What Is Common Rail Construction?

Common rail is a fuel injection system found in modern diesel engines. Common rail systems provide a level of flexibility which can be exploited for class leading emission control, power and fuel consumption.

Pressure relief valve for common rail fuel system

Pressure limiting valve of common rail on engine fuel system made by Henshine

The pressure relief valve for a common rail fuel system consists of a hard ceramic ball valve element that engages and disengages the conical seat of the soft metal body. Fretting damage to the valve is suppressed by the use of dissimilar materials and the use of guide pins that allow movement on the spherical surface of the ceramic spherical valve member. The valve member may be composed of silicon nitride.

Outline

Rails in the part number series 095440-049# have a flow damper to suppress fuel pulsations.

Since rails in the part number series 095440-098# have a built-in function to suppress fuel pulsations, there is no flow damper.

Composition of a DENSO Common Rail 095440-049# on November 2003

March 2007, and June 2009 (Rail: 095440-098#)

The 2AD-FHV rail has been changed from a non-DENSO product to a DENSO-made rail.

Henshine PRV 095420-0670 used on Denso Common Rail

Pressure Discharge Valve used on Denso Common Rail 0620

Pressure Limiter 23280-E0020 shown the function in the Fuel Supply System of Denso N04C

Common rail systems use an accumulator chamber called a fuel rail to store pressurized fuel and inject the pressurized fuel into the combustion chamber using injectors that contain electronically controlled solenoid valves. The injection system (injection pressure, injection rate and injection timing) is controlled by the engine control module (ECM), so the common rail system can be controlled independently, independent of engine speed and load. This ensures stable injection pressure time, especially in the low engine speed range, and thus significantly reduces the black smoke characteristic of diesel engines during vehicle start-up or acceleration. As a result, exhaust emissions are clear and reduced, enabling higher output.

1. High pressure control

  High pressure injection from low engine speed range. Optimized control to reduce particulates and nitrogen oxide emissions.

2. Fuel injection timing control

Fine-tuned control can be fine-tuned as needed and operating conditions.

3. Injection rate control

Perform a small amount of pilot injection control Inject before main injection.

FUEL RAIL (COMMON RAIL) N40C Engine

1. Fuel Rail Bracket

2. Fuel Common Rail

3. Flow Damper

4. Pressure Limiter

5. Fuel Rail Pressure Sensor

6. High Pressure Fuel Inlet

7. To Fuel Tank

8. To Injectors

Pressure Limiter Construction

[1] Construction

The function of the rail is to distribute the high-pressure fuel pressurized by the supply pump to each cylinder injector. The rail pressure sensor, flow damper, and pressure limiter are mounted on the rail. A fuel injection pipe is attached to the flow damper to deliver high-pressure fuel to the injector. The pressure limiter piping is routed back to the fuel tank.

[2] Pressure Limiter

The function of the pressure limiter is to dispel abnormally high pressure by opening its valve to release pressure. The pressure limiter operates (opens the valve) when rail pressure reaches approximately 140MPa.

Then, when the pressure decreases to approximately 30MPa, the pressure limiter resumes (closes the valve) its function to maintain pressure.

Operation of the Pressure Limiter Valve

1. From Fuel Rail

2. Valve

3. Valve Body

4. Valve Guide

5. Spring

6. Housing

7. To Fuel Return Pipe

The pressure limiter valve relieves pressure by opening the valve (2) if abnormally high pressure is generated. The valve (2) opens when pressure in rail reaches approximately 200MPa (29000psi), and close when pressure falls to approximately 50MPa (7250psi). Fuel leaked by the pressure limiter valve re-turns to the fuel tank through the return line.

FUEL RAIL PRESSURE (FRP) SENSOR

The fuel rail pressure (FRP) sensor is installed in fuel rail, which detects fuel pressure in the fuel rail, convert pressure to voltage signal and send signals from the Engine Control Module (ECM). This ECM supplies 5 volts to the FRP sensor on 5 volts reference circuit. The ECM also provides a ground low circuit. Higher fuel pressure provides higher FRP sensor voltage, while lower pressures provide lower FRP sensor voltage. ECM calculates actual fuel rail pressure from the voltage signal (fuel pressure) and use the results for fuel injection control tasks. The characteristics of the FRP sensor are shown in Charts and tables. The output voltage can be found on Technology 2.

NOTE:

Do not attempt to remove or to reinstall the flow damper, pressure limiter, or rail pressure sensor.

If the pressure limiter valve is operated many times, opening pressure has fallen and it may cause fuel system DTCs set.

The fuel rail pressure display in the Tech 2 is difference pressure (actual value – desired value). This data display will be fixed to 0 MPa (0psi) when DTC is set relating to the FRP sensor open or short circuit. To diagnose this DTC, observe the “Volts” in the data display.

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