Please enable JavaScript.
Coggle requires JavaScript to display documents.
Combustion - Coggle Diagram
Combustion
What is combustion?
We find that a combustible substance cannot catch fire or burn as long as its temperature is lower than its ignition temperature
Very low ignition temperature and can easily catch fire with a flame are called inflammable substances
For combustion, air is
necessary
The fuel may be solid, liquid or gas. Sometimes, light is also given off during combustion, either as a flame or as a glow.
-
Examples of inflammable substances are petrol, alcohol, Liquified Petroleum Gas (LPG), etc
-
Types of combustion
Such a reaction is called explosion. Explosion can also take place if pressure is applied on the cracker.
-
-
When a cracker is ignited, a sudden reaction takes place with the evolution of heat, light and sound
We find that the gas burns rapidly and produces heat and light. Such combustion is known as rapid combustion
The type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion.
How do we control fire?
Water cools the combustible material so that its temperature is brought below its ignition temperature.
The job of a fire extinguisher is to cut off the supply of air, or to bring down the temperature of the fuel, or both
These are: fuel, air (to supply oxygen) and heat (to raise the temperature of the fuel beyond the ignition temperature).
Notice that the fuel in most cases cannot be eliminated. If, for instance, a building catches fire, the whole building is the fuel.
-
Prevents the fire from spreading. Water vapours also surround the combustible material, helping in cutting off the supply of air.
What is fuel?
Burning of coal and diesel releases sulphur dioxide gas. It is an extremely suffocating and corrosive gas.
Combustion of most fuels releases carbon dioxide in the environment. Increased concentration of carbon dioxide in the air is believed to cause global warming
Incomplete combustion of these fuels gives carbon monoxide gas. It is a very poisonous gas. It is dangerous to burn coal in a closed room.
-
The calorific value of a fuel is expressed in a unit called kilojoule per kg (kJ/kg). Calorific values of some fuels are given in Table 6.4.
The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value
Flame
Charcoal, on the other hand, does not evaporate and so does not produce a flame
Goldsmiths blow the outermost zone of a flame with a metallic blow-pipe for are mainly wood, charcoal, petrol, kerosene, etc. These substances are called fuels
For example, kerosene oil and molten wax rise through the wick and are vaporized during burning and form flames.
A good fuel is one which is readily available. It is cheap. It burns easily in air at a moderate rate.
The substances which evaporate during burning, give flames