DEUTZ Diesel Engine: Do you really understand the common rail system of DEUTZ diesel engine?

Fuel transfer pump

The fuel transfer pump is a gear pump, driven by a belt. Integrated in the pump is a pressure relief valve, whose function is to maintain the correct pressure in the fuel system, e.g. if the fuel filter is clogged, and a non-return valve for venting air. The pressure relief valve and non-return valve are not replaceable

FCU

The fuel control unit (FCU) is located between the high-pressure fuel pumps. Its task is to supply the high-pressure fuel pump with the required amount of fuel in order to achieve or maintain the correct pressure in the rail. The fuel quantity is regulated by a PWM-controlled solenoid valve located on the fuel distributor.

Fuel control unit (FCU)

The fuel control unit controls the fuel flow to the high-pressure fuel pump. It distributes the amount of fuel required to achieve or maintain the rail pressure.

A. Overflow valve

B. Fuel inlet

C. Fuel to high pressure fuel pump

D. Fuel return to tank

E. Solenoid valve

Fuel control unit (FCU)

- No fuel delivery at 100% duty cycle PWM

- Full fuel delivery at 0% duty cycle PWM

High pressure fuel pump

· Three cam lobes bring six pumping processes per camshaft revolution (each pump completes three pumping processes).

· Via high pressure fuel pipe to injector

· I/O valve (integrated)

· From fuel quantity control valve

I/O valve

The function is to isolate the pressure on the high pressure side of the pumping phase.

Pumping of the pump is only possible at a minimum pressure of about 1.7 bar. The I/O valve and pump plunger have C2 coating to better withstand wear resistance when the fuel quality is poor. In actual maintenance, the failure of the high pressure pump to reduce pressure is often encountered, which is caused by I/0 jamming.

The I/O valve is very sensitive to dust particles!

Rail

The high-pressure accumulator with the distribution pipe is also called the "rail". It is made of forged steel and generally has an internal volume of 35cm3 and an internal diameter of 10mm.

The stored oil volume is calibrated and buffers pressure changes caused by:

- Fuel pump supply pulses from the high-pressure fuel pump

- Short-term and large-scale fuel output through the injectors during injection

The capacity of the pressure working chamber (rail) must be optimized, because a larger oil volume can better buffer pressure pulses, which means that the control time for changing the pressure in the working chamber will be longer. The rail is sized to provide the full amount of fuel without significant pressure fluctuations.

The rail is equipped with a pressure sensor and a pressure limiting valve.

Rail pressure sensor

Responsible for monitoring pressure changes in the rail and feeding back to the EMR in real time.

If a corresponding fault occurs, the EMR forces the PRV to open by increasing the rail pressure.

The closed control loop of the injection pressure adjustment is a feature of a CR system. The rail pressure sensor measures the pressure in the rail and sends the data to the EMR, which compares the actual pressure with a reference value that depends on the engine speed and the amount of fuel injected.

A valve (PRV) mounted on the rail limits the system pressure to avoid system damage.

Rail pressure limiting valve

The pressure limiting valve is a mechanical safety component that opens at 1950 (-100) bar and protects the system from overpressure damage caused by a possible fault.

If the valve opens, the rail pressure is maintained between 650 and 850 bar (depending on engine speed and load). The engine continues to run, but with reduced performance (limp home).

Under normal operating conditions, the pressure limiting valve (PRV) does not open.

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