Fule Charger

INTRODUCTION

Air and fuel are supplied to an I.C.Engine where exothermic reactions take place inside the combustion chamber and the heat energy is converted into useful work.

To produce energy inside the engine , air fuel mixture is to be burnt in correct amount. For mixing the air and fuel in correct range different devices are used.

The preparation of a homogeneous mixture of air-fuel vapour mixture requires atomisation of liquid fuel droplets and mixing the finely divided fuel particles with air. The atomisation is accomplished by spraying the liquid fuel through a nozzle into a stream of air which is moving with large velocity.

CARBURETOR

Petrol vehicles use device called carburetor for supplying the air fuel mixture in correct ratio to cylinders in all rpm ranges. due to construction of the carburetor is relatively simple, it has been used almost exclusively on gasoline engines in the past.

These days in place of the carburetor, the MPFI (multi point fuel injection) system is used, assuring proper air fuel ratio to the engine by electrically injecting fuel in accordance with various driving conditions.  

FUEL ATOMISATION

During fuelling of a cylinder the fuel is pressurised which causes the fuel to become a vapour, allowing it to burn easily (compared to the fuel being delivered to the cylinder in liquid form)

OBJECTIVES OF FUEL INJECTION SYSTEM

The injection system of the compression ignition engine should fulfill the following objectives consistently and precisely:

1. Meter the appropriate quantity of fuel, as demanded by the speed of, and the load on, the engine at the given time.

2. Distribute the metered fuel equally among cylinders in a multi-cylinder engine.

3. Inject the fuel at the correct time (with respect to crank angle) in the cycle.

4. Inject the fuel at the correct rate (per unit time or crank angle degree).

5. Begin and end injection sharply without dribbling.

There are two major divisions of Fuel Injection systems: Solid Injection systems, which inject only the liquid

fuel through the injectors. Air Injection systems, which inject air along with the

liquid fuel

VARIOUS INJECTION SYSTEM

THROTTLE BODY INJECTION SYSTEM

The  throttle  body  injection  (TBI)  system uses one or two injector 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.

Throttle Body Injection System

L & D MPFI GASOLINE INJECTION SYSTEM

I-mpfi system stands for Intelligent-Multi Point Fuel Injection System , and

D-mpfi system stands for Direct-Multi Point Fuel Injection System.

D-MPFI GASOLINE INJECTION SYSTEM

The D-MPFI system is the manifold fuel injection system . In this type , the vacuum in the intake manifold is first sensed .In addition the volume of air is sensed by its density . As air enters into 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 command to the injector to regulate the amount of gasoline supply for injection . When the injectors spray fuel in the intake manifold the gasoline mixes with the air and the mixture enters the cylinder.

L & D MPFI GASOLINE INJECTION SYSTEM

INTRODUCTION

MPFI- a technology used in petrol engines

Uses a small computer to control the car’s engine

In MPFI engine one fuel –injector is installed near each cylinder ,that is why it is called multi point fuel injection.

Before MPFI system, there was a technology called “Carburetor” .

The computer in the MPFI system decides what amount of fuel to inject

System also learns from the drivers driving habits

MPFI system makes engine fuel efficient .

MAIN COMPONENTS OF MPFI SYSTEM

This system has four major components they are:

a)     Air intake systemi. Throttle bodyii. Idle air control valve

b)    Fuel delivery systemiii. Fuel pump iv. Pressure regulator systemv. Injector

c)     Electronic control systemvi. Engine Control Module (ECM)vii. On-Board diagnostic system

AIR INTAKE SYSTEM

The air (corresponding to the throttle valve opening) is filtered by the air cleaner, passes through the throttle body, and is distributed by the intake manifold and finally drawn into each combustion chamber. When the lAC valve is opened according to the signal from ECM, the air bypasses the throttle valve through bypass passage and is finally drawn into the intake manifold.

FUEL DELIVERY SYSTEM

The fuel in the fuel tank is pumped up by the fuel pump, filtered by fuel filter and fed under pressure to each injector through the delivery 'pipe. As the fuel pressure applied to the injector is always kept a certain amount higher than the pressure in the intake manifold by the fuel pressure regulator, the fuel is injected into the intake port of the cylinder head when the injector opens according to the injection signal form ECM. The fuel relieved by the fuel pressure regulator return through the fuel return to the fuel tank.

INJECTORS

The opening of the injector is controlled by the vehicles ECU

The injector is supplied with the battery voltage via a relay, the earth circuit is controlled by the ECU

When the circuit is completed by the ECU a solenoid operates, the injector valve opens, fuel is then able to be sprayed into the inlet manifold

The valve moves roughly 1.5-10 milliseconds. This is known an injector duration or opening time

The ECU will make amendments to the duration depending on engine temperature, loading air temperature and battery voltage

THE ROLE OF THE INJECTORS

The injector delivers a finely atomized spray of fuel into the inlet port

The injectors also vary the amount of fuel delivered to suit the engines conditions

The spray is obtained by passing fuel (that is

pressurised) through the nozzle of the injector

It is located in the inlet manifold near the cylinder head intake port

TYPES OF INJECTORS

1. Pintle Type Injector -Offers good atomization of fuel.

Prone to deposit build up on the Pintle valve (deposits can reduce the amount of fuel flow, and therefore the vehicle will run leaner than recommended.

2. Hole type injector - Fuel is delivered through holes drilled in a director plate at the injector tip.

Offers good fuel atomization and gives better resistance to deposit build-up.

The injector is placed on the side of the intake manifold near the intake port

Every cylinder is provided with an injector in its intake manifold .

ELECTRONIC CONTROL SYSTEM

The electronic control system consist of various sensors which detect the state of engine and driving conditions, ECM which controls various devices according to the signals from the sensors and Various controlled devices. The systems are

 Fuel injection control system                                       

 Idle speed control system  Fuel pump control system,  Ignition control system,  Radiator fan control system,

ELECTRONIC CONTROL UNIT’S CHIP

WORKING

Injection nozzle atomizes fuel into very small droplets.

Achieved by providing loaded valve needle forcing out fuel through small orifice.

Nozzle valve seats on conical seating due to spring pressure on spindle.

Spring pressure is suitably adjusted by adjusting screw to give correct opening pressure to fuel.

Fuel enters to passage drilled in nozzle holder and flows to an annular groove around needle seat.

The needle (nozzle) valve is then lifted against spring pressure to allow high pressure fuel to flow into combustion chamber.

Nozzle valve closes when fuel pressure becomes less than spindle spring pressure.

Extra fuel going up to nozzle spindle is carried away through leak-off pipe to fuel tank.

FUNDAMENTALS OF FUEL INJECTION

MPFI Systems can either be: Sequential Simultaneous Group

These techniques result in better ‘power balance’ amongst the cylinders, higher output from each one of them, along with faster throttle response .

TYPES OF MPFI SYSTEMS

Simultaneous injectors will operate all (or groups of injectors) at the same time

Sequential will operate independently and open and close at different times (determined by the ECU)

Group used in cylinder pairs [in V-series engines]

'Sequential' is the best from the above considerations of power balance/output

“Sefi’’-Sequential Electronic Fuel Injection - technically is the best of the above variants of MPFI

The ‘on-board’ ECU primarily controls the Ignition Timing and quantity of fuel to be injected .

ADVANTAGES OF MPFI1. Improved fuel consumption

2. Better for the environment

3. Better performance.

4. Immediate response, in case of sudden acceleration / deceleration.

5. No need to crank the engine twice or thrice in case of cold starting as happens in the carburetor system. 

6. More uniform A/F mixture will be supplied to each cylinder; hence the difference in power developed in each cylinder is minimum. Vibration from the engine equipped with this system is less, due to this the life of engine components is improved. 

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