fuel feed system

Fuel Feed System

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

Fuel Injection Systems

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


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)


How is fuel atomized in injector fuelling systems?


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

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


Single point injection or throttle body injection system uses a single injector to spray fuel in the air intake

side of the throttle butterfly (where the carburettor is situated)



Gives poor atomization of the fuel

Does not give precise control of the air/fuel ratio to meet emission regulations

However, it is easier to control electronically than a carburettor

The fuel pressure is less then that of a multi point injection system (usually 1 bar)

Individual injectors are used for each cylinder

An injector is positioned near the inlet valve of each

cylinder

This system was originally used on diesel engines but is

also now widely used on petrol engines


The multi point injection system is the most common type of fuelling system that is used on modern

vehicles today

This is mainly due to the fact that this injection system can be controlled easily by the vehicles ECU

Furthermore, this type of fuelling system provides a better method of burning the fuel without much

wastage. Compared with other fuelling systems


Name three advantageous of a single point injection system ?

Name three advantageous of a multi-point injection system ?


Pintle Type Injector

Original injector design

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


Was introduced on later engine models, initially to reduce the reduce concerns

with injector depositsFuel 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.


Two different types of injector windings are used

This is dependant on the type of drive circuit used,

And is also dependant of weather an external resistor is being used.


Low resistance injector windings

Range between 2-3Ώ at 21.1 ◦C

Used with an external resistor in a voltage controlled circuit

High Resistance circuits

Range around 13.8Ώ at 21.1 ◦C

Do not require the use of an external resistor in a voltage controlled driver circuit.

What resistance should you expect a high resistance

circuit to operate at ?


fuel feed system

Automotive