Current Poll - Flame Temperature

Hi,

sorry if this has already been discussed but I did a search and couldn't find anything.

Now, I don't mean to be a pedant (and I know this is a bit out of date, but i've only just seen the email), but i feel I must argue with Malcolm's opinion about the temperature at different points in a flame.

Taking a rather simplistic view, and splitting a flame into two parts - the blue bit in the middle, and the yellow bit round the edge - my understanding is that the hottest part of a flame is the blue bit in the middle.

Within the blue area the fuel is being entirely combusted as it mixes with the surrounding air (oxygen) and therefore burns at a high temperature. 'Above' the blue bit, the mixture is more air and less fuel, and so burns at a lower temperature.

This is what I was taught at school anyway, and 5 minutes spent on google seems to back me up.

Sorry if this was really long and boring but I thought it needed to be said.

Happy Spinning

boris

if i recall correctly, the last newsletter sent out talked about this poll and he said exactly what you said. the center of the flame is the hottest part. i'm not sure what you read, but i remember him agreeing with you on this one. and yes, you do remember correctly in your science stuff. same reason that blue stars are hotter than red stars (yes if you look closely you can actually see the different tints in color)

There is some confusion obviously about different types of flame here.

The type of flame from eg. a poi burning, recieves its oxygen from the outside and is therefore hotest at the edge of the fuel vapour/oxygen interface. The temperature decreases as you go inwards due to the lessening concentration of available O2.

Something like a Bunsen burner or gas stove has the oxygen premixed with the fuel (gas).
This means that yes the hottest part of the flame is just above the pale blue cone that you see in the heart of the gas jet. This is the region where the fuel is most efficiently oxidised and therefore produces the most heat.

Interestingly the temperature in a bunsen type gas jet changes twice as you move inwards from the edge.

-outside edge: hot; lots of air, some gas remaining
-just inside: cooler; less air, but gas remaining
-point of blue cone: hottest; best ratio of air to gas
-center of cone: coolest; correct mix of gas and air but combustion not yet occuring, it's just a stream of cool, mixed gases.

A bit much for a monday night I know, hope your brains haven't melted

From what little I remember from A Level Chemistry - the hottest part of any flame is the tip of the blue part.

Inside the blue part of the flame is at the same temperature as the rest of the room!

I think!!

most combustion doesn't have blue flames.

Also truely the hottest flames are invisible (really crazy ass cutting torches and burning race fuel are examples of this)

Yay - I was wondering when someone would discuss this further.

What was "Malcom's opinion"?

I must have missed it.

The flame temperature definitely does not increase as you go inward. That's way oversimplified. It totally depends on the interface of fuel and oxygen...

FLames are funny things aren't they...

But remembering that a flame is only coloured by the electrons leaping all over the place in super energised air molecules (and by this action fires out the photons that we perceive as a flame), it makes sense that the edge of the flame (which would be where the air molecules aren't recieving enough energy to be emit any light of any colour) would be coolest (less heat imparted to air=less energy=less flame). So by this logic, the closer to the point of combustion, the hotter the flame will be. This is why on bunson burners (those groovy flame emitting toys we played with in chemistry) the hottest part was at the peak of the blue cone in the middle of the flame where most of the gas was directed and burning in the heat (birdsanctuary got this pegged as well, in the middle of the blue flame is where the gas is still rushing out of the burner, if the flame fell into the burner there'd be a seriuos problem involving gas pipes exploding and all that amusementness)... Another interesting point is that the colour of the flame indicates the purity of the substance burning. SO as Astar says, uber hot flames are invisible, the more impurity in the combustion (like in the cooler parts of air) will go from white to blue to yellow, and this is also why flames burn different colours if you throw metal powders into the mix. I can't remember exactly how they go, but I think copper makes a green flame, iron makes a red flame, something like potassium or sodium makes purple flames, and of course Magnesium just blinds everyone looking at it with white flame (it burneth hot!) etc... I'm trying to think how I can apply these to a poi... Multi coloured fire poi are haunting my dreams right now...

Well, there... I didn't waffle too much there did I?...

NYC,

Poll was

quote:

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The further you reach to the center of the flame, the lower the temperature will be --TRUE/FALSE

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I think /believe it is true.

Research faradays candle, the hotest part of the flame is where the blue tip touches the yellow part

You can test out what Mr. hands and squarefish said with a candle.

inside the flame is cooler, it can be as low as a few hundred degrees. the outer envelope of a candle flame is over 3300°F

paraffin in it's solid form and kerosene, jet fuel and mineral oil have similar burn temperatures and flames so you can talk about the flames as if they are effectively from the same fuel.

the inner yellow part of the flame where much of the light comes from is uber hot carbon radicals absorbing the heat from the outer envelopes oxidization and producing visible light, as Mr.Hands said.

if you inject oxygen into the cooler yellow part of the flame and oxidise the carbon the flame will shrink and turn blue.

visa versa if you have a blue flame and starve it of oxygen it will yellow.

the more yellow a flame is or is not is NOT always indicative of it's overall temperature - you can burn the same mixture of fuel/oxygen yellow or blue, it just depends on the size of the flame front.

holding a piece of thin platinum wire against a candle/kerosene/lamp oil flame will result in a near white hot wire. in the inner envelope the wire will glow a weak red or not at all.

a blow torch flame can be thought of as a candle flame turned inside out. the blue cone is hottest at the tip.

Nice bump sir


I miss BorisMcNorris

hmm another 'I should have looked at the date of the posting...'