Multi Point Fuel Injection
The term MPFI is generally used to specify an
engine variant used in the petrol vehicles.
A small computerized system is used to control
the engine of the car.
A petrol car will have more than three cylinders.
The MPFI engine is abbreviated as the Multi point
fuel injection engine.
The MPFI engine got this name because of the
reason that each cylinder is having a fuel injector
installed near them. That is why they are called as
the Multi point fuel injection engine.
At first, the petrol is allowed to mix with air. It is then ignited
in a cylinder called as the combustion chamber.
This combustion of the petrol produces a sufficient energy
to run the engine.
Carburetor used to mix the fuel and air in a fixed air-fuel
ratio. The fuel thus mixed in the carburetor is then given to
the combustion chamber where this mixture gets ignited.
The power thus obtained from the ignition of gas is used to
drive the engine.
The main disadvantage of the Carburetor is that the mixing
of fuel and air is not in the proper ratio which leads to the
wastage of fuel and the pollution is high.
As we said earlier that the MPFI engine is having a fuel
injector for each cylinder. A computer is used to
control each and every fuel injector individually.
The computerized system of the car consists of a
microcontroller. This microcontroller monitors each
fuel injectors and keeps on telling each injector about
the amount of fuel to be injected to the cylinder so
that the fuel wastage can be reduced.
WORKING OF MPFI
THERE ARE A
SENSORS USED IN
THE MPFI ENGINE.
The engine temperature of the
The speed at which the engine is
The engine load.
The position of the accelerator.
The cylinder's air-fuel pressure.
The rate of exhaust.
The amount of fuel to be injected into the combustion chamber
is decided by analyzing the inputs given to the computerized
system of the MPFI engine.
In modern MPFI engines, a memory unit is additionally installed.
This will make the MPFI engine capable of storing the user
settings so that it can operate easily. The driving habits of a
driver can also be detected by this system so that the MPFI
system itself can change the predefined settings which suit the
Each cylinder or the air-fuel mixing chamber is supplied with the precise and
uniform quantity of the air-fuel mixture.
Engine crank is not necessary in cold climatic conditions.
Good engine response to the throttle applied.
Accurate supply of the air-fuel mixture.
ECM technique is used to control the engine.
High fuel efficiency or mileage.
Common Rail Diesel Injection
Common rail engines require a very short (< 10 seconds)
to no heating-up time, depending on ambient temperature,
and produce lower engine noise and emissions than older
Diesel engines have historically used various forms of fuel
injection. Two common types include the unit injection
system and the distributor/inline pump systems (See diesel
engine and unit injector for more information).
Solenoid or piezoelectric valves make
possible fine electronic control over the
fuel injection time and quantity, and the
higher pressure that the common rail
technology makes available provides
better fuel atomization.
To lower engine noise, the engine's
electronic control unit can inject a small
amount of diesel just before the main
injection event ("pilot" injection), thus
reducing its explosiveness and vibration,
as well as optimizing injection timing and
quantity for variations in fuel quality, cold
starting and so on.
The pumps are cam driven, and injection pressure
was proportional to engine speed. This typically
meant that the highest injection pressure could
only be achieved at the highest engine speed and
the maximum achievable injection pressure
decreased as engine speed decreased. This
relationship is true with all pumps, even those used
on common rail systems. With unit or distributor
systems, the injection pressure is tied to the
instantaneous pressure of a single pumping event
with no accumulator, and thus the relationship is
more prominent and troublesome.
They were limited in the number and timing of
injection events that could be commanded during a
single combustion event. While multiple injection
events are possible with these older systems, it is
much more difficult and costly to achieve.
For the typical distributor/inline system, the start of injection
occurred and ended at a pre-determined pressure. Once the
pressure in the injector reached a pre-determined level, the
plunger would lift and injection would start.
In common rail systems, a high-pressure pump stores a reservoir
of fuel at high pressure — up to and above 2,000 bars (200 MPa;
The term "common rail" refers to the fact that all of the fuel
injectors are supplied by a common fuel rail which is nothing more
than a pressure accumulator where the fuel is stored at high
pressure. This accumulator supplies multiple fuel injectors with
The fuel injectors are typically ECU-controlled. When the fuel
injectors are electrically activated, a hydraulic valve (consisting of
a nozzle and plunger) is mechanically or hydraulically opened and
fuel is sprayed into the cylinders at the desired pressure.
If the accumulator, pump and plumbing are sized properly, the
injection pressure and rate will be the same for each of the multiple