Sulzer RT Flex Marine Diesel Engine

The common rail system :

Although common-rail fuel injection is certainly not a new idea, it has only become truly practical in recent years through the use of fully-integrated electronic control based on high-performance computers which allow the best use to be made of the flexibility possible with common-rail injection. 

Sulzer low-speed engines have long had the benefits of double valve-controlled fuel injection pumps with variable injection timing (VIT), and a degree of variable exhaust valve timing being achieved hydraulically in the VEC system, the variation in timing so obtained has been very limited. 

The common-rail concept was adopted also because it has the advantage that the functions of pumping and injection control are separated.

The common-rail concept thus provides an ideal basis for the application of a fully-integrated electronic control. The combined flexibilities of common rail and electronic control provide improved low-speed operation, engine acceleration, balance between cylinders, load control, and longer times between overhauls. They also ensure better combustion at all operating speeds and loads, giving benefits in lower fuel consumption, lower exhaust emissions in terms of both smokeless operation at all operating speeds and less NOx, emissions, and also a cleaner engine internally with less deposits of combustion residues. Engine diagnostics are built into the system, improving engine monitoring, reliability and availability.

Supply unit:

               

The supply unit is naturally at the location of the gear drive: at the driving end for five- to seven-cylinder engines, and at the mid gear drive for greater cylinder numbers. The supply unit has a rigid housing of GGG-grade nodular cast iron. The fuel supply pumps are arranged on one side of the drive gear and the hydraulic servo-oil pumps are on the other side. This pump arrangement allows a very short, compact supply unit with reasonable service access. The numbers, size and arrangement of pumps are adapted to the engine type and the number of engine cylinders. For RT Flex Sizes I and IV, the supply unit is equipped with between four and eight fuel supply pumps arranged in Vee from. The size O supply unit, however, has just two or three supply pumps in-line.The fuel supply pumps are driven through a camshaft with three-lobe cams. This camshaft cannot be compared with the traditional engine camshaft. It is very short and much smaller diameter, and is quite differently loaded. There is no sudden, jerk action as in fuel injection pumps but rather the pump plungers have a steady reciprocating motion. With tri-lobe cams and the speed-increasing gear drive, each fuel supply pump makes several strokes during each crankshaft revolution.  engines with up to eight cylinders, the rail unit is assembled as a single unit. With greater numbers of cylinders, the engines have a mid gear drive and the rail unit is in two sections according to the position of the mid gear drive in the engine he fuel common rail provides storage volume for the fuel oil, and has provision for damping pressure waves. The common rail system is designed with very high safety margins against material fatigue. The high-pressure rail is trace heated from the ship's heating system, using either steam or thermal oil. The simplification of the fuel rail for Size IV, without intermediate flanges, compared with that for Size I allowed the trace heating piping also to be simplified. The trace heating piping and the insulation are both slimmer, allowing easier service access inside the rail unit.