Predicting the movement of fire

In summary, the flames of a barbecue shrink and resize randomly due to the chaotic interaction between local air temperatures, densities, flame source geometry, and probably a dozen more variables. Predicting the movement of a fire in real time is complicated and requires computer simulations.
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MevsEinstein
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Flames in a fire whips in "random" ways. Can they be predicted?
I was staring at this barbecue fire. While my family was enjoying the heat, I was wondering why the flames all of a sudden shrink and then resize, and also take different shapes. Is there a way to predict this movement? Just curious :smile:
 
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  • #2
MevsEinstein said:
I was wondering why the flames all of a sudden shrink and then resize, and also take different shapes.
It's a complex interplay between local air temperatures, densities, flame source geometry, and probably a dozen more variables, but mostly it's because of the chaotic way that air masses of different temperatures and densities interact that gives you the random 'whip' effect. A mass of rising hot air doesn't rise smoothly, it tends to make lots of 'whirls' and other instabilities, such as Rayleigh-Taylor and Kelvin-Helmholtz instabilities. Throw in some turbulence (not the same as instability) and you get the complicated hydrodynamic system that is a fire.

MevsEinstein said:
Is there a way to predict this movement? Just curious :smile:
Certainly. It's just very complicated and requires computer simulations.
 
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  • #3
Drakkith said:
Certainly. It's just very complicated and requires computer simulations.
So what are the formulas that determine its movement?:smile:
 
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Google thinks flame propagation is explained by heat conduction and diffusion.
 
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MevsEinstein said:
So what are the formulas that determine its movement?
You need a finite element model. Start by defining an element with fuel and air inputs.

Then run the model so air is drawn in from below, to the fuel, where the gas is heated and expands as oxygen is removed, and exhaust gasses are added, then the gas rises due to lower density. As the flame rises it radiates energy and cools to become smoke, water vapour and CO2 etc.
 
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  • #6
MevsEinstein said:
So what are the formulas that determine its movement?:smile:
Here's somewhere to start. It's a chapter on Governing Equations of Fluid Dynamics (air is a fluid) from the engineering department at Auburn University. Good luck.
 
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Drakkith said:
Certainly. It's just very complicated and requires computer simulations.
If the goal is to predict the behavior of a fire in real time then you are out of luck. By the time you get the required inputs to an acceptable accuracy and process them, it is tomorrow, the fire is out and your predictions were only good for a few seconds anyway.

https://en.wikipedia.org/wiki/Butterfly_effect
 
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Drakkith said:
Here's somewhere to start. It's a chapter on Governing Equations of Fluid Dynamics (air is a fluid) from the engineering department at Auburn University. Good luck.
And that's just the beginning, because combustion adds its own complexity, as @Baluncore noted, you have to account for the chemistry going on and the release of heat.
 
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Combustion is a very difficult problem. It is solved numerically using very large computers. It is of enormous commercial importance, and millions of dollars a year are spent studying it,
 
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  • #11
jbriggs444 said:
If the goal is to predict the behavior of a fire in real time then you are out of luck. By the time you get the required inputs to an acceptable accuracy and process them, it is tomorrow, the fire is out and your predictions were only good for a few seconds anyway.

https://en.wikipedia.org/wiki/Butterfly_effect
After reading the wikipedia article, my brain blew up. Before posting this, I knew that if there was a way to predict the movement of fire, it would be complex. But I didn't think of all the variables needed.
 
  • #12
MevsEinstein said:
After reading the wikipedia article, my brain blew up. Before posting this, I knew that if there was a way to predict the movement of fire, it would be complex. But I didn't think of all the variables needed.
I reached the point where I was considering a scattering matrix for the full EM spectrum. Then I had to stop thinking about the finite element equations because my head exploded.

I think a 1:1 scale model needs to be built. Then the experiment can be run, while it is observed for a few hours, through a glass of liquor.

It should be possible to observe reality, then extract the image parameters and typical variations over time. The statistical caricature of fire can then be generated as an extrapolation from any random image.
 
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Related to Predicting the movement of fire

1. What factors affect the movement of fire?

The movement of fire is affected by several factors, including wind speed and direction, topography of the land, fuel availability and moisture, and weather conditions such as temperature and humidity. These factors can all impact the rate and direction of fire spread.

2. How do scientists predict the movement of fire?

Scientists use various methods to predict the movement of fire, including mathematical models, computer simulations, and on-the-ground observations. These methods take into account the factors mentioned above and use data such as wind speed and direction, fuel moisture content, and topography to forecast the potential path of the fire.

3. Can scientists accurately predict the movement of fire?

While predicting the exact movement of fire is challenging, scientists have developed sophisticated tools and techniques that allow them to make reasonably accurate predictions. However, the unpredictability of weather conditions and other unforeseen factors can make it difficult to predict the movement of fire with 100% accuracy.

4. Why is it important to predict the movement of fire?

Predicting the movement of fire is crucial for effective fire management and emergency response. It allows authorities to plan and allocate resources, such as firefighters and equipment, in the most strategic way. It also helps in issuing evacuation orders and providing warnings to communities in the path of the fire.

5. How can the prediction of fire movement be used for prevention?

The prediction of fire movement can be used for prevention by identifying areas that are at high risk of fire spread and taking preventive measures such as controlled burns, clearing of vegetation, and implementing fire-safe building practices. This can help reduce the likelihood of large, uncontrollable fires and protect communities and ecosystems from the devastating effects of wildfires.

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