Common Rail Direct Injection System | Diagram , Advantages and Disadvantages

Common Rail Direct Injection System (CRDI)

Generally, diesel engines have the specific advantage of good fuel efficiency and low CO2 emissions. Therefore, various new technologies have been developed in order to reduce harmful emissions. One of such technologies is called Common Rail Direct Injection (CRDI) system of direct fuel injection. In this system, commencement of combustion takes place directly into the main combustion chamber located in a cavity on the top of the piston crown.
This system injects diesel five times more accurately than the normal injection system by high response injectors with electronic control. It results the greater reduction of particulate matter and NOx thereby improving the fuel efficiency and increasing its torque. So, they lead to reduce engine noise and vibration.

Various components of CRDI System are:

High Pressure Fuel Pump
Common Fuel Rail
Injectors
Engine Control Unit

A common rail system consists of pressure accumulator called common rail (or in simple words, a fuel distribution pipe) which is mounted along the engine block. The rail is fed by a high pressure multi-cylinder fuel pump. .The injectors are activated by solenoid valves. Both the solenoid valves and fuel pump are electronically controlled.

In the common rail injection system, the injection pressure does not depend on engine speed and load. So, the control of injection parameters is easy. Usually, a pilot injection is introduced in order to reduce engine noise and NOx emissions. The injectors use a needle-and seat- type valve to control the fuel flow. The fuel pressure is fed to both top and bottom of the needle valve. The pressure on the bottom will push the needle off its seat by bleeding some of the pressure off the top. Thus, the fuel will flow through nozzle holes.

Advantages:

(i) It delivers 25 % more power and torque than the normal direct injection engine.
(ii) Initial cost is low.
(iii) Superior pick up is possible.
(iv) It maintains lower levels of noise and vibration.
(v) Higher mileage is obtained.
(vi) Emissions are low.
(vii) Fuel consumption is less.
(viii) Improved performance is obtained.

Disadvantages:

(i) Many parts involve the complicated design.
(ii) Production cost is high.
(iii) High degree of engine maintenance is required.