How Does Common Rail Direct Injection (CRDI) Work?


Do you know the first passenger car that employed CRDI technology?

It was Alfa Romeo 156. The CRDI technology was first developed in the 1960s by Robert Huber and was successfully adopted in automobiles by 1990s. It could deliver diesel at a pressure of 20,000 psi through the injectors. Read ahead to know what is a common rail direct injection system, its working and common rail direct injection system advantages.


Common Rail Direct Injection System

how does crdi work?


What Is a Common Rail Direct Injection System?

The Common Rail Direct Injection system is an intelligent technology where the highly pressurized fuel is supplied to injectors through a common rail. As the name indicates it is a direct injection system where the injectors spray fuel directly into the cylinders. CRDI technology is used in diesel engines, while we have MPFI technology for gasoline engines. In the traditional diesel injection system, fuel was pressurised for every injection cycle.  Whereas in the CRDI system, constant pressure was maintained in the common rail irrespective of the injection cycle. Let us understand the working of CRDI in detail.


Working of Common Rail Direct Injection System

The common rail direct injection system is a modular design that has a common rail, electronic fuel pump, fuel tank, fuel filter, ECU, injectors and sensors. The fuel from the 

fuel tank is fed into the filter and then to the fuel pump. A high-pressure pump pressurises the fuel. A pressure regulating valve is attached to the high-pressure pump which gets input from ECU. The ECU receives signals from the throttle position sensor, temperature sensor, speed sensor and manifold pressure sensor. The pressurized fuel from the pump is sent to a common rail, and it acts as a reservoir. From the rail, fuel enters the injectors and then into the cylinder. The common rail has a pressure sensor which gives a signal to the ECU. Also, there is a pressure relief valve in the common rail, which is used to release the excess pressure. When the fuel in the common rail exceeds the determined pressure, fuel is sent back to the fuel tank through a separate line. The injectors are controlled by the ECU to release the correct quantity of fuel at the right time into the cylinder. This is how a common rail direct injection system is working.

Understand the flow of fuel through the below-given flow chart:

flow of fuel flow chart - crdi working

Advantages of Common Rail Direct Injection System

The common rail direct injection system has many advantages when compared to conventional fuel injection systems. 

  • The CRDI system can inject a small amount of fuel even before the main injection. This could prevent sudden explosion and reduces noise and vibration.
  • Based on the requirements, the CRDI system could inject 5 times per engine stroke.
  • Since the fuel is injected at a high pressure better atomisation of fuel takes place, thus increasing the fuel efficiency.

In older times, the fuel injection system is mechanical, and it depends upon the cam mechanism. Thus, it was directly dependent on the engine speed. In this, the pressure was low at lower speeds, and this led to poor atomisation. This has resulted in bad combustion as the fuel and air are not mixed properly. Also, the number of injections and time of injection is fixed. In order to overcome these difficulties, Common Rail Direct Injection System was discovered. The common rail direct injection system working is entirely controlled by ECU. The number of injections and pressure were all under the control of the ECU. Hence common rail direct injection is advantageous over the conventional fuel injection system for diesel engines. The Hyundai Aura, which is one of the best fuel-efficient diesel cars, employs CRDI technology. Thus CRDI is a proven technology fuel-efficient system.


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