Colors of Flames

I was wondering what is in fuels that makes the flame blue?
- Jordan (age 13)

It's easier to answer why many flames are yellow.  This has to do with the fact that when a flame doesn't have enough oxygen to completely burn the fuel, small carbon specks in the soot heat up to a high temperature and glow with a characteristic black body spectrum.  Additional sources of the yellow color come from excited sodium atoms.    If the flame has plenty of oxygen and more complete burning occurs then the temperature rises.   The blue color is then produced by molecular radicals, especially the emission from CH and C2.

See http://en.wikipedia.org/wiki/Flame  for some nice photographs and explanation.

LeeH

(published on 06/11/2008)