fuel supply system in petrol engines

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Fuel Feed System: • Fuel supply system is used for sending fuel into Internal combustion engine. Fuel supply systems are divided into two: Carburettor. Fuel Injection system. • Primary difference between Carburettor and Fuel Injection system is fuel injection atomize the fuel by pumping fuel through a small nozzle under high pressure, where as in carburettor relies on suction created by intake air.

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Fuel Supply systems in Petrol engines in Detail

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Page 1: Fuel Supply System in Petrol Engines

Fuel Feed System:

• Fuel supply system is used for sending fuel into Internal combustion

engine.

• Fuel supply systems are divided into two:

– Carburettor.

– Fuel Injection system.

• Primary difference between Carburettor and Fuel Injection system is

fuel injection atomize the fuel by pumping fuel through a small

nozzle under high pressure, where as in carburettor relies on

suction created by intake air.

Page 2: Fuel Supply System in Petrol Engines

Components of fuel feed system for petrol engines:

• Fuel Tank

• Fuel Pump

• Fuel Filter

• Carburettor

• Intake Manifold

• Fuel lines or tubes necessary for connections

• Gauge to indicate the fuel in the fuel tank

Page 3: Fuel Supply System in Petrol Engines

Functions of fuel feed system:

• To store the fuel in the fuel tank

• To supply the fuel to the engine to the required amount and in

proper condition.

• To indicate to the driver the fuel level in the fuel tank.

Page 4: Fuel Supply System in Petrol Engines

Fuel Feed Systems:

• Gravity system

• Pressure system

• Vacuum system

• Pump system

• Fuel injection system

• Gravity, pressure and vacuum systems are obsolete now. The pump

system is used universally on motor vehicles.

• Some gasoline engines are using fuel injection system instead of

carburettor.

Page 5: Fuel Supply System in Petrol Engines

Gravity fuel feed system:

• Fuel tank is maintained at a place higher

than that of the carburettor.

• Fuel flows due to the gravitational force.

• System does not require any fuel pump.

• It is cheap and simple system.

• Fuel tank is directly connected to the

carburettor.

• Scooters and motor cycles make use of

this system.

Page 6: Fuel Supply System in Petrol Engines

Pressure fuel feed system:

• A pressure sealed tank is used.

• The pressure is created in the tank by means of a separate air

pump.

• For starting, the pump is primed by cam which produces pressure in

the tank and the fuel flows to the carburettor.

• In this system the tank is placed above or below the carburettor.

Page 7: Fuel Supply System in Petrol Engines

Vacuum fuel feed system:

• The engine is used for sucking the fuel from the main task to the

auxiliary fuel tank from where it flows by the gravity to the

carburettor.

Page 8: Fuel Supply System in Petrol Engines

Pump feed system:

• Fuel pump is used to feed

the fuel from the fuel tank to

the carburettor .

• The pump is driven either by

the camshaft or electrically .

• In this system the fuel tank

is placed at any suitable

position in the vehicle.

Page 9: Fuel Supply System in Petrol Engines

Fuel injection System:

• In fuel injection system , a fuel injection pump is used in place of

carburettor.

• The fuel is atomized by means of a nozzle and then delivered into an

air stream.

• Separate fuel injection system is used for each cylinder which

controls the mixture under different load and speed conditions.

Page 10: Fuel Supply System in Petrol Engines

Fuel tank:

• It is made of sheet metal.

• Usually attached to the frame at the rear of vehicle.

• Capacity ranges from 70 to 120 litres.

• Filler neck of the tank is closed by the cap.

• In some tanks, a filtering element at the fuel line connection to collect

dirt and prevent it from reaching to the pump and carburettor.

• A drain plug is provided at the bottom for emptying the tank.

• It also contains the float unit of the fuel gauge.

Page 11: Fuel Supply System in Petrol Engines

Fuel Tank:

• It may also have vent pipe which allows air to escape when the tank

is being filled.

• VVR (Vehicle Vapour Recovery System) vent pipe is connected to

the condenser which contains the vaporized gasoline in the tank and

prevents its escape into the air.

Page 12: Fuel Supply System in Petrol Engines

Pumps used in fuel system:

• Mechanical Pump

• Electrical Pump

• Performance of the fuel pump is tested by pressure, volume and

vacuum.

• A pump must produce certain amount of pressure as per the

manufacturers specification.

• It is tested by placing a pressure gauge between the pump and the

carburettor and run the engine at the specific speed.

• Gauge will indicate the pressure created by the fuel pump.

Page 13: Fuel Supply System in Petrol Engines

Testing of Pump:

• For volume test , disconnect the fuel pump from the carburettor and

run the engine at the idling speed.

• Measure the fuel coming out from the pump by collecting it in a

separate container.

• For vacuum test , connect the suitable vacuum gauge between the fuel

tank and the pump and run the engine at the idling speed .

• The gauge will indicate the vacuum created inside the pump to suck

the fuel from the fuel tank.

• The vacuum must be retained for at least 10 seconds after closing the

engine.

Page 14: Fuel Supply System in Petrol Engines

A C Mechanical Pump:

Page 15: Fuel Supply System in Petrol Engines

AC Mechanical fuel pump:

Page 16: Fuel Supply System in Petrol Engines

A C Mechanical Pump:

Page 17: Fuel Supply System in Petrol Engines

Working of AC Mechanical Pump:

• Fig Shows a diaphragm type A C mechanical pump.

• It is bolted to the engine block or crankcase so that the rocker arm

slides on a cam on the engine camshaft .

• It consists of high grade cotton diaphragm impregnated with

synthetic rubber.

• The movement of the diaphragm sucks fuel from the tank and

pushes it to the carburettor.

• As the cam rotates it operates the rocker arm which in turn pushes

the diaphragm up and down.

Page 18: Fuel Supply System in Petrol Engines

Working of AC Mechanical Pump:

• The downward movement of the diaphragm sucks the fuel in through

the strainer from the fuel tank.

• The upward movement of the diaphragm pushes the fuel which causes

the inlet valve close and the outlet valve to open.

• The fuel through the out let valve goes to the carburettor.

• If the float chamber is completely filled with the fuel there is no need

of pumping the fuel.

• But the engine is running which in turn the pump is operating which

will cause the rise of pressure in the fuel pump which may damage the

pump.

Page 19: Fuel Supply System in Petrol Engines

Working of AC Mechanical Pump:

• To avoid this the connection between the rocker arm and the push

rod is made flexible with the help of springs.

• When the fuel pressure is increased the rocker arm will disconnect

from the eccentric, hence the pump is not operated even though the

engine is running.

Page 20: Fuel Supply System in Petrol Engines

Working of Electrical Fuel Pump:

• It also consists of a diaphragm and it is operated electrically.

• By turning on the ignition switch , the solenoid winding generates

the magnetic flux which pulls the armature and the diaphragm

moves up.

• The upward movement of the diaphragm creates the suction and the

fuel is drawn into the chamber through the inlet valve.

• As soon as the armature moves up it disconnects from the electric

supply and the magnetic flux dies and the armature falls down

which it causes to create pressure in the pump chamber.

Page 21: Fuel Supply System in Petrol Engines

Working of Electrical Fuel Pump:

• This causes the outlet valve to open and inlet valve to close.

• The fuel goes out to the carburettor.

• The downward movement of the armature against sets electric

supply to the solenoid and this process is repeated.

Page 22: Fuel Supply System in Petrol Engines

Carburetion:

• The process of mixture preparation in S I Engine is called as

carburetion.

• This air fuel mixture is prepared outside the cylinder in a device

called carburettor.

• The carburettor atomizes the fuel and mixes with air in different

proportions for various load conditions.

• Loads: starting, idling, Cursing, accelerating.

Page 23: Fuel Supply System in Petrol Engines

Factors affecting Carburetion:

• The time available for mixture preparation.

• The temperature of the incoming air

• The quality of fuel supplied

• The engine speed

• The design of the carburettor

Page 24: Fuel Supply System in Petrol Engines

Various Loading Conditions

• Idling/Starting: Engine runs at no load. Produces power just to

overcome the friction between the parts.

• Rich mixture (10:1) is needed to sustain the combustion.

• Normal power/Cruising mode/Medium load: engine runs for the

most of the period. Fuel economy is maintained.

• Lean mixture (17:1) is needed.

• Maximum power/Acceleration: Overtaking a vehicle ( short period)

• Rich Mixture is needed.

Page 25: Fuel Supply System in Petrol Engines

The main functions of a carburettor:

• It vaporizes and atomizes the fuel and mixes it with the air

The vaporization means the change of the fuel from a liquid to a

vapour whereas 'atomization' is the braking up of fuel by mechanical

system, so that every small particle of the fuel is surrounded by air

• It provides and controls the amount and strength of air fuel mixture

under varying conditions of load and speed of the engine.

• It provides easy starting while the engine is cold.

• It provides maximum acceleration without hesitation to pick up speed,

when the throttle is suddenly or slowly opened.

Page 26: Fuel Supply System in Petrol Engines

Main Components of Carburetor:

• Float Chamber: To store the fuel and adjust the fuel level

• Cylinder with venturi: For atomization of fuel

• Fuel nozzle : To atomize the fuel and produce spray of fuel

• Throttle valve : To Supply varying quantities of mixtures at

different load conditions.

• A choke valve: To control the air supply in order to provide a rich or

lean mixture.

Page 27: Fuel Supply System in Petrol Engines

Carburettor:

Page 28: Fuel Supply System in Petrol Engines

Carburettor:

Page 29: Fuel Supply System in Petrol Engines

Working Principle of Carburetor:

• Fuel supplied to the float chamber is controlled by the action of the

float.

• The suction stroke creates vacuum and because of the fall in the

pressure the atmospheric air rushes into the carburetor.

• Near the venturi the cross section decreases, the velocity increases

hence the pressure decreases and creates a partial vacuum known

as carburetor depression at the venturi throat and the fuel comes

out in the form of jet in the form of spray.

• The fuel gets mixed with air and enters into cylinder.

Page 30: Fuel Supply System in Petrol Engines

Idling system:

• During idling or starting engine

runs with out the load and the

throttle valve remains in closed

position.

• Idling system consists of an

idling fuel passage and an idling

port.

• There is separate passage for the

supply of fuel and air when the

throttle is at closed potion.

Page 31: Fuel Supply System in Petrol Engines

Auxiliary Port System:

• During the normal running conditions engine

has to be run for most of the time and hence

fuel economy has to be maintained. Hence it is

necessary to have a low specific fuel

consumption.

• Hence auxiliary port system has to be

maintained where opening of the butterfly

valve allows additional air to be admitted and

at the same time the depression at the venturi

throat will be reduced thereby decreasing the

fuel rate.

Page 32: Fuel Supply System in Petrol Engines

Classification of carburettor:

According to the direction of air flow.

• Down draft

• Updraft

• Sidedraft

According to the arrangement of float chamber

• Eccentric

• Concentric

According to the type of metering system

• Metering pin type

• Air-bleed jet

Page 33: Fuel Supply System in Petrol Engines

Classification of carburettor:

According to the number of units

• Single

• Double

• Four-barrel

According to the type of pressure above the fuel in the float chamber

• Atmospheric pressure carburettor

• Air pressure in the carburettor intake

According to the type of power system

• Manually operated

• Vacuum controlled

Page 34: Fuel Supply System in Petrol Engines

Based on direction of flow:

Updraft carburetorDown draft carburetorSide draft carburetor

Page 35: Fuel Supply System in Petrol Engines

Electronic Fuel Injection System:

• Modern gasoline injection systems use engine sensors, a computer

and solenoid operated fuel injector to meter and to inject the right

amount of fuel into the cylinder.

• These is called as electronic fuel injection (EFI) which uses electric

and electronic devices to control and monitor the engine operation.

• ECU Electronic control unit receives the electrical signals in the form

of current or voltage from various sensors.

• It then uses the stored data to operate the injectors, ignition system

and other engine related devices.

Page 36: Fuel Supply System in Petrol Engines

Different sensors used In the EFI:

• Exhaust gas or oxygen sensor

• Engine temperature sensor

• Air flow sensor

• Air inlet temperature sensor

• Throttle position sensor

• Manifold pressure sensor

• Camshaft position sensor

• Knock sensor

Page 37: Fuel Supply System in Petrol Engines

Functions of Sensors:

• Exhaust gas or oxygen sensor: Senses the amount of oxygen in the

engine exhaust and calculates air fuel ratio. Sensor output voltage

changes in proportion to the air fuel ratio.

• Engine temperature sensor: Senses the temperature of the engine

coolant and from this data the computer adjust the mixture strength

to rich side for the cold starting.

• Air flow sensor: Monitor the mass or volume of air flowing into the

intake manifold for adjusting the quantity of fuel.

• Air inlet temperature sensor: Checks the temperature of the ambient

air entering the engine for fine tuning the mixture strength.

Page 38: Fuel Supply System in Petrol Engines

Functions of Sensors:

• Throttle position sensor: Senses the movement of the throttle plate so

that the mixture flow can be adjusted for engine speed and

acceleration.

• Manifold pressure sensor: Monitors the vacuum in the engine intake

manifold so that the mixture strength can be adjusted with changes in

the engine load.

• Camshaft position sensor: Senses the rotation of the engine

crankshaft and the camshaft for speed and timing of injection.

• Knock sensor: Micro phone type sensor that detects the ping or

resignation noise so that the ignition time can be retarded.

Page 39: Fuel Supply System in Petrol Engines

Electronic fuel Injection system:

• The injection pulse width is an indication of the period for which

each indicator is energized and kept open.

• The computer decides and controls the injector pulse width based on

the signals received from the various reasons.

• Under full load, the computer will sense a wide open throttle, high

intake manifold pressure, and high inlet flow.

• The ECU will then increases the injector pulse width to enrich the

mixture, which will enable the engine to produce high power.

Page 40: Fuel Supply System in Petrol Engines

Electronic fuel Injection system:

• Under low load and idling conditions the ECU will shorten the pulse

width by which the injectors are kept in the closed position over a

longer period of time.

• Because of this air fuel mixture will become leaner and will result in

better fuel economy.

• EFI has a cold injector too. This is an extra injector that sprays fuel

into the center of the engine intake manifold when the engine is

cold.

• It serves the same purpose as the carburetor choke and this ensures

easy start up in the very cold weather.

Page 41: Fuel Supply System in Petrol Engines

Multi Point Fuel injection System:

• The main purpose of the multipoint fuel injection is to supply a proper

ratio of gasoline and air to the cylinders.

• These systems function under two basic arrangements:

• Port injection

• Throttle body injection

Page 42: Fuel Supply System in Petrol Engines

Port Injection:

• In this system, 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.

Page 43: Fuel Supply System in Petrol Engines

Port Injection:

• Every cylinder is provided with an injector in its manifold. If there

are six cylinders there will be six injectors.

• Figure shows port or multi point fuel injection system

Page 44: Fuel Supply System in Petrol Engines

Throttle body Injection:

• Figures gives the simplified sketch of the throttle body injection

system ( Single point injection system).

• This is similar to the carburetor throttle body with the throttle valve

controlling the amount of air entering the intake manifold.

Page 45: Fuel Supply System in Petrol Engines

Types of MPFI Systems:

• In some literatures MPFI is classified into 2 types:

• D MPFI

• L MPFI

Page 46: Fuel Supply System in Petrol Engines

D MPFI System:

• It is the manifold fuel injection system.

• In this type the vacuum in the intake manifold is first sensed.

Further it senses the volume of air by its density.

• Figure shows the block diagram regarding the functioning of the D

MPFI system.

Page 47: Fuel Supply System in Petrol Engines

D MPFI System:

• As the air enters the intake manifold the manifold pressure sensor

detects the intake manifold vacuum and sends the information to

the ECU.

• The speed sensor also sends the information about the rpm of the

engine to the ECU.

• The ECU in turn sends commands to the injector to regulate the

amount of gasoline supply for injection.

• When the injector sprays fuel in the intake manifold the gasoline

mixes with the air and the mixture enters the cylinder.

Page 48: Fuel Supply System in Petrol Engines

L MPFI System:

• In this system the fuel metering is regulated by the engine speed

and the amount of air that actually enters the engine. This is called

air mass metering or air flow metering.

• This is the block diagram of L MPFI system.

Page 49: Fuel Supply System in Petrol Engines

L MPFI System:

• As the air enters the intake manifold, the air flow sensor measures

the amount of air and sends the information to the ECU. Similarly

the speed sensor sends information about the speed of the engine to

the ECU.

• The ECU process the information received and send appropriate

commands to the injector to regulate the amount of gasoline supply

for injection.

• When injection takes place, the gasoline mixes the air and mixture

enters the cylinder.

Page 50: Fuel Supply System in Petrol Engines

Functional Divisions of the MPFI System:

• It can be functionally divided into the following three main

components:

• Electronic Control System

• Fuel System

• Air Induction System

Page 51: Fuel Supply System in Petrol Engines

MPFI Electronic System:

• The sensors that monitors intake air temperature, the oxygen, the

water temperature, the starter signal and the throttle position sends

the signals to the ECU

Page 52: Fuel Supply System in Petrol Engines

MPFI Electronic System:

• The air flow sensor sends the signals to the ECU regarding the

intake air volume.

• The ignition sensor send information about the engine speed.

• The ECU processes all these signals and sends the appropriate

commands to the injectors to control the volume of the fuel for

injection.

• When necessary the cold start injector is operated by the ECU

which is a part of the fuel system.

Page 53: Fuel Supply System in Petrol Engines

MPFI Fuel System:• Fuel is supplied by the fuel pump.

• At the time of starting the cold start

injector is operated by the cold start

injector time switch.

• The cold start injector injects fuel into the

air intake chamber thus enriching the air

fuel mixture.

• The pressure regulator regulates the

pressure of the fuel.

• The injectors receive signals from the

ECU and inject the fuel into the intake

manifold.

Page 54: Fuel Supply System in Petrol Engines

MPFI Air Induction System:

• In here the air cleaner, the

air flow meter, the

throttle body and the air

valve supply a proper

amount of air to the intake

chamber and intake

manifold.

• The quantity of air

supplied is just what is

required for complete

combustion.