Study Notes on Combustion and Flame

Combustion and Flame

Types of Fuel

  •     Fuels used at home, in industry, and for automobiles include:

    • Cowdung

    • Wood

    • Coal

    • Charcoal

    • Petrol

    • Diesel

    • Compressed Natural Gas (CNG)

Understanding Combustion

  • Definition of Combustion: A chemical process where a substance reacts with oxygen, producing heat and light. The combustible substance is referred to as fuel, which can be in solid, liquid, or gas form.

  • Examples of Combustible Substances: Magnesium burns to form magnesium oxide, and charcoal burns in air to produce carbon dioxide, heat, and light.

Experimenting with Combustion

Activity 4.1: Testing Combustibility

  • Materials used for testing: straw, matchsticks, kerosene oil, paper, iron nails, stone pieces, and glass.

  • Observation Process:

    • Attempt to burn materials one at a time under teacher supervision.

    • Mark each material as combustible or non-combustible based on whether combustion occurs.

Activity 4.2: Investigating Air's Role in Combustion

  • Setup:

    • Light a candle and place a glass chimney over it.

    • Notice the flame behavior under different conditions:

    • Case (a): Flame burns freely.

    • Case (b): Flame flickers and produces smoke due to limited airflow.

    • Case (c): The flame extinguishes when no air is available.

Activity 4.3: Behavior of Burning Charcoal

  • Objective: Observe a piece of burning charcoal or wood to see if it stops burning over time.

Ignition Temperature

  • Definition: The lowest temperature at which a combustible material catches fire.

  • Examples:

    • Kerosene oil catches fire at a lower temperature compared to wood.

    • Requires caution in storage of kerosene oil due to lower ignition temperature.

Activity 4.4: Effect of Heating on Ignition Temperature

  • Setup: Create two paper cups, one with water and one empty. Observe heating effects:

    • The paper cup with water does not catching fire due to the heat being absorbed by the water.

  • Conclusion: The presence of water keeps the paper’s temperature below its ignition point.

Inflammable Substances

  • Definition: Substances that catch fire easily due to low ignition temperatures. Examples: petrol, alcohol, LPG.

Fire Control Methods

Essential Requirements for Fire

  • Fire needs three essentials:

    1. Fuel

    2. Air (Oxygen)

    3. Heat

  • Control Measures: Removing one or more requirements can control fire.

Fire Extinguishing Techniques

  • Water as an Extinguisher: Effective for wood and paper but not for electrical equipment or oil-based fires.

  • Carbon Dioxide (CO2): Preferred for electrical equipment fires due to the prevention of oxygen contact and additional cooling effect.

Types of Combustion

  • Rapid Combustion: Occurs when gas burns quickly, producing heat and light. E.g., using a matchstick on a gas stove.

  • Spontaneous Combustion: Occurs when a material ignites without outside ignition; e.g., coal dust in mines.

  • Explosion: A rapid combustion reaction producing heat, light, and sound with significant gas volume release. E.g., fireworks.

Characteristics of Flames

Observing Flame Colors

  • LPG flame color differs from a candle flame; candles have visible zones (dark, luminous, and non-luminous).

Activity 4.5: Investigating Flame Structure

  • Introducing a glass tube into a candle flame shows that vapors from melted wax create a flame.

  • Smoke deposition indicates the presence of unburnt carbon in the luminous zone of the flame.

  • Temperature Zones in Flames: Different zones produce varying heat levels.

Definition and Characteristics of Fuels

  • Good Fuel: Readily available, economical, burns easily in air, produces high heat output, and leaves minimal harmful residues.

  • Calorific Value: Heat energy produced from complete combustion of 1 kg of fuel; expressed in kJ/kg (kilojoules per kilogram).

  • Table of Calorific Values of Fuels:

    • Cow dung cake: 6000-8000 kJ/kg

    • Wood: 17000-22000 kJ/kg

    • Coal: 25000-33000 kJ/kg

    • Petrol/Kerosene/Diesel: 45000 kJ/kg

    • Methane/CNG: 50000 kJ/kg

    • LPG: 55000 kJ/kg

    • Hydrogen: 150000 kJ/kg

Environmental Impact of Fuel Usage

  • Incomplete combustion leads to hazardous emissions:

    1. Carbon monoxide - poisonous gas released.

    2. Carbon dioxide - linked to global warming, causing iceberg melting and coastal flooding.

    3. Sulphur dioxide and nitrogen oxides contribute to acid rain, harmful to agriculture, buildings, and ecosystems.

Key Terms

  • Acid Rain: Rain containing acidic components resulting from air pollution.

  • Fuel Efficiency: The measure of fuels based on how much energy they produce relative to their cost.

  • Global Warming: The long-term heating of Earth’s climate due to human activities, exacerbated by CO2 emissions.

Exercise Questions

  1. List conditions necessary for combustion.

  2. Fill in the blanks related to burning processes and fuel characteristics.

  3. Compare the effectiveness and safety of CNG versus conventional automotive fuels.

  4. Explain strategies for controlling fire and proper extinguishing methods for different materials.

  5. Discuss the significance of fuel sources and their environmental implications.