INTERNAL COMBUSTION ENGINE
Classifications of Internal Combustion Engine:
a) Basic Design
b) Types of ignitions
c) Engine Working Cycle
d) Number of cylinders
1. Single cylinder engine – This type of engine consists of only one
cylinder. Generally, it is used on light vehicles such as scooters and
motorcycles. A single cylinder engine lacks mechanical balance
since there is only one piston and one connecting rod, which
reciprocate without any functioning components to offset their
weight. However, the counterweight linked to the crankshaft and a
flywheel with enough weight to create a relatively steady movement
help to balance the engine to some extent.
2. Multi-cylinder engine – This type of engine consists of two, three,
four, or eight cylinders. Specifically:
2.1. Two-cylinder engine - This type of engine consists
of two cylinders. Typically, it is used on tractors, German
automobile, and DAF of Holland car. It can be arranged in in
line vertical, V, and opposed type.
2.2. Three-cylinder engine - This type of engine consists
of three cylinders. It is used on a front-drive car, in which the
differential
is
located
between
the
engine
and
the
transmission. It uses two strokes, and the cylinders are
arranged in line.
2.3. Four-cylinder engine - This type of engine consists
of four cylinders. Mostly, it is used on ordinary cars. It can be
arranged in line vertical, V, and opposed type.
2.4. Six- and eight-cylinder engine - These types of
engine consist of six and eight cylinders, respectively. It can
be arranged in line, V, and opposed type. In most cases, in
line 6-cylinder engines and V-8 engines are used.
2.5. Twelve- and sixteen-cylinder engine - These types
of engine consist of twelve and sixteen cylinders, respectively.
Primarily, it is used in cars, buses, and trucks. It can be
arranged in v-type or pancake type with two rows of cylinders,
W-type with three rows of cylinders, and X-type with four rows
of cylinders.
e) Governing cycles of SI and CI engines:
1. Otto cycle is used for conventional SI engine. In this type of engine,
the heat is taken in at one constant volume of the cylinder and rejected
at another constant volume. The volume of the fuel is constant during
combustion. Otto cycle is used in petrol engines.
2. Atkinson cycle is used for complete expansion SI Engine. During
this cycle, work is done on the gas by the piston between isentropic
compression. Work is done by the gas on the piston between isentropic
expansion. The difference between the work done by the gas and the
work done on the gas is the net work produced by the cycle and it
corresponds to the area enclosed by the cycle curve. The work produced
by the cycle times the rate of the cycle (cycles per second) is equal to
the power produced by the Atkinson engine.
3. Miller cycle is used for early or late inlet valve closing type SI engine.
It is very similar to an Otto-cycle engine. The Miller cycle uses pistons,
valves, a spark plug, etc., just like an Otto-cycle engine does. However,
it depends on a supercharger and leaves the intake valve open during
part of the compression stroke, so that the engine is compressing
against the pressure of the supercharger rather than the pressure of the
cylinder walls.
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4. Diesel cycle is used for the ideal Diesel engine. In this type of engine,
the heat is taken in under constant pressure and rejected under constant
volume. Fuel burns at a constant pressure during combustion. This cycle
is used by diesel engines.
5. Dual cycle is used for the actual Diesel engine. In this type of engine,
some of the heat is extracted at constant volume, while the remainder is
extracted at constant pressure. At a constant volume, heat is rejected.
I. Diesel Engine
I.
Labelled Diagram
II.
Brief Description of Main Parts
The main parts of a diesel engine are:
1. Injector. It is utilized to inject fuel into the cylinder while the air
is being compressed.
2. Inlet valve. During the suction stroke, the air inside the cylinder
is drawn through the inlet valve.
3. Exhaust Valve. Through the exhaust valve, the entire burnt or
exhaust from the cylinder is released.
4. Combustion chamber. The combustion of fuel occurs in this
chamber.
5. Piston. It is the CI engine's reciprocating component that
causes the cylinder to turn back and forth. Its primary job is to
use the connecting rod to transfer the thrust force produced
during the power stroke to the crankshaft.
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6. Connecting rod. Connects piston to the crankshaft.
7. Crankshaft. It is utilized to change the piston's reciprocating
motion into rotary motion.
III. Working Principle
The working principle of a diesel engine is somewhat similar to
gasoline engine. It also has 4 strokes namely intake, compression,
power, and exhaust strokes.
In suction stroke, the piston moves from TDC to BDC during
this stroke, and air is suctioned through the inlet valve.
In a compression stroke, the air that was sucked into the cylinder
during the suction stroke is compressed during this stroke. The
temperature of the air rises as it is compressed and reaches the point
where the combustion of the diesel fuel occurs.
In a power stroke, the injector delivers the gasoline to the cylinder
just as the compression stroke is about to stop. The air is heated,
which causes the fuel to start burning and to ignite. Hot exhaust
gasses created during fuel combustion exert a strong downward
thrust on the piston, which causes it to move. The connecting rod
assists the piston in turning the crankshaft. Power is produced with
this stroke, hence the name "power stroke."
In exhaust stroke, the burnt gasses are forced through the
exhaust valve during this upward movement of the piston (from BDC
to TDC).
Following the exhaust stroke, each stroke is repeated once again.
In a two-stroke engine, each crankshaft rotation results in one power
stroke. In contrast, a four-stroke engine produces one power stroke
for every two crankshaft rotations.
Below is a description of the valve's position and the various
operations carried out during a compression-ignition engine's fourstroke cycle.
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II. Petrol Engine
I.
Labelled Diagram
II. Brief Description of Main Parts
1. Spark Plug – it is an important component of the ignition system
and is the one that must operate under the most severe
conditions. It ignites the fuel to be burned and makes power to
start the cycle of the engine or the piston to move.
2. Camshaft - which opens and closes the valves, and it is driven
from the crankshaft by a chain drive or gears.
3. Carburetor - a device for supplying a spark-ignition engine that
regulates the air-fuel ratio and also to mixes the fuels. It also
controls the engine speed.
4. Inlet Valve – serves as the entrance of air flow and fuel mixture
into the combustion chamber prior to compression and ignition.
5. Exhaust Valve – serves as an expulsion of exhaust gases from
the combustion process after ignition has occurred.
6. Combustion Chamber – it is a closed space inside an engine in
which air and fuel mixed and is burned.
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7. Piston - a sliding piece moved inside the cylinder by power
produced inside the combustion chamber.
8. Connecting rod – a rod that connects piston to the crankshaft.
9. Crank/crankshaft – it helps to utilized to change the piston’s
reciprocating motion into rotary motion.
III. Working Principle
The working principle of a spark-ignition (SI) engine is similar
to that of a compression ignition (CI) engine, with only minor
differences. The ignition process occurs in a diesel or CI engine
due to high compression of the air-fuel mixture, whereas ignition
occurs in a petrol engine due to a spark.
The Otto cycle governs the operation of a gasoline engine. A
gasoline engine works as follows:
1) Suction or Intake Stroke
The piston moves downward during the intake stroke. As it
descends, a vacuum is created inside the combustion chamber,
and the air-fuel mixture begins to enter from the outside. The
suction valve opens during this stroke, while the exhaust valve
remains closed.
2) Compression Stroke
When the suction process of the air-fuel mixture is complete,
the piston travels upwards for the air-fuel mixture compression.
As the piston rises, the mixture is pressed into the combustion
chamber. The intake and exhaust valves are closed during this
stroke. The temperature and pressure of the air-fuel mixture rise
dramatically as a result of the compression process. A spark plug
fires a spark and ignites the air-fuel mixture at the end of the
compression process.
The combustion process of the air-fuel mixture occurs inside
the combustion chamber due to the provided spark. Because of
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this combustion, the piston moves higher, increasing the
temperature and pressure of the mixture. Heat is generated
during this process.
3) Expansion Stroke
The power stroke is another name for the expansion stroke.
The heat generated in the previous stroke (compression process)
forces the piston downward (TDC to BCD) and turns the
crankshaft at this stage. The air-fuel mixture expands inside the
chamber as the piston descends, lowering the mixture’s pressure.
4) Stroke / Exhaust
The piston moves upward during this stroke, opening the
exhaust valve and releasing the waste gases from the combustion
chamber. After finishing the exhaust stroke, the piston moves
back down, and the process is repeated four times.
III. Comparison between the Diesel and Petrol Engine
Diesel and gasoline engines are the two most popular types of
engines. The majority of automobiles use either gasoline or diesel
engines. The basic difference between petrol and diesel engines is that
the former uses the Otto cycle while the latter uses the Diesel cycle. This
is the main distinction between the two types of engines. The design,
categories, and applications of these engines can be blamed for other
variations.
Petrol Engine
Natural combustion engines with spark ignition are petrol engines. Gas,
an unstable fuel, is used to power them. In these engines, the fuel and air
are normally mixed after compression. It also goes by the name of a gasoline
engine. Prior to compression, air and fuel are combined in petrol engines,
and an electric spark is then utilized to ignite the mixture. The lowest
temperature at which a fuel or combustible substance ignites when heated
is known as the ignition temperature. The Otto cycle illustrates how chemical
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energy in gasoline engines is transformed into thermal energy, which is
ultimately translated into motion.
Working of a Petrol Engine:
Step 1. Fuel (petrol) and air are added to the cylinder and mixed.
Step 2. The mixture of petrol and air is compressed by the use of a
crankshaft.
Step 3. Now spark is used in the mixture and the mixture forces the
piston down.
Step 4. Gases go out from the exhaust valve.
Gasoline Engine
An internal combustion engine known as a compression ignition engine
is a diesel engine. Due to adiabatic compression, the air in the cylinder is
heated to a high temperature, which causes the air to ignite the fuel when it
is pumped into a combustion furnace. These engines constrict the air. Diesel
fuel spontaneously ignites as it is pumped into the combustion chamber. The
diesel cycle, which consists of two isentropic cycles, a constant volume
process, and a constant pressure process, is used by these engines.
Working of a Petrol Engine:
Step 1. Induction Stroke – The piston of the engine goes down and air
comes into the cylinder.
Step 2. Compression Stroke – The piston goes up and compresses the
air. Now the air is getting hot.
Step 3. Power Stroke – Now, fuel or diesel is added to the cylinder.
Step 4. Exhaust Stroke – Fuel or diesel starts burning due to ignition
temperature provided by hot air. Smoke goes out from the valve.
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A. Problem Solving
1. The following observations are recorded during a test on a four-stroke petrol
engine:
•
Speed of the engine = 2500 rpm
•
F.C = 3000 of fuel in 12sec
•
B.P = 20KW
•
Air intake orifice diameter = 35 mm
•
Pressure across the orifice = 140mm of water
•
Coefficient of discharge of orifice = 0.6
•
Piston diameter = 150mm
•
Stroke length = 100 mm
•
Density of the fuel = 0.85gm/cc
•
Compression ratio (r) =6 .5
•
CV of fuel = 42000KJ/Kg,
•
Barometric pressure = 760mm of Hg
•
Room temperature = 24 ℃
Find:
a)
Volumetric efficiency on the air basis alone.
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b)
Air-fuel ratio.
c)
The brake mean effective pressure.
d)
The relative efficiency on the brake thermal efficiency.
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B. Conclusion:
Internal combustion engines have significantly seen numerous applications in
the field of engineering. They can be categorized according to their design, type of
ignition, type of fuel used, working principle, number of cylinders, operating cycle, and
many more. Each type of engines has some advantages over the other. Internal
combustion engines are composed of numerous parts that need to be maintained and
replace if worn out. It is crucial to remember that combustion duration, rate of pressure
rise, and pollutant accumulation are all significantly influenced by the characteristics
of gasoline in combination with combustion chamber geometry. In certain
circumstances, the mixture at the end gas may autoignite before the flame reaches
that area of the cylinder, causing knock that results in pressure oscillations with a high
frequency and intensity. It is recommended to determine the conditions of application
in the selection of appropriate engine. It is suggested that the design and development
of engine work on maximizing its work or power input, minimizing its energy
consumption, and reducing pollutants that may get in the process of converting
chemical energy into work.
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C. References:
o https://www.britannica.com/technology/gasoline-engine
o Compression Ignition Engine - Definition, Main Components, Working with
Application - Mechanical Booster
o https://www.theengineerspost.com/types-of-engines/#:~:text=5.,Classification%20by%20Number%20and%20Arrangement%20of%20Cylinde
rs,engine%20is%20used%20in%20tractors.
o https://www.mechanicalguruji.com/2020/10/classification-IC-Engine.html
o https://web.iitd.ac.in/~ravimr/courses/mel345/classification.pdf
o http://ecoursesonline.iasri.res.in/mod/page/view.php?id=100936
o https://www.thermal-engineering.org/what-is-atkinson-cycle-atkinson-enginedefinition/
o https://auto.howstuffworks.com/question132.htm
o https://www.linquip.com/blog/diesel-engine-vs-petrol-engine/
o https://byjus.com/chemistry/difference-between-diesel-and-petrolengine/#:~:text=The%20primary%20difference%20between%20Petrol,type%
20of%20fuel%20they%20use.
o https://www.vedantu.com/chemistry/difference-between-petrol-and-dieselengine
o https://diferr.com/difference-between-petrol-and-diesel-engine/
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