A fuel supply system in which two or more high-pressure pumps supply a common manifold or rail. Timing valves determine the timing and extent of fuel delivery to the cylinder injectors. The benefits of common rail technology are smokeless operation, lower, stable running speeds (down to about 10 rpm for 2-stroke engines) and reduced fuel consumption at part load.
With mechanical injection systems the fuel injection pressure is a function of engine speed and engine load. When the injection pressure drops at lower loads, the fuel droplets grow bigger and there is not enough time to complete combustion of these droplets. The result is the cloud of smoke. Common-rail injection technology offers the possibility to maintain high injection pressure all the way down to idling and to achieve “ no smoke at any load”.
The common rail is a manifold running along the length of the engine at just below the cylinder cover level. It provides a certain storage volume for the fuel oil, and has provision for damping pressure waves. Fuel is delivered from the common rail through a separate injection control unit for each engine cylinder to the standard fuel injection valves. The control units regulate the timing of fuel injection, control the volume of fuel injected, and set the shape of the injection pattern. The three fuel injection valves in each cylinder cover are separately controlled so that they may be programmed to operate separately or in unison as necessary.
A major seamark was passed on 18 September 2001 when the sea trials of the new 47,950dwt bulk carrier GYPSUM CENTENNIAL were successfully completed. The vessel is propelled by the world first low-speed diesel engine with common-rail fuel injection: the Wärtsilä Sulzer 6RT-flex58T-B developing 11,275 kW at 93 rev/min. This engine has no standard camshaft and its gear drive, fuel injection pumps, exhaust valve actuator pumps and reversing servomotors. It is equipped with a common-rail system for fuel injection and exhaust valve actuation, as well as full electronic control of these engine functions. The first commercial 4-stroke engine with common rail entered service in early 2001, with a Wärtsilä 9L46D on board a cruise vessel CARNIVAL SPIRIT.
