Common Rail Direct Injection

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CRDi stands for Common Rail Direct Injection meaning, direct injection of the fuel into the cylinders of a diesel engine via a single, common line, called the common rail which is connected to all the fuel injectors.

Whereas ordinary diesel direct fuel-injection systems have to build up pressure anew for each and every injection cycle, the new common rail (line) engines maintain constant pressure regardless of the injection sequence. This pressure then remains permanently available throughout the fuel line. The engine's electronic timing regulates injection pressure according to engine speed and load. The electronic control unit (ECU) modifies injection pressure precisely and as needed, based on data obtained from sensors on the cam and crankshafts. In other words, compression and injection occur independently of each other. This technique allows fuel to be injected as needed, saving fuel and lowering emissions.

More accurately measured and timed mixture spray in the combustion chamber significantly reducing unburned fuel gives CRDi the potential to meet future emission guidelines such as Euro V. CRDi engines are now being used in almost all Mercedes-Benz, Toyota, Hyundai, Ford and many other diesel automobiles.


Gasoline or petrol engines were using carburetors for supply of air-fuel mixture before the introduction of MPFI system .but even now carburetors are in use for its simplicity and low cost. Now a day the new technology named Gasoline Direct Injection (GDI) is in use for petrol engines. The GDI is using the principle of CRDi system. Now let us examine the various factors that lead to introduction of GDI technology.

The fall of carburetor

For most of the existence of the internal combustion engine, the carburetor has been the device that supplied fuel to the engine. On many other machines, such as lawnmowers and chainsaws, it still is. But as the automobile evolved, the carburetor got more and more complicated trying to handle all of the operating requirements. For instance, to handle some of these tasks, carburetors had five different circuits:

Main circuit Provides just enough fuel for fuel-efficient cruising

Idle circuit Provides just enough fuel to keep the engine idling

Accelerator pump Provides an extra burst of fuel when the accelerator pedal is

first depressed, reducing hesitation before the engine speeds


Power enrichment Provides extra fuel when the car is going up a hill or

Circuit towing a trailer

Choke Provides extra fuel when the engine is cold so that it will

start effortlessly

In order to meet stricter emissions requirements, catalytic converters were introduced. Very careful control of the air-to-fuel ratio was required for the catalytic converter to be effective. Oxygen sensors monitor the amount of oxygen in the exhaust, and the engine control unit (ECU) uses this information to adjust the air-to-fuel ratio in real-time. This is called closed loop control—it was not feasible to achieve this control with carburetors. There was a brief period of electrically controlled carburetors before fuel injection systems took over, but these electrical carburetors were even more complicated than the purely mechanical ones.

At first, carburetors were replaced with throttle body fuel injection systems (also known as single point or central fuel injection systems) that incorporated electrically controlled fuel-injector valves into the throttle body. These were almost a bolt-in replacement for the carburetor, so the automakers didn't have to make any drastic changes to their engine designs.

Gradually, as...
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