Fuels: Characteristics and Properties

• Fuels are any material that stores potential energy in forms that liberate heat energy upon burning in oxygen.
• The calorific value of fuel is the total quantity of heat liberated when a unit mass or volume of fuel is completely burnt.
• Higher or gross calorific value (HCV) in the total heat produced when a unit mass/volume of fuel has been burnt completely and the combustion products have been cooled to room temperature (15°C or 60°F).
• Lower or net calorific value (LCV) is the heat produced when the fuel's unit mass (volume) is burnt completely, and the products are permitted to escape.

LCV = HCV – Latent heat of water formed

• Natural or primary fuels, such as wood, peat, coal, natural gas, and petroleum, are found in nature.
• Artificial or secondary fuels are prepared from primary fuels like charcoal, coal gas, coke, kerosene oil, diesel oil, petrol, etc.

Fuels are further classified as

1. Solid Fuels
2. Liquid Fuels
3. Gaseous Fuels

Characteristics of solid fuels

1. Ash is high.
2. Low thermal efficiency
3. Form clinker
4. Low calorific value and require large excess air.
5. The cost of handling high
6. It cannot be used in IC engines.

Characteristics of liquid fuels

1. High calorific value
2. No dust ash and clinker
3. Clean fuels
4. Less furnace air
5. Less furnace space
6. Used in IC engines

Characteristics of Gaseous Fuels

1. Have high heat content
2. No ash or smoke
3. Substantial storage tanks are required

An ideal fuel should have the following properties:

1. High calorific value
2. Moderate ignition temperature
3. Low moisture content
4. The low NO_n combustible matter
5. Moderate velocity of combustion
6. Products of combustion are not harmful
7. Low cost
8. Easy to transport
9. Combustion should be controllable
10. No spontaneous combustion
11. Low storage cost
12. It should burn in the air efficiently.