The Sulzer RT-fl Ex Common-Rail System Described

The Sulzer RT-flex Common-Rail System DescribedSummaryThis paper provides a description of the Sulzer RT-flex electronically-controlled common-rail system embodied in Sulzer RT-flexlow-speed marine engines. It covers the main elements of the RT-flex system – the supply unit, rail unit and electronic controlsystem. The system’s benefits are reviewed, together with its reliability and built-in redundancy. It also provides a reference tothe RT-flex chronology leading up to the 12RT-flex96C – the world’s most powerful common-rail engine.ContentsIntroductionSulzer RT-flex systemRT-flex SizesSupply unitServo oilControl oilRail unitInjection control unit (ICU)Exhaust valve controlOperating pressures and system energyStarting air systemPage12335578999Electronic controlReliability and redundancyOperation and maintenanceKey features of the Sulzer RT-flex systemBenefits from the Sulzer RT-flex systemLow exhaust emissionsVery slow runningFuel consumption flexibilityConclusionChronology for Sulzer RT-flex enginesBibliographyIntroductionAlthough common-rail fuel injection is certainly not anew idea, it has only become truly practical in recentyears through the use of fully-integrated electroniccontrol based on high-performance computers whichallow the best use to be made of the flexibility possiblewith common-rail injection.The traditional camshaft has the considerablelimitation of fi xed timing given mechanically by thecams. Although Sulzer low-speed engines have long hadthe benefits of double valve-controlled fuel injectionpumps with variable injection timing (VIT), and adegree of variable exhaust valve timing being achievedhydraulically in the VEC system, the variation in timingso obtained has been very limited.Instead electronically-controlled common-rail systemshave been adopted in the new Sulzer RT-flex engines togive complete control of the timing, rate and pressure offuel injection and the exhaust valve operation, allowingpatterns of operation which cannot be achieved by purelymechanical systems.Rather than ‘electronically controlled’, it would bemore accurate to describe Sulzer RT-flex engines asbeing computer controlled. This is because in the RT-flexsystem, engine functions are fully programmable, perhapslimited only by the designers’ imagination and the lawsof nature. The challenge is to use this freedom to createPage910111112121212131415practical benefits for engine users.The common-rail concept was adopted also becauseit has the advantage that the functions of pumpingand injection control are separated. This allows astraightforward approach to the mechanical andhydraulic aspects of the design, with a steady generationof fuel oil supply at the desired pressure ready forinjection. The common-rail concept also has the uniqueadvantage that it allows the fuel injection valves to beindividually controlled. Usually there are three fuelinjection valves in each cylinder cover, and in the SulzerRT-flex engines they are operated mostly in unison butunder certain circumstances they are operated separatelyfor optimum combustion performance.The common-rail concept thus provides an idealbasis for the application of a fully-integrated electroniccontrol. The combined flexibilities of common rail andelectronic control provide improved low-speed operation,engine acceleration, balance between cylinders, loadcontrol, and longer times between overhauls. They alsoensure better combustion at all operating speeds andloads, giving benefits in lower fuel consumption, lowerexhaust emissions in terms of both smokeless operation atall operating speeds and less NOX emissions, and also acleaner engine internally with less deposits of combustionresidues. Engine diagnostics are built into the system,improving engine monitoring, reliability and availability.As the common-rail system is built specifically for—1— Wärtsilä Corporation, August 2004This document, and more, is available for download from Martin's Marine Engineering Page - www.dieselduck.net

Rail unit withelectronic controlunitsDuplicated supply lines forfuel and servo oilIntegrated automatic finefilter for servo and control oilSupply unitFuel pumpsCrank angle sensor at free endServo oil pumpsFig. 1: Principal elements of the common-rail system on a Sulzer RT-flex engine. Note that there are variations on thisarrangement in the various RT-flex engine types depending upon the engine type and number of cylinders.[02#072]concept was recognised as essential. Common rail wasseen as the road ahead and it is applied in Sulzer RT-flexengines.Sulzer RT-flex engines are thus notably different fromother electronically-controlled low-speed diesel enginestoday as Sulzer RT-flex engines are unique in combiningthe benefits of both common-rail systems and electroniccontrol.reliable operation on heavy fuel oil, it detracts nothingfrom the well-established economy of low-speed marinediesel engines but rather opens up new possibilities foreven better economy, ease of operation, reliability, timesbetween overhauls and lower exhaust emissions.It is more than ten years since development of theSulzer RT-flex common-rail system began and morethan 20 years since the first tests were made withelectronically-controlled fuel injection in Winterthur,Switzerland.The early camshaftless systems developed for Sulzerengines relied on integral electronic control but usedindividual, hydraulically-operated fuel injection pumps.However the change in injection concept from theindividual, hydraulically-operated fuel injection pumpsto a common-rail system in 1993 was made because thesystem with individual pumps did not offer potentialfor further technological development despite it havingintegral electronic control. Electronic control was foundto be insufficient by itself and a new fuel injectionTable 1: Sulzer RT-flex engine programme 2004Engine TypeRT-flex50 RT-flex58T-BBore, mm500580Stroke, mm20502416Power, R1 kW/cyl16202180Speed, rpm124105BMEP, bar19.519.5Piston speed, m/s8.58.5No. cylinders5–85–8RT-flex Size0ISulzer RT-flex systemSulzer RT-flex engines are essentially standard SulzerRTA low-speed two-stroke marine diesel engines exceptthat, instead of the usual camshaft and its gear drive, fuelinjection pumps, exhaust valve actuator pumps, reversingservomotors, and all their related mechanical control gear,they are equipped with a common-rail system for fuelinjection and exhaust valve actuation, and full electroniccontrol of engine functions.There are four principal elements in the Sulzer RT-flexRT-flex60C RT-flex68T-B VRT-flex96C9602500572010218.68.56–12, 14IV Wärtsilä Corporation, August 2004This document, and more, is available for download from Martin's Marine Engineering Page - www.dieselduck.net

Exhaust glesensor50µ6µExhaust valveactuating unitVolumetricfuel injectioncontrol unitFig. 2: Schematic of the common-railsystems in Sulzer RT-flex engines.[02#007]1000bar fuel HFO / MDO200bar servo oil and control oil30bar starting aircommon-rail system: the rail unit along the side of thecylinders, the supply unit on the side of the engine, a filterunit for the servo oil, and the integrated electronic controlsystem, including the crank angle sensor.The RT-flex engines are thus equipped with commonrail systems for: heated fuel oil at pressures up to 1000 bar, servo oil at pressures up to 200 bar, control oil at a constant pressure of 200 bar, engine starting air system.RT-flex SizesThe hardware in the RT-flex system is being developedin four principal sizes for the six engine types currentlyin the programme (see Table 1). The six RT-flex enginetypes cover a power range of 8100 to 80,080 kW (11,000to 108,920 bhp).This illustrates one of the advantages of the common-rail system in that hardware is standardised for groups ofengine types, not just for the various cylinder numbers.Supply unitFuel and servo oil are supplied to the common-rail systemfrom the supply unit which is driven through gearingfrom the engine crankshaft.In the first few RT-flex engines, the supply unit is onthe exhaust side of the engine so that it could be lowerdown without interfering with access to the crankcase.However, for all subsequent engines, the location of thesupply unit has since been standardised on the front ofthe engine (on the same side as the rail unit) and at aboutmid height. This keeps the engine ‘footprint’ small sothat the engines can be located far aft in ships with fineafterbodies.The supply unit is naturally at the location of thegear drive: at the driving end for five- to seven-cylinderFig. 3: Supply unit for a Sulzer 12RT-flex96Cengine with the fuel pumps in a Vee-formarrangement on the left and servo oil pumps onthe right-hand face of the central gear drive. Thefuel pumps all deliver into the collector seen abovethe fuel pumps.[04#074]—3— Wärtsilä Corporation, August 2004This document, and more, is available for download from Martin's Marine Engineering Page - www.dieselduck.net

Fig. 4 above: Supply unit on a Sulzer 12RT-flex96C engine with the fuel pumps ina Vee-form arrangement on the left and servo oil pumps on the right-hand face of thecentral gear drive. [04#111]Fig. 5 right: Cutaway drawing of the fuel supply pump element for RT-flex96Cengines. [04#017]engines, and at the mid gear drive for greater cylindernumbers.The supply unit has a rigid housing of GGG-gradenodular cast iron. The fuel supply pumps are arrangedon one side of the drive gear and the hydraulic servo-oilpumps are on the other side. This pump arrangementallows a very short, compact supply unit with reasonableFig. 6: Close view of the fuel supply pumps in figure 4showing the regulating linkage.[04#112]service access. The numbers, size and arrangement ofpumps are adapted to the engine type and the number ofengine cylinders.For RT-flex Sizes I and IV, the supply unit is equippedwith between four and eight fuel supply pumps arrangedin Vee-form. The Size 0 supply unit, however, has justtwo or three supply pumps in-line.Two sizes of fuel pumps are employed for all RT-flexengines, both based on the well-proven injection pumpsused in Sulzer Z-type medium-speed four-stroke enginesthough with some adaptations to suit their function assupply pumps and to raise their volumetric efficiency upto a very high degree. For Sizes 0 and I, the fuel pumpelements are based on the injection pumps of SulzerZA40S engines, while the Size IV pumps are based on theinjection pumps of the Sulzer ZA50S engine type.The fuel supply pumps are driven through a camshaftwith three-lobe cams. This camshaft cannot be comparedwith the traditional engine camshaft. It is very short andof much smaller diameter, and is quite differently loaded.There is no sudden, jerk action as in fuel injection pumpsbut rather the pump plungers have a steady reciprocatingmotion. With tri-lobe cams and the speed-increasing geardrive, each fuel supply pump makes several strokes duringeach crankshaft revolution. The result is a compact supplyunit.Two designs of camshaft are employed. For Size I it ismanufactured in one piece. For Size IV, the camshaft isassembled from a straight shaft on to which the tri-lobecams are hydraulically press fitted. This latter form of—4— Wärtsilä Corporation, August 2004This document, and more, is available for download from Martin's Marine Engineering Page - www.dieselduck.net