Diesel common rail injection system

The Diesel Common Rail Injection System is a fuel injection system used in today's diesel engines. Although the Common Rail System technology has been around for a long time, due to the need for greater engine power with more environmentally friendly exhaust emissions, Common Rail has experienced significant developments to become the current trend of car technology with diesel engines.

The Common Rail System on a diesel engine can be similar to the Electronic Fuel injection System on a gasoline engine. The working principle is also the same, namely to inject fuel into the engine with electronic control.

It means diesel engines that use Common Rail System technology have also used the Engine Control Module (ECM), known as the engine computer, to regulate the fuel system.

I. Common rail system components

There are five main components in the diesel Common Rail System: ECM, Sensors, High-pressure supply pump, fuel rail, and Injectors. The following is an explanation of each component in the Common Rail System.

1. Engine Control Module (ECM)

The Engine Control Module on the Common Rail System functions to read data from sensors. Analyze all data from sensors, then instruct the actuators (e.g., injectors, Suction Control Valve, EGR, etc.) to work according to engine needs so that the output produced is always optimal and efficient.

2. Sensors

There are also many sensors in the Common Rail System, similar to the EFI system. Sensors function to detect and measure physical values that occur in the engine and then converted them into electrical values that the ECM will use as input data about the current conditions in the engine.

The following are common sensors in the Common Rail System

Camshaft Position Sensor
Crank Angle Position Sensor
Engine Coolant Temperature Sensor
Accelerator Pedal Sensor
Manifold Absolute Pressure Sensor
Barometric Pressure Sensor
Water Temperature Sensor
Oxygen Sensor
Fuel Temperature Sensor
Rail Pressure Sensor
Knock Sensor
etc.

3. High-Pressure Supply Pump

The High-Pressure Supply Pump on the Common Rail System raises or produces high-pressure fuel and supplies the engine through the Fuel Rail and Injectors.

A high-Pressure Supply Pump, in its working process, uses engine speed to generate fuel pressure. The resulting pressurized fuel is sent to the Fuel rail. A suction control valve (SCV) and a fuel temperature sensor (FT sensor) in the High-Pressure Supply Pump are installed.

4. Fuel Rail (Also know as Common Rail)

The Fuel Rail on the Common Rail System is a tube-shaped place that accommodates the high-pressure fuel that the Supply Pump has produced before the fuel flows to the injector to be injected into the engine.

In addition to storing fuel, this Fuel Rail also keeps fuel pressure high and constant according to engine needs. Therefore, there is usually a Fuel Pressure Limiter on this Fuel Rail, which functions to maintain that pressure.

The minimum pressure value to open the valve on this pressure limiter is above 220 MPa (32,000 psi). In contrast, if it is less than 50 MPa (7,250 psi), the valve will close by itself.

To read the fuel pressure in the Fuel Rail, the Fuel Rail is also installed with a Fuel Pressure Sensor sensor. That way, the ECM can easily read the pressure that occurs in the Fuel Rail.

5. Injectors

The injectors on the Common Rail System have a series of solenoids that are specifically designed so that the injectors can work to flow high-pressure fuel into the engine according to orders from the ECM. When the ECM provides electric current to the injectors, the valves will open, and pressurized fuel can be injected directly into the engine.

That way, the injector on the Common Rail System functions to spray high-pressure fuel into the engine combustion chamber. The injector is connected directly to the Fuel Rail via delivery pipes.

II. How the common rail system works

Look at the picture of the Common Rail System circuit below:

Here is the process and how it works on the common rail system

Fuel (diesel) from the fuel tank will be flowed to the Fuel Filter to be filtered
After being filtered, then fuel flows into the High-Pressure Supply Pump
In the High-Pressure Supply Pump, fuel is pumped and pressed into the Fuel Rail continuously to produce high pressure according to engine needs.
High-pressure fuel will also enter the injector and is already in a standby position, ready to be injected.
The ECM receives data from the sensor then analyzes and decides the injector to open by flowing electricity to the solenoid inside the injector.
When the injector is open, high-pressure fuel will be injected into the engine combustion chamber in the form of fog, then be burned by the engine so that the engine can work.

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III. Advantages of the common rail system

The Common Rail System offers improved fuel injection atomization that is even better than conventional systems. It will increase and make the combustion process perfect in the engine, and the effect will also increase engine power.
In addition to increasing engine power, the Common Rail System also provides more accurate engine work to reduce fuel consumption and make engine vibration smoother.
The next thing that we can obtain from using the Common Rail System in this diesel engine is a lower exhaust emission level and is environmentally friendly. It means that the Common Rail System can reduce air pollution so that it is always low.

IV. Disadvantages of the common rail system

The technology used in the Common Rail System is quite sophisticated, so the price of components for replacement and repair is quite high.
Common Rail System requires diesel fuel that is clean and of good quality. The use of bad diesel fuel can accelerate damage to the engine and its Common Rail system.
In terms of maintenance, engines with the Common Rail System are quite difficult to repair if carried out in public workshops, especially if the repairs have spread to the ECM and the electrical control system.