Flames and their Structure

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What is a Flame?

A highly exothermic reaction that occurs in a very small and thin zone is known as a Flame. Thus, it is a reaction which liberates a lot of energy but in a very narrow or small area. It is a visible part of a fire.

The difference between combustion and a flame is that a flame is produced only by substances that vaporise.

Let us understand this with a few examples.

• When the oil in the oil lamp burns, it gets converted into the gaseous state. It is the vaporisation of oil that keeps the lamp burning. This produces the
• In a wax candle, the wax melts and gets into the wick by capillary action. As a result, it rises up, burns and gets vaporised. This gives a flame when a candle is
• When a wooden log undergoes combustion, it burns without vaporising. Hence there are no small

Structure of a flame

Though a flame appears to be a single entity, it has three major parts. They are:

• Dark zone
• Luminous zone
• Non-luminous zone

Let us understand each of these parts by considering the candle as a source of flame.

Structure of flame

1. Dark zone

This is the innermost zone, which is next to the wick. Here the temperature is the least hot, mainly because the area belongs to unburnt wax vapours.

2. Luminous zone

This is the middle part of the flame. It is bright yellow and is hotter than the innermost zone. It is the area where partial combustion of the wax vapours takes place.

3. Non-luminous zone

This is the outermost part of the flame. It appears blue in colour and lies almost outside the flame. It has the highest temperature because this is where complete combustion occurs.

Complete combustion makes sure that energy liberated in the form of heat is maximum compared to others.

Why do Flames Appear in Different Colours?

The colours of a flame are influenced by many factors like material of the substance, temperature and level of combustion. Different colours of flames indicate different temperatures and different types of combustion. Let us understand this with a few examples:

• The candle flame shows a non-luminous blue zone and a luminous yellow zone. The blue indicates a higher temperature as compared to the yellow colour of the flame.
• When cooking gas (LPG) undergoes complete combustion it burns with a blue flame. And when it undergoes partial combustion, its flame is yellow. The yellow flame is an indication that there is wastage of gas, as all of it is not being

Summary