Chapter 4: Chemistry of Fuels and Lubricants Notes, Polytechnic 1st Semester Chemistry Notes - BTER

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Welcome to Rajasthan Polytechnic BTER! This blog post is dedicated to Chapter 4 of the Chemistry syllabus for 1st-semester Polytechnic students. Here, you'll find detailed notes on Chapter 4: Chemistry of Fuels and Lubricants , designed to provide you with all the essential information you need. For more quality content and notes, make sure to visit our website regularly.

This chapter discusses the various aspects of fuels and lubricants, crucial for understanding energy resources and their applications in different engines and machinery. We will cover definitions, classifications, calorific values, and important properties of both fuels and lubricants in detail. Understanding these concepts will help students grasp how different fuels work and how lubricants contribute to the efficiency and longevity of machinery.

4.1 Definition of Fuel

Fuel is any substance that, when burned in the presence of oxygen, produces heat energy. It is primarily used in engines and other systems to produce mechanical work, generate heat, or create power. Common examples include coal, petrol, diesel, natural gas, and wood.

4.1.1 Combustion of Fuel

Combustion is a chemical process in which fuel reacts with oxygen to release heat energy. This reaction usually results in the formation of carbon dioxide and water as by-products. For example, when petrol burns, it reacts with oxygen to produce energy, CO₂, and H₂O. The general formula for combustion is: $\text{Fuel} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{Heat Energy}$

4.1.2 Classification of Fuels

Fuels are classified into three categories based on their physical state:

1. Solid Fuels: Examples include coal, wood, and charcoal.
2. Liquid Fuels: Examples are petrol, diesel, and kerosene.
3. Gaseous Fuels: Examples include natural gas, LPG (Liquefied Petroleum Gas), and biogas.

4.1.3 Calorific Values (HCV and LCV)

Calorific value measures the energy produced when a specific amount of fuel is burned. It is expressed in kilojoules per kilogram (kJ/kg) for solid and liquid fuels and in kilojoules per cubic meter (kJ/m³) for gaseous fuels. There are two types of calorific values:

1. Higher Calorific Value (HCV): This is the total energy released during complete combustion, including the latent heat of water vapor.
2. Lower Calorific Value (LCV): This is the energy released during combustion, excluding the latent heat of water vapor. LCV is always lower than HCV.

4.1.4 Calculation of HCV and LCV using Dulong’s Formula

Dulong’s formula is used to calculate the calorific value of solid and liquid fuels based on their elemental composition. The formula is as follows:

$\text{HCV} = 1/100 \times \left[ \left( 8080 \times \% C \right) + \left( 34500 \times \% H \right) - \left( 2240 \times \% O \right) \right]$

Where:

• $$ = Percentage of Carbon
• $$ = Percentage of Hydrogen
• $$ = Percentage of Oxygen

To calculate the LCV, subtract the latent heat of vaporization of water from the HCV.

4.2 Petrol and Diesel - Fuel Rating (Octane and Cetane Numbers)

• Octane Number: This is a measure of a fuel's ability to resist knocking during combustion in a petrol engine. A higher octane number indicates better anti-knocking properties.
• Cetane Number: This measures the ignition quality of diesel fuel. A higher cetane number means the fuel ignites quickly when injected into the engine.

4.3 Chemical Properties of Lubricants

Lubricants are substances that reduce friction between moving parts, prevent wear and tear, and act as a cooling agent. The chemical properties of lubricants are crucial for their performance.

4.3.1.1 Coke Number

The coke number indicates the tendency of a lubricant to form carbon deposits at high temperatures. A lower coke number means fewer carbon deposits and better lubricant performance.

4.3.1.2 Total Acid Number (TAN)

Total Acid Number is a measure of the acidity of a lubricant. It indicates the amount of acidic compounds in the oil, which can cause corrosion and damage to engine components.

4.3.1.3 Saponification Value

Saponification value measures the amount of alkali required to saponify a given quantity of oil. It indicates the presence of fatty acids or esters in the lubricant. High saponification values may lead to soap formation, which can clog the engine.

This chapter provides a comprehensive overview of fuels and lubricants, covering their definitions, classifications, and key properties. For Polytechnic 1st Semester students, understanding these fundamentals is crucial for subjects like Chemistry and Mechanical Engineering. Keep revisiting Rajasthan Polytechnic for more such detailed notes and explanations to excel in your exams.

These Notes are according to Syllabus provided by BTER (Board of Technical Education Rajasthan, Jodhpur) for Polytechnic 1st Semester Students.

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Garima Kanwar