ch - combustion

Page 1: Introduction to Combustion and Flame

NCF Features

• Activity-based Learning

• Class Discussions

• Higher Order Thinking

• Strengthening Values

• Discovery-based Learning

• Digital Literacy

• Real-life Situations

Introduction to Combustion

• Observed in burning paper, wood, coal, LPG, and plastics.

• Combustion releases heat and light.

• Questions to explore:

  • Do all materials burn?

  • Do they all burn the same way?

Activity 1: Experimental Investigation of Combustion

• Materials Needed:

  • Coal, paper, wood, iron nails, dried leaves, cotton cloth, stone, wick dipped in kerosene, wick dipped in cooking oil.

• Instructions:

  • Hold each material with tongs over a Bunsen burner flame and observe results.

• Record in Table 6.1:

  • Material

  • Burns or Not

  • Is There a Flame?

Topics Covered

• Combustion

• Extinguishing a Fire

• Flame

• Fuels

• Impact of Burning Fuels on the Environment

Page 2: Conditions for Combustion

Understanding Combustion

• Combustion is a reaction of a substance with oxygen that produces heat and light.

• Activity 2:

  • Burn two candles to observe differences in combustion.

  • Cover one with a glass tumbler to see if it goes out.

Necessary Conditions for Combustion

• Combustible substance

• Supporter of combustion (oxygen)

• Sufficient heat to reach ignition temperature

Observations

1. A matchstick and burning substrance can ignite when heated properly.

2. Oxygen is crucial for combustion to occur.

3. Combustible substances must be heated above their ignition temperature to burn.

Complete and Incomplete Combustion

• Complete Combustion:

  • Occurs with sufficient oxygen, producing CO2 and water.

• Incomplete Combustion:

  • Occurs when oxygen is insufficient, producing carbon monoxide (CO) and water along with energy.

Page 3: Ignition Temperature and Fire

Ignition Temperature

• The lowest temperature at which a combustible substance ignites in the presence of air.

• Various materials have different ignition temperatures; e.g., paper does not ignite at room temperature.

Activity 3: Investigating Ignition Temperature

• Two paper cups are heated, one with water and one empty.

• The empty cup burns while the cup with water does not, as the water absorbs heat and keeps the cup's temperature below the ignition point.

Inflammable Substances

• Substances with low ignition temperatures that can easily catch fire (e.g., petrol, kerosene).

Types of Combustion

• Rapid Combustion:

  • Occurs quickly with heat and light present (like matches and LPG).

• Spontaneous Combustion:

  • Ignites without external heat when temperature exceeds ignition point (e.g., white phosphorus).

• Explosion:

  • Rapid reaction triggered by gas, causing heat, light, and sound.

Page 4: Fire Extinguishing Methods

Importance of Controlling Fire

• Uncontrolled fire can cause destruction and is why fire stations exist.

Fire Extinguishment Techniques

1. Removing Combustible Material:

   • Not feasible in buildings.

2. Cooling Below Ignition Temperature:

   • Typically done with water for wooden and paper fires.

3. Removing Air Supply:

   • Done through carbon dioxide gas or blanket methods.

Fire Extinguisher Mechanism

• Structure:

  • Container, sodium bicarbonate solution, bottle with concentrated sulphuric acid.

• When properly activated, CO2 is released to smother the flames.

Page 5: Flame Characteristics

Understanding Flames

• Not all burning materials produce flames; only those that vaporize do so.

• Examples:

  • Kerosene vaporizes and burns, producing a flame.

  • Charcoal burns without a flame, glowing instead.

Types of Flame

• Non-luminous Flame:

  • Complete combustion gives a blue flame (e.g., LPG).

• Luminous Flame:

  • Incomplete combustion produces a yellow flame due to unburnt carbon.

Candle Flame Structure

• A candle flame consists of multiple zones:

  • Non-luminous zone:

    • Complete combustion occurs, visible blue flame.

  • Luminous zone:

    • Incomplete combustion, gives off soot.

  • Dark zone:

    • No visible combustion, least hot area.

Page 6: Experimental Investigation of Candle Flame

Performing Activities

• Light a candle and observe flame shapes in a non-airy environment.

• Explore zones of the flame using glass tubes and slides to notice combustion effects.

Page 7: Discussion Questions

Classroom Discussion Topics

1. Effects of burning hydrocarbons and the production of CO2 and water vapor.

2. The importance of the ignition temperature for fuels and its implications for safety.

3. The properties of carbon dioxide that make it effective in extinguishing fires.

4. The significance of gas emissions on environmental health and pollution.

Calorific Value of Fuels

• Defines the heat released when one kilogram of fuel combusts in oxygen. Higher values indicate better fuels.

• Examples:

  • Cow dung cake: 7000 kJ/kg

  • Kerosene: 45000 kJ/kg

  • Methane: 55000 kJ/kg

Page 8: Environmental Impacts of Fuel Combustion

Negative Environmental Effects

• Burning of fuels adds pollutants (e.g., carbon soot) to the air, which contributes to global warming.

• Oil spills from tankers cause ecological damage, harming aquatic life.

• Dams for hydropower can displace people and wildlife, causing habitat destruction.

• Nuclear plants pose risks of radiation pollution in case of accidents.

• Contamination from vehicle emissions can lead to harmful gas exposure.