Combustion and flame

5,591 views

Published on

Its a ppt on Science(combustion and flame), hope its helpful!!!!

Combustion and flame

  1. 1. Combustion And Flame Made By:- Anmol Pant VIII-C 31
  2. 2. 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.
  3. 3. 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.
  4. 4. Fuels The substance that undergoes combustion is said to be combustible. It is called a fuel. Fuels exist in three states:- a) Solid b) Liquid & c) Gaseous
  5. 5. Solid Fuels Wood Cow dung Cakes Charcoal Coal
  6. 6. Liquid Fuels Ethanol Kerosene Hydrogen Diesel Petrol
  7. 7. Gaseous fuels LPG CNG Bio gas Coal Gas
  8. 8. Nuclear Reactions In the sun, heat and light are produced by nuclear reactions.
  9. 9. Ignition Temperature The lowest temperature at which a substance catches fire is called it’s ‘Ignition Temperature’
  10. 10. 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
  11. 11. Inflammable Substances The substances which have very low ignition temperature and can easily catch fire with a flame are called ‘Inflammable Substances.’ Examples a) Petrol b) Alcohol c) LPG( Liquified Petroleum Gas)
  12. 12. 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.
  13. 13. 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.
  14. 14. Fireman extinguishing fire using water as extinguisher
  15. 15. 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. 2
  16. 16. Types of Combustion Combustion can be classified into three types:- a) Rapid Combustion b) Spontaneous Combustion c) Explosion d) Slow Combustion
  17. 17. 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.
  18. 18. 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’
  19. 19. Examples of Spontaneous Combustion. Forest Fires caused by spontaneous combustion. Spontaneous combustion of coal dust in coal mines.
  20. 20. 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
  21. 21. Slow Combustion The type of combustion which takes place at a slow rate at low temperatures is called ‘Slow Combustion.’ Example:- a) Respiration b) Rusting of Iron.
  22. 22. 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.
  23. 23. Substances which give out flame. The substances which vaporize during combustion give flames. Example:- a) Kerosene and Wax burn with a flame b)Whereas Charcoal, on the other hand, does not vaporize and so does not produce a flame.
  24. 24. Different zones of candle flame
  25. 25. Goldsmiths Goldsmiths blow the outermost zone of a flame with a metallic blow-pipe for melting gold and silver.
  26. 26. 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)
  27. 27. Calorific Value of different Fuels Fuel 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
  28. 28. 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.
  29. 29. 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.’
  30. 30. 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.

×