Apart from the very high pressures which common rail equipment can generate, it removes the injection noises by means of an adjustable, constant high pressure in the injection pipes of the equipment. The full pressure is available right from the word go. Injection pressure and injection time can be freely selected, and independent of each other by the control device.
Through short pre-injecting of approx. 0.4 milliseconds in the partial load area, the rise in temperature (nitrogen oxide emission) and the maximum pressure are reduced, also a particular air movement in the cylinder is supported. The more the main injection is divided, the more the hardness of the combustion and thus the combustion noise, decreases. This is valid to an increasing degree for newer equipment in which the injection amount is split (only with the passenger car) in up to five subsets. In this case, the injections occurring after the main amount are responsible for an improvement of the exhaust gases through better oxidation in the cylinder and higher temperature in the exhaust gas system. At the same time the injection pressure rises, at present, (2005) up to 2000 bar.

The English expression 'common rail' refers to the common high-pressure injection pipe (figure 3) which supplies all cylinders and above all, also serves as a pressure accumulator. The fuel for the 'rail' is supplied by the high-pressure pump which is mechanically driven by the engine , a smaller fuel pump brings the fuel through the pre- heating equipment and the filter, to the high-pressure pump (figure 4). This is also driven either by the engine or electrically.

The high pressure reduces the engine power and lowers the efficiency. When unnecessary for certain operational areas, it is reduced. Under driving conditions, for example, the overrun cut-off, it can be also switched off completely. The high-pressure injection pipes, ideally all the same length, connect the injectors to all the cylinders (figure 5). The pressure accumulator can also be spherical in shape. It is important that the pressure, when injecting to one cylinder, does not drop for the others. The pressure regulating valve (on the right of the rail in figure 1) allows excessive fuel to flow through the cooler back into the tank. The pressure in the high-pressure pipe is regulated by a pressure sensor control device on the left of the rail.