[Stoves] Role of secondary air on wood burning and charcoal stoves

[Ronal W. Larson]

Joshua, Sarbagya, etal

    I like very much your Roket  (not Rocket) design, but it falls outside Sarbagya's scope.  You are producing char;  he is not after char.

   One difference to note from TLUDs, is that you have a significant amount of secondary air enter in with the primary air at the fuel port.   In TLUDs, the flames or flamelets are usually "anchored" at the secondary air holes.  Do you see that in your design  (see note below)?  If not, you might consider moving the secondary air holes closer to the inside end of the fuels, where the (sideways, outward-moving) pyrolysis front got started.  My recollection from looking at Rob Oblak videos, was that he had a flame attached to the different parts of the holey briquette, indicating enough secondary air there already.

  See insert below also

On Aug 22, 2013, at 2:33 PM, Joshua Guinto <jed.building.bridges at gmail.com> wrote:

> Dear Sarbagya, Crispin and Ron
> 
> Jed here from the Philippines. 
> 
> Could you please take a look at my attempt..... the holey roket as a char making stove.  I thought i designed the holes to make a flow of secondary air in the roket stove. There are eight holes by the elbow, a little above the height of the fuel feeder. One hole is directly poking opposite the fuel feeder to reduce the stress of the high intensity flame on the stove wall (as Crispin advised me before)I made the holes to follow a co centric circle to make the secondary air twist. The stove wall is 3 cm thick and so the incoming air  would go about 6 cm through.  I thought this would add to the pre heating of the incoming air, to compensate for the absence of a double wall. And then to make the flame twist in the same manner as the fins of those from the designs of the recho roket would. 
     [RWL:  Both seem good.]
> 
> And so i observed that the flame twists and very clean, yellow with blue streaks shooting off from the holes. Please see  the attached pdf file.
    [RWL:  Blue streaks (streaking) maybe not desired??  Sounds like particulates.  What was the fuel?  Pili shells?]
> 
> Is this already the pre heated secondary air at work? 
    [RWL:  I'm not sure one can see the impacts of preheating - but certainly you have some.
> 
> My limitation is that i do not have instruments to verify all these observations. Perhaps your opinion could help for the meantime. 
>    [RWL:  It's going to be tough.  Comparing time to boil and comparing with true TLUDs via water boiled away will tell something on the efficiency side, but nothing on CO and particulates
> 
> Ron
> 
> 
> 2013/8/22 Sarbagya R. Tuladhar <sarbagya007 at gmail.com>
> Hi Ron,
> 
> I am basically looking at natural draft front loading continuous feeding wood stoves and natural draft charcoal stoves. The reason I am investigating these is that for a wood stove, having secondary air component "really" did impact on the CO and PM production. The two stoves similar in design had the same thermal efficiency but then differed a lot with the emissions. The secondary air supposedly used was via the exterior gap ( I am guessing similar to the Philips TLUD). However, I am not talking about the TLUDs here but just normal front feeding wood cookstoves. 
> 
> Heard from Crispin regarding the role of secondary air in charcoal cookstoves. So it is used to burn the evaporated volatiles and the CO to CO2. Designs of the Benin charcoal stove have a simple concept of having holes on the bottom of the outer body which allows air to flow through it and then this pre-heated air is exited out to the combustion chamber to aid in the combustion of the volatile unburnt gases. Does this feature work?
> 
> Looking to hearing from you.
> 
> Cheers
> 
> Sarbagya
>  
> On 21/08/2013, at 1:25 AM, Ronal W. Larson wrote:
> 
>> Sarbagya:
>> 
>>    Can you narrow down the type of stoves you are looking at?  And why?  
>> 
>>    You seem to be talking of TLUDs, and when mentioning consuming char is that in a TLUD?
>> 
>>    We have seen some nice designs with secondary being preheated with a central pipe, not the exterior gap you describe.
>> 
>>    At least one stove developer (Kirk Harris) has argued for using that exterior space for added insulation.  A topic fairly easy to compare in the lab you appear to have available.
>> 
>> Ron
>> 
>> On Aug 20, 2013, at 6:44 AM, Sarbagya R. Tuladhar <sarbagya007 at gmail.com> wrote:
>> 
>>> Hi stovers,
>>> 
>>> The debate on the role of secondary air both for natural draft and forced draft has been raging for quite some time now. Obtaining secondary air in pre-heated form has been the research area for me in the laboratory for the past few weeks. However, one conclusion I obtained was that secondary air if not pre-heated would have the tendency to put off the fire by blowing in cold air. 
>>> 
>>> Hence my question is:
>>> 
>>> What is the role of secondary air for wood burning stoves ? Is there an optimum gap for the secondary air to travel between the jackets of the combustion chamber before ejecting out into the combustion chamber ? How does this effect the performance of the cookstove ? I know a few cookstoves which have secondary air concept included and which seemed to decrease the CO and PM up to some extent. 
>>> 
>>> What is the role of secondary air for charcoal burning stoves ? Quoting Crispin "Secondary air is necessary to burn charcoal in a low O2 environment at a high temperature." How does this effect the performance of the charcoal cookstove?
>>> 
>>> Waiting for the responses.
>>> 
>>> Cheers
>>> 
>>> Sarbagya Tuladhar
>>> Pondicherry, INDIA

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