Unit-4: Fuels & Combustion

Mr. Santosh DamkondwarMonday, April 10, 2023

Introduction

• Fuels

• Non-renewable Conventional Sources

• In Mechanical, Electrical & Chemical

operations.

Characteristics of Good Fuels:

• High Calorific Values

• Moderate Ignition Temperature

• Low Moisture Content

• Low Ash Content

• Moderate Velocity of Combustion

• Should not produce harmful products

• Low Cost

• Easy Storage & Transportation

• Easily Controllable

Classification

• Natural or Primary Fuels

Solide.g.

Wood, Peat, Lignite, Bituminous

Coal, Dung

Gaseouse.g.

Natural Gas

Classification

• Artificial or Secondary or Derived Fuels

Solide.g.

Coke,Charcoal,

Gaseouse.g.

Coal Gas, Water Gas,

Bio-Gas

Calorific Values:

• Calorific Value of fuel is the total quantity of heat liberated by complete combustion of a unit mass (or volume) of the fuel.

• It can be expressed for Solid Fuels in terms of :

Cal/gm (CGS Unit)Kcal/Kg (MKS Unit)J/Kg (SI Unit)B.Th.U. / lb (British Thermal Unit)

1 cal/gm 1 Kcal/Kg 1.8 B.Th.U./lb 4.187 J/Kg

Calorific Values

Calorific Values:

• Calorific Value of fuel is the total quantity of heat liberated by complete combustion of a unit mass (or volume) of the fuel.

• It can be expressed for Gaseous Fuels in terms of :

Cal/lit (CGS Unit)Kcal/m3 (MKS Unit)J/m3 (SI Unit)B.Th.U. / Ft3 (British Thermal Unit)

1 Kcal/m3 0.1077 B.Th.U./Ft3

Calorific Values

1 B.Th.U./Ft3 9.3 Kcal/m3

Calorific Values

Lower Calorific Value

Higher Calorific Value

Calorific Values

Higher Calorific Values:

• It is the total amount of heat liberated, when unit mass / volume of the fuel is burnt completely and the products of combustion have been cooled to room temperature (i.e. 15oC).

Lower Calorific Values:

• It is the net amount of heat liberated, when unit mass / volume of the fuel is burnt completely and the products of combustion are allowed to escape.

Relation between GCV & LCV:

• These can be related as:

NCV = GCV – Latent heat of water vapor formedor

= GCV – (Mass of Hydrogen × Latent heat of steam)

= GCV – [(9 × Mass of hydrogen) × Latent heat of steam]

If mass of hydrogen is expressed as % of H, thenNCV = GCV – [9× H/100 × 587] cal/gm

Determination of Calorific Value:

• Calorific Value of the fuel is determined by heating known amount of fuel, in presence of oxygen in calorimeter.

• Principleo Total heat liberated by complete combustion

of known amount of fuel is absorbed by the known mass of water in calorimeter. From the rise in temperature of water, the calorific value of fuel is determined.