Common Rail - what is it? Principle of operation

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

Characteristic

Common Rail is a fuel injection system for diesel engines. Its principle of operation is based on the supply of fuel to the injectors of the total ramp pressure.

The system was developed by German specialists of the company "Bosch". Bosch Common Rail is commonly used on cars such as Volvo, Mercedes, BMW and others.

What is special about it?

The main feature of the system is the abilityto deliver the desired power with a minimum fuel consumption. Also, fuel Common Rail can reduce the level of toxicity of exhaust gases. Reviews of motorists say that a car with such an injection system is much quieter (there is no such characteristic “rumble” as on older diesel engines). Common Rail has a wide range of fuel pressure control and injection start points.

Device

By design, the common rail systemis a high pressure circuit. When the engine is running, the fuel is directly injected (that is, the fuel enters directly into the cylinder chamber). There are several elements that are associated with the operation of the Common Rail system. What are these ingredients? First of all it is a high pressure fuel pump. Also in work the valve of dispensing and pressure regulator is used.

In addition, the design has a fuel rail and injectors. Common Rail is a rather complicated system, and in order to understand its working principle, we will consider the features of each component.

Pump

So, the fuel pump.This mechanism serves to create a high pressure fluid. The level depends on the engine load and crankshaft speed. As is known, on diesel engines, the speed is not regulated by the opening of the throttle valve, namely, a portion of the supplied fuel. The fuel pump is responsible for this. The device is quite complicated, so this element is the most expensive component in a diesel car (of course, with the exception of basic units, such as the engine and gearbox).

Common Rail Regulator and Valve

What is this item? The valve is used to adjust the amount of fuel that is supplied to the pump.

Structurally, the element is combined with the pump. There is also a fuel pressure regulator. It is installed in the fuel rail and controls the operation of the engine depending on its load.

Ramp

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

Nozzles

Стоит отметить, что таковые устанавливаются как on petrol (injector), and on 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 into the cylinder. The element is directly linked to the ramp. At the moment, two types of nozzles are used:

• Piezoforsunki ("Bosch").
• Electro-hydraulic (the main manufacturer is Delphi).

In the latter case, the fuel supply is due to the operation of the solenoid valve.

In the piezoforsunks, special ones are responsible for this.crystals. The speed of such elements is much higher, so they are more common. However, repair Common Rail (nozzles) to make their own hands is impossible because of the complexity of the design and precise settings. Therefore, all system maintenance work is carried out only at 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 system.diesel control. The latter includes actuators, sensors and ECUs. 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, they are the above-mentioned nozzles, ramp, injection pump, regulator and valves.

So how does this system work?Based on the signals that the monitoring sensors perceive, the system forms the necessary amount of fuel. It is fed through the metering valve. Fuel will enter the pump and then pressurized to the ramp. The required pressure in it is held by a special regulator. At a certain point, the ECU receives a signal at the injectors, and they carry out the opening of 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 data from the oxygen sensor. However, the run should be small. Significant deviations indicate faults with the Common Rail system.

Common Rail Injection Types

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

• Preliminary.
• Main.
• Additional.

The first is made before the main purpose.increase the pressure and temperature in the combustion chamber. This accelerates the self-ignition of the main charge and reduces the noise of the engine. Pre-injection may be different, depending on the mode of operation of the engine. So, at idle it is made twice. With increasing load - once. At full load, pre-injection is not carried out.

Цель основного впрыска – обеспечить directly work the engine. It is not divided into subtypes. Additional injection serves to reduce the level of toxicity of exhaust gases. Thus, information from the oxygen sensor is fed to the ECU, after which another portion of the fuel is supplied. Harmful substances are burned in the catalytic converter (also called a particulate filter).

Generations "Common Rail"

It is worth noting that the first generation systemappeared in 1999 year. She gave a pressure of 145 MPa. Two years later, the next generation of the system appeared (160 MPa). Common Rail 3 was developed in 2005. At the moment, cars are equipped with a system of Common Rail, the fourth generation. The nozzles operate at a pressure of 220 MPa. Why is this focus on pressure? The higher this figure, 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 system isdirect injection, how it works and how it works. It is worth noting that Common Rail is used on most diesel cars, in particular, of European production. The system, despite its complexity, has great potential.