Diesel injection systems in history
In-line pumps Distributor pump VE
Distributor pump VP Pump-injector
The system common rail (CR) is now the fuel system of the fuel mostly used in
compression ignition engines
Major advantages over predecessors:
Pressure Injection independent of the rotation regime of the engine
Flexible control of injection pressure (pressure range 300 2200bar)
Flexible and accurate control of the injection quantity
Possibility of several injections per cycle depending on the operating condition
Flexibility in the timing of the injections of TDC engine
Alfa Romeo 156 1.9JDT the first car equipped with
the common rail system (1997)
Pressure regulatorr Pressure sensor
High pressure circuit
Low pressure circuit
Main components of the hydraulic layout:
Low-pressure pump (usually installed inside the tank)
Pompa high pressure
Pressure sensor installed on the rail
Flow regulator (FMV) or pressure regulator (PCV)
Electronic control unit
The engine control unit (ECU) has as its main function is to manage the system injection:
Monitors the pressure inside the rail (injection pressure)
Controls the flow regulator or the pressure regulator
Controls the injectors managing the duration, the number and timing of the injections
High pressure pump
The high-pressure pump receives the fuel from the low pressure circuit and sends it
to the rail at pressures are in the range 300 to 2200 bar depending on the operating
condition of the engine and on which the system is installed.
It is generally composed of a shaft with eccentric (1) realizes that by rotating the
suction stroke and the delivery of a number of pumping elements (3).
The pump is lubricated by the fuel itself and on it you can be installed of devices for
adjusting the delivery pressure.
High pressure pump
CR 1° generation
CR 2° generation
A pressure regulating valve electronics (PCV) is installed on the high
pressure side of the pump. It is controlled by the control unit to adjust
the injection pressure by downloading or less fuel from the high
A flow control valve electronics (FMV) is installed on the low pressure
side of the pump. It is controlled by the control unit to regulate the
inflow of fuel to the pump in relation to the injection pressure required.
Pump CP1 with integrated
pressure regulator to the outlet (PCV)
Pump CP4 with flow
regulator integrated suction (FMV)
The rail is an accumulator fuel to which are connected
the high-pressure pump and the injectors.
On it is installed a pressure sensor that the control unit
uses to monitor the injection pressure (PRAIL).
It may also be present a pressure regulator (PCV),
if it is not already present on the pump. Is there any
configuration of the system where the regulator on rail
is coupled to the flow control (FMV) installed on the
Pressure control (hints)
How realize the conditions of the mapping for a given operating condition?
The control unit must be able to adjust the pressure inside the rail to
obtain the value required by mapping (PRAIL).
Reading of the pressure inside the rail by means of
the integrated pressure sensor.
Control the pressure in the
rail by adjusting the flow
rate sucked by the high
Control the pressure in
the rail by recirculating or
less part of the fuel in the
Comparison of the detected
pressure with the required
value in the corresponding
map for a given operating
The injectors are classified according to the type of drive according to the type
of hydraulic layout. In the solenoid-operated injector,
an electromagnetic force,
generated in a solenoid crossed by
current, is exploited to actuate the
In the piezo injectors utilizes the inverse
piezoelectric effect, that is the capacity of the
piezoelectric material to deform when subjected
to an electric voltage.
The electric drive is not directly
connected to the pin, there is
interposed a pilot valve.
The electric drive is directly
connected to the needle through
a mechanical linkage.
Injectors indirectly actuated
Injectors direct actuated
Injectors are indirectly actuated, the solenoid controls a pilot valve the opening of which
causes an imbalance of the forces acting on the needle such as to allow the lifting.
A injector at rest
B injector operating
1) Fuel recirculation
2) Electrical connector
4) Input fuel (by rail)
5) Ball valve
6) Hole A
7) Hole Z
8) Control chamber
9) Control rod
10) High pressure line
Because of the complex internal hydraulic circuit and the presence of mechanical parts
with a not negligible inertia, the injection is not synchronized with the electrical
command supplied to the injector from the engine control.
Piezo injectors (indirect drive)
The piezoelectric actuator, the extension of which is amplified hydraulically, it acts on a
pilot valve which opens to download the environment upstream of the needle, which then
will rise due to the effect of the pressure of the fuel in the delivery chamber.
The layout of the valve is such that the
leaking fuel are much lower than those of
the injectors solenoid seen previously.
Control chamber Bypass
Piezo injectors (direct drive)
The piezoelectric actuator is directly connected to the pin by means of a mechanical
linkage, then NOT is no pilot valve.
1) The dynamics of the injector is improved;
2) It is not necessary to recirculate fuel to actuate the injector(efficiency ).
1) The piezoelectric actuator must be larger in order to generate the forces necessary to raise the needle;
2) It is necessary to control the injectors with very high voltages (≈ 160 volts) that may require a special
shielding of the electric circuit of the injection system
ECU - injection strategy (hints)
The basic strategy of injection include:
Reading throttle position (load);
Reading of the speed of rotation of the engine (rpm);
Reading maps of control:
1. Depending on the load and the speed of rotation
is chosen, the related map, the amount of fuel
to be injected to the cycle (mb) and the injection
2. Based on the amount to be injected (sc) and the
injection pressure (PRAIL) is chosen, from
another map, the duration of the electrical
command to be supplied to the injectors (ET).
ECU - injection strategy (hints)
After choosing injection pressure and
duration of the electrical control to the
injectors, the control unit must choosing a
number of other parameters with the aim to
maintain the engine in top
possible conditions, minimizing (to the extent
possible) the emission of pollutants and fuel
In addition the unit constantly monitors the
conversion efficiency of the devices of after-
treatment of the exhaust gas (oxidizing
catalyst, DPF, DeNOx) using, when
appropriate, strategies regeneration.