Thermal Engineering-1 ME3005 all units in English

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Garima Kanwar This Side. These Notes are short notes for revision purpose only. Please Refer Your college study material & Reference Book for Complete Study.

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Course Code : ME 3005 
Course Title : THERMAL ENGINEERING - I

💥💥UNIT 1💥💥

1. Sources of Energy

Energy sources are classified based on their origin, use, and environmental impact. The following sections provide a basic introduction to various energy sources, which are crucial in meeting the global demand for power and reducing reliance on non-renewable resources.

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1.1 Brief Description and Classification of Energy Sources:

Energy sources can be broadly classified into two categories:

1. Renewable Energy Sources:

These are energy sources that are replenished naturally and can be used repeatedly. They are environmentally friendly and sustainable in the long term.

• Solar Energy: Comes from the sun, which is harnessed using photovoltaic (solar panels) or concentrated solar power (CSP) systems.
• Wind Energy: Generated by harnessing the kinetic energy of wind using wind turbines.
• Biomass: Organic materials (e.g., wood, agricultural residues) used to produce energy.
• Geothermal Energy: Heat from the Earth's interior used for power generation and direct heating applications.
• Hydropower (Hydraulic Energy): Energy obtained from flowing or falling water, typically in dams or rivers.
• Ocean Energy: Includes tidal energy and ocean thermal energy, derived from the movement of water and temperature differences in the oceans.

2. Non-Renewable Energy Sources:

These are finite and deplete over time. They have a higher environmental impact, contributing to pollution and climate change.

• Fossil Fuels: Coal, oil, and natural gas are the most common examples.
• Nuclear Energy: Harnesses the energy from nuclear reactions, usually fission, to produce electricity.

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1.2 Solar Energy Applications (Basic Introduction):

Solar energy is derived from the sun's radiation. It is one of the most abundant and cleanest renewable energy sources available.

• Photovoltaic (PV) Systems: Solar panels convert sunlight directly into electricity using semiconductor materials (e.g., silicon).
• Concentrated Solar Power (CSP): Mirrors or lenses focus sunlight to generate high temperatures, which are used to produce electricity through thermal processes.

Applications of solar energy:

• Residential power generation (rooftop solar panels).
• Solar water heating systems.
• Large-scale solar power plants.
• Solar-powered vehicles and devices (calculators, street lights).

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1.3 Wind Energy (Basic Introduction):

Wind energy is harnessed from the movement of air in the Earth's atmosphere, driven by the sun's uneven heating of the Earth's surface.

• Wind Turbines: Convert the kinetic energy of wind into mechanical power, which can be converted into electricity.
• Offshore Wind Farms: Wind turbines installed in bodies of water, where wind speeds are generally higher.

Applications of wind energy:

• Large-scale wind farms (onshore and offshore).
• Small-scale wind turbines for residential or industrial use.
• Wind-powered water pumps in rural areas.

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1.4 Tidal Energy, Ocean Thermal Energy, Geothermal Energy (Basic Introduction):

1. Tidal Energy:

   • Derived from the gravitational forces between the Earth, moon, and sun.
   • Tidal turbines or barrages capture the energy from rising and falling tides to generate electricity.
   • Applications: Coastal regions with high tidal ranges, such as the Severn Barrage in the UK.

2. Ocean Thermal Energy:

   • Relies on the temperature difference between the warm surface water and cold deep-water layers of the ocean.
   • Ocean Thermal Energy Conversion (OTEC): Uses this temperature differential to generate electricity.
   • Applications: Tropical coastal regions where the temperature difference is significant.

3. Geothermal Energy:

   • Comes from the heat stored beneath the Earth's surface, often in the form of hot water or steam.
   • Geothermal power plants use this heat to generate electricity or provide direct heating.
   • Applications: Regions with high volcanic or tectonic activity, like Iceland or parts of the U.S. (e.g., The Geysers).

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1.5 Biogas, Biomass, Bio-diesel (Basic Introduction):

1. Biogas:

   • Produced from the anaerobic digestion of organic matter (e.g., agricultural waste, animal manure).
   • Consists mainly of methane, which can be used for cooking, heating, and electricity generation.
   • Applications: Biogas plants, rural energy solutions, waste management.

2. Biomass:

   • Organic materials (e.g., wood, agricultural residues, animal waste) are burned or processed to generate heat or electricity.
   • Can also be converted into liquid fuels.
   • Applications: Biomass power plants, biofuel production, residential heating.

3. Bio-diesel:

   • A renewable fuel made from vegetable oils, animal fats, or algae.
   • Can replace or be blended with conventional diesel fuel for vehicles and machinery.
   • Applications: Transport (vehicles), industrial machinery, and energy production.

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1.6 Hydraulic Energy, Nuclear Energy (Basic Introduction):

1. Hydraulic Energy (Hydropower):

   • Generated from the movement of water, usually through dams, rivers, or waterfalls.
   • Applications: Hydroelectric power stations, flood control, irrigation systems.
   • Advantages: It’s a clean, renewable source of energy that can produce large amounts of electricity.
   • Challenges: Environmental impact on aquatic ecosystems and displacement of local populations due to dam construction.

2. Nuclear Energy:

   • Generated through nuclear reactions (typically fission), where the nucleus of an atom is split to release a large amount of energy.
   • Applications: Power generation in nuclear power plants.
   • Advantages: Can produce large amounts of energy with minimal fuel compared to fossil fuels.
   • Challenges: High risks, radioactive waste disposal, safety concerns (e.g., Fukushima, Chernobyl), and limited fuel sources (Uranium).

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1.7 Fuel Cell (Basic Introduction):

Fuel cells are devices that convert chemical energy directly into electrical energy using a fuel (often hydrogen) and an oxidant (usually oxygen from air) through an electrochemical reaction.

• Working: The hydrogen fuel is introduced to the anode, where it is split into protons and electrons. The electrons travel through an external circuit (producing electricity) while protons pass through an electrolyte to the cathode, where they combine with oxygen to form water.
• Applications:
  • Transport: Fuel cell vehicles (cars, buses, trucks).
  • Stationary power generation: Backup power supplies, distributed energy generation.
  • Portable power systems: Small electronics and remote power sources.
• Advantages: Clean, renewable energy with water as the only byproduct.

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Summary:

1. Solar Energy: Capturing energy from sunlight through PV systems or CSP technologies.
2. Wind Energy: Harnessing the wind’s kinetic energy to generate electricity through wind turbines.
3. Tidal, Ocean Thermal, Geothermal: Using ocean movements, temperature differences, and Earth's internal heat for power generation.
4. Biogas, Biomass, Bio-diesel: Converting organic materials into energy, reducing waste, and creating sustainable fuels.
5. Hydraulic Energy: Utilizing water movement (such as dams and rivers) to generate electricity.
6. Nuclear Energy: Producing energy through nuclear fission reactions.
7. Fuel Cells: Converting chemical energy directly into electricity through electrochemical reactions, primarily using hydrogen.

These renewable and non-renewable energy sources form the backbone of energy generation worldwide, each with its unique applications, challenges, and benefits. 

💥💥UNIT 2💥💥

2. Internal Combustion Engines (I.C. Engines)

Internal Combustion Engines (I.C. Engines) are widely used in various applications, including automobiles, power generation, and industrial machinery. These engines burn fuel within the engine itself to produce mechanical work.

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2.1 Assumptions Made in Air Standard Cycle Analysis:

In air standard cycle analysis, assumptions are made to simplify the complex processes within an I.C. engine. These assumptions help in deriving ideal performance characteristics.

1. Ideal Gas Behavior: The air inside the engine is assumed to behave as an ideal gas (i.e., it follows the ideal gas laws).
2. No Heat Losses: There is no heat loss to the surroundings, and all heat input is converted into work.
3. Adiabatic Process: Processes like compression and expansion are assumed to be adiabatic (i.e., no heat is exchanged during these processes).
4. Constant Specific Heats: The specific heats of air (Cp and Cv) are considered constant throughout the cycle.
5. Perfect Gas Flow: The intake and exhaust processes are ideal, meaning no friction or turbulence in the airflow.

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2.2 Brief Description of Carnot, Otto, and Diesel Cycles with P-V and T-S Diagrams:

Carnot Cycle (Theoretical Ideal Cycle):

• Description: It is the most efficient cycle for a heat engine, consisting of two isothermal processes (heat intake and rejection) and two adiabatic processes (compression and expansion).
• P-V Diagram:
  • Isothermal expansion at high temperature.
  • Adiabatic expansion (temperature decreases).
  • Isothermal compression at low temperature.
  • Adiabatic compression (temperature increases).
• T-S Diagram:
  • Shows temperature vs. entropy, with the isothermal processes being horizontal lines and the adiabatic processes being vertical lines.

Otto Cycle (Used in Petrol Engines):

• Description: The Otto cycle consists of two adiabatic processes and two isochoric (constant volume) processes. It is used in spark-ignition (S.I.) engines.
• P-V Diagram:
  • Intake stroke (constant pressure).
  • Compression stroke (adiabatic).
  • Ignition and combustion at constant volume (isochoric).
  • Expansion (adiabatic).
• T-S Diagram:
  • The isochoric heat addition and rejection occur at constant volume, resulting in vertical jumps on the T-S curve.

Diesel Cycle (Used in Diesel Engines):

• Description: The Diesel cycle consists of two adiabatic processes, one isochoric heat addition, and one isobaric heat rejection. It is used in compression-ignition (C.I.) engines.
• P-V Diagram:
  • Intake stroke (constant pressure).
  • Compression stroke (adiabatic).
  • Heat addition at constant pressure (isobaric).
  • Expansion stroke (adiabatic).
• T-S Diagram:
  • The heat addition process occurs at constant pressure, causing a horizontal shift on the T-S curve.

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2.3 Difference Between Internal and External Combustion Engines:

Internal Combustion Engine	External Combustion Engine
Combustion occurs inside the engine cylinder.	Combustion occurs outside the engine, in a separate combustion chamber (e.g., steam engines).
Direct conversion of energy into mechanical work.	Energy is converted to heat and then transferred to the engine via a working fluid (steam).
Faster response time, compact size.	Slower response, larger size due to heat exchange system.
Examples: Petrol and Diesel engines.	Examples: Steam engines, Stirling engines.

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2.4 Advantages of I.C. Engines Over External Combustion Engines:

1. Compact Size: I.C. engines are much smaller and more compact compared to external combustion engines.
2. Better Efficiency: They have higher thermal efficiency due to direct combustion within the engine cylinder.
3. Quicker Response: I.C. engines respond faster to changes in load and speed.
4. Less Complex: They do not require a separate heat exchanger, unlike external combustion engines that rely on a boiler and turbine.
5. Lower Initial Cost: I.C. engines are generally cheaper to produce than external combustion engines.

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2.5 Classification of I.C. Engines:

I.C. engines can be classified based on several factors:

1. By Fuel Type:

   • Petrol Engines (Spark Ignition): Uses petrol (gasoline) as fuel, ignited by a spark.
   • Diesel Engines (Compression Ignition): Uses diesel fuel, which is ignited by compression (no spark plug).

2. By Cycle:

   • Four-Stroke Engines: Require four strokes of the piston to complete one cycle (intake, compression, power, exhaust).
   • Two-Stroke Engines: Complete the cycle in two strokes of the piston.

3. By Stroke Arrangement:

   • Single Cylinder: One piston operates within the cylinder.
   • Multi-Cylinder: Multiple cylinders are arranged to improve power output and reduce vibrations.

4. By Cooling Method:

   • Air-Cooled Engines: Uses air to dissipate heat.
   • Water-Cooled Engines: Uses water or coolant to absorb heat.

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2.6 Working with Neat Sketch of I.C. Engine Indicating Component Parts and Function of Parts:

Basic Components of an I.C. Engine:

1. Cylinder: The main chamber where fuel combustion occurs.
2. Piston: Moves up and down inside the cylinder, converting pressure into mechanical work.
3. Crankshaft: Converts the linear motion of the piston into rotational motion.
4. Valves (Intake & Exhaust): Control the intake of air-fuel mixture and the exhaust of combustion gases.
5. Spark Plug (for Petrol Engines): Ignites the air-fuel mixture.
6. Fuel Injector (for Diesel Engines): Injects fuel into the combustion chamber.

Working Principle: The fuel-air mixture is ignited in the cylinder, causing a high-pressure force on the piston. This pressure drives the piston down, which rotates the crankshaft, producing mechanical work.

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2.7 Working of Four-Stroke and Two-Stroke Petrol and Diesel Engines:

Four-Stroke Engine:

• Four distinct strokes:
  1. Intake Stroke: Intake valve opens, and the piston moves down to draw in the air-fuel mixture.
  2. Compression Stroke: Intake valve closes, and the piston moves up to compress the mixture.
  3. Power Stroke: The mixture is ignited (spark or compression), causing combustion, and the piston moves down.
  4. Exhaust Stroke: Exhaust valve opens, and the piston moves up to expel the gases.

Two-Stroke Engine:

• Two strokes per cycle:
  1. Compression Stroke: The piston moves up, compressing the air-fuel mixture.
  2. Power Stroke: The mixture is ignited, and the piston moves down, pushing exhaust gases out and drawing in a new mixture.

Diesel Engine Operation: In diesel engines, air is compressed to a high temperature, and fuel is injected, causing spontaneous ignition due to high pressure (no spark plug).

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2.8 Comparison of Two-Stroke and Four-Stroke Engines:

Feature	Two-Stroke Engine	Four-Stroke Engine
Power Stroke	1 per 2 piston strokes	1 per 4 piston strokes
Efficiency	Lower efficiency	Higher efficiency
Fuel Consumption	Higher consumption	Lower consumption
Complexity	Simpler, fewer parts	More parts, complex
Lubrication	Requires oil mixture with fuel	Separate lubrication system
Emissions	Higher emissions	Lower emissions
Applications	Small engines (mowers, chainsaws)	Cars, trucks, motorcycles

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2.9 Comparison of C.I. and S.I. Engines:

Feature	C.I. Engine (Diesel)	S.I. Engine (Petrol)
Ignition Method	Compression ignition	Spark ignition
Fuel Type	Diesel	Petrol (Gasoline)
Compression Ratio	Higher (14:1 to 23:1)	Lower (6:1 to 10:1)
Efficiency	Higher	Lower
Power Output	Lower	Higher
Fuel Consumption	Lower	Higher
Applications	Trucks, buses, industrial machinery	Cars, motorcycles, light vehicles

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2.10 Valve Timing and Port Timing Diagrams for Four-Stroke and Two-Stroke Engines:

Valve Timing Diagram (Four-Stroke Engine):

The valve timing diagram shows the opening and closing of the intake and exhaust valves relative to the position of the piston in the cycle.

• Intake Valve Opens: A little before the piston reaches the bottom of the compression stroke.
• Exhaust Valve Closes: After the piston has started to move up during the exhaust stroke.
• Duration: Intake and exhaust valves have specific timings to optimize the engine's breathing.

Port Timing Diagram (Two-Stroke Engine):

Port timing refers to the timing of the exhaust and intake ports in a two-stroke engine.

• Port Openings: The exhaust port opens just before the piston reaches the bottom of the stroke, and the intake port opens as the piston moves upward.
• Overlap: There is an overlap of exhaust and intake strokes to allow for continuous scavenging.

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These topics encompass the working principles, types, and operation of I.C. engines, explaining the fundamental components, cycles, and comparisons between various types of engines. 

💥💥UNIT 3💥💥

3. I.C. Engine Systems

Internal Combustion (I.C.) engines are made up of several systems that work together to provide power. These systems include the fuel system, cooling system, ignition system, lubricating system, governing system, and more. Let’s take a detailed look at each of these systems.

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3.1 Fuel System of Petrol Engines:

The fuel system in petrol engines is responsible for storing and delivering the fuel to the engine in the correct quantity and mixture with air for combustion. It includes:

1. Fuel Tank: Stores the petrol and supplies it to the fuel pump.
2. Fuel Pump: Delivers fuel from the tank to the carburetor or fuel injectors under pressure.
3. Carburetor (in older engines) or Fuel Injectors (in modern engines):
   • Carburetor: Mixes air and petrol in the correct ratio before entering the engine.
   • Fuel Injectors: Directly inject petrol into the combustion chamber or intake manifold, precisely controlling the air-fuel mixture.
4. Fuel Filter: Filters any impurities or debris in the fuel before it enters the carburetor or injectors.
5. Fuel Lines: Connect the fuel tank, pump, carburetor/injector, and engine.

In petrol engines, the air-fuel mixture is essential for efficient combustion. The system is designed to ensure a smooth flow and correct mixture ratio.

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3.2 Fuel System of Diesel Engines:

The fuel system in diesel engines is more complex than that of petrol engines because of the high-pressure conditions required for fuel injection. It includes:

1. Fuel Tank: Stores diesel fuel and supplies it to the fuel system.
2. Fuel Pump: Draws fuel from the tank and supplies it under high pressure to the injectors.
3. Fuel Filter: Removes dirt and contaminants from the diesel fuel to prevent clogging of the injectors.
4. Fuel Injectors:
   • Diesel engines use high-pressure injectors to inject fuel directly into the combustion chamber at the correct time and under high pressure.
   • This direct injection allows for more efficient combustion due to the high pressure and temperature.
5. Common Rail System (in modern diesel engines): A high-pressure fuel rail connects all injectors to supply fuel at a consistent pressure for more precise control.

In diesel engines, there is no spark plug. The fuel is injected into highly compressed air, and the heat from compression causes spontaneous ignition.

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3.3 Cooling System:

The cooling system in an I.C. engine is crucial for maintaining an optimal operating temperature and preventing overheating. It includes:

1. Water-Cooled Systems (most common in modern engines):

   • Radiator: Cools the coolant, usually a water-antifreeze mixture.
   • Water Pump: Circulates the coolant through the engine block, radiator, and hoses.
   • Thermostat: Controls the flow of coolant to maintain the engine at the correct operating temperature.
   • Coolant: A mixture of water and antifreeze, which absorbs heat from the engine and releases it in the radiator.

2. Air-Cooled Systems (used in smaller engines like motorcycles or some old car engines):

   • The engine itself has fins that radiate heat, and fans blow air over the engine to cool it.

3. Oil-Cooled Systems (used in some heavy-duty engines):

   • Uses oil to cool the engine, absorbing heat and transferring it to an oil cooler, typically placed in the engine compartment.

Cooling is vital to prevent engine damage due to excessive heat buildup.

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3.4 Ignition Systems:

The ignition system in I.C. engines is responsible for igniting the air-fuel mixture in the engine's combustion chamber. There are two main types of ignition systems:

1. Spark Ignition (S.I.) Engines (Petrol engines):

   • Components:
     • Battery: Provides electrical power for the ignition system.
     • Ignition Coil: Converts the low voltage from the battery to a high voltage required for sparking.
     • Distributor: Distributes the high voltage to the correct cylinder at the correct time.
     • Spark Plugs: Spark the air-fuel mixture at the correct moment in the combustion cycle.
   • Working: The ignition coil generates high voltage, which is delivered to the spark plug, creating a spark to ignite the air-fuel mixture.

2. Compression Ignition (C.I.) Engines (Diesel engines):

   • Diesel engines don’t use spark plugs. Instead, the fuel is injected into highly compressed, hot air, causing it to spontaneously ignite due to the high pressure and temperature.

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3.5 Types of Lubricating Systems Used in I.C. Engines:

Lubrication in I.C. engines is essential for reducing friction between moving parts, preventing wear and tear, and maintaining engine efficiency. The common types of lubrication systems include:

1. Splash Lubrication:

   • Used in small engines.
   • The crankshaft dips into the oil reservoir and splashes oil onto engine parts like the bearings.

2. Pressure Lubrication:

   • Involves a pump that circulates oil under pressure to various parts of the engine.
   • Full Pressure Lubrication: Oil is pumped under pressure to all the critical engine parts.
   • Partial Pressure Lubrication: Oil is pumped to high-wear parts (e.g., bearings, cams), and the remaining parts rely on splash lubrication.

3. Dry Sump Lubrication:

   • Used in high-performance engines.
   • The oil is stored in a separate tank, and a pump circulates it to the engine.
   • This system helps in better oil control and is used in racing cars.

4. Wet Sump Lubrication:

   • The oil is stored in the bottom of the engine block.
   • It is commonly used in most conventional engines.

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3.6 Types of Governing of I.C. Engines:

Governing refers to controlling the engine speed or RPM. There are two main types of governing systems:

1. Mechanical Governors:

   • Centrifugal Governor: Uses centrifugal force to control the speed of the engine by adjusting the fuel supply.
   • As the engine speed increases, the governor moves, reducing the fuel supply to bring the engine back to a set speed.

2. Electronic Governors:

   • Uses electronic sensors to monitor the engine speed and adjusts the fuel supply electronically to control the speed.
   • Found in modern engines with electronic fuel injection (EFI) systems.

3. Load Governors:

   • Regulate the engine speed depending on the load applied to the engine.
   • As the load increases, the engine speed tends to drop, and the governor adjusts the fuel supply to compensate.

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3.7 Objective of Supercharging:

Supercharging is the process of forcing more air into the combustion chamber of an engine, thereby increasing its efficiency and power output.

1. Increase Power Output: Supercharging allows more air and fuel to be compressed and ignited, which increases the power output of the engine.

2. Improved Performance at High Altitudes: At high altitudes, the air density decreases, leading to lower engine performance. A supercharger compensates for this by increasing the intake air pressure.

3. Enhanced Efficiency: By compressing the intake air, the engine can burn more fuel efficiently, leading to better fuel combustion.

4. Types of Superchargers:

   • Root Type: Compresses the air using two rotors that mesh together.
   • Centrifugal Type: Uses a centrifugal force generated by a spinning impeller to increase air pressure.
   • Twin-Screw: A combination of the Root and centrifugal types, providing higher efficiency.

Superchargers are commonly used in racing and performance vehicles to increase horsepower and engine performance.

💥💥UNIT 4💥💥

4. Performance of I.C. Engines

Understanding the performance of Internal Combustion (I.C.) engines is vital for evaluating their efficiency, power output, and fuel consumption. Here, we discuss key performance parameters, tests, and methods used to assess I.C. engine performance.

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4.1 Performance Parameters in I.C. Engine:

To assess the performance of I.C. engines, several key parameters are used. Some of the most commonly used performance parameters are:

1. Brake Power (B.P.):

   • It is the power output from the engine's crankshaft, available to do useful work, like driving a vehicle or machinery.
   • Measured at the output shaft using a dynamometer.

2. Indicated Power (I.P.):

   • The power developed inside the engine’s cylinders.
   • It accounts for all the power generated by the combustion of fuel, but before losses due to friction and other external factors.
   • Measured using pressure measurements inside the cylinders.

3. Friction Power (F.P.):

   • The power lost due to friction within the engine, including friction from bearings, pistons, and valves.
   • Measured by subtracting Brake Power from Indicated Power: $$F.P. = I.P. - B.P.$$
     

4. Mechanical Efficiency:

   • The ratio of Brake Power to Indicated Power, indicating how much of the energy produced by combustion is converted to useful power.
   $$\eta_m = \frac{B.P.}{I.P.} \times 100$$
   

5. Thermal Efficiency:

   • The ratio of Brake Power to the thermal energy supplied by fuel.
   • It indicates how effectively the engine converts the chemical energy in fuel to mechanical energy.
   $$\eta_t = \frac{B.P.}{\text{Energy supplied by fuel}} \times 100$$
   

6. Specific Fuel Consumption (S.F.C.):

   • The amount of fuel consumed per unit of power output (usually expressed in kg/kWh or g/kWh).
   • Brake Specific Fuel Consumption (BSFC) measures fuel consumption per unit of brake power.

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4.2 Performance Test:

To assess engine performance, various tests are conducted. The following are some common performance tests:

1. Full Load Test:

   • The engine is operated at full load, and parameters like Brake Power, fuel consumption, and exhaust temperature are measured to evaluate efficiency.

2. Part Load Test:

   • The engine is tested at different loads (less than full load) to determine how it performs under varying conditions.

3. Speed Test:

   • The engine’s power output and efficiency are tested at different RPM (speed) settings.

4. Exhaust Emission Test:

   • Used to measure harmful emissions like CO, NOx, and particulate matter in the exhaust gases. This test helps assess the environmental performance of the engine.

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4.3 Morse Test:

The Morse Test is used to determine the Indicated Power (I.P.) of an engine, especially multi-cylinder engines, by measuring the power developed in each cylinder.

Process:

• Step 1: The engine is first run at a steady speed, and brake power is measured.
• Step 2: One or more cylinders are disabled (cut-off) by blocking their intake and exhaust valves. This isolates the cylinder(s) from the power-producing process.
• Step 3: After cutting off each cylinder, the brake power is measured again.
• Step 4: The difference in brake power is used to calculate the indicated power of the disabled cylinder.

Formula:

The indicated power can be found using:

$$I.P. = B.P. + F.P.$$

The Morse Test allows for a comparison of the performance of individual cylinders in multi-cylinder engines, helping identify misfiring or underperforming cylinders.

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4.4 Heat Balance Sheet:

The Heat Balance Sheet helps evaluate how efficiently the engine converts fuel energy into useful work and the losses that occur during the operation.

The heat balance equation for an I.C. engine is as follows:

$$\text{Heat supplied by fuel} = \text{Heat used for work} + \text{Heat lost to exhaust} + \text{Heat lost to cooling system} + \text{Heat lost to friction} + \text{Heat lost to radiation}$$

The Heat Balance Sheet typically includes the following components:

• Heat Supplied: The energy input from the fuel (calculated by multiplying the fuel consumption rate by the calorific value of the fuel).
• Useful Work Output: The brake power (B.P.) produced by the engine.
• Exhaust Losses: Heat energy carried away by exhaust gases.
• Cooling Losses: Heat dissipated through the engine’s cooling system.
• Friction Losses: Heat lost due to friction within engine parts (engine components like bearings, pistons, etc.).
• Radiation Losses: Heat lost through radiation from the engine body.

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4.5 Methods of Determination of B.P., I.P., and F.P.:

1. Brake Power (B.P.):

   • Measured directly by a dynamometer connected to the engine's output shaft.
   • The dynamometer measures the torque and speed of the engine, and the brake power is calculated using the formula: $$B.P. = \frac{2\pi N T}{60}$$ where:
     • $N$ = Speed of the engine (in RPM)
     • $T$ = Torque (in Nm)

2. Indicated Power (I.P.):

   • Indicated Power is determined using a pressure-measuring device (like a pressure gauge) to measure the pressure inside the cylinders.
   • The I.P. is calculated from the pressure-volume diagram (P-V diagram) obtained from the indicator card, using the formula: $$I.P. = \frac{P \times V \times N}{2}$$ where:
     • $P$ = Pressure inside the cylinder
     • $V$ = Volume of the cylinder
     • $N$ = Number of power strokes per minute

3. Friction Power (F.P.):

   • F.P. is determined by subtracting the brake power from the indicated power: $$F.P. = I.P. - B.P.$$
     

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4.6 Simple Numerical Problems on Performance of I.C. Engines:

Let's go through a simple example:

Problem: An engine consumes 0.8 kg of fuel per hour. The calorific value of the fuel is 42,000 kJ/kg. The brake power of the engine is measured as 25 kW. Calculate the brake thermal efficiency of the engine.

Solution:

1. Heat Supplied by Fuel:

   $$\text{Heat Supplied} = \text{Fuel Consumption} \times \text{Calorific Value}$$
   $$= 0.8 \, \text{kg/hr} \times 42,000 \, \text{kJ/kg} = 33,600 \, \text{kJ/hr}$$
   

2. Brake Thermal Efficiency (BTE):

   $$\text{BTE} = \frac{\text{Brake Power} \times 3600}{\text{Heat Supplied by Fuel}}$$ $$=\frac{25\text{kW}\times 3600}{33,600\text{kJ/hr}}=0.25=25\mathrm{\%}$$

Thus, the brake thermal efficiency of the engine is 25%.

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These are some of the basic methods and calculations used to determine the performance of I.C. engines.

💥💥UNIT 5💥💥

5. Air Compressors

Air compressors are devices that increase the pressure of air by reducing its volume. Compressed air is widely used in various industries for powering equipment, tools, and in many other applications.

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5.1 Functions of Air Compressors:

The primary function of an air compressor is to take in atmospheric air, compress it to a higher pressure, and store it in a tank for use when needed. Key functions include:

• Compression: Air is drawn into the compressor, compressed, and stored under pressure.
• Power Supply: Compressed air is used to power pneumatic tools, machinery, and instruments.
• Storage: Compressed air is stored in tanks for later use, providing a steady supply of air on demand.
• Cooling and Lubrication: Some compressors provide cooling or lubrication to extend the life of the machinery.

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5.2 Uses of Compressed Air:

Compressed air is used in a variety of applications across different industries. Some common uses include:

• Powering Pneumatic Tools: For example, drills, wrenches, and sanders.
• Cleaning: Compressed air is used for cleaning machinery, equipment, and components.
• HVAC Systems: In systems for controlling temperature and humidity.
• Automated Manufacturing: To control actuators and robots.
• Medical Applications: To power respiratory devices and other medical equipment.
• Transportation: Used in braking systems for trucks, buses, and trains.

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5.3 Types of Air Compressors:

Air compressors are classified into various types based on their design, working principle, and application. The main types are:

1. Positive Displacement Compressors:

   • These compressors work by trapping a certain volume of air and then reducing its volume to increase pressure.
   • Example: Reciprocating compressors, rotary screw compressors.

2. Dynamic Compressors:

   • These compressors rely on the movement of air at high speed to increase pressure.
   • Example: Centrifugal compressors, axial compressors.

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5.4 Single Stage Reciprocating Air Compressor - Construction and Working:

A single-stage reciprocating air compressor works on the principle of converting mechanical energy into air pressure through a piston mechanism.

Construction:

• Cylinder: Houses the piston which moves back and forth.
• Piston: Moves within the cylinder to compress the air.
• Crankshaft: Converts rotary motion into the reciprocating motion of the piston.
• Inlet and Outlet Valves: Control the entry and exit of air in the cylinder.
• Flywheel: Helps maintain smooth motion by storing rotational energy.
• Air Filter: Filters the air before it enters the compressor.

Working:

1. Suction Stroke: During the piston’s downward movement, air enters the cylinder through the inlet valve.
2. Compression Stroke: The piston moves upwards, compressing the air. The inlet valve closes and the compressed air is forced out through the outlet valve.
3. Exhaust: The compressed air is discharged into a storage tank or pipeline.

P-V (Pressure-Volume) Diagram:

A P-V diagram for a single-stage compressor typically shows the compression process as a curve, with pressure increasing as the piston compresses the air.

• The horizontal axis represents the volume of air, and the vertical axis represents the pressure.
• During the intake stroke, the pressure remains constant (at atmospheric pressure).
• As the piston compresses the air, the pressure increases along the curve. Once the compression is completed, the air is discharged.

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5.5 Multi-Stage Compressors – Advantages Over Single-Stage Compressors:

Multi-stage compressors have more than one compression stage. The air is compressed in several stages, with cooling between each stage, before being discharged.

Advantages over single-stage compressors:

1. Higher Efficiency: Multi-stage compressors are more efficient, as the air is cooled between each stage, which reduces the overall work required to compress the air.
2. Lower Temperature: Cooling between stages prevents excessive heat buildup, which can damage components.
3. Higher Pressure Capability: Multi-stage compressors can achieve much higher pressures than single-stage compressors.
4. Energy Saving: Due to better thermodynamic efficiency, multi-stage compressors consume less energy for the same output.

In multi-stage compressors, intercoolers are used between stages to cool the compressed air and prevent overheating.

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5.6 Rotary Compressors:

Rotary compressors use a rotary mechanism to compress air. They are often used in applications requiring continuous operation with steady airflow.

5.6.1 Centrifugal Compressor:

A centrifugal compressor works by converting the kinetic energy of air into pressure. It is a type of dynamic compressor where air is accelerated by a rotating impeller.

Working:

1. Air enters through an inlet and is accelerated by the rotating impeller.
2. The high-speed air is then directed into a diffuser, where its velocity decreases, and the kinetic energy is converted into pressure.
3. The compressed air exits through the discharge port.

Applications:

• Large industrial processes.
• HVAC systems.
• Gas turbines.

Advantages:

• Compact design.
• Continuous airflow with minimal pulsations.
• Suitable for large volumes of air.

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5.6.2 Axial Flow Compressor:

An axial flow compressor compresses air by passing it through a series of rotating and stationary blades (stators and rotors). It is widely used in aircraft engines.

Working:

1. Air flows through the compressor axially (in a straight line).
2. The rotors accelerate the air, and the stators slow it down, causing the air to compress as it moves through multiple stages.

Applications:

• Jet engines.
• Large-scale industrial processes.

Advantages:

• High flow rates and efficiencies.
• Suitable for high-speed applications like aviation.

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5.6.3 Vane Type Compressor:

A vane-type compressor uses a rotor with several sliding vanes to compress air. The vanes are mounted in slots on the rotor, which rotates inside a chamber.

Working:

1. The rotor with vanes rotates inside the casing, creating expanding and contracting chambers as the rotor turns.
2. As the air enters the chamber, it is trapped between the vanes and compressed as the volume of the chamber decreases.

Applications:

• Small to medium-scale industrial applications.
• Automotive and HVAC systems.

Advantages:

• Simple construction.
• Quiet operation.
• Suitable for moderate pressure applications.

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Summary of Key Types of Compressors:

Compressor Type	Description	Applications	Advantages
Single-Stage Reciprocating	Piston compresses air in one stroke.	Small scale, intermittent use	Simplicity, lower initial cost
Multi-Stage Reciprocating	Air is compressed in multiple stages with cooling in between.	Heavy-duty, high-pressure applications	Higher efficiency, better cooling
Centrifugal Compressor	Uses rotating impellers to accelerate and compress air.	Large-scale industrial, turbines	Continuous operation, high flow
Axial Flow Compressor	Air flows in an axial direction through stages of rotating and stationary blades.	Aircraft engines, high-speed applications	High efficiency at high speeds
Vane Type Compressor	Air is compressed between rotating vanes and chamber walls.	Automotive, HVAC, small industries	Simple, quiet operation

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These are the essential details regarding air compressors, their types, and applications.