Common Rail is a modern electronically controlled fuel injection system used in diesel engines. Unlike older mechanical or semi-electronic systems, where pressure was created separately in front of each injector, here the fuel accumulates in a common rail under stable high pressure. The injectors receive fuel in metered doses on command from the electronics, which increases the accuracy of the supply and the efficiency of the engine. The idea of the system appeared in the 1980s, but it became widespread by the end of the 1990s due to the development of reliable electronics and materials. Today, Common Rail is the standard for modern diesels.
The system consists of several key components. A low-pressure pump supplies fuel from the tank to the filter, which removes water and contaminants. A high-pressure pump (HPFP) compresses the fuel to 1000-2500 bar and sends it to the common rail. A pressure sensor monitors the current state, and a regulator adjusts the pressure in real time. The injectors inject fuel into the cylinders with an accuracy of up to a milligram, and an electronic control unit controls the entire system.
The main difference between Common Rail and classic systems is the constant high pressure in the common rail. The fuel first passes through filters and pumps, then accumulates in the rail, after which the injectors receive a dose on a signal from the ECU. Sometimes several injections occur during one working cycle, which improves combustion, reduces noise and emissions. Excess fuel is returned to the tank via a return line.
The advantages of the system are obvious: high injection accuracy increases power and reduces consumption, flexible control allows multiple injections per cycle, noise and vibration are reduced, cold start is improved and emissions of harmful substances are reduced. The disadvantages are related to the high cost of components, sensitivity to fuel quality, complexity of repair and dependence on electronics.
Typical Common Rail malfunctions are most often related to fuel: wear or failure of the HPFP, jammed injectors, problems with sensors and pressure regulators, air leaks or clogged filters. Symptoms include loss of power, uneven engine operation, smoke, jerks and difficult starting. Due to the complexity of the system, accurate diagnostics are only possible with specialized equipment.
In practice, Common Rail differs from a classic diesel in that pressure is created in advance in a common rail, and not by each injector before injection. Marketing designations, such as TDI for VAG, may hide any technical implementation, but modern TDIs use Common Rail. The system is critical to fuel quality - microscopic contaminants can quickly disable injectors and HPFP.
The advantages of Common Rail make it preferable for modern heavy-duty diesels, providing fuel economy, high efficiency, comfort and compliance with environmental standards. However, the cost of repair and replacement of components is higher, and operation requires fuel control and regular diagnostics.
Today, the Common Rail system is used in almost all new diesels. It provides multiple accurate injections, stable pressure and long engine life, remaining the standard for modern diesel vehicles.