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• Combustion: The process of burning in the presence of oxygen to produce heat and light
• Examples of combustion: Burning of paper, burning of coal, burning of CNG, etc.
• Necessary conditions for combustion: Fuel, air or oxygen, temperature above ignition temperature
• Ignition temperature: Minimum temperature at which substance catches fire. Below ignition temperature substance do not catch fire.
• Types of Combustion :
  • Rapid combustion – Burns rapidly producing heat and light. Eg. Gaseous fuel
  • Spontaneous combustion – Combustion in which the substances catches fire by itself without the help of external heat. E.g. Yellow phosphorus
  • Explosion – Produces heat, light and sound on large amount. E.g. firecrackers
• Fire control:
  • Use of blanket
  • Use of fire extinguisher
  • Fire brigade
• Flame: Burning part of candle producing light
• Structure of flame
  • Outer zone (blue zone) – It is the outermost part and hottest part of the flame where vapours undergo complete combustion.
  • Innermost zone (dark zone) – In this region vapor remains unburnt and temperature is coolest comparatively.
  • Middle zone (illumination zone) – In this region, vapor undergo partial combustion producing heat and light. Temperature is hotter than the innermost zone and cooler than outer zone.
• Fuel: Substances that undergo combustion in the presence of air producing large amount of energy
• Types of fuels and examples:
  

  Types of fuels	Examples
  Solid fuels	Coal, wood, charcoal, etc.
  Liquid fuels	Petrol, diesel, ethanol, kerosene, etc.
  Gaseous fuels	LPG, CNG, hydrogen, biogas, etc.

• Calorific value: It is the amount of heat energy produced during complete combustion of 1kg of a fuel. Higher the calorific value larger will be the heat produced by the fuel.
• Unit of calorific value – kilojoule per kg (kJ/kg)
• Properties of good fuel:
  • It is cheap and readily available.
  • It is easy to store and transport.
  • Ignition temperature must be moderate and calorific value must be higher.
  • Must not produce harmful products
• Harmful effects of burning fuels
  • Burning coal and petroleum produces soot particles, which remains in the air for a longer time. This causes diseases like asthma.
  • Incomplete combustion of fuel produces carbon monoxide. It is a poisonous gas, if breath in such air may prove fatal to life.
  • Use of fossil fuel produces large amounts of carbon dioxide, which ultimately result in the greenhouse effect.
  • Burning coal, diesel and petrol produces sulphur dioxide and releases nitrogen in the air. This mixes with rain water causing acid rain.