4 stroke petrol engine

It contains Working, Construction of 4 stroke petrol engine with PV Diagram and Advantages & Disadvantages.Very useful & all info compiled at same place.

1. THERMODYNAMICS LAB REPORT
4 STROKE PETROL ENGINE

Submitted to:
Dr. M.M. Bhutta
Submitted by:
Haris Riaz
2020-ME-61

2.  INTRODUCTION:
 Engine:
An engine is motor which converts chemical energy into
mechanical energy.
 Fuel/petrol engine:
A petrol engine is an internal combustion engine with spark-
ignition, designed to run on petrol (gasoline) and similar
volatile fuels.
 Four Stroke Engine:
A four-stroke engine (also known as four-cycle) is an internal
combustion engine in which the piston completes four
separate strokes which comprise a single thermodynamic
cycle. A stroke refers to the full travel of the piston along the
cylinder, in either direction.
 FOUR STROKE PETROL ENGINE:
 Four stroke cycle engine completes four stroke of the piston or two
revolution of the crank shaft.
 It has two types of valves. These are:
 Inlet valve
 Exhaust valve
 Four stroke petrol engine working at the four types of stroke:
 Intake (Suction stroke)
 Compression stroke
 Power stroke or expansion stroke
 Exhaust stroke

3.  OTTO CYCLE:
In 1862, a German Engineer Nikolaus Augustus Otto began experimenting with
different kinds of engines. His first experiment was conducted on a 4-stroke
engine. 10 years later, he introduced to the world the Otto engine. The 4-stroke
engine consists of a 4- stroke cycle better known as the Otto cycle.
 CONSTRUCTION:
 Various Parts:
 Inlet valve
 Exhaust valve
 Piston
 Piston ring
 Cylinder
 Connecting rod
 Crank shaft
 Crank pin
 Spark plug
 Crank Case
 Inlet Valve:
Its function is to intake the fresh air-fuel mixture
into the cylinder.
 Exhaust Valve:
Its function is to exhaust is the
burnt gases by the force of piston.
Figure 1:Intake & Exhaust
Valve

4.  Piston:
A piston is a moving disk enclosed in a
cylinder which is made gas-tight by piston rings.
Pistons work by transferring the force output of an
expanding gas in the cylinder to a crankshaft, which
provides rotational momentum to a flywheel.
 Piston Ring:
A piston ring is a metallic split ring that is
attached to the outer diameter of a piston in
an internal combustion engine or steam engine.
The main functions of piston rings in engines are:
1. Sealing the combustion chamber so that there is
minimal loss of gases to the crank case.
2. Improving heat transfer from the piston to the cylinder wall.
3. Maintaining the proper quantity of the oil between the piston and the
cylinder wall
4. Regulating engine oil consumption by scraping oil from the cylinder walls
back to the sump.
 Connecting Rod:
A connecting rod, also
called a con rod, is the part of
a piston engine
which connects the piston to the crankshaft. Together with the crank,
Figure 2: Piston
Figure 4: Connecting
Rod
Figure 3: Piston Ring

5. the connecting rod converts the reciprocating motion of the piston into
the rotation of the crankshaft.
 Crank Shaft:
A crankshaft is a shaft driven
by a crank mechanism, consisting of a series of
cranks and crankpins to which the connecting
rods of an engine are attached. It is a mechanical
part able to perform a conversion between
reciprocating motion and rotational motion.
 Crank Pin:
A crankpin is the part of the crank
of a crankshaft to which the connecting rod is
attached. Crankpins transfer up-and-down motion
between the crankshaft and connecting rod. The big end of the
connecting rod is connected to the crankpin of the crankshaft by way of
a bearing.
 Crank Case:
A crankcase is the housing for the
crankshaft in a reciprocating internal combustion engine.
In most modern engines, the crankcase is integrated into
the engine block.
 Spark Plug:
Figure 5: Crankshaft
Figure 6:Crankpin
Figure 7:Crankcase

6. A spark plug is a device for
delivering electric current from an ignition system to
the combustion chamber of a spark-ignition engine to
ignite the compressed fuel/air mixture by an electric
spark, while containing combustion pressure within
the engine.

 4 STROKE (OTTO) CYCLE
PROCESS:
Each movement of the cylinder up or down the cylinder is
one stroke of the four stroke combustion cycle or Otto cycle.
The four stroke cycle consists of:
 Intake stroke
 Compression stroke
 Ignition/power stroke
 Exhaust stroke
A single cycle requires two revolutions of the crankshaft to
complete.
1) INTAKE STROKE:
During a intake stroke, the piston moves downward from Top Dead Center (TDC)
To Bottom Dead Center (BDC) by the engine crankshaft either by the momentum
of flywheel and or the electric motor or the starter motor. During this stroke
piston moves downward and creates a vacuum inside the combustion chamber.
Figure 9:4 Stroke Engine Cylinder
Figure 8: Spark Plug

7. Inlet valve (Intake valve) opens during this stoke
allowing the air fuel mixture to enter the combustion
chamber. Here the fuel is petrol mixed with air broken
up into a mist and partially vaporized in the chamber.
Outlet valve will be closed and inlet valve will be open to
allowing the fresh charge of mixed fuel & air into the
cylinder. This stroke is also called Suction Stroke.
2) COMPRESSION
STROKE:
The compression stroke is when the trapped air-fuel mixture is compressed inside
the cylinder. The combustion chamber is sealed to form the charge. The charge is
the volume of compressed air-fuel mixture trapped inside the combustion
chamber ready for ignition. Compressing the air-fuel mixture allows
more energy to be released when the charge is ignited. Intake and
exhaust valves must be closed to ensure that the cylinder is sealed
to provide compression. Compression is the process of reducing or
squeezing a charge from a large volume to a smaller volume in the
combustion chamber. The flywheel helps to maintain the
momentum necessary to compress the charge.
When the piston of an engine compresses the charge, an increase in
compressive force supplied by work being done by the piston
causes heat to be generated. The compression and heating of the air-fuel vapor in
the charge results in an increase in charge temperature and an increase in fuel
Figure 10: Intake Stroke
Figure 11:
Compression Stroke

8. vaporization. The increase in charge temperature occurs uniformly throughout
the combustion chamber to produce faster combustion (fuel oxidation) after
ignition.
The increase in fuel vaporization occurs as small droplets of fuel become
vaporized more completely from the heat generated. The increased droplet
surface area exposed to the ignition flame allows more complete burning of the
charge in the combustion chamber. Only gasoline vapor ignites. An increase in
droplet surface area allows gasoline to release more vapor rather than remaining
a liquid.
The more the charge vapor molecules are compressed, the more energy obtained
from the combustion process. The energy needed to compress the charge is
substantially less than the gain in force produced during the combustion process.
For example, in a typical small engine, energy required to compress the charge is
only one-fourth the amount of energy produced during combustion.
The compression ratio of an engine is a comparison of the volume of the
combustion chamber with the piston at BDC to the volume of the combustion
chamber with the piston at TDC. This area, combined with the design and style of
combustion chamber, determines the compression ratio. Gasoline engines
commonly have a compression ratio ranging from 6:1 - 10:1. The higher the
compression ratio, the more fuel-efficient the engine. A higher compression ratio
normally provides a substantial gain in combustion pressure or force on the
piston. However, higher compression ratios increase operator effort required to
start the engine. Some small engines feature a system to relieve pressure during
the compression stroke to reduce operator effort required when starting the
engine.

9. 3) POWER STROKE:
The power stroke is an engine operation Stroke in which
hot expanding gases force the piston head away from the
cylinder head. Piston force and subsequent motion are
transferred through the connecting rod to apply torque to
the crankshaft. The torque applied initiates crankshaft
rotation. The amount of torque produced is determined
by the pressure on the piston, the size of the piston, and
the throw of the engine. During the power Stroke, both
valves are closed.
The ignition (combustion) event occurs when the
charge is ignited and rapidly oxidized through a chemical
reaction to release heat energy. Combustion is the rapid,
oxidizing chemical reaction in which a fuel chemically
combines with oxygen in the atmosphere and releases
energy in the form of heat.
Proper combustion involves a short but finite time to
spread a flame throughout the combustion chamber. The spark at the spark plug
initiates combustion at approximately 20° of crankshaft rotation before TDC
(BTDC). The atmospheric oxygen and fuel vapor are consumed by a progressing
flame front. A flame front is the boundary wall that separates the charge from the
combustion by-products. The flame front progresses across the combustion
chamber until the entire charge has burned. This stroke is also called Combustion
Stroke or Expansion Stroke.

4) EXHAUST STROKE:
The exhaust stroke occurs when combust gases are expelled from the combustion
chamber and released to the atmosphere. The exhaust stroke is the final stroke
Figure 12:Power stroke

10. and occurs when the exhaust valve is open and the intake
valve is closed. Piston movement evacuates exhaust gases to
the atmosphere.
As the piston reaches BDC during the power stroke
combustion is complete and the cylinder is filled with
exhaust gases. The exhaust valve opens, and inertia of the
flywheel and other moving parts push the piston back to
TDC, forcing the exhaust gases out through the open
exhaust valve. At the end of the exhaust stroke, the piston is
at TDC and one operating cycle has been completed.
 THERMODYNAMIC
PROCESS ANALYSIS:
Figure 13: Exhaust Stroke

11. ADVANTAGES:
 Less fuel
consumpt
-ion.
 Thermal
efficiency
is more.
 More
volumetri
-c
efficiency.
 Less wear
and tear.
DISADVANTAGES:
 More
components.
 Separate
valve
mechanism
is required.
 More cost.
 More
complicated
design.

12.  APPLICATIONS:

The four stroke engine is generally used for larger applications and is the most
common type of engine used in automobiles today. This type of engine is an
ingenious and practical design that has powered millions of vehicles. It produces a
large amount of power in an efficient and effective manner. It also generally
produces less pollution and lasts longer than a two stroke engine.