Exam Question

(a) The common rail is a manifold running the length of the engine at just below the cylinder cover. The high pressure fuel supply unit has number of high pressure pumps running on multi-lobe cams. Fuel is delivered from this common rail through a separate injection control unit for each cylinder to the fuel injection valves that are hydraulically operated by the high pressure fuel oil. The control units, using the quick-acting sulzer rail valves, regulate the timing of fuel injection, control the volume of fuel injected and set the shape injection pattern. Three fuel injectors in each cylinder cover are separately controlled so that they may be programmed to operate separately or in unison as necessary.
(b) Advantages of common rail fuel injection:
Smokeless operation: superior combustion performance with the common rail system is achieved by maintaining the fuel injection pressure at the optimum level at all engine speed range.
Reduced running costs: As engine settings are made electronically, the ‘as-new’ settings are retained so that engine performance such as fuel consumption does not deteriorate over time.