http://www.girlmark.com/blog/index.php?p=250
I finally got around to getting a cheap Harbor Freight digital thermometer with a K Thermocouple probe, and measuring the flame temperature of my very simple, not-optimised Turk Burner. The temperature inside the flame hit 2000F before the thermometer maxed out. Strangely, on the Celcius setting, it went higher, to 1150C, where it fluctuated back and forth a few degrees like I'd expect. I don't know that I trust a HF thermometer, but it's relatively accurate at lower temps. No, I can't use an IR thermometer, the cheap ones max out at about 1000F.

This is pretty good news as the temperature is an indication of how complete the combustion is, and it's been a big subject of speculation in the biodiesel world for a while. If the vegoil/glycerine/whatever didn't burn close to completely, there are questions about what pollutants the unit would emit.

I was really hoping that the Turk reached at least 1500F. 2000 is much better.

I'd been working for a few hours already and got so excited that I messaged a bunch of nerdy people the news about the flame temp. Then I realized that it was only 7:30 am in California and that I'd probably woken several people up. Oops.

I was burning washed/dried biodiesel. I also did a batch of FFA/biodiesel mixture from acidulating glycerine, and it hit more or less the same temperatures, assuming I trust my thermometer. The difference is that the washed biodiesel left no ash, which is to be expected, whereas the FFA/biodiesel mix left almost as much ash as I get when I burn unwashed biodiesel. I was actually doing this experiment just to look at ash production- to see if the salts from acidulation stayed in the FFA/biodiesel layer or if they sank to the glycerine/water/water-soluble contaminants layer. I had used HCl to acidulate the glycerine's soaps, which produces non-precipitating salts in this case. I'm sure that if I used sulfuric acid, which is DANGEROUS to use by the way (boiling acid/glycerine results when you first add it), it would have had fewer salts in the oily layer, as it forms a large 'cottage cheese' looking layer of insoluble salts.

The fact that it hits 2000F means a few interesting things:
-that should be a high enough combustion temperature to stop worrying about acrolein emissions. While acrolein isn't the only pollutant created by combustion, it's one that gets brought up over and over again as a concern with vegetable oil burning or glycerine burning.

-you can't of course actually capture all 2000F worth of energy with a heat exchanger as that was just the flame temperature itself, but the air temperature right above the flame was "only" 800C, which is plenty.

-flame color is caused by something other than incomplete combustion. The Turk makes a really bright flame on some fuels (like you need cutting goggles to look at it, which you'd never know by looking at photos of Turk Burners on the Internet, as they all look yellow due to bad photography of bright objects), and a yellower flame on others (however, it doesn't smoke or smell during the 'good' part of the burn cycle, till the levels drop too low and it starts to smolder at the very end of use). I was wondering if the yellow flame was due to poor combustion or due to other colorants in the container I was using, the fuels I'm using, or something else.

-I need a smaller Turk Burner so that I can actually use reasonable heat exchanger that can keep up with the heat. I think that mine consumes about 1.25 gallons of biodiesel an hour. I'd be wasting most of the BTU's if I couldn't get a better heat exchanger.

Photos from last summer (2007) experiments with Turk Burner fuels:

Don't have any better info on temp measurments. I do have 48 inch long type "K" SS thermocouuple elements available, these are new overstock from a local commercial ceramic kiln, plain thermocouples with just an inch or so of the two thermocouple wires exiting one end of the 1/8 inch diameter ss tube.

Have you yet tried putting a turk burner inside any type of enclosure or enclosed heat exchanger, all the posts that I have read of folks doing this indicate it changes the burn considerably and causes MUCH smoke and soot even when the burner burns clean out in the open. A friend here tried this and had this same problem, put a 6 inch diameter (straight pipe) turk inside a 3ft X 3ft X 3ft coal/wood furnace unit and it produced a couple inch layer of soot and sootsicles covering the entire inside surface in just a few hours of burning, the fuel was used engine oil but this same fuel had burnt cleanly outside of the enclosure.

I have a couple pipe-coil type heat exchangers from oil fired steam cleaners, these don't have a direct flue opening, the heat excapes between the spaces between the wraps of the pipe, probably won't work with a turk unless it will burn very cleanly, may work if burning biodiesel, havent tried it. These works fine when burning diesel or fuel oil in a normal fueloil pressure type burner even though there is a slight puff of smoke each time the burner cycles the flame on.

Type K are useful up to 1250 C.
Type R are useful up to 1450.
Type C and D are useful up to 2320.
To measure the max temperature ranges requires different equipment than the cheap HF gage.

Each needs different wiring, cold junctions and amplifiers. I recommend reading the thermocouple guide at Omega Engineering for options, and also read how to make your own cold junction the old-fashioned way (a cup of ice water). Then you can measure the voltage with a good DVM, and find the temperature using a look-up table.
Cheers,
JohnO

I use the cheap hf thermocouple display for bronze casting, and it's usually within 30*c of a much pricier one. I just prefer it because it's small and battery operated. I don't know how well it's cold junction calibration works, but it's plenty close enough for turk burners. It's the display electronics that can't go over 1999*f, not the thermocouple. I bet it's reasonably linear up to about 1800*f. It's probably +/-20*c up to 1100 c

quote:

Originally posted by johno:
I recommend reading the thermocouple guide at Omega Engineering for options,

JohnO

duh, thanks. I forgot about that resource.

Theoretical flame temperatures: Diesel/air 1455 degC (2651 degF)
Biodiesel/Veg oils/air (varies, depending on oil properties) 1350 to 1420 degC (2471 - 2588 degF).

Some different high-temperature thermocouples and their max temperature ranges:
90% Platinum/10% Rhodium, up to 1750 degC (18.55 milliVolts)
87%Platinum/13% Rhodium, up to 1650 C (20.37 mV)
Chromel-Alumel (Type-K), up to 1400 C (55.81 mV)

Cheers,
JohnO

(I just posted this to the MI biofuels list, then I saw this thread).

Mark,

I read your bolg post about the turk burner stuff. I have an idea,
and some hardware, for a smaller scale turk burner with a longer
aspect ratio.

Most burners I see are made from 25 lbm propane tanks. Usually the
burn chamber is about as wide as it is tall. I have the idea to make
one which is narrower and much longer.

What I have for material is a driveshaft tube. The inner diameter is
3.25 inches, length about 36 inches. This started out life as my
abmerlite tower - a project which has since been abandoned.

The base of the driveshaft is steel, the tube is aluminium, with a
friction weld joint between them. he far end has been cut off.
There is already threaded in a 1/2 inch NPT port at the steel base.
This could be used for fuel input.

What isn't in place is a section for air intake. This would either
have to be done directly with a small tangential inport, or more
traditionally, with some canister being placed over a setion in the
lower part of the tube for air input.

I think the interesting part of such a design is that with the long
aspect ratio, there is more residence time before the fuel/air
mixture is exhausted. You could probably instrument the thing to
take temepratures at different points up the tube to determine
tempertaure profiles, burn completeness, etc.

Since the tube is aluminium, it may also integrate well into a
section of a concentric tube type heat exchanger. Aluminum conducts
heat better than steel. I have to check, but I think the tube wall
is 1.5 mm thick.

I doubt I'll ever get around to building this, so if you want what I
have so far, let me know and I'll ship it down there. I can send
some photos along beforehand if you want.


Regarding the thermocouple stuff, I'm with johno. My data acquisition equipment tops out at 1372 C (2500F) for K type thermocouples. Probably its internal linearization function won't give required accuracy for that last bit.

Flame temperatures are very tricky to accurately measure, especially if transient. Thermocouples indicate the temperature of themselves, not the temperature of what is around them (plagerized from a former instructor). Use the smallest T/C you can get and sample quickly. Our sister company does a lot of exhaust temperature / catalytic converter temperature measurements. They use K Type thermocouples which are as small as 0.5 mm diameter.

Horn

Super interesting, thanks. I'll reply more later.

I'm actually planning on making the next Turk with refractory cement, a small pool of liquid, and one blower tube instead of a bunch of tiny holes- I saw a really good one locally that a guy who apparently posts as "Bubba NC" (he's the furthest thing from a Bubba that you can imagine btw) built that way. I think the solution is small flames because of issues with harvesting that much heat at once.

I'll write more later, thanks for the posts!