COMMON RAIL DIRECT INJECTION

COMMON RAIL DIRECT INJECTION

INTRODUCTION:

Today we are seeing an increasing number of passenger cars powered with high speed direct injection diesel engine. This is primarily due to clear advantage of the direct injection combustion process in terms of fuel economy and power density compared to indirect injection concept. The increase in the application of this technology to passenger cars, and the implementation of low emission regulation raise the requirement for more flexible and fully electronic controlled high pressure fuel injection equipment. The common rail has been identified by the automatic market as an attractive injection system for future diesel passenger cars. This injection system operates at very high pressure with a flexible electronic control of fuel delivery, injection timing, injection strategy as shown in fig no1. By controlling these parameters, the common rail is capable of achieving a level of performance and driving comfort for diesel cars similar to that of gasoline powered models with significant fuel economy and low exhaust emission.
The common rail has the potential to achieve a very high pressure capability throughout the whole speed range with pilot and post injections respectively for noise reduction and DeNOx catalyst efficiency improvement. The common rail system (figure1), which has been designed for modern passenger cars and other application.
Common rail direct injection used in S320 CDI and S400 CDI, Mercedes-Benz has achieved an ideal compromise between economy, torque, ride comfort and long life. Whereas conventional direct injection diesel engine must repeatedly generate fuel Pressure for each injection in the common rail engine the pressure is built up independently of the injection sequence and remains permanently available in fuel line.
The common rail upstream of the cylinder acts as an accumulator, the fuel to the injector at a contact pressure of up to 1600bar.Here high speed solenoid valve is regulated by the electronic engine management, separately control the injection timing and the amount of fuel injected for each cylinder as a function of the cylinder’s actual need. In other words, pressure generation and fuel injection are independent of each other. This is an important advantage of common rail injection over conventional fuel injection system.


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