wholeheartedly
recommend this to others:

   First, I spent full time on this sort of testing for several years in the mid-90's.  I have viewed a lot of small flames near holes.    Tom Miles started the stoves list in late 1995 just because there was plenty of dispute over whether one could make a TLUD work at all.  I don't think I can contribute much more now besides cheer-leading.  We need people with good equipment and modeling capabilities.

    Second, you and others are doing great work here.

    More importantly (to me) is the policy side of Biochar - and not enough time in the day.

Ron


On Jun 7, 2011, at 10:14 AM, Jock Gill <jg45 at me.com> wrote:

> Ron,
> 
> The best thing for you to do is to make a Model II and watch the flames.  It takes a while for the wood gases to build up, but at the half way pint, about 9 minutes, you will see the flames start at the edges of the secondary air holes and form the most interesting, swirling,  3D patterns.  It is quite interesting to watch the flames through the secondary air holes.  I find it fascinating that much of the time most of the flames appear to go DOWN into the iCan towards the fuel load.
> 
> I do not have access at the moment to a high temp thermometer so can not measure the temp of the stack gases as they exit the system.  But it would be a good thing to do.  I am know that there is a balance between stack gas temp and the amount of secondary air.  Too much secondary air and things are too cool.  Too little and the stack gases are dirty.  SO the trickis to find an amount that works pretty well most of the time.  I figure about 15 % - 25%  of the time the air:fuel mixture will be too rich.  This is a good reason for primary air controls -- choke back the pyrolysis rate by reducing primary air to keep the air:fuel mix 'just right'.
> 
> In a couple of weeks, when I can resume stoving, I will make an iCan and insulate it.  I expect I will be able to use much smaller primary air holes as I will be retaining a great deal more thermal energy in the system -- more like a retort.  I will keep you posted.
> 
> Please do make a model II and play around with it.  I would love to learn your results.
> 
> Cheers,
> 
> Jock
> 
> 
> Jock Gill
> P.O. Box 3
> Peacham,  VT  05862
> Carbon Negative Solutions
> (G) (802) 503-1258
> 
> 
> 
> On Jun 7, 2011, at 12:17 PM, Ron Larson wrote:
> 
>> Jock etal
>> 
>> New thought (I should have had last time).
>> 
>> I think a major reason for the reduced primary air is that the extra secondary air is lowering the temperature of the air in the short "chimney".  That in turn will change the pressure distributions.
>> 
>> You might (or might not) be improving the combustion efficiency.  Heat transfer efficiency presumably went down (if you could get back to the same power level). A good reason to have control over primary air.  
>> 
>> Another major reason to worry about hole diameter is to be able to get a flame "holding" on the hole edge.
>> 
>> Ron
>> 
>> 
>> On Jun 7, 2011, at 8:57 AM, Jock Gill <jg45 at me.com> wrote:
>> 
>>> Ron,
>>> 
>>> I have arrived at the same conclusion as you.  As you increase the secondary air in an iCan you simultaneously reduce the up draft and thus the amount of primary air pulled into the system.  I expect the rate of primary air through the pyrolysis zone controls the temperature in the zone and thus the rate of pyrolytic gas formation.  Of course this effect will only show up if the primary air is not wildly over supplied, creating run away pyrolysis.
>>> 
>>> As for the hose clamp, it only acts as a sleeve.  The two cans interlock quite well so not too much secondary air enters there -- esp. when the secondary air holes are relatively large.  There is much less resistance for the incoming air at the secondary air holes.  This reduction in resistance also must apply to the primary air holes/supply as well.  It is easier to pull air through 5/16ths holes than through 1/8th inch holes.   I believe this accounts for the "decreased [in] the pressure difference across the fuel supply".
>>> 
>>> I look forward to learning more.
>>> 
>>> Thanks,
>>> 
>>> Jock
>>> 
>>> Jock Gill
>>> P.O. Box 3
>>> Peacham,  VT  05862
>>> Carbon Negative Solutions
>>> (G) (802) 503-1258
>>> 
>>> 
>>> 
>>> On Jun 7, 2011, at 11:00 AM, Ron Larson wrote:
>>> 
>>>> Jock etal (adding stoves list)
>>>> 
>>>> If asked in advance, I would probably have guessed wrong.  Obviously you decreased the pressure difference across the fuel supply - but why is not clear to me.
>>>> 
>>>> How much secondary air is entering at the hose clamp?
>>>> 
>>>> Anyone reading this have a thermodynamic/flame model that would cover this very interesting question?
>>>> 
>>>> Ron
>>>> 
>>>> 
>>>> 
>>>> On Jun 7, 2011, at 7:47 AM, Jock Gill <jg45 at me.com> wrote:
>>>> 
>>>>> Doug,
>>>>> 
>>>>> [Update] When the 12 secondary air holes were enlarged to 5/16ths, but he primary air holes were unchanged,  the results from the modified two can system were good.  A load of 50 grams of fuel showed an increase of about 10% in the amount of time flammable gas was produced; the  post flame smoke was gone in less than 90 seconds; and the biochar passed all of the usual tests very well.  
>>>>> 
>>>>> Question for students:  Can you think of why the gas production time increased when the secondary air holes were enlarged from 1/4 inch to 5/16ths inch?
>>>>> 
>>>>> The above results increase my confidence level in my new secondary air design.
>>>>> 
>>>>> It is SOOO easy, I hope you will give t a try.
>>>>> 
>>>>> 
>>>>> <Model II modified.jpeg>
>>>>> 
>>>>> 
>>>>> 
>>>>> Regards,
>>>>> 
>>>>> Jock
>>>>> 
>>>>> Jock Gill
>>>>> P.O. Box 3
>>>>> Peacham,  VT  05862
>>>>> Carbon Negative Solutions
>>>>> (G) (802) 503-1258
>>>>> 
>>> 
> 



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