Automobile

Understanding Common Rail Direct Injection System

Modern diesel engines use a common rail fuel injection system. Common rail systems offer a level of flexibility that can be used to achieve best-in-class emission control, power, and fuel efficiency. Original Equipment Manufacturers (OEMs) may now design for maximum performance and end-user value across a broad range of machines and applications.

For the flexibility they enable while satisfying the most strict pollution control standards, a growing number of modern diesel engines use common rail direct injection (CRDi) fuel systems. Fuel is delivered to the engine under pressure and electronically controlled precision in common rail systems. This gives a level of flexibility that can be used to achieve best-in-class emissions control, power, and fuel consumption.

In this article, you’ll learn the definition, functions, components, diagram, working, advantages, and disadvantages of a common rail direct injection system.

common rail direct injection system

Read more: Understanding diesel engine

What is a common rail direct injection?

Diesel engines, in general, offer the distinct advantage of high fuel efficiency and low CO2 emissions. As a result, a number of new technologies have been created to limit harmful emissions. The Common Rail Direct Injection (CRDI) system of direct fuel injection is one of these technologies. In this design, combustion begins in the main combustion chamber, which is positioned in a cavity on the top of the piston crown.
This system uses high-response injectors with electronic control to inject diesel five times more precise than a standard injection system. As a result, there is a larger decrease in particulate matter and NOx, which improves fuel efficiency and torque. As a result, engine noise and vibration are reduced.

In 1997, Bosch introduced the first common rail system. The system gets its name from the common high-pressure reservoir (common rail) that supplies gasoline to all of the cylinders. Fuel pressure must be generated individually for each injection in traditional diesel injection systems. The common rail system, on the other hand, separates pressure generation and injection, ensuring that the fuel is always accessible at the proper pressure for injection.

Applications

The common rail system is appropriate for all sorts of diesel-powered road vehicles, from city cars (such as the Fiat Panda) to executive vehicles (such as the Audi A8). BOSCH, Delphi, Denso, and Siemens VDO are the leading manufacturers of current common rail systems (now owned by Continental AG).

Functions

The followings are the major functions of a common rail direct injection system in its various applications:

Fuel Feeding:

The injection pump body contains pump parts such as the cylinder and plunger. When the cam lifts the plunger, the fuel is squeezed to high pressure and transferred to the injector.

Adjustment of fuel quantity:

Regardless of the spinning speed or load, the intake of air in diesel engines is nearly constant. The output and fuel consumption fluctuates when the injection quantity changes with the engine speed while the injection timing remains constant. The accelerator pedal is used to modify the engine output, which is almost proportionate to the injection quantity.

Injection adjustment timing:

The interval between when the fuel is injected, ignited and combusted and when maximum combustion pressure is reached is known as the ignition delay. Because this time period is nearly consistent regardless of engine speed, a timer is utilized to adjust and modify injection timing, allowing for optimal combustion.

Atomizing fuel:

Fuel is thoroughly mixed with air when it is pressurized by the injection pump and then atomized from the injection nozzle, which improves ignition. The end consequence is total combustibility.

Read more: Understanding two-stroke diesel and gasoline engines

Components of a common rail direct injection

The major components of a common rail direct injection system include:

  • Fuel injection pump – pressurizes fuel to high pressure
  • High-pressure pipe – sends fuel to the injection nozzle
  • Injection nozzle – injects the fuel into the cylinder
  • Feed pump – sucks fuel from the fuel tank
  • Fuel filter – filtrates the fuel
  • Engine control unit

Diagram of a CRDi

Common-Rail-Direct-Injection-System

Working Principle

The working of a common rail direct injection system CRDi is less complex and can be easily understood. A common rail system is made up of a pressure accumulator (or, to put it another way, a gasoline distribution pipe) positioned along the engine block. A high-pressure multi-cylinder fuel pump supplies the rail. Solenoid valves are used to turn on the injectors. Both the solenoid valves and the fuel pump are controlled electronically.

The injection pressure in a common rail injection system is independent of engine speed and load. As a result, controlling injection parameters is simple. In order to reduce engine noise and NOx emissions, a pilot injection is usually used. The fuel flow is controlled by a needle-and-seat type valve in the injectors. Both the top and bottom of the needle valve are provided with fuel pressure. By bleeding some of the pressure off the top, the pressure on the bottom will drive the needle out of its seat. The fuel will then pour through the nozzle openings.

Read more: Understanding fuel injection system in automobile engines

Watch the video below to learn more about how a common rail direct injection system works:

Advantages and disadvantages of a common rail direct injection system

Advantages:

The following are the benefits of a CRDi in its various applications:

  • It produces 25% more power and torque than a conventional direct-injection engine.
  • The initial investment is minimal.
  • It is possible to get a better pick up.
  • It keeps noise and vibration to a minimum.
  • It is possible to get more mileage.
  • Emissions are minimal.
  • The amount of fuel consumed is reduced.
  • It is possible to achieve better results.

Disadvantages:

Despite the good advantages of the CRDi system, some limitations still occur. Below are the disadvantages of a common rail direct injection in its various applications:

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  • Expensive Vehicle
  • Expensive parts
  • Maintenance cost is high
  • Complicated design due to many parts

Read more: Understanding an indirect injection system

Conclusion

Common rail systems offer a level of flexibility that can be used to achieve best-in-class emission control, power, and fuel efficiency. Original Equipment Manufacturers (OEMs) may now design for maximum performance and end-user value across a broad range of machines and applications. That is all for this article, where the definition, applications, functions, components, diagram, working, advantages, and disadvantages of a common rail direct injection are been explained.

I hope you learn a lot from the reading, if so, kindly share with other students. Thanks for reading, see you around!