Combustion: Fuels, Conditions & Pollution

• Combustion is defined as the burning of a substance in the presence of oxygen.

Conditions for Combustion

• Air or oxygen must be present.
• Fuel must be present.
• Ignition temperature must be maintained, where ignition temperature is the lowest temperature at which a substance catches fire.

CNG in Automobiles and Pollution Reduction

• CNG is a cleaner fuel compared to others.
• CNG serves as an alternative to diesel, petrol, and propane/LPG.
• CNG contains fewer undesirable gases than the other fuels.
• Combustion of fuels like petroleum causes unburnt carbon particles and carbon monoxide leading to respiratory diseases, a problem reduced by CNG.

Comparison of LPG and Wood as Fuels

Wood

• Used traditionally for domestic and industrial purposes.
• Produces a lot of smoke, polluting the atmosphere and causing respiratory diseases.
• Causes deforestation due to widespread usage.
• Calorific value ranges from 17000 to 22000 kJ/kg.
• Can be used indoors as a furnace, stove, or fireplace, and outdoors for campfires or furnaces.

LPG (Liquefied Petroleum Gas)

• Has replaced wood as a preferred fuel.
• Does not release smoke or other pollutants.
• It is a cleaner fuel.
• Has higher fuel efficiency than wood.
• Calorific value is 55000 kJ/kg.
• Is the most preferred choice of fuel.

Reasons

Water and Electrical Fires

• Water is a good conductor of electricity, so using it on an electrical fire can spread the electricity.
• The person dousing the fire could get an electric shock.

LPG vs. Wood as Domestic Fuel

• LPG is cleaner, releasing no smoke or pollutants.
• Wood releases smoke and fumes, polluting the atmosphere and causing respiratory diseases.

Paper and Aluminum Pipe

• Paper catches fire easily due to its low ignition temperature.
• Paper wrapped around an aluminum pipe does not catch fire because aluminum is a good conductor of electricity.
• Wrapping paper around an aluminum pipe increases the ignition temperature, and heat transfers from the paper to the aluminum pipe.

Candle Flame Zones

• Hottest Part: For complete combustion on the outer zone.
• Moderately Hot: For partial combustion in the middle zone.
• Least Hot: The innermost zone of unburnt wax vapours.

Calorific Value Unit

• Calorific value, the energy contained in a fuel, is expressed in kJ/kg (kilojoules per kilogram).

CO2 in Controlling Fires

• CO2 is a non-combustible gas that extinguishes fire.
• CO2 is heavier than oxygen, covering the fire like a blanket and cutting off contact between oxygen and fuel.
• In cylinders, CO2 is kept as a liquid, expanding enormously when released and lowering the fuel temperature.

Burning Green vs. Dry Leaves

• Green leaves contain a lot of moisture, resulting in a high ignition temperature; therefore, they do not catch fire easily.
• Dry leaves have low moisture content and a low ignition temperature, hence they catch fire easily.

Goldsmiths and Flame Zones

• Goldsmiths use the non-luminous flame as the outermost part of the flame for melting gold and silver.
• The outermost flame undergoes complete combustion and is the hottest part.

Calorific Value Calculation Example

• 4. 5 kg of fuel produces 180,000 kJ of heat when completely burned, so the calorific value of the fuel is 40,000 kJ/kg.

Rusting vs Combustion

• Rusting is not combustion.
• Rusting is an exothermic process where heat is released.
• Combustion involves a substance reacting with oxygen to release energy as heat or light.

Heating Water in a Beaker Experiment

• Ramesh's water will heat faster using the non-luminous outermost flame, because it is the hottest part of the flame.
• The luminous (yellow) flame where Abida placed the beaker is comparatively less hot.

Explore the conditions necessary for combustion, including the presence of oxygen, fuel, and ignition temperature. Compare CNG, LPG and wood as fuels, discussing their environmental impacts and calorific values. Learn about CNG's role in reducing pollution in automobiles.