[Stoves] Trials on TLUD gas burners

[Ronal W. Larson]

Paul,  list  and Julien  (who I addressed last message to but failed to send to; apologies)

	See inserts


On May 2, 2014, at 7:38 PM, Paul Anderson <psanders at ilstu.edu> wrote:

> Ron,        
> 
> I agree that it is better to have some blockage of the central part of the riser/combustion area.  But in the burner called "rectangular" (which could also be called "annular with interruptions") Julien is forcing the combustible gases to the periphery but then lets the flaming gases be pushed back into the center.  
	[RWL:  Maybe your are arguing for a second upper blockage?  I hope someone will try that but the fact that the no-blockage case looked pretty good doesn’t encourage me on that.
	I think it OK that the flames are centered - as they hit the pot where you want them to (in the center).

> 
> 
> My preference (subject to further experimentation) is for the ConcBelow  to also have a buff body or other obstacle into the center of the rising gases, keeping them forced to the periphery where the secondary air is entering.   The advantage of ConcBelow is that IF pyrolysis is not uniform in the fuel chamber and is sending more gases up one side than the other sides, those gases should be required to go through a central concentrator hole.   And then be spread out as uniformly as possible to all of the sides.
	[RWL:   It  has been a long time since I did any testing, but my recollection is that the pyrolysis front only very rarely did not go downward extremely uniformly.  If your pyrolysis front doesn’t behave that way, you are in a degree of trouble that a blockage can’t help.  With a fuel as uniform as pellets, there much be some physical phenomenon that keeps the pyrolysis front uniform.
	So I am not yet ready to agree on the uniform spreading theory of your last sentence.  Julien’s results says otherwise, as did all my early work.
> 
> Historical note:   The original and famous Reed-Larson (1996) natural draft TLUD did not have any effort at concentration, and it can be faulted for having flames on one side without ability to propagate flames on the rest of the annual ring of rising gases.  
	[RWL:  I’m not understanding “on one side”.  The flames were certainly started only on the outside and traveled up the chimney on the inside.  Also not understanding anything on the last part of the sentence.   There was generally an unbroken “cone” - because I rarely used holes for secondary air - usually just a slit where two cans of equal size were “cobbled” together some way (often paperclips).  This slit could be an eighht to a quarter inch wide.  Pertinent to comments below, the flame was (I recall) usually attached to both the upper and lower can.  The paper was ’96, but the work was first on Tom Mile’s “bioenergy” list in 1995, and people saw early work I think even in ’93.

> There is a "wick" (obstacle) in the riser.  
	[RWL:  I have never used the term wick - and only vaguely recall obstacles in the center.  That was Tom’s word and approach.   The central object I am not objecting to at all, but the “Concabove” (washer shape above) now seems to be questionable.  I hope many others can replicate Julien’s tests.
	
> In contrast, the major accomplishment of Paal Wendelbo was with the concentrator disk (or hole) in the early 1990s, which I independently also accomplished in 2005 with the Champion TLUD design.   Some of us did put buff bodies into the rising flames (I suspect Wendelbo did), but we were always with the basic configuration that Julien has called ConcAbove.  
	[RWL:  But that is now being called into question.  That is Julien's C design, which gave a lot of soot.   Until Julien’s message I had no idea this would be wrong - but I never tried that approach.  I have no idea why the difference in soot should be so profound.
> 
> The only person that I recall as advocating what would be a form of ConcBelow is Crispin.   He has pestered me about it, and doing that research was on my list of things to do (but the list is far to long).   I thank Julien for doing that task on his own.  It is highly interesting that the work of Julien Winter was not done in all those intervening years.   
	[RWL:   Can you (or Crispin) give a cite for that design.  In general Crispin has been discouraging about making char, so I wonder what he did.  This also brings up the issue of using concentrators  with Rockets - to the best of my knowledge, not done.
	With Kirk Harris, I have been exploring other options - but it is premature to discuss that since the ideas haven’t been tested.  
	One of the best looking flames I have seen had a secondary air interior pipe, with radially oriented flames butting into each other. Had wonderful turbulence.  But that group disappeared - from my view at least.
> 
> And also, Alexis Belonio was advocating in January 2014 at the Aprovecho Open House about some form of spreading the gases that need to reach the secondary air that is coming in from the sides.  
	[RWL:   That would seem to be Julien’s design “C”.   But to the best of my knowledge Alexis is not working in this type of TLUD.  See Paul Olivier’s site for a description of the flamelets, which are unchanged from Alexis designs.
	
> Alexis affirms that we should be able to have a blue flame from wood gas.  
	[RWL:  I confess to not understanding either how to obtain blue or how much advantage there is to it.  I only saw yellow.  But the yellow is/was quite clean.  The advantage of yellow is radiant heat transfer to where there is a mixture ready to ignite.  Also radiant heat going to the cook pot.  I’d like to hear more from anyone on how to achieve blue.
	In Julien’s short nighttime video, the design “C” is blue at the the base, but mostly is yellow.

> It is all about mixing (especially pre-mixing if possible).   
	[RWL:  To my knowledge the only char-making stove that has pulled pre-mixing off is Nat Mulcahy’s World Stove “Lucia”.  We met in 2008 - and I stopped thinking much about stove design thereafter.  Pre-mixing should be the “Holy Grail”.  But yes mixing is essential - Turbulence - to go with two other T’s:  Time and Temperature.
> 
> ***** change of topic ***********
> 
> I comment on Ron's statement:
>> 
>> By looking closely, counterintuitively, the flames seem attached  NOT over the gas apertures, but rather between them.  I think this is true in all cases but can’t see the case C “attachment” points.  Except in private dialogs with Paul O, I have not seen this stated before in print  - and don’t know if it should be encouraged or discouraged.  
> I think this has been considerably discussed or at least observed.  
	[RWL:  If anyone can provide a link, that would be much appreciated.  Paul Olivier and I never found a write-up - and it still baffles me.  Are there other TLUD photos around I can look at, that show the flame appearing between secondary air holes - not over them?
> It relates to the phenomenon of the "inverted flame" in which the air enters a zone of combustible gases instead of the combustible gases entering a zone of air (which is the case of common gas burners on stoves.  
	[RWL:  Well,  I think there is another explanation.  Paul Olivier has his gas flamelets enter into air - not the "inverted flame”, which I agree is or could be substantially different.  But the Olivier/Belonio flamelets (very short - not the typical long flames of most TLUDs) look remarkably similar to small match or candle flames.  I think the diffusion process is substantially similar, in both normal and “inverted” flames.  I think the results obtained by Jim Jetter showing low particulates and CO with many TLUD tests indicate the regular and inverted flames can’t be widely different.  The emissions are arguably superior with TLUDs - and (maybe) independent of whether these flames seem to originate from over or between holes.
> In the TLUD gasifiers, the secondary air holes are sufficiently close together that the inverted flames are filling the space between the apertures of the incoming gas (which is actually air).
	[RWL:  As noted above, I mostly operated with a continuous circumferential narrow slit - and never saw this - which is why I used “counterintuitively”  Has anyone ever seen this with a natural gas multi-hole burner?  My discussions with Paul Olivier centered on the importance of radiation - possibly coupled with the fact that pyrolysis gases have a chemistry (not try for methane) which gives you a smaller number of reaction particles at the end than going in.  Makes for a helpful pressure difference.  (This holds for whether there is gas entering air or air entering gas.)
	Re the last clause ("which is actually air") needs more discussion.  There has to be some gas there in order to have a flame.  If there were still eight input ports, but appreciably smaller, would we see the same thing?  Does it have to do with a big air speed through the input ports?
	I think there is a doctoral thesis lurking in here somewhere.   There may be some optimum of hole diameters, spacings, shapes, separations, etc - to get the best flames (better “flamelets”).

Ron
> 	
> Paul A.
> Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD  
> Email:  psanders at ilstu.edu   
> Skype: paultlud      Phone: +1-309-452-7072
> Website:  www.drtlud.com
> On 5/2/2014 7:44 PM, Ronal W. Larson wrote:
>> Julien,  cc list:
>> 
>>  Nice report.  Thanks for sharing. 
>> 
>>   1.  My conclusion is that the best results were from what you call the “rectangular hole design” - generally the right-most in your figures.  I put the difference down to the fact that you are blocking the central part of the combustion area, so the pyrolysis gases are much closer to the secondary air supplies.  Call this A.
>> 
>>  Next best is what you called concentrator below  (the left one - which has 16 air ports (presumably smaller??).  Call this B.  (Do you see any preference for 16 over 8 secondary air ports?
>> 
>>  It seems very wrong to place concentrators above the secondary air ports.  Call this C.
>> 
>>  2.   In your Figure 3, this is B, C, A from left to right.  (OK?)  The middle figure is the worst?
>> 
>>  My criterion is the set of photos in Figure 4, with very clean combustion for A, next best for B, and bad for C.  In Figure 4, in the top row, B is at the right, and th bottom row, you have C left and A right.  I see A as better than the open chimney - but no videos or photos of the open chimney in action.  Can you compare A and open further?
>> 
>>  3.    In the still photo and the two videos, I perceive a phenomenon I have seen before (with Paul Olivier’s deign).   By looking closely, counterintuitively, the flames seem attached  NOT over the gas apertures, but rather between them.  I think this is true in all cases but can’t see the case C “attachment” points.  Except in private dialogs with Paul O, I have not seen this stated before in print  - and don’t know if it should be encouraged or discouraged.   I believe if your large outer air ports in A, were made narrower and longer in a circumferential direction, there might be a more continuous flame, through which little pyrolysis gas could pass without being combusted.
>> 
>>  My guess is that you now have considerable excess air, and so could get better het transfer to the cook pot, with less secondary air aperture.
>> 
>>  4.  In the design A, all the holes cut be cut so as to create a swirl - which might give improved combustion - and allow a shorter chimney.
>> 
>>  5.   You would have a more “salable” design if you could control primary air.  A short piece (or two?) of electrical conduit (1/2 “ ID, 7/8’OD - or larger??) costs hardly anything and could be fitted with a conical plug to control primary air.  It would have to penetrate the vertical walls of both cans, but wouldn’t have to have a really tight fit - just a lot more control through the pipe rather than air slipping around it.   This would replace your present multi-hole bottom, and you would have to put in a different “holey” plate for the pellets to rest on.  Of interest to all would be how large a TDR (turn down ratio) you could achieve (run for 1.5 hours??) 
>> 
>>  6.  So lots of suggestions that need not be on your plate.  But I think you are really on to something with A vs B or C.  Congratulations for what you have already accomplished.
>> 
>> Ron
>> 
> 
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