Common Rail - what is it? Principle of operation

In recent years, more and more motorists prefer to use diesel cars. Previously, such engines were installed only on commercial vehicles. However now they are actively used and on passenger cars, especially in the countries of Europe. Surely, each of us has heard of a system such as Common Rail. What this is and how it is arranged, we will consider in our article.

Characteristic

"Common Rile" is a fuel injection system for diesel engines. Its principle of operation is based on the supply of fuel to the injectors from the total pressure of the ramp. The system was developed by the German specialists of the company "Bosch". Common Rail Bosch is widely used on such cars as Volvo, Mercedes, BMW and others.

What is special about it?

The main distinguishing feature of the system is the ability to produce the right power with minimal fuel consumption. Also common rail fuel can reduce the level of toxicity of exhaust gases. Reviews of motorists say that a car with such an injection system works much quieter (there is no such characteristic "rumble" as on old diesel engines). "Common Rail" has a wide range of fuel pressure regulation and the timing of the injection.

Device

By its design, the Common Rail system is a high-pressure circuit. When the engine is running, direct fuel injection (i.e., the fuel flows directly into the cylinder chamber). There are several elements that are related to the operation of the Common Rail system. What are these components? First of all, this is a high-pressure fuel pump. The dispensing valve and the pressure regulator are also used in this work. In addition, the structure has a fuel rail and injectors. Common Rail is quite a complicated system, and to understand its principle of operation, we will consider the features of each component.

Pump

So, injection pump. This mechanism serves to create a high pressure fluid. The level depends on the engine load and the crankshaft speed. As you know, on diesel engines, the revolutions are regulated not by opening the throttle, but by the portion of the fuel supplied. For this, and meets injection pump. The device is quite complicated, so this element is the most expensive component in a diesel car (it's over, except for the main units, such as ICE and CAT).

Common Rail Control and Valve

What is this element? The valve serves to adjust the amount of fuel that is supplied to the pump. Structurally the element is integrated with the injection pump. There is also a fuel pressure regulator. It is mounted in the fuel rail and controls the operation of the engine depending on its load.

Ramp

This node performs several functions at once. This is the accumulation of fuel under high pressure, the mitigation of pressure fluctuations and the distribution of fuel along the nozzles. It is part of the intake system.

Injectors

It should be noted that these are installed both on petrol (injector) and diesel engines. However, their main difference is the pressure they create. In our case, the Common Rail injector also controls the amount of fuel that is fed directly to the cylinder. The element is connected directly to the ramp. At present two types of injectors are used:

• Piezo-fittings ("Bosch").
• Electrohydraulic (the main producer is Delfi).

In the latter case, fuel is supplied by the operation of a solenoid valve. In piezoelectric jets, special crystals are responsible for this. The speed of these elements is an order of magnitude higher, so they are more common. However, repair of Common Rail (injectors) is impossible to produce by oneself due to the complexity of the design and precise settings. Therefore, all work on the maintenance of the system is carried out only on specialized service stations. This is the main drawback of such cars.

How does it work?

The operation of the injection system is controlled by the diesel control system. The latter includes actuators, sensors and ECU. All parameters are taken into account - the position of the gas pedal, the temperature of the coolant, the amount of air supplied, and even the composition of the exhaust gases (lambda probe). As for the actuators, these are the above mentioned injectors, ramp, injection pump, regulator and valves. So, how does this system work? Based on the signals received by the monitoring sensors, the system generates the right amount of fuel. It is fed through a metering valve. Fuel will fall into the pump, and then under pressure goes to the ramp. The necessary pressure in it is held by a special regulator. At a certain moment, the signal from the computer comes to the injectors, and they open the channels for a certain period of time. Depending on the mode of operation of the engine, the amount of fuel and pressure can be automatically changed by the system based on the data from the oxygen sensor. However, the take-off should be small. Significant deviations indicate a malfunction with the Common Rail system.

Types of Common Rail Injection

What it is? There are several types of fuel injection in the system:

• Preliminary.
• Main.
• Additional.

The first is made before the main one in order to increase the pressure and temperature in the combustion chamber. Thus, the accelerated autoignition of the main charge and the reduction of engine noise are realized. The preliminary injection can be different, depending on the engine operating mode. So, at idle it is produced twice. With increasing the load - once. At full load, the pre-injection is not carried out. The purpose of the main injection is to provide the engine itself. It is not subdivided into subtypes. Additional injection serves to reduce the level of toxicity of exhaust gases. So, the information from the oxygen sensor is sent to the computer, after which another portion of fuel is fed. Harmful substances are burned in the catalytic converter (it is also called a particulate filter).

Generom Rail Generations

It is worth noting that the first generation of the system appeared in 1999 year. It produced a pressure of 145 MPa. Two years later, the next generation of the system (160 MPa) appeared. Common Rail 3 was developed in 2005 year. At the moment, cars are equipped with the Common Rail system of the fourth generation. The nozzles operate at a pressure of 220 MPa. Why such attention is given to pressure? The higher this index, the more fuel is injected into the cylinder. Accordingly, for a certain period of time more power is realized, the efficiency of the engine increases.

Conclusion

So, we found out what the direct injection system is, how it works and how it works. It should be noted that the Common Rail is used on most diesel cars, in particular, European production. The system, despite its complexity, has great potential.