Sulzer RT-flex. Injection control unit
Fuel is delivered from the common rail to the injection valves through a separate ICU for each engine cylinder. The ICU regulates precisely the timing of fuel injection, accurately controls the volume of fuel injected, and sets the shape of the injection pattern. The ICU has an injection control valve and a Sulzer electro-hydraulic rail valve for each fuel injection valve. The rail valves receive control signals for the beginning and end of injection from the respective electronic unit of the WECS (Wartsila Engine Control System).
There are three fuel injection valves in each engine cylinder except for the RT-flex50 which has two. The fuel injection valves are the same as those already employed in RTA engines, and are hydraulically-operated in the usual way by the high-pressure fuel oil. Each fuel injection valve in a cylinder cover is independently controlled by the ICU for the respective cylinder so that, although all the injection valves in an individual cylinder normally act in unison, they can also be programmed to operate separately as necessary.
For Size I, the individual ICU are arranged between the sections of rail pipe but for Size IV the individual ICU are mounted directly on the rail pipe. The ICU for Size IV was adapted from that in Size I with the same function principles for integral injection volume flow but to suit the greater flow volumes involved.
Fig 7. Injection control unit (ICU) for the three fuel injection valves of one cylinder. The dashed line marks the separation between the control oil and the fuel oil sides.
The common-rail system is purpose-built for operation on just the same grades of heavy fuel oil as are already standard for Sulzer RTA-series engines. For this reason, the RT-flex system incorporates certain design features not seen in other common-rail engines using middle-distillate diesel oils. The key point is that, in the ICU, the heated heavy fuel oil is isolated from the precision rail valves.
The Sulzer rail valves are bi-stable solenoid valves with an extremely fast actuation time. To achieve the longest possible lifetime, the rail valves are not energised for more than 4 ms. This time is sampled, monitored and limited by the WECS. The valve’s bi-stability allows their position and status to be reliably controlled.