contd..

low at low engine speeds which increase due to inertia effects at high speeds. It is therefore, difficult to obtain the required engine performance with low emissions throughout the engine speed range with inline fuel injection systems. Electronic unit injectors are better than the inline systems but the CRDI provides more flexibility as a constant injection pressure is maintained at all engine speeds. In the common rail systems, the injection timing and rate can be varied precisely depending upon the engine requirements.
As very high injection pressures are possible with electronically controlled CRDI, its benefits are available through out the engine speed range. Because of reduction in particulate emissions due to high injection pressures, higher EGR rates can be used at part loads to reduce NO_x emissions, which lead to a better NO_x-particulate trade off. With the common rail systems, injection rate shaping and pilot injection are also easier to implement.