Diesel direct injection with common rail system (JTD)

Fuel is delivered from the electric fuel pump to the high-pressure pump at a pressure of 5 bar. The high-pressure pump builds up a constant high pressure of up to 1350 bar, even at low engine speeds.

A common fuel line (common rail) runs from the high-pressure pump to the individual cylinders. The common fuel line acts as a pressure accumulator and distributes the fuel at constant pressure to the injectors.

The engine control module precisely meters the required fuel injection quantity to the individual cylinders via the electromagnetic injectors. For example, if the microcomputer of the engine control module closes the solenoid valves, fuel injection stops immediately.

In other words, pressure generation and fuel injection take place independently of each other. This has the advantage that injection can be optimized for demand and emissions, and can take place independently of engine speed.

Fuel is injected directly into the combustion chamber in two stages using multi-hole injectors. First, a small quantity of fuel is pre-injected, which improves the ignition conditions for the main fuel quantity. This results in a softer and therefore quieter combustion.

Note: Due to the good cold-start properties of the direct-injection diesel engine, glow-plug preheating is generally only required at temperatures below approx. 0 °C.