Rk215 Engine

The 215 mm bore/275 mm stroke RK215 engine (Figure 24.4) was originally produced in in-line six and V8 versions but V12 and V16-cylinder models later extended the upper power limit to 3160 kW at 720-1000 rev/min. RK215 engines have earned references in commercial and naval propulsion and genset applications, Ruston summarizing the benefits of the design to operators as: cost effective; high power-to-weight ratio; reduced space requirements; ease of installation; fuel efficient; and minimized environmental impact.

The general layout of the engine is conventional with wet cast iron liners and an underslung crankshaft. The latter feature was a departure for Ruston which had formerly produced bedplate-type engines (see

Figure 24.4 Fusion R.K215 engine in V8-cylinder form

RK270 model above). The change in design philosophy reflected the high cylinder pressures (up to 180 bar), dictating a level of crankcase strength that could only be obtained from an underslung configuration.

The combustion space is sealed by a steel ring, and each cylinder is held down by six bolts. The underslung crankshaft is mounted to the block with rigid bearing caps, each having two studs; in addition, the V-cylinder engine uses cross-bolts for cap location. Hydraulic tensioning is applied to secure the vertical studs. The alloy steel crankshaft is a die forging with bolted-on balance weights, two for each throw, to maximize bearing oil film thicknesses. The bearing shells are of bimetal construction with an aluminium-tin-silicon running surface which has a very high strength. In spite of the high cylinder pressures, the designer claims, the bearings are not highly loaded: the large end being under 41 MPa.

A two-piece die forging forms the connecting rod, with the large end split at 50 degrees to the vertical to allow removal through the cylinder bore. The split angle was optimized through model tests and finite element analysis to provide minimum bending at the split position under both firing and inertia load conditions, while maintaining an adequate bearing diameter and large end bearing housing rigidity. Each cap is retained by four bolts. The small ends of the connecting rods are stepped to minimize pressures on both small end bearing and piston boss.

The pistons are one-piece nodular iron castings with an integral cooling gallery fed with oil through drillings in the connecting rod and gudgeon pin. A three-ring pack is specified for the piston, all the rings having chrome running faces; the top ring is asymmetrically barrelled and the second ring is taper faced. The grooves for the compression rings have hardened surfaces. The oil control ring is one piece with a spring expander. Six drilled holes in the piston drain excess oil from the oil control ring back inside the piston.

Oil, water and fuel lift pumps are all driven by hardened steel gears located at the non-flywheel end of the crankshaft. The rotor-type oil pump delivers up to 400 litres/minute for lubrication and cooling via an engine-mounted cooling and filtration system which incorporates a change-over valve to enable continuous operation. The standard freshwater pump may be supplemented by one or, in special cases, two additional pumps to supply heat exchangers. The standard cooling system incorporates a freshwater thermostat and water bypass. Also standard is the fuel lift pump and pipework incorporating a pre-filter, fine filter and pressure regulating valve. The pump is sized to give a 3:1 excess feed capacity to provide cooling for the injection pumps.

Unit injectors for each cylinder were specified (reportedly for the first time in British medium speed engine practice), operating at pressures up to 1400 bar. The injectors, purpose-developed for the RK215 by L'Orange in conjunction with Ruston, are operated from the camshaft via a pushrod. A characteristic cited for unit injector engines is a low level of exhaust smoke in all operating conditions.

Fuel is supplied to the injectors through drillings in the cylinder head, dispensing with high pressure fuel lines and removing a potential cause of engineroom fire.

The iron cylinder heads are of two-deck construction with a very thick bottom deck which is cooled by drilled passages. Inlet and exhaust valve pairs are generously proportioned at 78 mm and 72 mm diameter respectively, and also feature wide seats to foster low seating pressures and good heat transfer from the valves to the seat inserts. This is particularly important because the exhaust seat insert incorporates a water-cooled cavity to maximize heat flow from the valves. The cooled exhaust seat is made from steel with a hardened surface, while the inlet valve uses the more common high chromium content iron.

Both inlet and exhaust ports are located on the same face of the cylinder head. The valves, which have hardened seat faces, are operated by rocker levers and bridge pieces. A third rocker lever between the valve rockers operates the unit fuel injector. All rocker levers on each line are actuated by pushrods and lever-type followers from the induction-hardened alloy steel camshaft. All bearings, including those for the follower roller and the spherical pushrod ends, are positively lubricated from the main oil supply at full pressure.

Two Garrett TV94 turbochargers were specified for the six-cylinder in-line model, each mounted on a very short manifold served by three cylinders. Charge air is fed from both units via a manifold to a single, integrally mounted air/water charge cooler. This arrangement is facilitated by the positioning of the inlet and exhaust on the same side of the engine. The resulting small volumes of both inlet and exhaust systems, plus the low turbine and compressor inertia, reportedly promote excellent load acceptance. A similar concept is applied to the V8-cylinder model but with the Garrett turbochargers replaced by dual ABB RR151 units.

V-cylinder models use similar line components to the in-line cylinder models: the cylinder head, piston, liner and connecting rod are the same, as are the cam followers, pushrods and camshaft drive. The crankcase and crankshaft, of course, are different.

To ensure that the underslung main bearing cap is rigidly located it is provided with cross-bolts in addition to the hydraulically tensioned main studs. V-engines use side-by-side connecting rods, and the crankshaft—while having the same size of crankpin as the in-line engine—has a 25 per cent larger main bearing journal diameter. The resulting overlap between pin and journal imparts strength and rigidity to the crankshaft.

A completely new medium speed engine, the RK280 design, joined the Ruston programme in 2001, offering a considerably higher output than the long-established RK270 series for commercial and naval propulsion and genset drive applications (Figure 24.5). The 280 mm bore engine was introduced as the world's most powerful 1000 rev/ min design, released with an initial rating of 450 kW/cylinder. The programme of V12, 16 and 20-cylinder models thus covers a power range from 5400 kW to 9000 kW. An output of 500 kW/cylinder was specified for the design, however, equating to a future rating of 10 000 kW for the 20RK280 engine.

Figure 24.5 V16-cylinder version of the RK280 engine
RK280 design data

Bore

280 mm

Stroke

330 mm

Cylinders

V12, 16, 20

Output*

450 kW/cyl

Rated speed

1000 rev/min

Mean effective pressure

26.5 bar

Mean piston speed

11 m/s

Power range

5400-9000 kW

Power density

< 5.1 kg/kW

Fuel consumption

< 190 g/kWh

* Continuous rating

* Continuous rating

A competitive specific fuel consumption of under 190 g/kWh is reported, with NOx emission levels of less than 10 g/kWh from primary reduction measures alone. Compactness and lightness are reflected in a dry weight of 46 tonnes and a power density of 5.1 kg/kW for the V20-cylinder version, which measures 7.33 m long X 2.1 m wide X 3.18 m high.

The RK280 design benefited from experience with RK270 engines powering fast ferries, as well as feedback from RK215 engine installations. Advantage was also taken of advanced software packages, new development methodologies and project management techniques. Areas of the RK270 design that had proved particularly successful—such as the integrity of the bottom end in a dynamic fast vessel application exploiting an elastic mounting system—were thus translated into the design parameters of the RK280 engine. At the same time the opportunity was taken to address other features in eliminating the possibility of problems in service: for example, minimizing overhangs and induced stress in the engine, and reducing pipework on and off the engine. Among the measures adopted to enhance performance, fuel economy, reliability and serviceability were:

• Electronically-controlled pump-pipe fuel injection system to foster a low specific fuel consumption and reduced NOx and particulates emissions throughout the load range.

• Simple, single-stage high efficiency turbocharging based on ABB Turbo Systems' TPL 65 turbocharger for improved specific fuel consumption and lower operating temperatures; and a simple exhaust system with rigid heat shields helps to minimize and ease maintenance.

• Integrated pipe design with four-pipe connection to reduce vibration and ease installation and serviceability.

• Two-stage fresh water-cooled high efficiency intercooler in the centre of the engine to improve specific fuel consumption and curb NOx emissions while reducing mechanical loading.

• Reduced number of components (40 per cent fewer than the RK270 engine) for higher reliability and lower servicing costs.

• Rigid dry crankcase design for reduced weight and easier servicing.

• Low inertia/low friction two-piece pistons with alloy steel crowns to reduce weight and improve specific fuel consumption; three-ring pack.

• Simplified gear train of robust construction; water and lube oil pumps driven from the free end of the engine through gears housed in the pump drive casing (Figure 24.6).

• External viscous damper for ease of maintenance.

The New RK 280

up to 9000 kWb

Figure 24.6 Cutaway of RK280 engine showing the gear train for the camshaft and service pump drives

Key to main components

A Turbocharger B Air filters C Fresh water pumps D Sea water outlet E LT water outlet F Fuel Inlet

G Lubricating oil filter & dipstick H Fuel lift pump I Lubricating oil pump J Fuel filters K HT water outlet L Duplex lubricating oil filter M Lubricating oil cooler N Heat shields O Intercoolers

Figure 24.6 Cutaway of RK280 engine showing the gear train for the camshaft and service pump drives

The New RK 280

up to 9000 kWb

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