Common Rail Fuel Supply System

The system known in English as Common Rail, or common fuel supply line system, is a type of fuel injection system used in modern diesel vehicles. Although some manufacturers had previously used systems with similar basic features, it was in 1997 that Robert Bosch GmbH, in collaboration with Mercedes-Benz, adapted this system for automobiles, making it efficient and suitable for new generation diesel vehicles through complete injection.

^{Common rail system on engine}

Diesel engines are currently the most widely used internal combustion systems. They typically use diesel fuel and offer higher efficiency and lower fuel consumption compared to gasoline engines. The principle of operation involves the sudden ignition of diesel fuel that has been compressed with air inside the cylinders. This combustion pushes the pistons, generating the engine’s power. However, if this process is not properly managed, diesel consumption may increase and performance may decline. Therefore, fuel injection systems are crucial for enhancing diesel engine performance and reducing emissions.

Fuel injection systems consist of components that ensure the correct amount of fuel is injected into the cylinders at the precise moment. These systems can take various forms, including mechanical pump systems, electronic control systems, common-rail systems, and pump-nozzle systems such as.

Injection pump units used in older diesel engines were more complex in structure and more detailed in function due to the number of components involved. However, their performance levels were significantly lower compared to today’s new generation diesel engines.

In recent years, heightened focus on environmental protection and emission reduction targets has further increased pressure on fuel injection systems. As a result, these systems are continuously being improved to achieve even lower emission levels.

^{Common rail system on engine}

Expectations from diesel fuel systems have steadily increased over time. Higher injection pressures, faster response times, and variable injection rate curves tailored to engine operating conditions have made diesel engines more economical, environmentally friendly, and powerful. As a result, diesel engines have even entered the premium sports sedan segment. Today, the common hat system is the most widely used fuel injection system in high-speed, direct-injection modern automobile engines.

The Common Rail (CR) system is a diesel fuel injection system. It has been clearly demonstrated to be superior to previous systems of its kind in terms of fuel consumption, exhaust gas emissions, operational performance, and noise generation. The Common Rail system distributes fuel to the injectors through a common rail pipe at pressures up to 2000 bar. The electronic control unit (ECU) adjusts this high pressure according to engine speed and load.

The feed pump’s function is to supply fuel regularly to the high-pressure pump. As in other injection systems, the low-pressure feed stage forms the first phase of the Common Rail system.

The high-pressure pump is a rotary pump driven by a timing belt. It contains an internal feed pump (5 bar) to draw fuel from the tank. The maximum injection pressure is 2000 bar. Unlike older diesel engine pumps, this pump does not perform the functions of “fuel metering and injection timing.”

The function of the pressure regulator (pressure control valve) is to maintain the high-pressure fuel circulation in the rail at the desired levels, as controlled by the ECU according to engine operating conditions fixed.

The fuel rail, also known as the high-pressure fuel distribution pipe or simply rail, delivers pressurized fuel to the injectors via high-pressure lines. The fuel rail (rail) dampens pressure fluctuations caused by the three pump strokes and the opening of injectors during each pump revolution reason.

Injectors are supplied with fuel from the injection rail via high-pressure lines. The number and position of the orifices vary depending on the system. Lubrication of moving parts is performed using diesel fuel. The key difference between conventional diesel injectors and Common Rail injectors is that Common Rail injectors do not open due to fuel pressure alone. Common Rail injectors are electronically actuated by the ECU, enabling complete control over the timing and quantity of injection. Additionally, the system enables multi-stage injection, including pilot or pre-injection. Electromagnetically controlled injectors designed for Common Rail systems feature high precision and extremely tight tolerance limits.

In the engine management system, all information required for controlling the drivetrain is processed. Sensors collect data on the engine’s current operating conditions. The engine control unit adjusts injector operation based on this data and driving conditions. Sensors convert various physical parameters such as fuel temperature, engine speed, or load into electrical electricity signals. The most critical sensors for the Common Rail injection system are the engine speed sensor, fuel temperature sensor, rail pressure sensor, intake manifold pressure sensor, and camshaft position sensor for the first cylinder location.

In the Common Rail injection system, efficiency reaches approximately 45 percent, which is a very high value.

Since fuel is injected gradually into the combustion chamber (via pilot injection), Common Rail engines operate with less vibration and lower noise levels.

The Common Rail system is precisely controlled by an electronic control unit. In the event of a fault, the system can perform self-diagnosis (on-board diagnostic) and trigger a driver warning light.

The Common Rail system, with fewer components and a simpler structure, reduces the likelihood of failure. Combined with turbocharging, it enables the generation of very high engine power and torque. Thanks to the system’s high efficiency, fuel consumption is reduced. Exhaust emissions are lower, and fewer harmful gases are released due to higher combustion efficiency.

Maintenance and repair costs are high, spare parts are expensive, component repair is difficult, and many parts cannot be repaired—only replaced by authorized service centers. In case of failure, components are replaced with new ones.