When a candle is lit, it looks like the radiated heat melts the wax near the wick, which goes by the same, to reach the top it evaporates. Immediately above the fuse there is a dark cone surrounded by a yellow zone, which is the main cause of luminosity. Next to the flame near the wick is a blue zone. The existence of these zones, instead of one, is one of the characteristics of diffusion flames . This type of flame is produced when fuel and the oxidant are not mixed before ignition occurs. In this case, what happens is the molecular diffusion of oxygen through the surface of the volume of fuel gas. This process is slow, but speed can increase the temperature rises. Diffusion flames usually are yellow due to the carbon filament that forms in the process. Around the wick is the coldest area (600 ° C) of the flame. As the temperature rises in height progressively increased to reach the 1200 º C in the central part of the yellow zone. Outside the center, at the edges of the yellow flame is reached around 1400 ° C.
By evaporating the wax on the end of the wick (dark area), the heat causes the hydrocarbon chains break down into single atoms or diatomic molecules.
By passing these to the blue zone is mixed with oxygen diffused from the air around the candle. As the temperature increased the C2 and CH particles emit blue light. The main reation is carried out at the ends of the flame coming out the products CO2 and H2O at the top of the flame. The yellow zone is where sólidasde C particles that have formed in the center of the candle glow enter due to high temperatures.
On the other side are the premixed flames, which are produced when fuel and oxidizer are mezclanpreviamente, with a ratio within the range of flammability, before ignition. An example is a torch or a Bunsen burner
