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Combustion and Flame Notes for Class 8 Ideal for CBSE Board followed by NCERT

Important topics in Combustion and flame notes:

  • What is Combustion?
  • Ignition temperature
  • Inflammable substance
  • How Do We Control Fire?
  • Types of Combustion
  • Flame
  • Structure of a Flame
  • What is a Fuel?
  • Fuel Efficiency
  • Global warming
  • Ideal Fuel

What is combustion?

  • Burning of a substance is said to be combustion.
  • Or simply, the chemical process in which a substance reacts with oxygen to give off heat and light is known to be combustion.
  • Oxygen is necessary for combustion.
  • Combustible substance: Those substances which undergo combustion are said to be combustible substance.
  • Non-combustible substances: Those substances which do not burn in air are said to be non-combustible substances.

Ignition temperature

  • The lowest temperature at which a substance catches fire is said to be ignition temperature.
  • If the temperature of the substances is below the ignition temperature then that substance will not burn.
  • Have you ever seen the oil kept in pan catches fire when kept for long on a burning stove? You can conclude that the temperature of oil reaches the ignition temperature then catches fire.

Inflammable substances:

  • Those substances which catch fire easily are said to be inflammable substances.
  • These have a low ignition temperature.
  • LPG, Petrol are some of its examples.

Essential condition for burning:

  • Presence of combustible substances or fuel
  • Presence of air containing oxygen
  • A temperature above ignition temperature is required.

How Do We Control Fire?

how can we extinguish fire

  • Generally, we use water to extinguish fire.
  • For fires that are caused by petrol, diesel or highly inflammable substance we don’t use water.
  • In these cases we use carbon dioxide, sand etc. to extinguish fire.
  • When a person catches with fire he should use blankets to escape or save themselves.
  • Forest fires are uncontrollable as they spread rapidly.

Types of combustion

Different types of combustion are:

Rapid combustion:

rapid combustion

  • The combustion which occurs rapidly yielding large amount of heat and light.
  • External heat source is required for rapid combustion.
  • Burning of gas stove when a burning matchstick is taken near it is an example of rapid combustion.

Spontaneous combustion:

sponteneous combustion

  • The combustion which occurs without any application of external source of heat and burst out into flames.
  • No external heat sources are required.
  • Forest fires are spontaneous combustion.



  • The combustion in which sudden reaction results in a large amount of heat, light and sound.
  • A heavy amount of gases are also gets released.
  • Firecracker after combustion releases a large amount of heat and light.



  • Flames are the region of burning of gases.
  • The combustible substances vaporize during burning produces flame.

Structure of flame:

structure of flames

  • There are different zones of flame of candle.
  • Blue zone: It is near the base of the flame. Carbon monoxide burns completely with a blue flame in this zone.
  • Luminous zone: The region of the flame in which hydrogen burns with a bright yellow luminous flame. The soot of the flame rises due to some unburnt carbon particles which are left in it.
  • Dark Zone which is the middle layer of flame.
  • Non-luminous zone which is the outermost zone of the flame. As here complete oxidation takes place, it is the hottest part of the flame.

What is fuel?


  • Fuel is another name for combustible substances.
  • The fuel should be cost-effective, easily available, and less amount of it must be capable of producing a large amount of heat.
  • They should produce less undesired material after burning.
  • Petrol, kerosene, hydrogen etc. are some examples of fuel.

Global warming:

global warming

Most fuels on combustion release carbon dioxide in the environment. Increase in concentration of carbon dioxide in the air is believed to cause global warming.

The efficiency of fuel:

  • The efficiency of fuel is the amount of energy it releases during burning.
  • We can determine the efficiency of fuel by its calorific value.

Calorific value:

  • The calorific value is the measure of efficiency of fuel.
  • The unit of calorific value is expressed in Kilojoule per kg.

Ideal Fuel:

  • Those fuel which can meet most of the requirements for a particular use can be said as ideal fuel.
  • For instance, probably no fuel is there that could be considered as an ideal fuel.

Characteristics of a good fuel

  • Cheap and readily available.
  • Burn at a quiet slow rate and its combustion should be controllable.
  • Easy to store.
  • Low ignition temperature.
  • Produce a very small amount of residues such as ash.
  • Should possess high calorific value.
  • Do not produce gases which pollute the air.
  • Easily transportable.

Harmful impacts of burning fuel:

The increase in burning of fuel on this earth affects environment in many ways.

  • The unburnt particle of carbon fuels are dangerous pollutants and causes respiratory diseases, such as asthma.
  • Incomplete combustion some fuels gives carbon monoxide gas which is a very poisonous gas. It can kill persons sleeping in a room containing carbon dioxide.
  • Must fuel on oxidation releases carbon dioxide which is the major cause of global warming.
  • Burning of coal and diesel in vehicles releases sulphur dioxide gas which is responsible for acid rain.
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