printable version

Features of the injection

Characteristics normal injection system

In conventional systems, the fuel injection control system and fuel injection pump of direct injection includes only the main injection phase - without control and late injection. On the distribution fuel pump with electromagnetic control actions take place with the approach to the control of fuel injection phase. In conventional systems, the pressurizing operation and the fuel injection quantity control are connected with each other through the interaction of the cam and the plunger of the fuel pump. This has the following impact on the characteristics of the fuel injection:

- Injection pressure increases with increasing speed and amount of air supplied to the engine;
- During the actual injection process, the injection pressure increases and then decreases until the final injection pressure.

As a result, we have the following consequences:

- Minimal amount of fuel is injected at a lower pressure than the amount of air entering the engine;
- Peak pressure is more than twice the average value of the injection pressure;
- As required for efficient combustion rate discharge curve actually is triangular.

Peak pressure is decisive for the mechanical elements of the load of the fuel pump and its drive. In conventional fuel injection systems it is crucial to the quality of mixture formation in the combustion chamber.

Rate discharge curve for a conventional fuel injection system

Characteristics injection system ?�Common Rail?� (common rail system)

Compared with conventional injection systems for ideal injection characteristics necessary to meet the following requirements:

- For each operating condition of the engine is necessary to split the node, creating pressure, and injection site;
- At the initial moment of injection of the fuel injection amount should be low as possible (ie, should be considered between the initial moment of inertia of the injection and the start of ignition).

These requirements are fulfilled by the injection system ?�Common Rail?� - common rail system - with its control and the main injection phase.

?�Common Rail?� is a block system and, in fact, these units are responsible for the characteristics of fuel injection:

- Injector with electromagnetic control, is screwed into the cylinder head;
- High-pressure accumulator (rail);
- High pressure fuel pump.

Curve rate relief for the fuel injection system ?�Common Rail?�

Also, for the operation of the system requires the following components:

- Electronic control unit ECU;
- Speed sensor crankshaft;
- The camshaft position sensor (encoder phase).

The cars used to create pressure radial piston high-pressure pump, and the pressure is generated independently of the fuel injection. Pump capacity is directly proportional to the frequency of rotation of the crankshaft of the engine. Compared with conventional systems the actual injection fuel injection is homogeneous, i.e. in the Common Rail fuel injection pump is not only smaller, but his drive is less exposed to peak loads.

The fuel injectors are connected to pipelines and short rail substantially include dispensers and solenoid valve controlled by ECU. After the termination of the supply voltage on the solenoid valve fuel injection is terminated. Assuming constant pressure, the fuel injection amount is directly proportional to the length of time during which the solenoid valve is open. This process is entirely independent of the engine speed of the engine and pump speed (fuel injection depending on the time).

High speed switching solenoid achieved through the use of high voltage and current. This means that it is necessary to use a specially designed solenoidal valve that provides a site in the opening. The moment of injection is determined by the control system EDC (Electronic Diesel Control - Electronically controlled diesel engine) which uses the speed sensor crankshaft and camshaft position sensor for determining the phase of the working cycle.