Flare Color and Meaning

This is something I would like to get schooled in here.

Ive noticed many different color flares that have come out of my units. What I like to know is what is happening inside my units when certian colors are present. Ive seen just about every color under the sun come out of my units. Ive even seen a really cool looking green color once.

Most of the time the flare is blue or purple but at times it will change temperarily to a peach/white color and then go back to the blue purple color. It took a lot of tuning to get these machine to this point. I think if I had a better understanding of how to read the flare it would be much easier to tune. So having some sort of reference would be a nice tool for tuning.

Is there a chart any where that shows all the posibilities of whats going on inside when certain colors are present.


Hi Matt
Fuel air mix will change the color of the flare, blue-white = lean mix, red-orange = rich mix, green in the flare would be some form of copper burning and rich red may have some iron in the flame.
hope this helps some

Well kinda sorta.

Are you refering to the jet size?

What about grate settings and char bed density, moisture content, jet lengths vs CFM. restrictor openning vs jet hight. restrictor openning vs CFM. I could go on and on. All of this has an effect on the gas quality. Id like to see a detailed chart of all posibillities.

Yes the introduction of other elimates contaminating the gas is good to know as well.

Yeah the green flame did just happen before my inadiquate blower blue up. I figured that was what it was. I actually learned a lot form those POS blowers the first ones I used introduced air into the gas and gave false info when I was trying to read the flame to figure out what was going on. But now the new ones are bullet proof and do not introduce any air into the gas.

But for example an orange flame and a peach color flame are not the same thing. Below is pure hydrogen. it burns an orangeish white color. There are other observations Ive made as well . The sharpness of the flame I think we could learn from as well. Hydrogen has a very dirferent burn quality for intstance.

Sounds like you are headed to a really scientific journey that requires a lot of knowns - hard to get outside of a lab. For the air part - are you force feeding the air into the gasifier, or drawing the air through using a venturi ejector ? you got air, fuel and temperature and duration of the gas at temperature to fully react it. all those (and probably more variables) would make a difference in the gas quality.

Are you tuning the gasifier based on the flare color ? I am planning to bring my new pellet burner online this weekend, and would like to know all this as well.

Thats what I was sort of thinking. Yes Im looking for an indepth explination that might posibly show all posibilities in a quick reference guide.

The reason I want this is for trouble shooting machines over the phone. I have a good idea how to handle this but if there was a guide like this I thought it would come in handy. The units are set-up here at the shop just as our test unit. However, the end users are going to be in diferent locations around the world and stuffing all different sorts of stuff in them. The units are very versital as far as adjustments go. The grate sytem has over 4" of depth adjustment, the jets can be changed out the restrictor/reduction bell is a drop in and this can be modified or changed out for one with diferent geometry.

The good news is they are out in the world and the customers so far are blown away by em. They are running clean gas right out of the box.

My systems are negative presure only. Ive played around with force feeding air and the tar ruined my paint job. lol

But thanks for the info. Maybe at some point Ill try and put something like this together as I gather info as I go.

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Well maybe we could start here with identifing what the compostion of the gas is when certain colors are present. Dave ahs already got us to good start.

Here is my understanding so far into this and also some of this is my speculation. So any one who has a better knowlege please verify, set me straight. or add additional.

Brilant Blue Color = Methane
Purple = Methane and ?
Fluffy Peach/White = Judging from what I know about hydrogen, I think this is a high consentration of H and maybe coming from extra moisture being cracked.
Campfire Orange = Tars and ?

Ive also seen a sharp orange flame with a blue exterior. I have no idea what this is or what causes this. I dont think ive seen this on the new blower set up though.But usually when I would see this it would eventually change to a solid blue.

Carbon? Orange appears when poking.

It would be good to include references so we can learn from published works too. I know I have seen this type of info a couple of times. I think DJ has some color info. Maybey in The book by Vesa Mikkonen. Also on the Fluidyne archive site too, I think. I will be sure to link next time I see one of these.

Also remember reading a flame temp around 1050 C is good gas and the shape of the flame sputtering or nice poit shape have meaning too. (tar for sputter?)

Excellent Thank You! I will do the same.:slight_smile:

Check this write up by Mr. Doug Williams of Flidyne at http://www.fluidynenz.250x.com/

Tar Impurities from Dutch John’s site at http://woodgas.nl/microgasifiers/microgasifiers.html#Tar_impurities

Now where getting some ware. The first one Ive never heard of before. That was a good read.

Yeah DJ has a great site. Thank you DJ for your work. Ive learned much from you. This is probably why my units work. There were only a few sources that I really payed any attention too during my research and your site was one of em.

Thank you for the kind words.
About flame colors: I have spark ignition on the Volvo’s chimney, so one can observe even the very first partly ignition of the flare. It always starts with a magnificent whimpy blue. Since a starting woodgasfier has no vaporising tars to crack yet, it begins as a charcoal gasifier. This means the blue must be carbonmonoxide. A minute later this turns into purple, when the hydrogen and methane come along. Few minutes later an orange tang appears over the flame. Carbon dust or carbon black. For me this is an indication that the glow in the hearth has expanded far enough, temperature is high enough. An engine always starts when the orange tang is present. When the flare speed is high, rich gas also make a thundering sound.
A grey cone at the root of the flame is water vapor. Water vapor also changes the color, but will depend on the amount of water. Although I have never seen a rich tar laden flame, it seems to be yellow or red. Soot cannot be detected in the flame.

It is also good to define carbon dust, soot and tar. Wet carbon dust looks and feels like soot. Wet soot feels like tar. Carbon dust can be washed off with pure water. For soot you also need soap. Well, and for tar you need paint thinner. Tar is also an excellent anti-women perfume, should you feel the urge or need to scare them away…
Soot is partly cracked tar or recombined hydrocarbons mixed with carbon dust. It is an indication that the gasifier needs some tweaking or a better insulated oxidation/reduction zone in case of an Imbert. Soot, tar and carbon black mostly settle after a pressure drop, for example just after and on a throttle valve. It doesn’t hurt to have some distance between throttle valve and engine intake.

Odor. Even a tar and almost soot free gasifier can have gas that smells like tar. This is probably phenol. Cooler condensate often has the typical phenol smell. But the lesser this smell is present, the cleaner the gas. But an engine will not die on phenol, so don’t worry.


this is some good reading… wish i had more to contribute.

John “Dutch”, Great post !! You should see all these folks in Indiana. I have an air leak in my system (of course) so the flare flame keeps running back to the single bilge blower but the truck is running good at 55 to 60 mph in this flat country pulling the trailer system and an extra load. It was fun last night watching folks light off their stuff. A few odd folks have crawled out of the woodwork and shown up here as well … Mike LaRosa

I saw all of the colors described by DJ on my first test run last night. This is from my small scale G3-1 with insulation techniques by Mr.Keith. I call it a G5-WK.

We start with the redder flame…
The purpl-ish flare is a bit closer to the photo on Dutch John’s site, although not as pure… closer to what I should be tuning air/fuel, etc to (?)
The blue flare with the center glowing like the sun means I am burning charcoal and need to “add more fuel”.

I am pushing air through the system and operating at 4 inches of water on the first two photos, the last photo is building pressure because it spit all my water (more than 15 inches) out of the manometer.

Great job Gary!!

Thats Awsome Gary,

I think I am going to learn o lot from this thread and I hope its helpfull to others as well. Once there is a enough info compiled here I will try and make a simple trouble shooting guide. Any one willing to help with it is more than welcome.

Thanks so much for sharing your build techniques on the site and for the encouragement !

It should be pretty easy to make a run from startup to shutdown with pictures or video showing the flare colors and temperature of gas combustion. Actually if there are two thermocouples, you could show gas temperature after the cooler but before combustion to get more information on the gas quality with some basic tools. I am looking for a flow meter to measure the CFM of air being put into the system. That should help get in the ballpark of what the gas could support for HP.

Here is a sequence showing the flare colors the last 20 seconds before running out of fuel. This is from a pellet fired unit and I am using an ejector to produce vacuum on the gasifier to pull the gas out. The thermocouple was reading upwards of 1200F.

Here are a few frames from a video while burning some pellets, showing what I think could be “layers” where mixing of combustion air and gas produce color bands (?). It could also be an artifact of the video camera and how it picks up on infrared heat (it can see even faintly glowing metal really nice) The point is that using an ejector and using a pusher fan will give very different results when trying to compare flares and flare colors. Cameras also may make a difference.

That is very interesting. It looks like you have a lot hydrogen coming out at the beginning. I bet you have very little condensation.

Hopefully by the end of next week, Ill have a new demo unit to play with once agian. This one is for the JD conversion. Im going to use the little tractor as a model for the Farm All.