ECU sI -fuel injection

SRI KRISHNA COLLEGE OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF MECHATRONICS ENGINEERING
Session: Electronic controlled fuel
injection system for SI - Engine
11/24/2020 16MT407 - Theory of Automobile Engineering 1
MODULE 1

SESSION OBJECTIVES
 On the completion of this session, the students might
be able to understand,
 How the electronics system plays a role in SI
Engine fuel supply system

Topics
 Function of Fuel supply system for SI Engine
 Types of Fuel supply system for SI Engine
 Electronic controlled fuel supply system for SI
Engine
 Role of sensors

FUNCTION OF FUEL SUPPLY SYSTEM FOR SI ENGINE
 Units of fuel supply system
 The Carburetor,
 Fuel Pump.
 Fuel filter
 Fuel tank
 Various fuel pipes
connect them together
 Role of Carburetor is to mix
Air & Fuel in proper ratio for
begin the combustion
process
Carbureted Based Fuel supply system for SI Engine:

 The fuel supply function is
controlled by an electronically
controlled fuel injection
system.
 The fuel supply pressure is
much higher than carburetor
system
ECU Based Fuel supply system for SI Engine:

 To store fuel in a tank for running several hundred kilometers of vehicle.
 To deliver the fuel to the engine from the fuel tank
 To mix air with fuel in the proper ratio for efficient burning in the cylinder.
Function of fuel supply system:

Important terms used in combustion of fuel :
1. Atomization : The process of breaking
the fuel into fine drops is known as
atomization.
2. Vaporization :
 The process of changing the liquid
fuel into vapours is know as
vaporization.
 When gasoline evaporates, It
changes into vapours state
 In order to mix fuel with air, the
fuel is atomized during, which
evaporation takes place.

TYPES OF FUEL SUPPLY SYSTEM FOR SI ENGINE
Types of Fuel supply system for SI Engine :
1. Gravity feed system : Use
the influence of gravity to feed
the fuel to engine.
2. Vacuum System : Suction
stroke of the engine to suck
the fuel from main tank to
auxiliary tank & use gravity
force to drawn into carburetor
float chamber.

3. Pressure feed
system : Use air
pump to pressurized
the fuel to the
carburetor
4. Pump System :
High pressure fuel
pump used to
pressurized the fuel,
run either
mechanically or
electrically.

5. Fuel Injection system :
 Carburetor is replaced with fuel
injector.
 The fuel injector supply fuel in
atomized form into the intake
manifold where it uniformly
mixes with air the air stream
 The operation of fuel supply
system is controlled by an ECU
unit
 This is most accurate fuel supply
system

Types ECU Based SI Engine fuel injection : According to the location of
injector
1. Throttle body Injection system :
 Initially carburetor were replace
by this system only

injector
1. Throttle body Injection system :
 Injector located inside throttle
body, sits on top of the inlet
manifold
 Injector sprays fuel from above
throttle valve
 ECU Controls Injector Opening

injector
2. Intake Port Fuel Injection
system :
 An injector is placed near each
cylinder
 The fuel is sprayed into each
intake port on the manifold side
of the inlet valve

injector
3. Direct Injection system:
 Also called gasoline direct
injection system
 No air fuel pre mixing
 Optimal spray pattern is
obtained, that breaks gasoline
into smaller droplets
 Complete combustion is possible
 Compare to other system more
costly.
 Injector should withstand High
pressure & Heat
 Theme is High power & Less Pollution

Types ECU Based SI Engine fuel injection : According to the Duration &
Timing of injection
1. Continuous Injection Type:
 Fuel flows at all times from the
fuel injectors but at variable
flow rate.
 The continuous injection
systems can be built multi point
or single point. But not Direct

Timing of injection
2. Intermittent Injection Type:
 The injector nozzles are
opened only for the time period
required.
 Also called the jerk type or
batch type

Timing of injection
3. Sequential Injection Type:
 The fuel is injected at the exact moment when it will be most useful
 i.e Towards the opening of the intake stroke
Advantage:
 Fast response time when driver makes the quick change.
 Less pollution & Even more Economy
Disadvantage:
 More cost for providing additional control to ensure that the injector pulse
sequentially occurs

Types ECU Based SI Engine fuel injection : According to the number of
injector:
1.Single point (or Central)
Injection: Throttle Body Injection
2. Multi point (or Multiport
injection): Separate injector for
each cylinder mounted in intake
port.

Types ECU Based SI Engine fuel injection : According to the Control
Methods:
1.Mechanical Fuel injection
system:
 Fuel injection are by mechanical
means
 Timing, Pressure and
distribution were all controlled
by Mechanical means.
Disadvantage:
 It had only throttle opening &
RPM Control
 Engine output was linear.
Fuel requirement by an IC Engine at
different condition are against linear. This
will results in wide mixture variation.

Methods:
1.Mechanical Fuel injection
system:
 Fuel injection are by mechanical
means
 Timing, Pressure and
distribution were all controlled
by Mechanical means.
Disadvantage:
 It had only throttle opening &
RPM Control
 Engine output was linear.
Fuel requirement by an IC Engine at
different condition are against linear. This
will results in wide mixture variation.

Methods:
2.Electronic fuel injection system:
 All modern electronic fuel injection
works in same way
 Sensors converts the various
physical conditions both inside &
outside the engine into electrical
voltage.
 Based on the signal CPU find the
fuel requirement for the engine.

Methods:
 The computer converts the final
calculation of fuel requirement into
timed voltage pulse which prompts
the injector to open at a specific
time and for a specific duration.
 The injector through its one or
more holes, forces the very fine
atomized fuel, making it more
thoroughly vaporized & therefore
more readily combustible

Methods:
Purpose
 To Regulate the engine.
 To regulate the other engine
devices to maintain smooth &
stable operation
 Maintain optimum air-fuel mixture
is supplied at appropriate timing,
based on driver accelerator inputs
& other sensor inputs.

Methods:
Layout:

ECU FOR SI ENGINE FUEL SUPPLY SYSTEM

What is engine control unit/Electronic control unit:
 Brain of the electronic fuel
injection fuel injection system.
 Microprocessor is most important
unit
 It is relayed on different sensors &
data stored in its memory
ECU Function :
i.) Produce the relevant control
output signal
ii.) Determines the actuator control
amounts

Function of ECU:
Fail safe function : When an abnormality occurs in a signal from a sensor, the
ECU Ignores that the signal assume a pre – programmed value that allows to
continue to operate.
Backup Function : When an abnormality occurs in the ECU itself, the injectors
are controlled by a backup circuit independent of the system in order to permit
minimum driving.
Self diagnosis Function: When an abnormality occurs in a signal from a sensor,
the ECU lights up the check engine warning light & indicates the faulty system
with codes any time when ignition is on.

Some important terminology in SI Engine Fuel control:
Swept volume or displacement
Volume:
 It is the volume swept through
by the piston in moving between
TDC & BDC
𝑉𝑆 = 𝐴 × 𝐿 = 𝜋
4 𝑑2
𝐿
A – Area of the cylinder
L – Length of the cylinder
D- Diameter of the cylinder

Clearance Volume:
 It is the volume contained in the
cylinder above the top of the
piston, when the piston at TDC,
 It tells how much original volume
is compressed.

Volumetric Displacement:
 Engine displacement is the
swept volume for all piston inside
the cylinders of a reciprocating
engine in a single movement
from TOP Dead center(TDC) to
Bottom dead center (BDC).
 It is commonly specified in cubic
centimeters (cc or cm3 ), liters or
cubic inches

Volumetric Displacement:
 For eg : 1000 cc 1000 cm3 =
1Litre = 1.0L
Similarly
 800cc = 800cm3 = 0.8 Liter =
0.8 L
 How to measure the capacity of
the Engine volume
𝑉 = 𝜋
4 × (𝐷)2
× 𝐻 × 𝑁
V – Volume, D – Bore Dia,
H – Stroke Length, N- No of
Cylinders.

Volumetric Efficiency:
 Volumetric Efficiency (VE) in internal combustion engine engineering is
defined as the ratio of the mass density of the air fuel mixture drawn into the
cylinder at atmospheric pressure (during intake stroke) to the mass density of
the same volume of air in the intake manifold.

Volume flow rate of air:
Va = ev
N
2
VD
𝑁 =
𝑅𝑃𝑀
60
Role of fuel injection:
 Mass flow rate of air:
Ma = Vaρa
Where, ρa =
P
R Ti
Note: Volume flow rate mainly rely on Throttle angle
RPM: A look table is formed in ECU for 𝑀 𝑎
𝜌 𝑎 − 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑎𝑖𝑟
𝑃 − 𝐴𝑖𝑟 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒
𝑇𝑖 − 𝐼𝑛𝑡𝑎𝑘𝑒 𝑎𝑖𝑟 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒

Role of fuel injection:
 Mass flow rate of fuel:
Mf =
𝑀 𝑎
14.7
14.7:1 = stoichiometric air fuel
mixture ratio

Electronic controlled fuel injection for SI Engine: Schematic Layout

Manifold absolute pressure sensor (MAP):
 Pressure sensing element is silicon chip with an integral sensing diaphragm and
Piezo electric resistor.
 The sensor converts the manifold absolute pressure to a voltage signal &
transmits it to the ECU.
 The voltage signal & Engine revolution signal determines the fuel injection

TDC,CKP,CYP - SENSOR:
 These sensors provide the accurate
information of engine position. Which
determine the Injection & Ignition
timing.
 Each sensors comprises of a pickup
coil and a rotor which rotates in
unison with either crankshaft or a
camshaft.
 A signal is generated whenever one
rotor teeth is passes by the pick up
coil

TDC SENSOR: (TOP Dead Center
Sensor)
 Indicates the position of the piston at
TOP Dead center.
 TDC generates the four pulses per
cam/Crank shaft rotation
 To determine injection timing &
ignition timing

CKP SENSOR: (Crankshaft Position
Sensor)
 Indicates the crankshaft’s rotation
angle.
 The output voltage signal from the
sensor determine the Injection &
Ignition timing & Duration

CYP SENSOR: (Cylinder Position
Sensor)
 Indicates which cylinder at TDC
 For sequential fuel injection first
cylinder will be the reference for fuel
injection.

Barometric Pressure Sensor:
 The sensor converts the atmospheric
pressure into voltage signal.
 For changes in atmospheric pressure,
the discharge duration can be
modified.

Vehicle speed Sensor:
 The sensor detects speed of the
vehicle by taking account of gear shaft
revolution.
 It contains a rotor within the rotating
mechanism and a magnetic sensor
among other components.
 The vehicle speed sensor converts the
basic voltage signal basic ON/OFF
signal & send it to cpu.
 To determine fuel injection & Ignition
timing & Duration

Throttle position sensor:
 The sensor is made of potentiometer
connected to the throttle shaft.
 The sensor detects the throttle valve
opening angle as a resistance value.
 Converts it to a voltage signal.
 The signal increase during
acceleration
 Cut it off during deceleration.

Intake air temperature sensor:
 It is temperature dependent resistor
(i.e thermistor)
 The resistance of sensor decrease
with rise of intake air temperature.
 It converts air temperature into a
voltage signal & send this to ECU.
 This will modified the injection
duration

Engine coolant temperature sensor :
 It is temperature dependent resistor
(i.e thermistor)
 Mounted in the cylinder block
 The resistance of sensor decrease
with rise of Engine coolant
temperature.
 It converts engine coolant
temperature into a voltage signal &
send this to ECU.
 This will modified the injection
duration

Oxygen Sensor:
 The oxygen sensor uses hollow closed end shaft of zirconia with platinum
plated inner & outer surface.
 The inner surface is open to the atmosphere and the outer surface is exposed
to the exhausted gas.
 It generates the voltage signal for oxygen density difference between
atmospheric & Exhaust.
 This will determine the fuel injection duration.

Knock sensor:
 This sensor is mounted on the cylinder block and it detects knocking by sensing
vibration.
 It converts the engine knock vibration into voltage signal.
 Knocking happen because of incorrect air fuel mixture.
 Which leads to burn the fuel into uneven packets rather than uniform bursts.

Battery voltage
sensor:
 The battery voltage
is used to power the
ECU
 If voltage drop
occurs, the ECU
initiates the control
to correct the
corresponding delay
in the fuel injector
operation.

END

ECU sI -fuel injection

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