ME−401

ICE Fuel Metering System

 Basic Requirements
❑ In SI Engine, torque and power output are regulated by
varying the quantity of combustible mixture supplied to the
cylinder.

❑ Mixture quantity is regulated by means of a throttle valve,

now mostly the butterfly type. These are installed downstream of
the main jet of the carburetor. If it were installed upstream, it
would obstruct the flow and cause wide variations in the
depression over the flow jet, and would change the direction of air
flow relative to the jet issues.
 Requirements for Metering &
Mixing
The (carburetor) system must supply continuously a mixture in
proportions such that:

❑ In all circumstances, it can be easily ignited by the spark.

❑ The maximum possible amount of chemical energy can be

extracted from it and converted by the engine into mechanical
energy.

❑ All fuels must be oxidized completely; i.e. without producing

carbon-monoxide in the exhaust.
 Requirements for Metering &
Mixing
The actual Process of carburetion comprises three phases:

❑ Metering the fuel through the jets in proportion to the air

flowing into the engine.

❑ Breaking up the liquid into fine droplets, or atomizing it, to

assist evaporation.

❑ Distributing the evaporating fuel uniformly into the air flow

to form a homogeneous mixture.
 Carburetor
⬥ Carburetor is the means for obtaining combustible
air-fuel mixture in correct ratio in all rpm ranges.
⬥ Basic parts:
• A venturi
• A fuel nozzle/capillary tube with metering system
• A reservoir of fuel in the float chamber
• A throttle and
• A choke.
 Carburetor System
⬥ Air at about atmospheric pressure, is drawn through the venturi
when the piston descends on the intake stroke. For smaller
diameter at the throat of the venturi, the velocity of the air
increases and therefore its pressure decreases. But then the
pressure at the tip of the nozzle/ capillary tube is less than the
pressure (atmospheric) inside the float chamber. Because of this
pressure difference, fuel will be sprayed into the air stream, of
amount determined by the size of the metering orifice/valve. If the
speed of the engine increases, an increased amount of air is drawn
through the venturi and therefore a greater pressure drop is
created and a proportionately greater amount of fuel is sprayed
into the air stream. The amount of mixture entering the cylinder
on the intake strokes is controlled by throttle. The choke enables
the engine to receive an additional amount of fuel for starting
 Carburetion System

❑ The carburetor uses the venturi principle: the inlet air flows
through a necked-down area (venturi). where the flow increases in
speed and decreases in pressure.

❑ The pressure drop at the venturi increases with engine

speed and with throttle position, thus causing fuel flow from the
reservoir to the venturi to increase as engine speed and throttle
position increase.
 Carburetion System

❑ Carburetion system consists of the following subsystems:

❖ Inlet system to maintain a constant level of fuel in the
reservoir.
❖ Metering system to maintain the desired air-fuel ratio.
❖ Accelerator-pump system to provide extra fuel during
acceleration.
❖ Power enrichment system to provide extra fuel during
periods of high demand.
 Throttling

❑ Choke valve and throttle valve are used in petrol

engines. Both these valves are found in the throttle
body or the carburetor. They both control the
amount of air entering the engine in different ways.
Throttle valve is connected to the throttle control or
the accelerator pedal. As the pedal is pushed, the
throttle valve open. The valve is controlled either by
mechanical linkages like lever, wire etc or by
electronic control like ride by wire technology.
 Throttling

⬥ As the valve opens to it fullest, maximum air can flow

through the carburettor and into the engine. As the flow of
air increase more fuel is mixed with the air in the carburetor
and hence more power is produced by the engine
⬥ During cold start conditions high rich fuel-air mixture is
required for starting the engine. To provide that high rich
mixture either more fuel has to added to the incoming air or
the air flow has to be cut off so that less air is mixed which
in turn give a high rich mixture. The choke valve just does
that, it basically cuts off and minimize the air supply to the
engine so that a rich mixture is supplied.
 Throttling

Four important conditions are:

❑ Low speed, small throttle opening (engine idling).

❑ Low speed, large throttle opening (at the beginning of

acceleration, or when the engine is labouring during the ascent of
a hill).

❑ High speed, small throttle opening (descending a hill).

❑ High speed, large throttle opening (fast motoring on level

ground).
 Electronic fuel injection (EFI)

This type of system uses

computer-controlled fuel injectors
to spray fuel into the engine’s
intake ports rather than
mechanically controlled injectors
or a carburetor. Electronic fuel
injection is considered to be
superior to carburetion because it
allows more precise fuel metering
for easier starting, lower
emissions, better fuel economy
and performance.
 Typical EFI components

❑ Fuel Pump
❑ Injectors
❑ Fuel Pressure Regulator
❑ ECM - Engine Control Module; includes a digital
computer and circuitry to communicate with sensors and
control outputs.
❑ Wiring Harness.
❑ Various Sensors.
 Electronic Fuel Injection ( SI Engine)

EFI comes in several varieties:

1. Throttle Body Injection (TBI).

1. Multi Port Fuel Injection (MFI).

3. Gasoline direct Injection (GDI).

 Fuel Injection ( SI Engine)

❑ Fuel injection system can be divided into two basis types:

❖ Manifold:
(a) Throttle body & (b) Port Injection
❖ Gasoline Direct Injection (GDI)
 Throttle Body Injection
❑ Incorporated electrically
controlled a single injector or
pair of injectors mounted in a
centrally located throttle body.
The injector sprays gasoline into
the air in the intake manifold
where the gasoline mixes with
air. This mixture then passes
through the throttle valve and
enters into the intake manifold.
 Port Fuel Injection
❑ In the port injection
arrangement, the injector is placed
on the side of the intake manifold
near the intake port. The injector
sprays gasoline into the air, inside
the intake manifold. The gasoline
mixes with the air in a reasonably
uniform manner. This mixture of
gasoline and air then passes through
the intake valve and enters into the
cylinder. Every cylinder is provided
with an injector in its intake
manifold.
 Gasoline Direct Injection (GDI)

❑ Fuel is injected directly into the

cylinder chamber.
❑ All newer diesel engines use direct
fuel injection.
❑ Much higher fuel pr than indirect
fuel injection.
 Gasoline Direct Injection (GDI)

❑ Injection/Injector Timing is critical.

❑ Equipped with in-line pumps,
distributor pumps, rail injection systems,
or pump injector units.
 Merits of EFI System

a. Improvement in the volumetric efficiency due to

comparatively less resistance in the intake manifolds which will
cause less pr losses. It eliminates majority of carburetor pr losses
and almost eliminates the requirement of manifold heating.

b. Manifold wetting is eliminated due to the fuel being

injected into close to the cylinder and need not flow through the
manifold.

c. Atomization of fuel is independent of cranking speed and

therefore starting will be easier.
 Merits of EFI System

d. Better atomization and vapourization will make the engine

less knock prone.
e. Formation of ice on the throttle plate is eliminated.
f. Distribution of fuel being independent of vapourization,
less volatile fuel can be used.
g. Variation of air-fuel ratio is almost negligible even when
the vehicle takes different positions like turning, moving on
gradients, uneven roads etc.
 Demerits of EFI System

a. High maintenance cost,

b. Difficulty in servicing, and

c. Possibility of malfunction of some sensors .
 Objectives of CIE Injection System

❑ Meter the quantity of fuel demanded by the speed of, and

the load on, the engine.
❑ Distribute the metered fuel equally among the cylinders.
❑ Inject the fuel at the correct time in the cycle.
❑ Inject the fuel at the correct rate.
❑ Inject the fuel with the spray pattern and atomization
demanded by the design of the combustion chamber.
❑ Begin and end the injection sharply without dribbling or
after-injections.
 Elements of CIE Injection System

To accomplish these objectives, a number of functional elements

are required. These elements are as follows:

1. Pumping elements to transfer the fuel from the tank to

the cylinder, along with the associate piping and hardware.

2. Metering elements to measure and supply the fuel at the

rate as desired by the speed and load conditions prevailing.

3. Metering controls to adjust the rate of the metering

elements for changes in load and speed of the engine.
 Objectives of CIE Injection System

4. Distributing elements to divide the metered fuel equally

among the cylinders in a multi cylinder engine.

5. Timing controls to adjust the start and stop of injection.

6. Mixing elements to atomize and distribute the fuel within

the combustion chamber.
 CI Injection Systems

❑ Individual Pump Systems. A separate metering and

compression pump for each cylinder.
❑ Distribution Systems. A single pump for compressing the
fuel (which may also meter), plus a dividing device for distributing
the fuel to the cylinders (which may also meter).
❑ Common Rail Systems. A single pump for compressing the
fuel, plus a metering element for each cylinder.
 Unit Injection System

❑ The pump and the injector

nozzle are combined in one
housing. Each cylinder is provided
with one of these unit injectors.
Fuel is brought up to the injector
by a low pr pump, where at the
proper time, a rocker arm actuates
the plunger and thus injects the
fuel into the cylinder.
 Common Rail Systems
❑ In common rail fuel
injection system employing a
common pr accumulator, called
the rail, which is mounted along
the engine block. The rail is fed by
a high pr fuel pump. The
injectors, which are fed from the
common rail, are activated by
solenoid valves.
 Common Rail Systems

❑ The solenoid valves and the

fuel pump are electronically
controlled. In the common rail
injection system the injection pr
is independent from engine
speed and load. Therefore, the
injection parameters can be
freely controlled.
 Indirect Injection Engine (IDI)

⬥ In an indirect injection
(abbreviated IDI) diesel engine,
fuel is injected into a small pre-
chamber, which is connected to
the cylinder by a narrow opening.
⬥ The initial combustion takes
place in this pre-chamber.

⬥ This has the effect of slowing the

rate of combustion, which tends
to reduce noise.
 Direct Injection Engine (DI)

❖ A direct injection diesel engine

injects the fuel directly into the
combustion chamber. Many designs do
not use a glow plug.

❖ While in pre-chamber engines,

injection prs of approx. 400 bar are
sufficient, for direct injection they have
to be between 1200 and 2000 bar.
 Fuel Injector ( SI Engine)
❑ A fuel injector is nothing but an
electronically controlled valve. It is supplied
with pressurized fuel by the fuel pump in the
car, and it is capable of opening and closing
many times per sec.

❑ When the injector is energized, an

electromagnet moves a plunger that opens
the valve, allowing the pressurized fuel to
squirt out through a tiny nozzle. The nozzle is
designed to atomize the fuel - to make as fine
a mist as possible so that it can burn easily.
Fuel Injector (SI Engine)
 Fuel Injector ( CI Engine)
❑ Quick and complete
combustion is ensured by a well
designed fuel injector. By
atomizing the fuel into very fine
droplets, it increases the surface
area of the fuel droplets
resulting in better mixing and
subsequent combustion.
Atomization is done by forcing
the fuel through a small orifice
under high pr.
 Fuel Injector ( CI Engine)

❑ The injector assembly consists of

❖ A needle valve
❖ A compression spring
❖ A nozzle
❖ An injector body
 Fuel Injector ( CI Engine)
❑ When the fuel is supplied by the injection pump it exerts
sufficient force against the spring to lift the nozzle valve, fuel is
sprayed into the combustion chamber in a finely atomized
particles.
❑ After, fuel from the delivery pump gets exhausted; the
spring pr pushes the nozzle valve back on its seat.
❑ For proper lubrication between nozzle valve and its guide
a small quantity of fuel is allowed to leak through the clearance
between them and then drained back to fuel tank through leak
off connection.
❑ The spring tension and hence the valve opening pr is
controlled by adjusting the screw provided at the top.
 Nozzle

❑ Nozzle is that part of an injector through which the liquid

fuel is sprayed into the combustion chamber. The nozzle should
fulfill the following functions:
❖ Atomization.
❖ Distribution of fuel. Factors affecting this are:
▪ Injection pr.
▪ Density of air in the cylinder.
▪ Physical properties of fuel like self ignition temp,
vapor pr, viscosity, etc.
❖ Prevention of impingement on walls.
❖ Mixing.
 Factors Affecting the Performance of
Nozzle
a. Injection pressure: Higher the injection pressure better
the dispersion and penetration of the fuel into all the desired
locations in combustion chamber.

b. Density of air in the cylinder: If the density of compressed

air in the combustion chamber is high then the resistance to the
movement of the droplets is higher and dispersion of the fuel is
better.

c. Physical properties of fuel: The properties like self ignition

temp, vapour pr, viscosity, etc. play an important role in the
distribution of fuel.
 Factors Affecting the Performance of
Nozzle

d. Prevention of Impingement on walls: Prevention of the

fuel from impinging directly on the walls of combustion chamber or
piston. This is necessary because fuel striking the walls
decomposes and produces carbon deposits. This causes smoky
exhaust as well as increase in fuel consumption.

e. Mixing: Mixing the fuel and air in case of non-turbulent

type of combustion chamber should be taken care of by the nozzle
 Types of Nozzle

❑ Various types of nozzles are used in CI engines. The most

common types are:

❖ The pintle nozzle

❖ The single hole nozzle
❖ The multi-hole nozzle
❖ Pintaux nozzle
 Pintle Nozzle
Nozzle valve is extended to form a pin or pintle
which protrudes through the mouth of the
nozzle. Spray cone angle is about 60 degree.

Advantages:
❑ it avoids weak injection and dribbling.
❑ It prevents the carbon deposition on the nozzle-hole.
❑ Excellent clog resistance.
 Single Hole Nozzle

At the centre of the nozzle body there is

a single hole which is closed by the
nozzle valve. The size of the hole is
usually of the order of 0.2 mm. Injection
pr is of order of 8-10 MPa and spray
cone angle is about 15°. Major
disadvantage with such nozzle is that
they tend to dribble. Besides, their
spray angle is too narrow to facilitate
good mixing unless higher velocities are
used.
 Multi-hole Nozzle

It consists of a number of holes bored in the

tip of the nozzle. The number of holes
varies from 4 to 18 and the size from 35 to
200 mm. The hole angle may be from 20°
upwards. These nozzles operate at high
injection prs of the order of 18 MPa.
Advantage:
Ability to distribute the fuel properly even
with lower air motion available in open
combustion chambers.
 Fuel Spray Structure & Characteristics

Fuel is injected in to the cylinder at high pr in

order to atomize the jet in to small droplets.
Atomization increases the surface area of the jet
and hence increases rate of evaporation. The pr
differential across the nozzle also helps in
effective dispersion of the spray across the
combustion chamber. As the fuel jet leaves the
nozzle, it becomes turbulent (if it is not already
so) and spreads entrains the surrounding air and
simultaneously atomizes. The distance from the
nozzle exit where jet breakup in to droplets first
occurs is known as the break up length.
 Fuel Spray Structure & Characteristics

As the spray penetrates further, it

diverges and decelerates. The fuel
droplets evaporate as the spray entrains
air. Spray penetration is an important
factor to be taken into account when
designing injection system to suit a given
combustion chamber shape. For
instance, over penetration may cause
spray wall impingement while under
penetration may lead to poor mixing and
reduced utilization of the available air
during the combustion process.