Flame: Introduction, Types, Components, Structure

We sometimes light a candle in the dark when suddenly the light goes off; we also light candles on our birthday cakes! These simple candle flames hold many lessons for us. Have you ever closely observed the burning of candles? If yes, you must have seen that the wax near the wick melts as soon as we light it, and we get a flame of light. It happens because as we ignite a candle, its wax reacts with oxygen in the air to produce carbon dioxide, light and heat. This chemical reaction is known as combustion that is often associated with flame.

When something is burnt, we observe a hot, luminous gas emerging out of the substance. This hot and luminous gas is known as flame. Flame is a result of high exothermic chemical reactions taking place in a substance when ignited. Only those substances that evaporate on burning produce flame. For example, kerosene, melted wax rise through the wick, vaporise and give off the flame. On the other hand, the substances that do not evaporate on burning do not produce a flame—for example, charcoal and coal. In this article, let’s learn everything about flame in detail.

Flame Meaning

The meaning of flame is the hot glowing gaseous part of the fire generated when a substance is ignited. It is the region where the combustion of fuel takes place.

How is the Flame of a Candle Produced?

An ignited matchstick provides the initial heat energy to light a candle. As the burning matchstick is brought near the candle, the wick quickly catches fire and melts the solid wax. This molten wax travels up by the capillary action of the cotton in the wick. The heat causes molten wax to evaporate and burn in the presence of oxygen. We may call this combustion as candle wax burns in the presence of the air to produce light, heat and carbon dioxide gas.

Types of Flame

Flames are divided into two types:

1. Luminous Flame: The burning flame that is bright and visible as yellow or orange is known as luminous flame. It is a result of partial combustion due to insufficient oxygen. We get light from luminous flames only.

2. Non-luminous Flame: The blue flame that appears due to complete combustion due to the availability of sufficient oxygen is known as a non-luminous flame. This type of flame can be observed in our kitchen LPG stoves as complete combustion takes place. It is the hottest flame and is used for cooking, welding, and many other works that require heat.

Structure of a Flame

On observing a flame keenly, we can observe different colours in it, its unique shape, along with its fascinating movement. The colour of flames depends on factors like the nature of the combustible substance, amount of oxygen and temperature. Based on these characteristics, a flame is divided into three zones; outer zone, middle zone and inner zone.

Outer zone: This is the non-luminous zone and appears blue. The outermost zone has plenty of oxygen, due to which complete combustion takes place. As a result, this is the hottest part of a flame but thinner than the middle zone.
Middle Zone: This is the luminous zone and appears in varying shades of yellow and orange. This is the biggest part of the flame and emits light. This part gets a limited supply of oxygen, so incomplete combustion takes place here. As a result, it appears yellow. Due to partial burning, the middle zone produces carbon particles that leave the flame in the form of soot and smoke. The temperature in this zone is moderate.
Inner Zone: This is the innermost part of the flame that is closest to the wick. This part consists of unburnt vapours or combustible substances. As a result, it appears black, and it is the least hot. In other words, we can say that it is the coldest part of a flame.

Combustion and Flame

Combustion is a type of reaction in which a substance gives off the heat on reacting with oxygen. Such substances which undergo combustion are known as combustible substances. As a result of combustion, heat and light are produced in the flame. Thus, we can say that the act of burning is combustion while the visible part of the fire is flame.

The primary difference between combustion and flame is that combustion is an oxidation reaction of fuel that produces heat, and flames may or may not be created because much of the energy is converted to light energy in burning. As a result, the flame has less heat energy as compared to combustion. If a flame is produced in a combustion process, it is referred to as burning.

Flame Propagation

Flame is a mixture of air and combustible gases that moves rapidly. They give light, heat and are self-propagating. Flame propagation refers to the propagation of the combustion reaction or combustion wave.

Flame Test

The flame test is a qualitative analysis test used in chemical laboratories to determine the identity of a metal or metalloid ion found in an ionic compound. In flame tests, the aqueous solution of salts is evaporated using a hot flame. The solid salt of the compound, when placed in the flame of a gas burner, gives off a characteristic colour that is visible to the naked eye. In the flame test, the electrons of the metal atoms get excited and produce their characteristic spectrum of light. This test is used to detect metal ions in salt. For example, Sodium gives intense yellow flame, Lithium gives crimson flame, Potassium gives lilac flame, and Rubidium gives red-violet flame.

Summary

It can be concluded that on ignition of a substance, the hot and glowing gas produced by a substance is known as flame. Flame produces fire on propagation. Some materials burn with a flame-like candle, camphor, kerosene stove, gas stove, etc., as the flame results from a substance that gets vaporised on burning. We often observe that goldsmiths use the outermost zone of the flame to melt gold and silver because this is the hottest part and helps the metals like gold and silver melt easily.

A flame is divided into three zones; the outermost zone of the blue flame is the hottest part of a flame. It appears blue as complete combustion takes place in this region. The middle zone is the bright yellow part which is moderately hot compared to the blue flame zone. It appears yellow as incomplete combustion takes place in this region. The innermost zone consists of unburnt vapours or combustible substances. As a result, it appears black, and it is the least hot region of the flame. Combustion and flame are interrelated to each other. In short, we can say that flame is a result of combustion. Fire is a chemical reaction in which energy is produced in the form of heat. This chemical reaction is known as combustion, which is an oxidation reaction. Combustion occurs when fuel or other combustible substance reacts rapidly with oxygen, giving off light, heat energy, and flame.

FAQs

Q.1. What is a flame?
Ans: Flame is the hot, glowing and luminous gaseous part of the fire produced when a combustible substance is ignited. It is the region where the combustion of fuel takes place.

Q.2. Which flame is suitable for cutting operations?
Ans: The oxy-acetylene flame is used for cutting operations. They are said to be carbonising (aka reducing), neutral, or oxidising. The flame is adjusted by adding more or less oxygen to the acetylene flame. The neutral flame is used chiefly for welding or cutting.

Q.3. What is the difference between combustion and flame?
Ans: The fundamental difference between combustion and flame is that combustion is an oxidation reaction of fuel that produces heat, and flames may or may not be created during the combustion reaction because much of the energy is converted to light energy in burning. As a result, the flame has less heat energy as compared to combustion.

Q.4. What is the flame front in combustion?
Ans: Flame combustion is a result of an oxidation reaction. The combustion reaction in such flames occurs within a narrow zone that is several micrometres thick. This zone of combustion is usually called the flame front.

Q.5. Is flame a type of combustion?
Ans: Flame is a result of combustion, which is an oxidation reaction. Combustion may or may not have a flame, but the flame is only produced when combustion occurs.

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