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October 16, 2002

 First RTflex60 completes shop trials

First RT-flex60C completes shop trials
The first Sulzer RT-flex60C low-speed marine engine has successfully completed its official shop test.

The Sulzer RT-flex60C is the first low-speed marine engine type designed from the outset to incorporate electronically-controlled common-rail systems for fuel injection and valve actuation.

The shop test took place at Wärtsilä Corporation's Trieste factory in Italy.The seven-cylinder engine was first started on September 15, 2002, and completed the official shop test on Octobe 14.

The new engine will be installed in the first of two 13,200 dwt containerized reefer ships being built at Estaleiros Navais de Viana do Castelo in Portugal. These ships have been contracted by the Agricultural Export Co (Agrexco) through Münchmeyer, Petersen GmbH & Co KG in Hamburg. Their Sulzer 7RT-flex60C engines have a maximum continuous output of 16,520 kW (22,470 bhp) at 114 rev/min.

The official shop test was witnessed by representatives of the shipowner, shipbuilder and classification society. All the tests with the engine were completed without difficulty. The engine ran very satisfactorily with all test results coming up to expectations.

Manufacture by the Trieste factory of the first RT-flex60C, says Wartsila, "followed the usual course for the first of a new engine type, but with particular care owing to the incorporation of the new RT-flex technology."

Technical background
Wartsila says the Sulzer RT-flex60C is a forward-looking engine offering a new range of benefits to shipowners. Not only does it bring the new benefits of electronically-controlled common-rail fuel injection, such as low emissions and very slow running capability, but embodies stepwise improvements in basic diesel engine technology which will give shipowners better reliability and longer times between overhauls.

With cylinder dimensions of 600 mm bore by 2,250 mm stroke, the RT-flex60C has a maximum continuous output of 2,360 kW/cylinder (3,210 bhp/cylinder) at 114 rev/min.

It is available with five to eight cylinders covering an overall power range of 8,250-18,880 kW (11,200-25,680 bhp) at 91-114 rev/min. It thus offers optimum powers and speeds for a wide range of 'faster' ships such as medium-sized containerships, car carriers, reefers, etc.

The RT-flex60C builds upon experience gained with the latest Sulzer RTA engine designs and incorporates the latest technological improvements. It thereby, says Wartsila, offers clear and substantial benefits in terms of reliability, three years between overhauls, low maintenance costs, and low exhaust emissions.

Additional benefits come from the Sulzer RT-flex system by which electronically-controlled common-rail systems replace the usual camshaft-based systems.

The key feature of the RT-flex system is that it gives complete freedom in the timing and operation of fuel injection and exhaust valve actuation. This flexibility has been employed to provide smokeless operation at all ship speeds, and steady running of the engine at very low speeds, down to about 10-12 per cent nominal speed, also without smoke.

The precise volumetric fuel injection control given by the RT-flex system reduces maintenance costs through extending times between overhauls. Engine availability is increased by both the integrated monitoring functions and by the redundancy in pumps, piping and electronics of the RT-flex system.

The RT-flex system was first applied to a full-size research engine in June 1998. Then the first RT-flex engine, a 6RT-flex58T-B, entered service in September 2001 in the bulk carrier Gypsum Centennial. The service experience with this engine has since been very good, with currently more than 4000 hours' operation.

The RT-flex system is seen on the engine as two principal elements: the supply unit on the side of the engine and the rail unit along the side of the cylinder covers.

In the supply unit, a number of high-pressure pumps deliver heated fuel at the usual pressure ready for injection. The pumps have suction control to regulate the fuel delivery volume according to engine requirements. Servo oil for injection control units and for exhaust valve actuation is provided at a lower pressure by a number hydraulic pumps also on the supply unit.

Fuel is delivered from the common rail through an individual injection control unit for each engine cylinder to standard fuel injection valves. The control units, using quick-acting Sulzer rail valves, 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 normally act in unison but are separately controlled so that they can also be programmed to operate separately at very low engine speeds.

The exhaust valves are operated in much the same way as in existing Sulzer RTA engines by a hydraulic pushrod but with the actuating energy now coming from a servo oil rail at 200 bar pressure. The electronically-controlled actuating unit for each cylinder gives full flexibility for valve timing and operating patterns.

A marine engine needs more than electronically-controlled fuel injection to ensure satisfactory performance and service behavior, says Wartsila. It needs to be a good basic engine.

For example, attention to piston-running behavior is essential for engine reliability and long times between overhauls. For this reason the RT-flex60C incorporates TriboPack technology. TriboPack comprises a combination of design measures, including deep-honed liners of appropriate material with sufficient hard phase, multi-level lubrication, pre-profiled rings in all four piston grooves, chromium-ceramic coating on the top ring, anti-polishing ring at the top of the liner, increased thickness of chromium layer in the piston ring grooves, insulating tubes in the cooling bores of the liner, and mid-stroke liner insulation according to the engine rating. It is expected that this approach will enable times between overhauls to be extended to at least three years.

In the design of the RT-flex60C, careful attention was also paid to the structural design to achieve a reasonable engine weight, economy in manufacturing and above all, safety.

It has a very rigid structure comprising a fabricated bedplate, fabricated box-type columns and cast cylinder block, all secured by pre-tensioned vertical tie rods. The structural design is based on extensive stress and strain calculations using a full three-dimensional multi-cylinder finite-element model. Careful consideration was also given to the structure to ensure that welding and casting quality can be good.

Minimum engine length is important for today's ship designs. This has had an influence on bearing design. Certain features are incorporated in the thrust bearing and the connecting rod bottom ends to minimise engine length.

All bearings - main, bottom and crosshead - are fitted with thin shell bearings having a white-metal running layer. Similar bearings are now standard in the latest version of other Sulzer engines, and are running well.

However, with the flexibility of the thin steel shells of the main bearings, it proved necessary to improve the geometry of the bearing housings. Thus the main bearing bores are machined with the bearing caps in place and tightened. The main bearings each have four elastic holding-down studs. Two pairs of studs give the most even distribution of holding-down load and also allow the tie rods to be located close to the bearing for efficient transfer of firing pressure loads.

The cylinder covers are secured by eight elastic holding-down studs arranged in four pairs. This arrangement is compact, so helping to achieve a short engine length, while giving good security and accessibility.

The combustion space of the RT-flex60C follows well-established Sulzer RTA practice. All the surrounding components are bore cooled. The piston crown employs the usual jet-shaker oil cooling principal with an arrangement of cooling bores in the crown so that the surface temperatures of the crown are moderate with a very even distribution.

Scavenge air is delivered by the latest generation of turbochargers, the TPL-B from ABB Turbo Systems and the equivalent from other manufacturers. The first RT-flex60C, a seven-cylinder engine, is equipped with two ABB TPL73B turbochargers. The scavenge air receiver is of a simplified and modular design with integral non-return flaps, hanging cooler bundles and two auxiliary air blowers.

The receiver also incorporates, after the scavenge air cooler, a new design of water separator of higher efficiency than in other Sulzer RTA engines. Removing all water condensate from the air before it enters the engine cylinders has proven vital for satisfactory piston running. The condensed water is collected by a new pressure-balanced arrangement without moving parts.

Principal particulars of the Sulzer RT-flex60C engines

  • Bore,mm 600
  • Stroke, mm 2250
  • Cylinders 5 - 8
  • Power, R1 kW/cylinder 2,360 --bhp/cylinder 3,210
  • Speed range, R1-R3 rpm 114 - 91
  • BMEP at R1 bar 19.5
  • Mean piston speed at R1 m/s 8.55
  • Maximum cylinder pressure bar 155
  • Fuel consumption: at full load, R1 g/kWh 170--g/bhph 125 at 85% load, R1 g/kWh 167--g/bhph 123

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