COMBUSTION & FLAME
INTRODUCTION
The most important source of energy is fuels. Flame is a region where combustion (or
burning) of gasesous substance takes place. Most of the combustible substances on
burning produce a flame. A flame is obtained by burning of vapours of the substances.
Whenever a substance is burnt it produces heat. The heat is produced due to a chemical
reaction.
What is combustion?
A chemical process in which a substance reacts with oxygen to give off heat is called
combustion. Combustion is the exothermic process. The substance that undergoes
combustion is said to be combustible substance and it is also called a fuel.
For example : Charcoal burns in air to give carbon dioxide and heat.
C + O2 → CO2 + Heat
Methane burns in air forming carbon dioxide. Water and heat.
CH4 + 2O2 → CO2 + 2H2O + Heat
Inflammable substances :-
The substances which have very low ignition temperature and can easily catch fire with a
flame are called inflammable substances. Examples of inflammable substances are
petrol, alcohol, Liquified Petroleum Gas (LPG) etc.
What happens to the flame?
The candle burns freely in case (a) when air can enter the chimney from below. In case (b)
when air does not enter the chimney from below, the flame flickers and produces smoke,
in case (c) the flame finally goes off because the air is not available. This shows that air is
necessary for combustion.
Combustible and Non combustible substances : Substances such as paper, kerosene,
petrol, straw and wood etc, which burns easily are known as combustible substances.
Substances that don't burn easily are called non combustible substances. For example
iron, glass, diamond etc.
, Ignition temperature or kindling temperature : The lowest temperature at which a
substance starts burning is known as its kindling temperature or ignition temperature.
For example, the ignition temperature of white phosphorous is 35°C. Hence it catches fire
on slight heating. The ignition temperature of red phosphorus is 260°C. Therefore, white
phosphorus is kept immersed in water. Whereas red phosphorus is stored in ordinary
bottles.
Conclusion : The heat supplied to the paper cup is transferred to water by conduction. So
in the presence of water, the ignition temperature of paper is not reached. Hence it does
not burn.
Condition necessary for combustion or Fire :
For combustion, the following three conditions are essential.
✓ Fuel
✓ Air (to supply oxygen)
✓ Heat (to raise the temperature of the fuel beyond the ignition temperature)
How do we control fire?
We pours water on the fire. Water cools the combustible material so that its temperature is
brought below its ignition temperature. This prevents the fire from spreading. Water
vapours also surround the combustible material, helping in cutting off the supply of air.
So, the fire is extinguished.
But the Fire produced by the burning of oil or petrol cannot be controlled by throwing water
on it because water being heavier than oil, settles down below the oil and oil continues to
burn. In the case of fires caused by burning liquid fuels such as kerosene oil can be
controlled by throwing sand or soil over it.
There are various types of fire extinguishers used for controlling a fire. The job of a fire
extinguisher is to cut off the supply of air or bring down the temperature of the fuel.
✓ Soda-acid fire extinguisher is based on the principle of cooling the fire.
✓ Carbon dioxide liberated by the reaction of sulphuric acid with sodium bicarbonate
solution comes out with a stream of liquid water at high pressure.
INTRODUCTION
The most important source of energy is fuels. Flame is a region where combustion (or
burning) of gasesous substance takes place. Most of the combustible substances on
burning produce a flame. A flame is obtained by burning of vapours of the substances.
Whenever a substance is burnt it produces heat. The heat is produced due to a chemical
reaction.
What is combustion?
A chemical process in which a substance reacts with oxygen to give off heat is called
combustion. Combustion is the exothermic process. The substance that undergoes
combustion is said to be combustible substance and it is also called a fuel.
For example : Charcoal burns in air to give carbon dioxide and heat.
C + O2 → CO2 + Heat
Methane burns in air forming carbon dioxide. Water and heat.
CH4 + 2O2 → CO2 + 2H2O + Heat
Inflammable substances :-
The substances which have very low ignition temperature and can easily catch fire with a
flame are called inflammable substances. Examples of inflammable substances are
petrol, alcohol, Liquified Petroleum Gas (LPG) etc.
What happens to the flame?
The candle burns freely in case (a) when air can enter the chimney from below. In case (b)
when air does not enter the chimney from below, the flame flickers and produces smoke,
in case (c) the flame finally goes off because the air is not available. This shows that air is
necessary for combustion.
Combustible and Non combustible substances : Substances such as paper, kerosene,
petrol, straw and wood etc, which burns easily are known as combustible substances.
Substances that don't burn easily are called non combustible substances. For example
iron, glass, diamond etc.
, Ignition temperature or kindling temperature : The lowest temperature at which a
substance starts burning is known as its kindling temperature or ignition temperature.
For example, the ignition temperature of white phosphorous is 35°C. Hence it catches fire
on slight heating. The ignition temperature of red phosphorus is 260°C. Therefore, white
phosphorus is kept immersed in water. Whereas red phosphorus is stored in ordinary
bottles.
Conclusion : The heat supplied to the paper cup is transferred to water by conduction. So
in the presence of water, the ignition temperature of paper is not reached. Hence it does
not burn.
Condition necessary for combustion or Fire :
For combustion, the following three conditions are essential.
✓ Fuel
✓ Air (to supply oxygen)
✓ Heat (to raise the temperature of the fuel beyond the ignition temperature)
How do we control fire?
We pours water on the fire. Water cools the combustible material so that its temperature is
brought below its ignition temperature. This prevents the fire from spreading. Water
vapours also surround the combustible material, helping in cutting off the supply of air.
So, the fire is extinguished.
But the Fire produced by the burning of oil or petrol cannot be controlled by throwing water
on it because water being heavier than oil, settles down below the oil and oil continues to
burn. In the case of fires caused by burning liquid fuels such as kerosene oil can be
controlled by throwing sand or soil over it.
There are various types of fire extinguishers used for controlling a fire. The job of a fire
extinguisher is to cut off the supply of air or bring down the temperature of the fuel.
✓ Soda-acid fire extinguisher is based on the principle of cooling the fire.
✓ Carbon dioxide liberated by the reaction of sulphuric acid with sodium bicarbonate
solution comes out with a stream of liquid water at high pressure.
