Combustion and Flames

What is Combustion?

Combustion is defined as a rapid exothermic reaction that liberates substantial energy as heat and flames as combustion reactions with the ability to propagate through a suitable medium.

Actually, combustion is a result of dynamic or time dependent events that occur on a molecular level among atoms, molecules, radicals and solid boundaries. Combustion generates air pollution, pollutant formation and oxidation kinetics as well as their reduction techniques are explained in this chapter.

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Types of Combustion

  1. Rapid combustion – When combustion occurs rapidly, it is called rapid combustion.
  2. Spontaneous combustion – The types of combustion in which material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion. Eg, Burning of phosphorus.
  3. Complete combustion – Complete combustion is the mixture of fuel with oxygen without remaining fuel over time, friction and high enough temperature to ignite all the fuel components.
  4. Incomplete combustion – Incomplete combustion is typically caused by inadequate air-fuel mixing, insufficient residence time, insufficient temperature and low total excess air.
  5. Explosion – When a sudden reaction takes place with the release of heat and light and evolution of a large amount of gas takes place it is called an explosion. Eg, firecrackers.

Necessary Conditions for Combustion

There are three necessary conditions for combustion. These are

  • Presence of a combustible substance.
  • Presence of a supporter of combustion.
  • Heating the combustible substance to its ignition temperature.
  • The presence of fuel plays an important role.
  • The presence of air or oxygen.
  • Ignition temperature is maintained (it is defined as the substance that catches fire at its lowest temperature).

Flames and Fuels

Substances that produce heat on combustion are called combustion fuels. In many rural parts of our country people still use wood as a fuel because of its easy availability and low cost. Global warming is the result of an increase of CO2 concentration in the atmosphere mostly due to the combustion of fuels.

  • Solid Fuels – Examples are wood and coal. These are used to cook food in homes. Coal is also used in industries.
  • Liquid Fuels – Examples are kerosene and petrol. Kerosene is used in stoves and in lamps to cook food and petrol is used as a fuel in automobiles.
  • Gaseous Fuels – Examples are natural gas and petroleum gas. These are used in industries. CNG is used to run automobiles.

Pollution Caused by Combustion of Fuels

  • Burning of coal and diesel releases sulphur dioxide gas. It is an extremely suffocating and corrosive gas. Moreover, petrol engines give off gaseous oxides of nitrogen. Oxides of sulphur and nitrogen dissolve in rain water and form acids.
  • Carbon monoxide (CO) is a toxic air pollutant produced largely from vehicle emissions.
  • Fuels like wood, coal, petroleum etc, which are carbon fuels produce unburnt carbon particles, which cause respiratory diseases and skin diseases.
  • Generally CO2 is released during burning of fuels. It causes the rise in the temperature of the atmosphere of earth, which is called global warming.
  • Incomplete combustion of fuel releases many poisonous gases such as carbon monoxide. It can kill people sleeping in a room by causing suffocation.
  • Combustion of coal and diesel generates sulphur dioxide. It can kill people sleeping in a room by causing suffocation.
  • Burning of fuel releases oxides of nitrogen and sulphur. They dissolve in rain water and form acid. Such rain is called acid rain.

Frequently Asked Questions on Combustion and Flames

What are the types of flame?

There are three types of natural flames, which carburized flames and oxidize flames. Natural flame has balanced fuel-oxygen combination, carburizing flame has more fuel and oxidizing flame has more oxygen. Based on the weld state various materials used various flames.

What is called combustion?

Combustion is a chemical reaction where a material quickly reacts with oxygen and gives off heat. The initial material is called a gasoline, and the oxidizer is considered the source of oxygen. The fuel may be a solid, liquid, or gas, although the fuel is typically a liquid for airplane propulsion.

Which flame has the highest temperature?

The candle flame’s inner center is light violet, with a temperature of around 1800 K (1500 ° C). That’s the flame’s heatmost part. In the blaze the color is yellow, orange and eventually red.

What is the difference between combustion and flame?

The fundamental difference is that combustion is heating and no flames are created because much of the energy is converted to light energy in burning, resulting in less heat energy compared to combustion. If a flame is created in a combustion process it is referred to as burning.

Does magnesium form flame on burning?

Many things, such as magnesium, catch fire when heated in air, and burn with a sparkling white flame. Likewise, when a piece of paper is brought near a burning candle, it burns, creating heat and light.

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