Combustion And Flame

Made By:-Anmol Pant

VIII-C31

A Flame or not?

Some substances burn with a flame whereas some do not.

Example:-a) Candle burns with

a flame.b) Whereas coal

does not.

What is combustion?

A chemical process in which a substance reacts with oxygen to give out heat is called combustion.

Example:-a) Burning of

Magnesium ribbon.

Fuels

The substance that undergoes combustion is said to be combustible.

It is called a fuel.Fuels exist in three states:-a) Solidb) Liquid &c) Gaseous

Solid FuelsWood Cow dung Cakes

Charcoal

Coal

Liquid Fuels

Ethanol

Kerosene

Hydrogen

Diesel

Petrol

Gaseous fuels

LPG CNG

Bio gas Coal Gas

Nuclear Reactions

In the sun, heat and light are produced by nuclear reactions.

Ignition Temperature

The lowest temperature at which a substance catches fire is called it’s ‘Ignition Temperature’

Ignition temperature of different materials

Material Ignition Temperature

White Phosphorus 35 degree Celsius

Petrol 246 degree Celsius

Kerosene 220 degree Celsius

Diesel 210 degree Celsius

Wood 300 degree Celsius

Coal 454 degree Celsius

Piece of paper 233 degree Celsius

Inflammable Substances

The substances which have very low ignition temperature and can easily catch fire with a flame are called ‘Inflammable Substances.’

Examplesa) Petrolb) Alcoholc) LPG( Liquified Petroleum Gas)

How can fire be extinguished?

Fire can be extinguished by:-a) Removing the combustible

substance (Fuel).b) Cutting off the supply of Oxygen.c) Reducing the temperature of the

fuel below its ignition temperature.

Fire Extinguisher(Water)

Water is an excellent extinguisher when it comes to paper, wood.

Water cools the combustible substance below the ignition temperature so that the combustion is stopped.

Water vapors also surround the flame so the supply of Oxygen is cut off.

Fireman extinguishing fire using water as extinguisher

Fire Extinguisher Co

Carbon dioxide is also a very effective extinguisher in all the cases especially involving electrical appliances and oil as in such cases water cannot be used.

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Types of Combustion

Combustion can be classified into three types:-

a)Rapid Combustionb)Spontaneous Combustionc) Explosiond)Slow Combustion

Rapid Combustion

The combustion in which a substance burns rapidly and produces heat and light is called ‘Rapid Combustion.’

Example:-a) Burning of white Phosphorus at room

temperature.

Spontaneous Combustion

The type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause is called ‘Spontaneous Combustion’

Examples of Spontaneous Combustion.

Forest Fires caused by spontaneous combustion.

Spontaneous combustion of coal dust in coal mines.

Explosion

A sudden reaction that takes place with the evolution of heat, light and sound. A large amount of gas is formed in the reaction is liberated. Such a reaction is called an ‘Explosion.’

Example:-a) Burning of crackers

Slow Combustion

The type of combustion which takes place at a slow rate at low temperatures is called ‘Slow Combustion.’

Example:-a) Respirationb) Rusting of Iron.

Flame

A flame  is the visible, gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone. Some flames are hot enough to have ionized gaseous components of sufficient density to be considered plasma. However, a candle flame which has a temperature below 1500 °C produces too low an ion density to be considered a plasma.

Substances which give out flame.

The substances which vaporize during combustion give flames.

Example:-a) Kerosene and Wax burn with a flameb)Whereas Charcoal, on the other hand,

does not vaporize and so does not produce a flame.

Different zones of candle flame

Goldsmiths

Goldsmiths blow the outermost zone of a flame with a metallic blow-pipe for melting gold and silver.

Calorific Value

The amount of heat energy produced on complete combustion of 1kg of a fuel is called its ‘Calorific Value’

The calorific value of a fuel is expressed in a unit called ‘Kilojoule per kg (kJ/kg)

Calorific Value of different FuelsFuel Calorific Value (kJ/kg)

Cow dung cake 6000-8000

Wood 17000-22000

Coal 25000-33000

Petrol 45000

Kerosene 45000

Diesel 45000

Methane 50000

CNG 50000

LPG 55000

Biogas 35000-40000

Hydrogen 150000

Disadvantages of burning fuels

Carbon fuels like wood, coal, petroleum release unburnt carbon particles. These are pollutants and cause respiratory diseases.

Incomplete combustion of these fuels gives Carbon Monoxide gas. It is a very poisonous gas and can kill people who inhale this gas.

Disadvantages of burning fuels

Combustion of most fuels releases carbon dioxide in the environment. Increased concentration of this gas leads to ‘Global Warming’.

Burning of coal and diesel releases oxides of Sulphur and nitrogen dissolve in rain water and form acids. Such rains are called ‘Acid Rains.’

Global Warming

Global Warming is the rise in temperature of the atmosphere of the earth. This results in the melting of polar glaciers, which leads to rise of the water in the sea. Low lying coastal areas may even be submerged under water.

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