Because the color of fire depends on the temperature at which it burns, and generally each part of the flame has a different temperature. The color of fire is actually the result of the color of the light it emits. This light is formed by photons, very small particles that behave like an electromagnetic wave. Depending on the length of this wave, it will have a different color.
The size of the wave, in turn, depends on the amount of energy it carries: the more energy, the shorter the wave. “Smaller” waves are blue, while “bigger” waves are red. The base of a candle flame, for example, has a lot of heat and forms waves of light with a lot of energy, shorter and bluer. The high part has less heat, so it forms waves with less energy, longer and redder.
Some specific fuels can add new colors to the flames. When the inside of your stove is dirty, for example, its fire can turn green from the dirt, which can be dangerous. Methanol, the fuel used by Formula Indy teams, has an invisible flame. In order to fight possible fires in the pits, the teams add some impurities to the fuel, which is no longer colorless.
The airflow around the candle colors the different shades of the flame.• When we light the wick, a combustion reaction begins. The string, which is the fuel (and not the paraffin, as many people think), burns in the presence of oxygen, the oxidizer. The product of the reaction is water vapor and carbon dioxide, plus energy in the form of heat.
• The hotter and less dense gases that form from the reaction tend to rise, creating an upward air current around the flame. The air that comes from below is full of oxygen, while at the top of the flame it is saturated with the carbon dioxide that has just formed in the combustion.
• The effect is the same as blowing on a barbecue grill. The air that comes from below oxygenates the combustion, which generates more heat (about 1400ºC), forming a blue light. At the top, with little oxygen and a lot of carbon dioxide, combustion is weaker, the temperature is lower (800 °C) and the light is yellowish, almost red.
ZERO GRAVITY
In an environment without gravity there is no force to pull denser gases down and let lighter ones rise. Then there is no air current around the sail. Thus, oxygen and carbon dioxide spread evenly in all directions, creating a homogeneous combustion around the wick, with that round flame
Did you see this one?
Not everything that is light we see! Some waves are “invisible” to the human eyeDepending on the wavelength at which the energy propagates, our eyes “see” or not – infrared and ultraviolet pass by human vision. The band on the side shows the size of various wave types