Fuel Injection System

What is Fuel Injection System?

Fuel injection is a system for admitting fuel into an internal
combustion engine by atomizing the fuel through a small nozzle (fuel
injector) under high pressure created by the fuel pump.
In order for the engine to effectively make use of this fuel:

 Fuel must be injected at the proper time, that is, the injection
timing must be controlled and
 The correct amount of fuel must be delivered to meet power
requirement, that is, injection metering must be controlled.

Additional aspects are critical to ensure proper fuel injection

system performance including:
 Fuel atomization
 Bulk mixing
 Air utilization

How does a Fuel Injection System Works?

Fuel Injection System starts with a high pressure fuel pump,
located inside the fuel tank. Fuel is pumped from the tank, through a
fuel filter, and to the injectors by way of a supply line. A fuel pressure
regulator on the supply line ensures the injectors get constant fuel
pressure. When the fuel leaves the injectors, the excess is returned to
the tank by way of the return line. This closed loop fuel supply
guarantees a consistent spray and amount of fuel from each of the
injectors. The injector(s) either sprays the fuel directly into an engine
cylinder for burning or into a manifold where it is mixed with air, and
drawn into the engine cylinders for burning.
The electrical section of the Electronic Fuel Injection System
consists of the ECU, wiring and sensors. A wiring harness connects the
injectors to the ECU and to a power source {the battery}. The ECU is
also connected to various sensors located within the engine
compartment. The ECU monitors engine conditions and the position of
the gas pedal in order to determine the correct amount of fuel that
needs to be sprayed from each injector.

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 Fuel Injection System

Fig. 3.0

The typical fuel injection system consists of 6 main parts and the sum
of all of these fuel injection parts takes the place of the carburetor. This
consists of the following
 Fuel Pump
 Fuel Pressure Regulator
 Fuel Injectors
 Engine Control Module/Unit – ECM or ECU
 Engine Sensors
 Wiring

MECHANICAL FUEL INJECTION

In the Lucas system, fuel from the tank is pumped at high

pressure to a fuel accumulator. From there it passes into the fuel
distributor, which sends a burst of fuel to each injector, from where it
is fired into the inlet port.

The airflow is controlled by a flap valve which opens in response

to the accelerator pedal. As the airflow increases, the fuel distributor
automatically increases the flow of fuel to the injectors to keep the
fuel/air mixture correctly balanced.

For cold starting, a choke on the dash or, on later models, a

microprocessor control unit brings a special cold-start injector into
operation, which injects extra fuel to create a richer mixture. Once the
engine has warmed up to a certain temperature, a thermoswitch
automatically cuts off the cold-start injector.

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 Fuel Injection System

Mechanical fuel injection was used in the 1960s and 1970s by

many manufacturers on their higher-performance sports cars and
sports saloons. One type fitted to many British cars, including the
Triumph TR6 PI and 2500 PI, was the Lucas PI system, which is a timed
system.

A high-pressure electric fuel pump mounted near the fuel tank

pumps fuel at a pressure of 100psi up to a fuel accumulator. This is
basically a short-term reservoir that keeps the fuel-supply pressure
constant and also irons out the pulses of fuel coming up from the pump.

From the accumulator, the fuel passes through a

paper element filter and then feeds into the fuel-metering control unit,
also known as the fuel distributor. This unit is driven from
the camshaft and its job, as the name suggests, is to distribute the fuel
to each cylinder, at the correct time and in the correct amounts.

The amount of fuel injected is controlled by a flap valve located

in the engine's air intake. The flap sits beneath the control unit and
rises and falls in response to airflow - as you open the throttle, the 'suck'
from the cylinders increases the airflow and the flap rises. This alters
the position of a shuttle valve within the metering control unit to allow
more fuel to be squirted into the cylinders.

From the metering unit, the fuel is delivered to each of the

injectors in turn. The fuel then squirts out into the inlet port in the
cylinder head. Each injector contains a spring-loaded valve that is kept
closed by its spring pressure. The valve only opens when the fuel is
squirted in.

For cold starting, you cannot just block off part of the airflow to
enrich the fuel/air mixture as you can with a carburetor. Instead a
manual control on the dash (resembling a choke knob) or, on later
models, a microprocessor alters the position of the shuttle valve within
the metering unit. This activates an extra injector mounted in the
manifold, causing it to squirt in extra fuel to enrich the mixture.

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 Fuel Injection System

Fig. 3.1

ELECTRONIC FUEL INJECTION

Electronic fuel injection requires various engine sensors and a

computer to monitor and determine the engine speed, load and
operating conditions. It also controls the fuel delivery to provide
efficient power and mileage.

ENGINE CONTROL MODULE/UNIT – ECM or ECU

Fig. 3.2

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 Fuel Injection System

The engine control unit is central to an EFI system. The ECU

interprets data from input sensors to, among other tasks, calculate the
appropriate amount of fuel to inject.

The relative richness or leanness of the fuel mixture in a fuel

injected engine is determined by varying the duration of theinjector
pulses (called pulse width). The longer the pulse width, the greater the
volume of fuel delivered and the richer the mixture.

The computer is calibrated with a fuel delivery program that is

best described as a three-dimensional map. The program directs the
computer as to how long to make the injector pulses as engine speed
and load change.During start-up, warm-up, acceleration and increased
engine load, the map typically calls for a richer fuel mixture. When the
engine is cruising under light load, the map allows for a leaner fuel
mixture to improve fuel economy.
The programming that controls the EFI system is contained on a
PROM (Program Read Only Memory) chip inside the engine
computer.Replacing the PROM chip can change the calibration of the
EFI system. This is sometimes necessary to update factory
programming or to correct a drivability or emissions problem. The
PROM chip on some vehicles can also be replaced with aftermarket
performance chips to improve engine performance, too.

ENGINE SENSORS
The primary factor used in determining the amount of fuel
required by the engine is the amount (by weight) of air that is being
taken in by the engine for use in combustion.
In order to provide the correct amount of fuel for every operating
condition, the engine control unit (ECU) has to monitor a huge number
of input sensors. Here are just a few:

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 Fuel Injection System

Fig. 3.3

1. Mass airflow sensor - Tells the ECU the mass of air entering the
engine. It uses some type of airflow sensor used to directly measure
airflow into the engine. It may be a mechanical flap style airflow
sensor or hot wire airflow sensor.
2. Manifold absolute pressure sensor - Monitors the pressure of the
air in the intake manifold. It may be mounted on the intake manifold
or attached to the intake manifold with a vacuum hose. The amount
of air being drawn into the engine is a good indication of how much
power it is producing; and the more air that goes into the engine, the
lower the manifold pressure, so this reading is used to gauge how
much power is being produced.
3. Coolant temperature sensor - Allows the ECU to determine when
the engine has reached its proper operating temperature. This tells
the computer when the engine is cold and when it is at normal
operating temperature. The computer needs to know the
temperature because a cold engine requires a richer fuel mixture
when it is first started. When the coolant reaches a certain
temperature, the engine goes into Closed Loop operation, which
means it starts using inputs from the oxygen sensors to fine tune
the fuel mixture. When it is operating in Open Loop (when cold or

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 Fuel Injection System

when there is no signal from the coolant sensor), the fuel mixture is
fixed and does not change.
4. Throttle position sensor - Monitors the throttle valve position
(which determines how much air goes into the engine) so the ECU
can respond quickly to changes, increasing or decreasing the fuel
rate as necessary. It is located on the side of the throttle body and
uses a variable resistor that changes resistance as the throttle opens
and closes.
5. Inlet Air Temperature (IAT) or Manifold Air Temperature (MAT)
sensor – Monitors the temperature of the air entering the engine to
compensate the changes in air density that occur (colder air is
denser than hit air). This may be built into the airflow sensor or
mounted separately on the intake manifold.
6. Oxygen sensor or Air/Fuel sensor(on many newer vehicles) -
Monitors the amount of oxygen in the exhaust so the ECU can
determine how rich or lean the fuel mixture is and make
adjustments accordingly. Mounted in the exhaust manifold and
monitors unburned oxygen levels in the exhaust as an indicator of
the relative richness or leanness of the fuel mixture. The feedback
signal from the oxygen sensor or air/fuel sensor is used by the
engine computer to constantly fine tune the fuel mixture to optimum
fuel economy and emissions.

Faulty inputs from any of the engine's sensors may cause

drivability, emissions or performance problems.

FUEL INJECTION VERSUS CARBURETORS

WHY CARBURETORS?
•Less expensive
•Easier to install and repair
•More power

WHY FUEL INJECTION SYSTEM?

 Reduced fuel consumption
 Exhaust emissions are cleaner
 No need for frequent tune-ups

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 Fuel Injection System

Fig. 3.4 Fig. 3.5

CARBURETORS EFI
Winter Drivability Poor Excellent
Summer Drivability Excellent Excellent
Skill Level Required Average Advanced
Long-term Cost High Manageable
Performance Good Better
Turbo-compatible Poor Excellent
Supercharger- Depends Excellent
compatible
N2O-compatible Good Good
Emissions Friendly Poor Excellent
“WOW” Factor Fair Excellent
Reliability Good Excellent
Fuel Distribution Fair Excellent (Port &
Direct)
Intake Configurations Limited Unlimited (Port &
Direct)
Table 3.0

TYPES OF FUEL INJECTION SYSTEM

 Single Port/Throttle Body Injection System

 Multi-port injection System
 Batch Fuel Injection
 Sequential fuel injection
 Central Port Injection

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 Fuel Injection System

 Continuous injection system

1. THROTTLE BODY INJECTION SYSTEM

Also referred to as single port, this was the earliest type of fuel
injection to hit the market. The throttle body injection (TBI) system uses
one or two injection valves mounted in a throttle body assembly. The
injectors spray fuel into the top of the throttle body air horn. The TBI
fuel spray mixes with the air flowing through the air horn. The mixture
is then pulled into the engine by intake manifold vacuum.

The throttle body injection assembly typically consists of the

following: throttle body housing, fuel injectors, fuel pressure regulator,
throttle positioner, throttle position sensor, and throttle plates.

Fig. 3.6

Advantages of TBIS

1. It is less expensive than using other types of fuel injection

systems.
2. It is easier to clean and maintain.
3. It greatly improves the fuel metering compared to a carburetor.
4. It is cheaper to manufacture than a port injection system and
simpler to diagnose.

Disadvantages of TBIS

1. It is almost the same as a TBI carburetor wherein the fuel is not

equally distributed to all the cylinders.

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 Fuel Injection System

2. The possibility of condensation is much higher since the fuel

travels longer from the throttle body to the combustion
chamber.

2. MULTI-PORT INJECTION SYSTEM

Multi-port injection (sometimes called multi-point injection)

uses separate injectors to spray fuel into each cylinder. The injectors
are mounted into the intake ports, just outside each cylinder’s intake
valve.

Fig. 3.7

Advantages of MPIS

1. MPFI meters fuel more precisely than TBIS.

2. MPFI lessens the possibility that fuel will condense in the intake
manifold.
3. The mileage of the vehicle is improved.
4. Improvement in fuel economy

Types of MPIS:

 Batch Fuel Injection

In batched, fuel is injected to the cylinders in groups, without

precise synchronization to any particular cylinder's intake stroke.

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 Fuel Injection System

 Sequential Fuel Injection

Sometimes called sequential port fuel injection (SPFI) or timed

injection, SFI is a type of multi-port injection. Sequential fuel injection
triggers each injector nozzle independently and is timed like spark
plugs. SFI sprays the fuel immediately before or as the intake valve
opens. This type of injection also produces much lower emissions and
provides even better fuel economy. Because fuel only remains in the
port for a short amount of time, sequential injectors tend to last longer
and remain cleaner than other systems

3. CENTRAL PORT INJECTION

In central port injection, a central fuel unit sends fuel down a

series of legs which end in poppet valves. The look of this type of
injector led some people to refer to it as a spider injector.

Fig. 3.8

4. CONTINUOUS INJECTION SYSTEM

In a continuous injection system, fuel flows at all times from the

fuel injectors, but at a variable flow rate. This is in contrast to most fuel
injection systems, which provide fuel during short pulses of varying
duration, with a constant rate of flow during each pulse.

 Basic operation of a continuous fuel injection is as follows:

Fuel is fed to the system by an electric fuel pump that delivers fuel to
the mixture control unit. A fuel pressure regulator maintains fuel line
pressure and sends excess fuel back to the tank.

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 Fuel Injection System

The mixture control unit regulates the amount of fuel that is sent to the
injectors based on the amount of air flow through the intake and the
engine temperature. The unit is operated by the air flow sensing plate
and warm-up regulator.

The accelerator pedal regulates the rate of air flow through the intake
by opening and closing the throttle valve.

A cold-start injector is installed in the intake to provide a richer mixture

during engine start-up and warm-up. It is actuated by electric current
from the thermal sensor any time the temperature of the coolant is
below a certain level.

The injector for a continuous fuel injection system is a simple spring-

loaded valve. It injects fuel all the time the engine is running. A spring
holds the valve in a normally closed position with the engine OFF. This
action keeps fuel from dripping into the engine. When the engine
STARTS, fuel pressure builds and pushes the injector valve open. A
steady stream of gasoline then sprays toward each intake valve. The
fuel is pulled into the engine when the intake valves open.

Fig. 3.9

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 Fuel Injection System

Direct and Indirect Fuel Injection System

A four-stroke engine is an internal combustion engine in which
the piston completes four separate strokes while turning the
crankshaft.
1. Intake: This stroke of the piston begins at top dead center
(T.D.C.) and ends at bottom dead center (B.D.C.).
2. Compression: This stroke begins at B.D.C, or just at the end of
the suction stroke, and ends at T.D.C. Both the intake and
exhaust valves are closed during this stage.
3. Combustion: This is the start of the second revolution of the four
stroke cycle. At this point the crankshaft has completed a full
360-degree revolution.
4. Exhaust: During the exhaust stroke, the piston once again
returns from B.D.C. to T.D.C. while the exhaust valve is open.

Diagram of a cylinder as found in

4-stroke gasoline engines.:
C – crankshaft
E – exhaust camshaft
I – inlet camshaft
P – piston
R – connecting rod
S – spark plug
V – valves: exhaust and intake
W – cooling water jacket
grey structure – engine block

Fig. 3.10

A two-stroke (or two-cycle) engine is a type of internal combustion

engine which completes a power cycle with two strokes (up and down
movements) of the piston during only one crankshaft revolution. In a
two-stroke engine, the end of the combustion stroke and the beginning
of the compression stroke happen simultaneously, with the intake and
exhaust (or scavenging) functions occurring at the same time.
Direct Fuel Injection System is a fuel-delivery technology that
allows engines to burn fuel more efficiently, resulting in more power,
cleaner emissions, and increased fuel economy.

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 Fuel Injection System

How direct fuel injection works

1. In Gasoline engines work by sucking a mixture of gasoline and
air into a cylinder, compressing it with a piston, and igniting it
with a spark; the resulting explosion drives the piston
downwards, producing power.
2. In Diesel engines, virtually all diesel engines use direct fuel
injection. However, because diesels use a different process to
combust their fuel (gasoline engines compress a mixture of
gasoline and air and ignite it with a spark; diesels compress air
only, then spray in fuel which is ignited by the heat and
pressure), their injection systems differ in design and operation
from gasoline direct fuel injection systems.

Two positions of Direct Injection System

1. Wall-guided Direct Injection System

Fig. 3.11

2. Spray-guided Direct Injection System

Fig. 3.12

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 Fuel Injection System

Advantages of direct fuel injection

Combined with ultra-precise computer management, direct injection
allows more accurate control over fuel metering (the amount of fuel
injected) and injection timing (exactly when the fuel is introduced into
the cylinder). The location of the injector also allows for a more optimal
spray pattern that breaks the gasoline up into smaller droplets. The
result is more complete combustion.
Disadvantages of direct fuel injection
The primary disadvantages of direct injection engines are complexity
and cost. Direct injection systems are more expensive to build because
their components must be more rugged.

Indirect (traditional) fuel injection systems pre-mix the fuel and air
in a chamber just outside the cylinder called the intake manifold. In a
direct-injection system, the air and gasoline are not pre-mixed; air
comes in via the intake manifold, while the gasoline is injected directly
into the cylinder.

Combustion Chamber

A combustion chamber is that part of an internal combustion engine

(ICE) in which the fuel/air mix is burned

Fig. 3.13

Classification of indirect combustion chambers

1. Swirl chamber
It consists of a spherical chamber located in the cylinder
head and separated from the engine cylinder by a tangential
throat. About 50% of the air enters the swirl chamber during the
compression stroke of the engine, producing a swirl.

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 Fuel Injection System

2. Pre-combustion chamber
This chamber is located at the cylinder head and is
connected to the engine cylinder by small holes. It occupies 40%
of the total cylinder volume. During the compression stroke, air
from the main cylinder enters the pre-combustion chamber.
3. Air cell chamber
The air cell is a small cylindrical chamber with a hole in
one end. It is mounted more or less coaxially with the injector,
said axis being parallel to the piston crown, with the injector
firing across a small cavity which is open to the cylinder into the
hole in the end of the air cell. The air cell is mounted so as to
minimize thermal contact with the mass of the head. A pintle
injector with a narrow spray pattern is used. At TDC the majority
of the charge mass is contained in the cavity and air cell

Indirect and Direct Fuel Injection Systems Difference

The main difference between Direct and Indirect Injection is the layout
of the injection system, the Indirect Injection System actually has a
small swirl chamber above the cylinder, where the fuel is injected, this
chamber also contains the glow plug, which is much needed to start the
engine, the Direct Injection system has the injection nozzle actually
fixed to the top of the combustion chamber, usually the piston on the
engine with this type of injection system has a crown shape in the top
to create the needed swirl, the diagrams below show the difference
between both systems.

The Advantages of an ‘Indirect Injection’ system compared to

‘Direct Injection’ are:
 High rate of swirl over wide range of engine speeds
 Does not require expensive, ultra-high pressure injection
system
 Less chance of injector blockage due to self-cleaning pintle
injectors
The Disadvantages of an ‘Indirect Injection’ System compared to
‘Direct Injection’ are:
 Poorer fuel consumption due to lower thermal efficiency
 Higher compression ratio required to aid starting

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 Fuel Injection System

Direct Injection Cycle Indirect Injection Cycle

Fig. 3.14 Fig. 3.15

DIESEL AND GASOLINE FUEL INJECTION SYSTEMS

GASOLINE FUEL INJECTION SYSTEMS

A modern gasoline injection system uses pressure from an

electric fuel pump to spray fuel into the engine intake manifold. Like a
carburetor, it must provide the engine with the correct air-fuel
mixture for specific operating conditions. Unlike a carburetor,
however, PRESSURE, not engine vacuum, is used to feed fuel into the
engine. This makes the gasoline injection system very efficient.

The gasoline fuel injection system consists of:

 fuel injection pump - pressurizes fuel to high pressure
 high-pressure pipe - sends fuel to the injection nozzle
 injection nozzle - injects the fuel into the cylinder
 feed pump – sucks fuel from the fuel tank
 fuel filter - filtrates the fuel
 spark plug- produces spark to ignite the air/fuel mixture in the
combustion chamber

Cars that uses gasoline injection system (MPFI)

Honda Civic Reborn

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 Fuel Injection System

Honda City
Mitsubishi Mirage G4

GASOLINE DIRECT INJECTION (GDI)

A process where the air and fuel is directly injected to the
cylinder. The injector is connected along with the intake valve, exhaust
valve and the spark plug.

MAIN COMPONENTS OF GDI

 Engine Control Unit- is a computer that controls all of the
electronic Components on the engine
 Sensors - In order to provide the correct amount of fuel for every
operating condition, the ECU has to monitor a huge number of
input sensors
 High pressure Fuel Pump – pressurizes the fuel
 Fuel Injector - injects the fuel into the cylinder

Cars that uses gasoline direct injection system

Audi a6
Ford Edge
2016 Veloster turbo

WHY NOT CARBURETOR?

Carburetor has following Disadvantages:
 Vapour lock
 Perfect air/fuel mixture cannot be obtained
 Low volumetric efficiency

WHY THE GDI?

 Lower Fuel Consumption and More Output
 Better than the current MPI Style of Fuel Injection
 Less pollution from each drop of gasoline

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 Fuel Injection System

Advancement in technology

Fig. 3.16

DIESEL FUEL INJECTION SYSTEM

Unlike gasoline engines, diesel engines do not have a spark plug. In

these engines, the air is already present in the combustion chamber
and is compressed. Since no spark plug is present to produce spark,
the heated air will ignite the fuel that is injected into the combustion
chamber with high pressure.

The diesel fuel injection system consists of:

 fuel injection pump - pressurizes fuel to high pressure
 high-pressure pipe - sends fuel to the injection nozzle
 injection nozzle - injects the fuel into the cylinder
 feed pump – sucks fuel from the fuel tank
 fuel filter - filtrates the fuel

Cars that uses diesel injection system

Isuzu mu-X
Honda CR-V
Ford Everest

Operation of the injection system

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 Fuel Injection System

During the operation, the fuel from the tank enters the fuel feed pump.
In feed pump, the pressure of fuel is raised slightly. There the fuel is
drawn in to the filter where all the dust particles are removed. From the
filter, the fuel enters in to the injection pump where the pressure of air
in the cylinder at the end of compression. At this high-pressure fuel is
sprayed in to the engine cylinder by means of fuel injector. Any spill
over fuel in the injector is returned to the tank.

Fig. 3.17

Comparison of efficiency

Fig. 3.18

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