[Stoves] ND-TLUD Burners at ETHOS -- What Works Best?

Fri Feb 5 22:39:38 CST 2016

Dear David

>We may be talking about different phenomena.  By "puff," "flash," and "burst," do you mean a momentary increase in wood gas?  Seconds?  Less than a second?  Or a minute or longer?  

I would say it is a minute or longer. 

Here is Stove one, an example of such a ‘smoke puff’ result 30 minutes long. The fuel is raw lignite, 26% moisture, it is a TLUD with no secondary air provision. 

That PM number is not 1921mg, it is 1.92 mg PM2.5/MJ delivered (heating), about 1.4 of the PM2.5 of LPG. When the y fixed the operation a bit the number dropped to less than 0.7. Just for comparison, there was mentioned here recently a very clean stove the Mimi-Moto which claims 11 mg/MJ delivered (cooking). The heating efficiency is about twice the cooking efficiency so this means the above stove in its later state was 1/7th of the PM2.5 of the Mimi-Moto, which was using processed fuel (pellets).

Another question is whether or not the power jumped up at the same time. Was it just an increase in smoke, or was it a jump in power? It may be that the ‘increase’ per MJ delivered was not much different which changes the discussion a bit. That stove did in fact pick up a little power at the same time so it indicates it increased the burn rate at the same time.

Here is the CO/CO2 and excess air (notice the clipping of the readings overloading the instrument). The timeline is the same so the PM increased as the EA rose, and you can see clearly that there was a drop in the CO/CO2 ratio towards the end. That is the power picking up, and the smoke increasing as the last of the fuel burned in the freely available air. The peaks in CO are caused by the fact there is no secondary air – it was all supposed to come through the fuel, and the thing got so hot it started boiling out the volatiles from the fuel some considerable distance below the pyrolysis later. At the time the oxygen level in the chamber dropped to zero. Hence the big CO spikes.

>Also: are you noticing smoke or a long flame?  I notice a long flame.

Not on these stoves which are closed, but yes I have seen that clearly. Not all stoves make a tall flame, some have good secondary mixing and it only shows up as an increase in the flame power. A tall central flame is basically an indicator of inadequate air mixing. If it was well-mixed it would not be rising up still looking for oxygen.

Here is an example of a TLUD stove, not particularly good (68 mg/MJNET) that has no such increase at the end:

The PM emissions are basically negative from the 25 minute mark whereas the earlier one had negative PM emissions in the middle but not at each end. 

Just for fun, here is the real time heating efficiency of Stove one above as it heads towards the end of the fuel. The green line drops through the floor at low power.  After 250 minutes it used the fuel to drive warm air out of the room at an efficiency of -100%. That is a flue damper problem.

You can see the fire developing (orange line) and then making a completely straight line of slowly decreasing power. It is possible (zoom it) to see the slight increase in the cumulative power at the end. I don’t have a good plot of the real time power curve. 

Regards

Crispin

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