basic mechanical engineering - ic engines
TRANSCRIPT
M S Steve
Assistant professor
Dept of Mechanical Engineering
Amal Jyothi College of Engineering
Heat Engines
Absorb energy in the
form of heat
Convert part of it into
work
Reject balance as heat
Heat Engines
1. External Combustion Engines – steam engine
2. Internal combustion Engines – automobile engine
Internal Combustion Engine Burns fuel and air in enclosed space
Produces hot burned gases
Converts some of this heat into
useful work
Allows heat to flow from hot engine to cold outside air
Nikolaus Otto patented the 4-stroke engine when he was only 34!
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Internal Combustion Engines are those
heat engines where the combustion of
the fuel takes place inside the engines
Advantages of I C Engines
1. High thermal efficiencies ( 30 to 35%)
2. Higher power to weight ratio
3. Compact and suitable for portable applications
4. Quick-starting and simple in construction
Disadvantages of I C Engines
1. Since fuel combustion occurs in the cylinder, consequent
very high temperatures of engines necessitates engine
cooling arrangements
2. High temperatures restrict ICEngines to be single-acting,
reducing the power strokes per revolution
Classification of IC Engines
According to:
Fuel used
Strokes per cycle
Thermodynamic cycle
Speed of engine
Method of ignition
Method of cooling
Method of governing
Arrangement of engine cylinders
Number of cylinders
Application
Arrangement of Cylinders
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Comparison of Petrol and Diesel Engines
PETROL ENGINE
1. Works on Otto Cycle
2. Fuel-air mixture is admitted during suction stroke
3. Spark ignition
4. Low compression ratios (6 to 10)
5. Lower engine efficiency
6. Higher fuel consumption
7. Lower engine vibrations and noise
8. High running cost
9. Light duty application
DIESEL ENGINE
1. Works on Diesel Cycle
2. Fuel is injected at the end of compression stroke
3. Compression ignition
4. High compression ratios (10 to 20)
5. Higher engine efficiency
6. Lower fuel consumption
7. Higher engine vibrations and noise
8. Low running cost
9. Heavy duty application
IC Engine Parts
1. Cylinder Head
2. Cylinder Block and Liner
3. Piston
4. Connecting Rod
5. Crankshaft
6. Crank Case and Sump
Four Stroke I C Engine
In a four stroke I C Engine, one cycle of operation is
completed in four strokes of the piston in the engine
cylinder
The strokes are:
1. Suction (Induction) stroke
2. Compression Stroke
3. Power Stroke
4. Exhaust Stroke
Power Stroke
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Exhaust Stroke
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Inlet valve
closed
COMPRESSION STROKE
The four-stroke engine
Piston up
Exhaust valve
closed
Inlet valve
closed
COMPRESSION STROKE
The four-stroke engine
Piston up
Exhaust valve
closed
Inlet valve
closed
COMPRESSION STROKE
The four-stroke engine
Piston up
Exhaust valve
closed
Inlet valve
closed
POWER STROKE
The four-stroke engine
BANG
Exhaust valve
closed
Inlet valve
closed
POWER STROKE
The four-stroke engine
Piston down
powerfully
Exhaust valve
closed
Inlet valve
closed
POWER STROKE
The four-stroke engine
Piston down
powerfully
Exhaust valve
closed
Inlet valve
closed
EXHAUST STROKE
The four-stroke engine
Exhaust valve
open
Piston up
Exhaust gases
out
Inlet valve
closed
EXHAUST STROKE
The four-stroke engine
Exhaust valve
open
Piston up
Exhaust gases
out
1. Induction Stroke Engine pulls piston out of cylinder
Low pressure inside cylinder
Atmospheric pressure pushes fuel and air mixture into cylinder
Engine does work on the gases during this stroke
Engine – Stroke 1
Fuel and air mixture after induction stroke: Pressure = Atmospheric
Temperature = Ambient
2. Compression Stroke Engine pushes piston into
cylinder
Mixture is compressed to high pressure and temperature
Engine does work on the gases during this stroke
Engine – Stroke 2
Fuel and air mixture after compression stroke:
Pressure = High
Temperature = Hot
3. Power Stroke
Mixture burns to form hot gases
Gases push piston out of cylinder
Gases expand to lower pressure and temperature
Gases do work on engine during this stroke
Engine – Stroke 3
Burned gases after ignition: Pressure = Very high
Temperature = Very hot
Engine – Stroke 4
Burned gases after power stroke: Pressure = Moderate
Temperature = High
4. Exhaust Stroke
Engine pushes piston into cylinder
High pressure inside cylinder
Pressure pushes burned gases out of cylinder
Engine does work on the gases during this stroke
Two Stroke I C Engine
In a two stroke I C Engine one cycle of operation is
completed in two strokes of the piston in the engine cylinder
Stroke 1: Scavenging and Compression
Stroke 2: Power and Exhaust
Power and Exhaust
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Advantages of Two Stroke engines
1. One power stroke every revolution of crankshaft results in high power to weight ratio
2. Torque is more uniform needing lighter flywheel
3. Simpler in construction due to absence of valves and valve gear
4. Friction loss is less giving higher mechanical efficiency
5. Lower initial cost
6. Easier starting
Disadvantages of Two Stroke engines
1. Overall efficiency is less due to:
a) Inadequate scavenging as some combustion products remain in cylinder
b) Loss of fresh charge during scavenging
c) Less effective compression ratio for same stroke length
2. Engine overheating due to power stroke in every revolution
3. High lubricating oil consumption
4. Exhaust is noisier
Comparison of Four Stroke and Two Stroke Engines
FOUR STROKE ENGINE
1. One cycle in 4 strokes of piston or 2 revolutions of crankshaft
2. Valves are used for charge admission and exhaust
3. One power stroke in two revolution causing torque fluctuations needing heavy flywheel
4. Low power to weight ratios
5. Higher overall efficiency
6. Complex construction due to valve gear
7. Heavy duty applications
TWO STROKE ENGINE
1. One cycle in 2 strokes of piston or one revolution of crankshaft
2. No valves but ports are used for admission and exhaust
3. One power stroke in one revolution causing smoother torque and consequent lighter flywheel
4. Higher power to weight ratios
5. Lower overall efficiency due to loss of fresh charge
6. Simpler construction
7. Light duty applications
I C Engine Systems 65
I C Engine Systems
1. Air & Exhaust System
2. Fuel Systems
3. Ignition Systems
4. Cooling Systems
5. Lubrication Systems
AIR SYSTEM FOR PETROL ENGINE
AIR FROM ATM
SILENCER Product of combustion to atm
Engine AIR FILTER Carburettor
Fuel Systems
Petrol Engines
Correct quantity of petrol is mixed with air in carburettor before
being admitted into cylinder during suction stroke
Fuel storage tank
Fuel Pump Fuel Filter Carburettor Engine
FUEL SYSTEM FOR PETROL ENGINE
AIR FROM ATM AIR FILTER
combu
stion
FUEL SYSTEM FOR DIESEL ENGINE
AIR FROM ATM
SILENCER Product of combustion to atm
Engine
Low
pressure
pump
AIR FILTER
Fuel storage tank
filter filter High
pressure
pump
Fuel Injector
FUEL PUMP
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It pumps fuel from storage tank to carburetor
Actuated by cam, it is in touch with rocker arm
As the link is pulled downwards diaphragm will move down
and fuel will enter the chamber
Inlet and Exhaust valves are one way valves
One-way
Inlet Valve
One-way
Outlet Valve
Diaphragm
Driving Cam
Diaphragm Pump 76
Air
Filter
Tank
PETROL ENGINE – Carburettor Fuel System
Cockpit
Gauge
Pump
Carburettor
Exhaust Inlet
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SIMPLE CARBURETOR WORKING
FLOAT CHAMBER
FLOAT NEEDLE VALVE AIR VENT VENTURI
FUEL
FEED @
PUMP
JET
FLOAT
FUEL
LEVEL
Major function of carburetor is to provide air fuel mixture
Basic principle : When a volatile fuel is placed in the passage
of high velocity air, the fuel gets vaporized at a faster rate
Arrangement: • Jet and fuel nozzle
• Venturi tube & venturi throat
• Float chamber
• Throttle valve
• Float , float needle, air vent
Working
1. Petrol is pumped into the float chamber, level of petrol is
maintained by a float arrangement
2. Suction stroke of engine causes air flow through venturi tube.
3. VELOCITY of air at throat will increase & PRESSURE will
decrease at JET point(will be less than Atm. Pressure)
4. In float chamber the pressure acting is Atm. Pressure, due to this
pressure difference fuel will flow from FLOAT CHAMBER to
the JET
5. Function of throttle is to control speed and power to engine,
more the throttle is closed flow of air & fuel mixture to the
cylinder is less
AIR IS SUCKED THROUGH VENTURI …..
A PISTON MOVING DOWN ON SUCTION STROKE
SIMPLE CARBURETOR WORKING
MOVING AIR HAS LOWER PRESSURE
FUEL
FLOW AIR
FL
OW
AIR
FL
OW
THE LOWER AIR PRESSURE PULLS FUEL THROUGH THE JET
AIR/FUEL
MIXTURE
FLOWS TO
ENGINE
FUEL LEVEL DROPS
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PULLING AIR INTO FLOAT CHAMBER
SIMPLE CARBURETOR WORKING
FUEL LEVEL DROPS
FUEL LEVEL DROPPING LOWERS FLOAT
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AND ALLOWS FUEL TO ENTER FLOAT CHAMBER FROM PUMP
SIMPLE CARBURETOR WORKING
FUEL LEVEL DROPS
FUEL LEVEL RISING FORCES THE NEEDLE VALVE CLOSED
FUEL LEVEL DROPPING LOWERS FLOAT
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SIMPLE CARBURETOR WORKING
FUEL IS PULLED OUT OF THE FLOAT CHAMBER
ONLY WHEN PISTON IS ON THE INDUCTION STROKE
FUEL LEVEL RISING FORCES THE NEEDLE VALVE CLOSED
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We now need to look at controlling
the air/fuel mixture flowing into the
engine
Controlling the air/fuel mixture
means controlling the engine
The carburettor part which controls
the flow is….
THE THROTTLE
THROTTLE
VALVE
SIMPLE CARBURETOR WORKING 88
THROTTLE VALVE
THIS WOULD BE A HIGH THROTTLE SETTING OR ‘FULL –POWER’
OPEN THROTTLE ALLOWS VENTURI TO WORK AT MAXIMUM EFFICIENCY
SIMPLE CARBURETOR WORKING 89
LOW THROTTLE SETTING - CALLED ‘IDLE’ OR ‘TICK-OVER’
ALMOST CLOSED THROTTLE MEANS THE VENTURI DOES NOT WORK VERY
WELL
LOW AIR FLOW MEANS VERY LITTLE OR NO FUEL/AIR MIXING IN THE
VENTURI
SO AN ALTERNATIVE AND EFFECTIVE VENTURI NEEDS TO BE FOUND
SIMPLE CARBURETOR WORKING 90
T CONTROLS FUEL FLOW
LOW THROTTLE SETTING - CALLED ‘IDLE’ OR ‘TICK-OVER’
EDGE GAPS BECOME THE VENTURI FOR THE LOW AIR FLOW
AT IDLE - SLOW RUNNING JET
SIMPLE CARBURETOR WORKING 91
LIMITATIONS OF CARBURETTOR
• Distribution of air /fuel mixture to cylinder is not uniform
• Construction of venturi causes low volumetric efficiency
• There is a loss of volumetric efficiency also due to restricted
flow of mixture in various parts such as chokes, tubes, jets,
throttle valve, inlet pipe bends, etc.
All the above limitations of carburettor can be avoided by introducing the fuel
through injection rather than the carburettor
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FUEL INJECTION PUMP
A fuel injection pump is used to supply precisely metered quantity of diesel under high pressure to the injectors at the correct time.
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FUEL PUMP
Spring
Delivery valve
Fuel overflow port
Barrel
Rack
plunger
Inlet port
barrel
Barrel houses the inlet port and fuel overflow port
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Plunger
Plunger driven by cam & tappet
Plunger reciprocates in a barrel & fuel enters thru inlet port
Plunger have a vertical and helical groove which help in determining the amount of fuel supplied to the fuel injector
• Delivery valve is a non return valve,
kept in position by a spring.
When the Pr. In the barrel exceeds a
predetermined value and valve opens
against the compression of the spring
and the pressure of the fuel above.
Fuel pump is connected to the fuel
injector through a passage
Working
When the plunger is at bottom the fuel inlet & overflow
ports are uncovered and filtered fuel is forced into the barrel
Both ports are covered when the plunger moves upwards
Fuel will get compressed when the plunger moves further
forward
The high pressure lifts the delivery valve and fuel flows out
thru the delivery valve
With further rise of the plunger the overflow port is
uncovered by the plunger and pressure drops
The quantity of fuel pumped can be varied by the angular
position of the helical groove relative to the inlet port
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Diesel Fuel Pump
Plunger reciprocates on a barrel(hollow cylinder like
arrangement)
A rectangular helical groove in the plunger which extends
from top to another helical groove
When the plunger is at bottom -- fuel inlet and overflow port
are open,--fuel will come inside the barrel
When the plunger moves up– both ports are closed –and fuel
inside the barrel get compressed
Due to the high pressure of compressed fuel delivery valve
will get opened
FUEL INJECTOR
A fuel injector is used to inject the fuel in the cylinder in atomised form and in proper quantity. Fuel injectors are available in several designs. Main components of fuel injectors are : NOZZLE
VALVE BODY SPRING
The nozzle is its main part which is attached to the nozzle holder. Entry of fuel in the injector is from the fuel injection pump.
Spray Structure
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PARTS OF FUEL INJECTOR
1. Nozzle valve
2. Nozzle body
3. Spring
4. spindle
5. Adjusting screw
6. Lock nut
7. Passage
8. Nozzle
9. Leak of connection
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Nozzle valve is fitted in a nozzle body.
The spring retains the valve in its seating through a spindle.
Adjusting screw and lock nut- to adjust the lift of the nozzle
Working High pressure fuel from the fuel pump enters the injector
through the passage and lift the nozzle valve
Fuel travels down the nozzle and is injected into the engine
cylinder in the form of fine spray
When the fuel pressure drops the spring force overcomes the
fuel pressure and the valve get closed
Any leakage of the fuel at the end of the compression is fed
back to the fuel pump suction chamber by the leak off pipe
Nozzle valve is held on its seat by a spring which exerts
pressure through a spindle
Fuel from fuel pump enters the passage and lifts the
nozzle valve
then the fuel will sprayed through the nozzle and is injected
into the engine
When pressure drops the nozzle valve will occupy in its
seat under the compression of the spring
Ignition Systems Ignition process in Petrol Engines requires an electric spark
produced at the spark plug.
This spark is generated by an electric discharge produced by the ignition system.
Ignition systems in petrol engines are classified as :
1.Battery ignition system.
2.Magneto ignition system
• The difference between the two systems is in the source of primary voltage.
Ignition systems
Basic requirements of an ignition systems
A source of electrical energy
A device for boosting the low voltage to produce high voltage
A device for timing and distributing the high voltage to each
spark plug
Battery Ignition System.
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Battery ignition system
It is also called coil ignition system.
The source of energy to the primary windings is a 6V or
12V battery.
As the number of windings in the secondary is 50 to 100
times more than that of the primary , the output voltage
induced will be of the order of 10000v to 20000V.
Magneto Ignition System
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Magneto ignition system
The source of energy is either rotating magnets with fixed
coils or rotating coils with fixed magnets.
The rapid collapse and reversal of magnetic field induces a
very high voltage in the secondary winding.
It is generally employed in racing cars, motor cycles etc.
Spark plug
Task-
The spark plug ignite the suctioned and compressed fuel-air
mixture due to arcing between the electrodes.
Function-
The ignition voltage travels to the spark plug from directly
Connected ignition coils or over the ignition lines from the
Ignition coils causing arcing in the air gap between the center
and ground electrodes.
The Spark Plug
Centre electrode receives coil voltage.
Insulator prevents high voltages
from shorting to ground.
Terminal
Gap
Insulator
Gasket
Thread
Metal
shell
Hex
Centre
electrode
Side
electrode
Spark plug is located in the cylinder head,
it ignites the air and fuel mixture.
Has centre and side electrodes,
with an air gap between them.
High voltage jumps the
air gap, creating a spark.
Side electrode is grounded.
Next > 123
Lubricating Systems
Purpose:
1. To reduce friction and wear
2. To provide sealing between piston and cylinder
3. To cool piston heads, valves, etc.
4. To wash away carbon and metal particles
Lubrication Systems:
1. Petroil lubrication
2. Wet sump lubricating system
1. Splash lubrication
2. Pressure lubrication
3. Dry sump lubricating system
Petrol Lubrication System
This system of lubrication is used in scooters and motor
cycles.
About 3% to 6% of lubricating oil is added with petrol in the
petrol tank.
The petrol evaporates when the engine is working. The
lubricating oil is left behind in the form of mist.
The parts of the engine such as piston cylinder walls,
connecting rod are lubricated by being wetted with the oil
mist.
Wet sump lubrication system The splash system is used only on small four-stroke-cycle
engines.
As the engine is operating, dippers on the ends of the connecting rods enter the oil supply, pick up sufficient oil to lubricate the connecting-rod bearing, and splash oil to the upper parts of the engine.
The oil is thrown up as droplets, or fine spray, which lubricates the cylinder walls, piston pins and valve mechanism.
In the pressure-feed system, oil is forced by the oil pump through oil lines and drilled passageways.
The oil, passing through the drilled passageways under pressure, supplies the necessary lubrication for the crankshaft main bearings, the connecting-rod bearings piston-pin bushings, camshaft bearings, valve lifters, valve push rods, and rocker studs.
Splash lubrication
Simplest of all types, used only for small capacity engines.
Dry Sump Lubrication System In a wet sump, the oil pump sucks oil from the bottom of the
oil pan through a tube, and then pumps it to the rest of the
engine.
In a dry sump, extra oil is stored in a tank outside the
engine rather than in the oil pan. There are at least two oil
pumps in a dry sump -- one pulls oil from the sump and
sends it to the tank, and the other takes oil from the tank and
sends it to lubricate the engine. The minimum amount of oil
possible remains in the engine.
Dry sump lubrication
• The supply of oil is from an external tank.
• An oil pump is employed to circulate the oil under pressure
,from the tank to various bearings of the engine.
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Functions of a Lubricant Lubricant reduces friction between moving part.
It reduces wear and tear of the moving parts.
It minimizes power loss due to friction.
It provides cooling effect. While lubricating it also carries
some heat from the moving parts and delivers it to the
surroundings through the bottom of the engine (crank case).
It helps reduce noise created by the moving parts.
Purpose of cooling
To regulate the engines internal temperature
To remove excess heat from the engine
To prevent heat to the passenger compartment
To Control temperature of hot combustion,4000 degree temps. could seriously damage engine parts.
Cool Trans fluid & Oil
Cooling Systems Intense heat is generated during the combustion of fuels
inside the engine cylinder.
30% of heat generated is converted into mechanical work & 40% is carried away by exhaust gases to the atmosphere.
The remaining part of heat (30%) will be absorbed by the engine parts which leads to overheating of these parts.
In order to avoid the problem of overheating it is essential to provide some kind cooling systems.
The two important characteristics of cooling systems for
the efficient working are:
(i)It should not remove more than 30% of heat
generated.(larger amount of heat removal reduces the
thermal efficiency)
(ii)The rate of cooling should not be constant.(the rate
of cooling should increase with increase in heat
generated)
Two types of cooling systems used in IC engines are:
1.Air cooling system
2.water cooling system
Air cooling
The heat is dissipated directly in to the atmospheric air
by conduction through cylinder walls.
The rate of cooling is increased by increasing the outer
surface area of the cylinder by providing radiating fins &
flanges.
Normally it is used for the engines of motor cycles ,
scooters etc.
To increase the surface area exposed fins are provided
In some cases blower is provided to increase the heat tr. rate
Air cooling system
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Air cooling
Heat is dissipated to the surrounding air around the cylinder
Basic principle- to have continuous flow air around parts
which are to be cooled
The heat dissipated depends on :
The surface area of the metal, in contact with the air flow
The Temp difference between the surface & the air
Thermal Conductivity of the metal
Advantages of Air-cooled Engines:
Air-cooled engines are smaller and lighter because they don’t
need to house any of those parts like the Water cooled engines
In some climates, water has the tendency to freeze and this is a
problem for water-cooled engines.
Air-cooled engines warm up quickly and are easy to maintain.
Disadvantages of Air-cooled engines:
The cooling tends to be uneven and leads to cylinder distortion.
It is almost impossible to manage with air-cooling if the number
of cylinders increases beyond two.
The fins vibrate sometimes leading to a lot of noise.
Water cooling system.
It is also called thermosyphon system of cooling .
Water is circulated through water jackets around each of the
combustion chambers.
The circulating water is cooled by the air drawn through
radiator by a fan
Liquid cooling (water cooling)
Cooling medium – water
Water circulated through the passages
around the main components
Passages – water jackets
Water circulation- pump or by gravity
force
Water after passing through the jackets flows to a radiator.
Radiator cools hot water with the help of moving air around the
radiator tubes
Fans are provided to increase the heat transfer rate
This system also uses a thermostat to control the flow of the
coolant
Antifreeze added to avoid freezing of coolant- ethylene glycol
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Water Jackets Surrounds the cylinders
with water passage.
Absorbs heat from the
cylinder wall.
Pump move water to
radiator where heat is
exchanged to the air.
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Radiators
A radiator is a heat
exchanger.
Tube and fin style the
most popular.
Made of copper and
brass or aluminum and
plastic.
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Its job is to block the flow of coolant to the radiator until the
engine has warmed up.
When the engine is cold, no coolant flows through the
engine. Once the engine reaches its operating temperature
(generally about 200 degrees F, 95 degrees C), the
thermostat opens.
By letting the engine warm up as quickly as possible, the
thermostat reduces engine wear, deposits and emissions.
INJECTION METHODS
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TYPES OF CI INJECTION SYSTEMS
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COMMON RAIL
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Working
HP fuel pump maintains fuel in the common rail at a pressure
of about 200 MPa.
Common rail branches off to ECU controlled injector valves
Valve contains precision machined nozzles and a plunger
driven by solenoid valves
ECU controls the timing and quantity of fuel injected
depending on the load conditions
Advantages of CRDI
Higher efficiency due to variable injection timing
Better combustion at low speeds
Better power balance- reduced vibration
Lesser moving parts
Compact engine
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AIR FURL SYSTEM IN SI (PETROL)
ENGINES
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Gasoline direct injection
Petrol Direct Injection or Direct Petrol
Injection or Spark Ignited Direct Injection
(SIDI) or Fuel Stratified Injection (FSI)
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Components of GDI engine
Pumping element
Metering element
Mixing element
Mixture control
Distributing element
Ambient control
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MULTI POINT FUEL INJECTION Petrol vehicles used carburettor for supplying the air fuel mixture in
correct ratio to cylinders in all rpm ranges.
Carburettor achieves this by breaking up fuel into minute particles and
mixing it with air.
But this process may not always be perfect and might reduce the
performance of the engine.
Therefore, multi point fuel injection system (MPFI) is used, which can
assure proper air fuel ratio to an SI engine.
MPFI
MPFI stands for multi-point fuel injection
It allows more efficient combustion of fuel, thereby
producing more power with less emissions
It is similar to CRDI in diesel engines
All modern petrol engines use MPFI systems
MULTIPOINT INJECTION
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MPFI System
MPFI does the same function as the carburettor
It has injectors which spray correct quantity of fuel for each
cylinder
The fuel and air are mixed in the intake manifold before
admission to the cylinder
Components of MPFI
Electronic Control Unit (ECU)- sometimes called Engine
Control Module (ECM)
High Pressure Pump Module-pump, filter, pressure
regulator, common rail, sensor
Injector for each cylinder, also controlled by ECU
The function of ECU is to receive inputs from various sensors, compare them with pre-loaded engine and throttle parameters and send control signals to the actuators. Sensors: Sense different parameters (Temperature, Pressure, Engine Speed etc.) of the engine and send signal to ECU. Actuators: Receive control signal from ECU and actuates pump and injectors
ECU
Ambient temperature
Coolant temperature
Exhaust temperature
Exhaust oxygen content
Inlet manifold vacuum
Throttle position
ECU Inputs
Engine RPM
Vehicle road speed
Crankshaft position
Camshaft position
Outside air pressure
Pressure on throttle
For the Inputs, the microprocessor (or ECU) reads a number of
sensors:
Based on all these inputs from the sensors, the computer in the
MPFI system decides what amount of fuel to inject, when, for what
duration, and into which cylinder. It then sends signals to actuators
for injection of correct quantity of fuel.
Thus it makes the engine cleaner, more responsive, ensures
complete combustion, and uses less fuel as it knows what
amount of petrol should go in.
Modern cars’ ECUs have memory, which will remember
your driving style and will behave in a way so that you get the
desired power output from engine based on your driving
style.
For example, if you have a habit of speedy pick-up, car’s
computer will remember that and will give you more power
at low engine speeds by putting extra petrol, so that you get a
good pick-up. It will typically judge this by the amount of
pressure you put on accelerator.
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A multi-point injection system, also called port injection, has an
injector in the port (air-fuel passage) going to each cylinder.
Gasoline is sprayed into each intake port and toward each intake
valve. Thereby, the term multipoint (more than one location)
fuel injection is used.
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Advantages of MPFI:
More uniform fuel-air mixture will be supplied to each cylinder.
Thus the power developed by different cylinders will be more
uniform.
More appropriate fuel-air mixture will be supplied, which will
increase the combustion efficiency.
Cold starting can be improved.
Immediate response in case of sudden acceleration and
deceleration.
ADVANTAGES OF MPFI SYSTEMS OVER
SPFI SYSTEM
MPFI SPFI
Better power Low power
Better refinement of engines Lesser refinement of engines
Better control over the process Lesser control over the process
Longer life due to lesser load per injector Lesser life due to higher load
Cleaning not required frequently Frequent cleaning is required
No delay in response Delay in response
No difference in delivery to each cylinder Difference in delivery to each cylinder
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