Message Board Thread - "What is the emissivity of a flame?"

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What is the emissivity of a flame? IRImager 7/17/2008
I have used an IR camera (FLIR S65) and captured many images of a large flame at high emissivity setting on the camera. I then used more relistic emissivity value in QuickReport 1.1 and found unrealistic temperatures. My question is about the correct emissivity value. What this value should be when viewing a flame with the cold sky in the background in daylight or in the darkness? Your comments and answers would be appreciated.
 
Re:What is the emissivity of a flame? IRImager 7/18/2008
IRImager wrote:
used an IR camera (FLIR S65) and captured many images of a large flame at high emissivity setting on the camera. I then used more relistic emissivity value in QuickReport 1.1 and found unrealistic temperatures. My question is about the correct emissivity value. What this value should be when viewing a flame with the cold sky in the background in daylight or in the darkness? Your comments and answers would be appreciated.
Isn't there ANY body ANY where to make ANY comments on this topic?
 
Re:What is the emissivity of a flame? Top Gun 7/22/2008
Let me speculate. Emissivity is a physical/optical quality of a surface. Flames do not have a "surface". Flames also are hot gases. Most surfaces are static without chemical changes occurring. Flames are dynamic and full of chemical change where a substrate chemical is undergoing pyrolysis and combustion. The flame itself is an energy source of high intensity, as compared to most items that are investigated using thermography.
There is the issue of transparency. Gases temd to be transparent. Gases in a flame may have this quality to an extent, but how much? Anyone know? I would expect that if there is enough flame depth, the camera would see a consistent energy from the flame and not a degree of transparency.
Suggestion: use emissivity value of 1.0
You have my speculation on this subject. Good luck!
 
Re:What is the emissivity of a flame? Gary Orlove 8/4/2008
Infrared cameras are designed to look through common atmospheric gases like water vapor. While you can sometimes see these gases, they are very difficult to measure unless you have a camera specifically designed to do so (and even then it is difficult because gases are volume emitters, emission depends on thickness of the gas cloud , pressure, temperature, and wavelength).

When it comes to flames we are experiencing the same thing, we have hot gases usually with water vapor and carbon dioxide and perhaps some other gases depending on what is being burned. Some flames will also have particulates which tend to increase the emissivity.

Any emissivity measurement however has to be carried out on the particular flame you are working with. One technique is to place a high emissivity surface inside the flame and measure the temperature of the surface with the IR camera or a thermocouple. Then you can change the emissivity setting in the camera to match the value.
 
Re:What is the emissivity of a flame? Ron Ruiz from JPL 8/7/2008
This is what is generally called "A Loaded Question". Although many factors influence the combustion of an object to produce a flame i.e. (Fuel, Air (gas), Pressure...), we can still use the infrared camera to adjust the emissivity against a known temperature of a “Blue Flame” which burns between 2950-3050 degrees Celsius ("Flame Analysis." Macmillan Encyclopedia of Chemistry. New York: Simon & Schuster, 1997: 626.). Also, consider using a flame filter with your camera so that you have enough dynamic range to process your images later. That is where I would begin, but I you want to know how people with a lot of time and money do it, read the paper “Intelligent System for Flame Analysis”, www.icgst.com. Good Luck
 
Re:What is the emissivity of a flame? IRImager 8/7/2008
Many thanks for the comments so far. I am hoping for more, and for a plausible answer to "what is the emissivity of a flame?"

When we are dealing with a laboratory setting we have the luxury of using thermocouples and blackbody surfaces to find flame temperature. But for a real application no such options are available. IR imaging requires an emissivity value to estimate the actual temperature. Are there "laboratory" results available that can be extrapolated to real flames? How do we find real flame temperatures such as in a bush fire, or in the flare in an oil and gas plant?
 


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