How A Candle Burns

People have been burning candles for thousands of years... and I know I, at least, have been taking the science for granted.  It wasn't until I listened to last week's "Science Friday" on NPR that I finally "got" why the candle works.

Host Ira Flatow and staffer Flora Lichtman talked about how Brigham Young engineers have been taking high-speed videos of flames in order to figure out how to reproduce one in digital 3-D. Lichtman spent some time with these engineers as they accomplished this task, and shared what she had learned with Flatow:

LICHTMAN: But - here's one that I thought was pretty amazing. A flame, a candle flame, for example, is just an envelope of fire around this sort of center area. So the wax, which is the fuel, goes up through the wick. It melts, goes up through the wick, and then evaporates into a gas. And that is - the part around the wick is actually not on fire. So the wick is actually not on fire. 

FLATOW: That's why it doesn't burn away, I guess. 

LICHTMAN: That's why. 

FLATOW: Yeah. Hey, you're right. You know, the wick is not on fire - so there's an envelope of gas around the wick, and it's the gas that's burning. 

LICHTMAN: And it's the gas that's burning, and it only burns when it hits oxygen. So the gas on the inside that doesn't have access to oxygen isn't burning, and it's actually cool inside the flame.

And then they posted the following video of the candle wick "sucking up" the wax (among with other interesting fire facts). It's very cool!



You can listen to the whole interview here. It's full of good stuff!