Structure of a Flame: Zones, Premixed Flame, Spray Combustion Flame

Flame is referred to as a visible, gaseous component of fire. It is caused by a highly exothermic chemical reaction in a thin zone. Very hot flames have ionized gaseous components of sufficient density to be considered plasma. Combustion on the other hand is a chemical procedure that involves the reaction of a substance with oxygen to produce light and heat. This article will discuss flames and combustion in detail.

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Flame

The region where the combustion of gaseous materials takes place producing heat and light is known as a flame. All liquid and gaseous combustible substances burn with a flame. For combustion to produce a flame, both the combustible substance and the supporter of combustion must be gases.

For example, when kerosene is burned in a stove, it rises with the wick and vapourises before burning with flames. The case of a candle flame is similar. Charcoal, on the other hand, does not vapourize. As a result, they burn with a glow rather than a flame.

Flame: Classifications

Flame can be classified into two classes. Namely,

1. Premixed Flames: Premixed flames are of two types: laminar premixed Flame and turbulent premixed Flame.

For example, Bunsen burner, LPG domestic burner, SI engine.

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2. Non-premixed Flames or Diffusion Flames: An example of non-premixed Flame is candle flame.

Candle Flame

A candle is a source of light. It consists of a solid fuel block with an integrated wick. Candles can also be made with beeswax, soy wax, and other plant waxes. The majority of today’s candles are made of paraffin. Gel candles are manufactured from a blend of paraffin and plastic. The heat from the match melts and vaporizes a small amount of wax when you light a candle. After being vaporized, it mixes.

Once evaporated, it reacts with oxygen in the environment to generate a flame. Through a self-sustaining cycle of actions, this Flame delivers enough heat to keep the candle burning:

• 1. The heat of the Flame melts the top end of the solid fuel.
• 2. The liquefied fuel then moves upward through the wick.
• 3. The liquefied fuel is then vaporized to burn within the candle’s Flame.

Structure of Flame of a candle

A candle flame consists of the following three zones:

The Outer Zone

The non-luminous zone or zone of complete combustion refers to the outer zone of the Flame. Because the wax vapours can obtain enough oxygen from the air, complete combustion occurs. This zone is blue in colour due to complete combustion, and no residue is left on objects that come into contact with it. This is the hottest zone, and it is only barely visible. This zone of the Flame is very useful for goldsmiths.

The Middle Zone

The pale-yellow zone is the luminous zone or zone of incomplete combustion. The middle zone of the Flame is moderately hot. The wax vapours do not receive enough oxygen to completely burn here. Partial combustion produces carbon monoxide and some carbon particles. Some carbon particles are left unburned as well. Unburned carbon particles become white-hot and turn the flame yellow. This zone leaves a residue of black soot or carbon particles on objects that come into contact with it.

The Innermost Zone

The dark zone or the zone of no combustion is the area around the wick, which is black in colour, due to which it is called the dark zone. There is no combustion in this zone because there is no oxygen available for burning because it is the innermost zone of the Flame. It is primarily made up of wax vapours.

A goldsmith uses a blowpipe to intensify a kerosene lamp flame in order to melt and shape pieces of gold and silver into desired shapes for making jewellery. When air is blown into the Flame through a blowpipe, it aids in the combustion of unburned fuel, making the Flame hotter.

Premixed Flame: Structure

When a premixed flame burns in the open air with an excess of fuel, a diffusion flame forms in addition to the flame zone, which is explained by atmospheric oxygen diffusion.

For example, in a Bunsen flame produced by a burner with a regulated air intake, the flow can be changed from an extremely hot one in which most of the fuel gases are oxidized to carbon dioxide and water to a low-temperature flux in which most of the fuel gases are only partially oxidized.

Such flames are made up of an inner cone and an outer cone-two zones where different chemical reactions take place, known as the reducing and oxidizing zones. The oxidizing nature of the outer cone is due to excess oxygen.

Spray Combustion Flame: Structure

The liquid fuel jet fed into the combustion chamber in liquid-fueled combustion devices breaks up into droplets, resulting in a spray. Fuel sprays normally evaporate and burn in a group, despite the possibility of individual droplet combustion. Many complicating features, such as the different length and time scales associated with the rapid chemistry and the multiphase structure of the flow, which is extremely turbulent in most applications, make numerical calculations of spray combustion difficult.

Summary

The region where the combustion of gaseous materials takes place producing heat and light is known as a flame. All liquid and gaseous combustible substances burn with a flame. A candle is a light source. It is made up of a solid block of fuel with an embedded wick. A candle flame consists of three zones. Namely, the outer zone or non-luminous zone; this is the hottest zone, the middle zone or luminous zone; this zone is moderately hot, and the innermost zone or dark zone; there is no combustion in this zone.

Frequently Asked Questions Related to Structure of a Flame

Frequently asked questions related to the structure of flame is listed as follows:

Q. What are the \(3\) zones of flame?
Ans: The three zones of Flame are as follows:
1. The outer zone
2. The middle zone
3. The innermost zone

Q. What are different parts of a flame called?
Ans: Flame can be classified in the outer zone, the middle zone, and the innermost zone.

Q. What is flame and its parts?
Ans: The region where the combustion of gaseous materials takes place producing heat and light is known as a flame. The parts of Flame are the outer zone, the middle zone, and the innermost zone.

Q. How many layers are there in flame?
Ans: A flame consists of three zones.

Q. What is the hottest fire color?
Ans: The hottest fire colour is blue.

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