P2: - Task 1 (Out of Class work) A: Internal combustion engines can be classified based on various criteria. Here's a
breakdown according to the items you've listed:
1. Type of Ignition:
• Spark Ignition (SI) Engines: Ignition is initiated by a spark plug.
• Compression Ignition (CI) Engines: Ignition occurs due to the heat generated
by compressing the air-fuel mixture.
2. Fuel Type:
• Gasoline Engines: Use gasoline or petrol as fuel.
• Diesel Engines: Utilize diesel as fuel.
3. Working Cycle:
• Two-stroke Engines: Complete the power cycle in two strokes of the piston
(intake/compression and power/exhaust).
• Four-stroke Engines: Complete the power cycle in four strokes of the piston
(intake, compression, power, exhaust).
4. Number of Strokes:
• Two-Stroke Engines: Complete a power cycle in two strokes.
• Four-Stroke Engines: Complete a power cycle in four strokes.
5. Type of Cooling System:
• Air-Cooled Engines: Use airflow directed over the engine fins to dissipate heat.
• Liquid-Cooled Engines: Utilize a liquid coolant circulated through the engine
block and radiator to dissipate heat.
6. Cylinder Charging Methods:
• Naturally Aspirated Engines: Rely on atmospheric pressure for air intake.
• Supercharged Engines: Use a mechanical compressor to force more air into the
combustion chamber.
• Turbocharged Engines: Utilize a turbocharger driven by exhaust gases to
increase air intake into the combustion chamber.
Each of these classifications describes different characteristics of internal
combustion engines, and many engines can fall into multiple categories based on
these criteria.
P2: - Task 1 (Out of Class work) B: Sure, here are the definitions for the terms you've mentioned in relation to internal
combustion engines:
1. Cylinder:
• In an engine, a cylinder is a hollow tube within which a piston moves. It forms
the primary space where combustion occurs. The cylinder houses the piston and
is sealed at one end by the cylinder head and at the other by the cylinder block.
2. Stroke:
• In an engine, stroke refers to the movement of the piston from one end of the
cylinder to the other. There are typically two types of strokes in an engine:
• Intake Stroke: The piston moves downward, drawing in the air-fuel
mixture (or air in the case of a diesel engine).
• Power/Exhaust Stroke: The piston moves upward, compressing the airfuel mixture (compression stroke), igniting it (power stroke), and then
expelling the exhaust gases (exhaust stroke).
3. Compression Ratio:
• The compression ratio of an engine is the ratio of the total volume of the cylinder
when the piston is at the bottom of its stroke (bottom dead center) to the volume
when the piston is at the top of its stroke (top dead center). It indicates the degree
of compression applied to the air-fuel mixture before ignition and affects engine
efficiency and performance.
4. Clearance Volumes:
• Clearance volumes refer to the spaces within the engine cylinder that exist when
the piston is at the top dead center and bottom dead center positions. These
volumes include the combustion chamber volume (when the piston is at top dead
center) and any additional spaces, such as the volume between the piston crown
and the cylinder head or valves, representing the minimum volume when the
piston is at bottom dead center.
5. Top and Bottom Dead Centers:
• Top Dead Center (TDC): This refers to the position of the piston at the extreme
top of the cylinder. It's when the piston is at its highest point in the cylinder
during its stroke.
• Bottom Dead Center (BDC): This refers to the position of the piston at the
extreme bottom of the cylinder. It's when the piston is at its lowest point in the
cylinder during its stroke.
P3: - Task 1 C: - Explain thermodynamic processes that represents the actual cycle
of the two types of internal combustion engines. (Petrol engine, Diesel engine)
Show the two cycle’s P-V diagrams.
The two primary thermodynamic processes that represent the actual cycles in
internal combustion engines, specifically petrol (spark ignition) and diesel
(compression ignition) engines, are the Otto cycle and the Diesel cycle, respectively.
P-V Diagram Otto Cycle (Petrol Engine)
1. (Otto Cycle (Petrol Engine):
•
The Otto cycle represents the ideal cycle for spark-ignition petrol engines. It consists of four
processes: two isentropic (adiabatic and reversible) processes and two constant-volume
processes.
•
Process 1-2 (Isentropic Compression): The air-fuel mixture is compressed adiabatically and
reversibly from point 1 (bottom dead center) to point 2 (top dead center).
•
Process 2-3 (Isobaric Heat Addition): The compressed mixture undergoes constant-volume
combustion at constant pressure, increasing the temperature and pressure in the cylinder from
point 2 to point 3.
•
Process 3-4 (Isentropic Expansion): The burnt gases expand adiabatically and reversibly,
pushing the piston down from point 3 to point 4.
•
Process 4-1 (Isochoric Heat Rejection): The exhaust gases are expelled at constant volume,
reducing the temperature and pressure in the cylinder from point 4 to point 1.
Diesel cycle PV diagram
2. Diesel Cycle (Diesel Engine):
•
The Diesel cycle represents the ideal cycle for compression-ignition diesel engines. It consists
of four processes: two isentropic processes and two constant-pressure processes.
•
Process 1-2 (Isentropic Compression): Air is adiabatically and reversibly compressed from
point 1 (bottom dead center) to point 2 (top dead center) without fuel injection.
•
Process 2-3 (Isobaric Heat Addition): Fuel is injected into the highly compressed air at
constant pressure, resulting in combustion and an increase in pressure and temperature from
point 2 to point 3.
•
Process 3-4 (Isentropic Expansion): The hot gases expand adiabatically and reversibly,
driving the piston from point 3 to point 4.
•
Process 4-1 (Isochoric Heat Rejection): The exhaust gases are expelled at constant volume,
reducing the temperature and pressure in the cylinder from point 4 to point 1.
These PV (Pressure-Volume) diagrams illustrate the thermodynamic processes within the
engine during a complete cycle. The x-axis represents volume, and the y-axis represents
pressure. The different processes are shown as lines or curves on the diagram, indicating the
changes in pressure and volume throughout the cycle.
P4: - Task 1 D: - Discuss the difference between ideal and real thermal cycles for
1-Petrol internal combustion engine (sketch on P-V diagram)
2-Diesel in internal combustion engine (sketch on P-V diagram)
1. Petrol Engine:
Ideal Otto Cycle:
•
1-2: Isentropic compression (adiabatic)
•
2-3: Constant-volume heat addition (isochoric)
•
3-4: Isentropic expansion (adiabatic)
•
4-1: Constant-volume heat rejection (isochoric)
Real Otto Cycle:
•
1-2': Non-isentropic compression (due to friction)
•
2'-3': Constant-volume heat addition with heat losses to walls
•
3'-4': Non-isentropic expansion (due to friction and incomplete combustion)
•
4'-1': Constant-volume heat rejection with residual gas remaining in the cylinder
P-V Diagram:
Key Differences:
•
Compression and Expansion: Real cycle has lower pressure and temperature due to friction.
•
Combustion: Real cycle shows a gradual increase in temperature, not a sudden jump, due to
incomplete combustion.
•
Exhaust: Real cycle does not reach the initial pressure due to residual gas.
2. Diesel Engine:
Ideal Diesel Cycle:
• 1-2: Isentropic compression (adiabatic)
•
2-3: Constant-pressure heat addition (isobaric)
•
3-4: Isentropic expansion (adiabatic)
•
4-1: Constant-volume heat rejection (isochoric)
Real Diesel Cycle:
• 1-2': Non-isentropic compression (due to friction)
•
2'-3': Constant-pressure heat addition with heat losses to walls, not perfectly constant due to
fuel injection time
•
3'-4': Non-isentropic expansion (due to friction and incomplete combustion)
•
4'-1': Constant-volume heat rejection with residual gas remaining in the cylinder
P-V Diagram:
Key Differences:
• Compression and Expansion: Similar to the Otto cycle, the real cycle has lower pressure and
temperature due to friction.
•
Heat Addition: Real cycle shows a less steep line in the heat addition process, not perfectly
horizontal due to fuel injection time.
•
Combustion and Expansion: Similar to the Otto cycle, the real cycle shows a gradual rise in
temperature and non-isentropic expansion due to incomplete combustion and friction.
P5: - Task 1 E: - Compare between spark and compression ignition engine
according to the following parameters: (Type of fuel, Ignition methods, The related
air standard cycle, Compression ratio, Thermal efficiency)
Comparison of Spark Ignition (SI) and Compression Ignition (CI) Engines:
Parameter
Spark Ignition (SI) Engine
Compression Ignition (CI)
Engine
Fuel
Gasoline (petrol)
Diesel
Ignition Method
Spark plug
Compression-induced ignition
Air Standard
Cycle
Otto Cycle
Diesel Cycle
Compression
Ratio
Lower (typically 8 - 10:1)
Higher (typically 15 - 25:1)
Thermal
Efficiency
Lower (typically 25% - 30%)
Higher (typically 30% - 35%)
Additional Differences:
•
Power Output: SI engines typically have higher power output per unit of displacement due to
higher RPMs.
•
Torque Output: CI engines have higher torque output per unit of displacement due to the higher
compression ratio and fuel characteristics.
•
Emissions: SI engines tend to emit more NOx due to higher combustion temperatures, while CI
engines emit more particulate matter (soot) due to incomplete combustion.
•
Applications: SI engines are commonly used in cars and light trucks, while CI engines are
commonly used in heavy-duty vehicles like trucks and buses.
Reasons for Differences:
•
Fuel: Gasoline is more volatile and easier to ignite, requiring a spark plug. Diesel is less volatile
and self-ignites under high pressure and temperature.
•
Ignition: Spark plugs require a complex electrical system, while CI engines rely on the engine's
mechanical design.
•
Compression Ratio: Higher compression ratios increase thermal efficiency but also increase the
risk of knocking in SI engines. CI engines can handle higher compression ratios due to their fuel
properties.
•
Combustion: SI engines have a more rapid combustion process due to the spark plug, leading to
higher power output. CI engines have a slower, more controlled combustion process, leading to
higher torque output and lower emissions.
Task 3 (In Lab Task)
Five Parts of Internal Combustion Engine with Functions and Simple
Sketches:
Part Name
Function
A cylindrical chamber
Cylinder
where the combustion
process takes place. The
piston moves up and
down inside the
cylinder, creating the
four strokes of the
engine cycle.
Piston
A reciprocating
component that moves
up and down inside the
cylinder, transferring the
force of expanding gases
created during
combustion into
mechanical energy.
Crankshaft
A rotating shaft
connected to the piston
by a connecting rod. The
piston's up-and-down
motion is converted into
rotary motion by the
crankshaft, which drives
the wheels or other
machinery.
Simple Sketch
Connecting
Rod
A rod that connects the
piston to the crankshaft.
It transmits the force of
the piston's up-anddown motion to the
crankshaft, causing it to
rotate.
Combustion The part of the cylinder
head where the fuel and
Chamber
air mixture are
compressed and ignited.
It is designed to promote
efficient combustion and
minimize heat loss.