Class 8 Science – Combustion and Flame

1. Introduction

• Combustion is the process in which a substance reacts with oxygen to release heat and light.

• Most fuels undergo combustion to provide energy for daily life.

• Flame is the visible, luminous part of a burning fuel.

Key Concept:

• Combustion is essential for energy production but must be controlled to prevent accidents.

2. Types of Combustion

1. Complete Combustion

   • Fuel burns completely in the presence of sufficient oxygen.

   • Produces maximum heat.

   • Flame is usually blue and clean.

   • Example: Burning of LPG, natural gas.

2. Incomplete Combustion

   • Fuel burns in limited oxygen supply.

   • Produces less heat, smoke, and toxic gases.

   • Flame is yellow or orange.

   • Example: Burning of kerosene or coal in poor air supply.

3. Spontaneous Combustion

   • Self-ignition of substances without external flame or spark.

   • Happens in stored oil seeds, haystacks, or coal piles under certain conditions.

4. Explosion

   • Rapid and violent combustion releasing large energy suddenly.

   • Example: Firecrackers, gas cylinder leaks.

3. Structure of a Flame

A flame has three distinct zones:

1. Inner Zone (Dark Zone)

   • Nearest to the fuel source.

   • Partially burnt fuel.

2. Middle Zone (Luminous Zone)

   • Bright yellow region.

   • Incomplete combustion occurs here.

3. Outer Zone (Non-Luminous Zone)

   • Blue in color.

   • Complete combustion occurs here.

   • Produces maximum heat.

Key Concept:

• Understanding flame zones is important in burning efficiency and laboratory experiments.

4. Fire Control Methods

1. Removing Fuel

   • Stop fuel supply → fire dies.

2. Removing Oxygen

   • Cover the fire with blankets, sand, or foam.

3. Cooling

   • Use water to lower the temperature below ignition point.

4. Chemical Fire Extinguishers

   • For electrical or chemical fires, special extinguishers like CO₂ or dry powder are used.

Key Concept:

• Fire control is essential to prevent loss of life, property, and environment.

5. Uses of Combustion

• Domestic: Cooking and heating.

• Industrial: Furnaces, engines, and factories.

• Transportation: Fuels like petrol, diesel, and LPG.

• Energy Production: Power plants using coal, petroleum, or gas.

6. Key Points to Remember

• Combustion = reaction of fuel with oxygen to release heat and light.

• Types of combustion: complete, incomplete, spontaneous, explosion.

• Flame has inner (dark), middle (luminous), and outer (non-luminous) zones.

• Fire control involves removing fuel, oxygen, or heat.

• Safety and proper handling of combustible materials are crucial.