[Stoves] Stove comparison/ PM

[Crispin Pemberton-Pigott]

Dear Alex

>Glad to know there are still mysteries to be probed.

Hey, no shortage on any front!

>One is a very low PM level from a TLUD stove with 0.5% excess air.

>I assume this is with coal. Do you have this data logged to share?  

I do. I will try to write up that test today - lots of time needed because
the mass data was taken down by hand... The SP232 chip stopped
communicating.

>Are you doing PM testing with wood fuel?

We actually ran one of the TLUD's with wood twice in a day to see what we
got. When we test a new equipment setup we need smoke so we just toss
something on the scale. TLUD wood, as a starter of fuel is pretty clean. The
cleanest stoves start with wood even though it is capable of making a great
deal of smoke if done incorrectly (like, putting coal on top of a wood
fire).

>Snuff a biomass fueled TLUD and its a PM cloud. 

Quite a bit of that is condensed water vapour. It seriously skews the PM
readings.

>So it's the burner that matters. 

Yup.

>If PM shows up above the flame then it is likely sneekage due 
to insufficient mixing and/or too large a space for the flame PM laden 
gasses slipping by in the outside lane.

Assuming you are not measuring moisture droplets, partly. Flames hitting a
pot are a major source. Flames hitting the side of the combustion chamber,
ditto. Poor mixing giving both high excess air and high PM even if the
chamber is hot. High oil content in the coal (Baganuur Mine) is an issue. It
takes more physical space to burn it - long orange flames. It needs a longer
flame tube. I burned if very cleanly in a DD stove that had a long 2" pipe
and no exits along the way. 

>Good wood pellet stoves have low PM without being gasifiers. 

Yup.

>Low moisture helps. 

I have data on that. Traditional coal stove with summer-air-dried fuel was
maybe 75% less PM in an identical burn.

>What role does the flue particle size and distribution and depth on the
grate play? 

Dominated by the draft and thus gas velocity. In a really low EA situation
the chimney gas speed is 100-150mm / second. Sucking up the ash is not
really a big issue. I have seen recently a case where the user was tossing
wood into the combustion chamber from above, creating a massive wood fire
for rapid cooking. That made a great deal of large PM - what seems to be
partially burned ash. It was pink, Cecil insists.

>Your coal is pea sized, I think? 

No. Mostly 25-30mm with some 12-16mm to start faster. The small stuff is
piled against the wood before lighting. The wood is lit on top and as it
burns down, the small bits of coal fall onto the wood and light rapidly.
They in turn light the larger coal. The Silver and other TLUD's all use
large coal 40mm or so. If it is too small it doesn't get enough primary air.

>Have you found any  differences with large sized fuel?

Only as it relates to pulling air through it. In fact people toss in
anything including powder. It helps in the hopper-equipped stoves to have
the powder near the top not the bottom. Works out better on average. The
hoppers are air-sealed so it has no effect to be on the top.

Regards
Crispin