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Ruston (MAN Diesel)
Chapter | twenty four
Ruston (MAN Diesel) A programme embracing three medium-speed designs—the RK215, RK270 and RK280 series—was developed and produced by Ruston Diesels, a pioneering British enginebuilder which was a member of the Alstom Engines group until acquired by MAN B&W Diesel AG (now MAN Diesel) of Germany in June 2000. The RK215 and RK270 engines are no longer manufactured but the RK280 continues to be in production as MAN Diesel’s 28/33D series (see Chapter 22). The RK270 engine entered service in 1982, the 270 mm bore/305 mm stroke design inheriting the pedigree of the 254 mm bore RK series which originated in the 1930s and continued in the programme as an upgraded RKC series also with a 305 mm stroke. The RK270 retained well-proven features of its predecessor but exploited new components to underwrite a higher performance and achieve enhanced lightness and compactness. A fast ferry version of the engine was progressively refined after entering service in 1990, with aluminium alloy specified in non-stressed areas and fabrications replacing castings where feasible. Attention was also paid to the weight of the ancillary equipment serving the engine. Later design refinements included revised cylinder heads with larger valves and upgraded fuel injection systems. Early fast ferry propulsion installations were based on 16RK270 engines with individual ratings of 3650 kW at 750 rev/min (Figure 24.1). The output was raised in succeeding ferry generations to 4050 kW at 760 rev/min, 4440 kW at 782 rev/min and 5500 kW at 1000 rev/min. Demand for higher powers stimulated Ruston in early 1995 to introduce a V20-cylinder model to the programme, supplementing the established six and eight in-line and V12 and V16 engines. An output of 6875 kW at 1000 rev/min on a mean effective pressure of 23.6 bar was quoted for the 20RK270 design; some fast ferries featured engines specified with continuous ratings of 7080 kW at 1030 rev/min; and a naval rating of 7550 kW at 1032 rev/min was sanctioned (maximum power required for no more than 5 per cent of the operating profile). The V-engines are arranged with 45° cylinder banks (Figures 24.2 and 24.3). 627
628 Ruston (MAN Diesel)
Figure 24.1 Two 16RK270 engines are arranged in each hull of the fast catamaran ferry Hoverspeed Great Britain
Figure 24.2 One of four V20-cylinder RK270 engines installed in a fast ferry, each rated at 7080 kW
Ruston (MAN Diesel) 629
Figure 24.3 V20-cylinder version of RK270 engine
Design refinements included the introduction of a revised configuration of compact pulse converter exhaust system in stainless steel, with a larger bore and optimized area ratios, fostering a better gas flow that improves fuel efficiency. The system became standard on new engines and has been retrofitted to existing V16- and V20-cylinder installations. Engine tests confirmed the performance simulation prediction that the larger flow area, if applied alone, would in fact reduce turbine energy in the turbocharger and actually increase exhaust temperature without any significant improvement in fuel economy. A turbocharger rematch, however, resulted in an overall reduction in turbine inlet temperature by up to 30°C and a reduction in specific fuel consumption of around 3 per cent. New 20RK270 engines also benefited from two TPL 65 turbochargers, the latest generation from ABB Turbo Systems (see Chapter 7). The higher efficiency of these units, compared with the previous VTC 304 type, yielded a further reduction in exhaust temperature and specific fuel consumption at full power. When applying such high-efficiency turbochargers to engines operating over a propeller law power curve, it is desirable to introduce an air bypass between the air manifold and the turbine inlet manifold over the lower part of the speed range. Such an arrangement delivers a further significant reduction in turbine inlet temperature in the region around 30 per cent power at 700 rev/min, and also improves the stability of the turbocharger compressor. The bypass valve is an integral part of the engine, programmed by the Regulateur Europa Viking 22 governor to open and close at pre-selected engine speeds: typically opening on a rising engine speed at 580 rev/min and closing at 920 rev/min.
630 Ruston (MAN Diesel) Two main modifications were made to ensure compliance with IMO’s Marpol Annex VI NOx emission requirements: l
The fuel injection timing was retarded by approximately 5°, this change alone resulting in a NOx emissions reduction of some 20 per cent when calculated in accordance with the E3 test cycle appropriate to a propeller law-operated engine. Unfortunately, the specific fuel consumption was adversely affected. l The compression ratio was increased from 12.3 to 13.3 by a simple adjustment that had been incorporated in the engine design; this allowed advantage to be taken of the increase in maximum cylinder pressure resulting from the fuel injection retardation. The change caused a rise in NOx emission but of less than 3 per cent, and the resulting emissions were compliant with the IMO requirements; furthermore, most of the fuel consumption ‘lost’ by the injection retardation was restored. The increased compression ratio also improved starting on poorer quality fuels and curbed particulate and smoke emissions, particularly at part load. Ruston gained valuable experience with selective catalytic reduction (SCR) installations required to satisfy extremely low NOx emission limits dictated in special regions. The four 20RK270 engines powering the 110 m long fast monohull ferry Gotland exhaust via Siemens SINOx systems which reduce emissions to below 2 g/kW h—less than 20 per cent of the IMO standard.
RK270 engine details The bedplate is machined from a high-grade iron casting. Transverse diaphragms for each main bearing provide rigid support for the crankshaft, and angled joint faces ensure positive locking of the main bearing caps in the bedplate. The crankshaft is machined from a single-piece alloy steel forging with bolted-on balance weights. There is an integral forged coupling flange for the flywheel, and the camshaft drive gear is split to facilitate replacement. The main bearings are pre-finished, steel-backed shells with bimetal linings and are retained in the housing by caps drilled to direct oil to the bearings. The caps are located transversely in large registers in the bedplate and held in position by studs and nuts. The bearings are easily removable through the crankcase doors. The crankcase housing has transverse diaphragms between each cylinder to provide water compartments around the cylinder liners. It incorporates an integral air chest and is machined from a high-grade ductile spheroidal graphite iron casting. Explosion relief valves are fitted to the crankcase doors which allow easy access to the connecting rods and main bearings and to the camshaft and drive. Separate wet-type liners cast in alloy iron are flanged at their upper ends and secured by the cylinder heads. Cutting rings are fitted at the top of the liner to prevent the build-up of carbon on the piston crowns. The lower ends of the
RK270 engine details 631 liners are located in the crankcase and sealed by synthetic rubber rings. The liners are machined all over and the bore is hone finished to secure good piston/liner compatibility. A single camshaft for each cylinder bank is installed from the side of the engine and run in generously proportioned bearings. The camshafts are of modular construction with single-cylinder sections joined by bearing journals. Individual sections can be replaced with the camshaft in situ or the complete camshaft removed from the side. The final timing is adjustable through a slotted driven gear and hub assembly. The camshafts are driven by a train of hardened and ground steel spur gears from the crankshaft split gear. A two-piece piston, comprising a steel crown and an aluminium skirt, features a combustion bowl of the Hesselman design. Cooling oil is fed from the connecting rod through the small end bush and drillings in the gudgeon pin and piston body to the cooling gallery. The connecting rods are manufactured from steel forgings. The shell bearings are carried in obliquely split big ends, with the cap located by serrations on the joint face (a feature reducing the bending and shear loads across the joint). The stepped small end has a large diameter gudgeon pin with bronze bushings. A drilling through the shank of the connecting rod delivers oil for small end bearing lubrication and piston cooling. Individual cylinder heads are machined from iron castings which accommodate two inlet and two exhaust valves surrounding a central fuel injector. Both the air inlet port and the exhaust port are located on the same side of the cylinder head. The inlet port draws air from the integral air chest, and the exhaust port feeds into a manifold system mounted above the air chest. Each pair of valves is operated via short stiff pushrods and conventional rockers. The pushrods are driven from the side entry camshafts via roller cam followers. The fuel injection system features individual pumps directly operated from the camshaft, and injectors for each cylinder. Air motor starting is standard, using one or two motors operating via spur gears on the flywheel rim. A sensitive hydraulic governor is bevel driven from the camshaft. Over speeding is prevented by a separate safety trip mechanism which returns the control shaft to the ‘No-Fuel’ position. A digital electronic governor is available as an option. Auxiliaries are driven from the free end of the engine through a spring drive and spur gears. The standard arrangement embraces one water pump for the jacket water, one water pump for the charge air coolers and lubricating oil cooler circuits, a fuel lift pump and lubricating oil pumps. A secondary water pump may be fitted optionally. An extension shaft may be fitted to allow power to be taken from the free end of the engine. The lubricating oil system includes single or twin engine-driven pumps, full flow filtration, thermostat and oil cooler. The oil pressure is controlled by a single or double spring-loaded relief valve. The jacket cooling system is thermostatically controlled and includes an engine-driven water pump.
632 Ruston (MAN Diesel) The turbocharger(s) is mounted as standard at the free end of the engine, although a flywheel end location can be arranged if required.
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 RK270 model in this chapter). 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.
Figure 24.4 Ruston RK215 engine in V8-cylinder form
RK215 engine 633 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 claimed, 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° 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 l/min 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 feature 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
634 Ruston (MAN Diesel) 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 inline 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.
Ruston RK280 engine An advanced 280 mm bore RK280 medium-speed design developed by Ruston for fast commercial and naval vessel propulsion, introduced in 2001, was taken under the MAN Diesel umbrella and is now produced in Germany as the 28/33D series (see Chapter 22 for details).
Ruston (MAN Diesel) A programme embracing three medium-speed designs—the RK215, RK270 and RK280 series—was developed and produced by Ruston Diesels, a pioneering British enginebuilder which was a member of the Alstom Engines group until acquired by MAN B&W Diesel AG (now MAN Diesel) of Germany in June 2000. The RK215 and RK270 engines are no longer manufactured but the RK280 continues to be in production as MAN Diesel’s 28/33D series (see Chapter 22). The RK270 engine entered service in 1982, the 270 mm bore/305 mm stroke design inheriting the pedigree of the 254 mm bore RK series which originated in the 1930s and continued in the programme as an upgraded RKC series also with a 305 mm stroke. The RK270 retained well-proven features of its predecessor but exploited new components to underwrite a higher performance and achieve enhanced lightness and compactness. A fast ferry version of the engine was progressively refined after entering service in 1990, with aluminium alloy specified in non-stressed areas and fabrications replacing castings where feasible. Attention was also paid to the weight of the ancillary equipment serving the engine. Later design refinements included revised cylinder heads with larger valves and upgraded fuel injection systems. Early fast ferry propulsion installations were based on 16RK270 engines with individual ratings of 3650 kW at 750 rev/min (Figure 24.1). The output was raised in succeeding ferry generations to 4050 kW at 760 rev/min, 4440 kW at 782 rev/min and 5500 kW at 1000 rev/min. Demand for higher powers stimulated Ruston in early 1995 to introduce a V20-cylinder model to the programme, supplementing the established six and eight in-line and V12 and V16 engines. An output of 6875 kW at 1000 rev/min on a mean effective pressure of 23.6 bar was quoted for the 20RK270 design; some fast ferries featured engines specified with continuous ratings of 7080 kW at 1030 rev/min; and a naval rating of 7550 kW at 1032 rev/min was sanctioned (maximum power required for no more than 5 per cent of the operating profile). The V-engines are arranged with 45° cylinder banks (Figures 24.2 and 24.3). 627
628 Ruston (MAN Diesel)
Figure 24.1 Two 16RK270 engines are arranged in each hull of the fast catamaran ferry Hoverspeed Great Britain
Figure 24.2 One of four V20-cylinder RK270 engines installed in a fast ferry, each rated at 7080 kW
Ruston (MAN Diesel) 629
Figure 24.3 V20-cylinder version of RK270 engine
Design refinements included the introduction of a revised configuration of compact pulse converter exhaust system in stainless steel, with a larger bore and optimized area ratios, fostering a better gas flow that improves fuel efficiency. The system became standard on new engines and has been retrofitted to existing V16- and V20-cylinder installations. Engine tests confirmed the performance simulation prediction that the larger flow area, if applied alone, would in fact reduce turbine energy in the turbocharger and actually increase exhaust temperature without any significant improvement in fuel economy. A turbocharger rematch, however, resulted in an overall reduction in turbine inlet temperature by up to 30°C and a reduction in specific fuel consumption of around 3 per cent. New 20RK270 engines also benefited from two TPL 65 turbochargers, the latest generation from ABB Turbo Systems (see Chapter 7). The higher efficiency of these units, compared with the previous VTC 304 type, yielded a further reduction in exhaust temperature and specific fuel consumption at full power. When applying such high-efficiency turbochargers to engines operating over a propeller law power curve, it is desirable to introduce an air bypass between the air manifold and the turbine inlet manifold over the lower part of the speed range. Such an arrangement delivers a further significant reduction in turbine inlet temperature in the region around 30 per cent power at 700 rev/min, and also improves the stability of the turbocharger compressor. The bypass valve is an integral part of the engine, programmed by the Regulateur Europa Viking 22 governor to open and close at pre-selected engine speeds: typically opening on a rising engine speed at 580 rev/min and closing at 920 rev/min.
630 Ruston (MAN Diesel) Two main modifications were made to ensure compliance with IMO’s Marpol Annex VI NOx emission requirements: l
The fuel injection timing was retarded by approximately 5°, this change alone resulting in a NOx emissions reduction of some 20 per cent when calculated in accordance with the E3 test cycle appropriate to a propeller law-operated engine. Unfortunately, the specific fuel consumption was adversely affected. l The compression ratio was increased from 12.3 to 13.3 by a simple adjustment that had been incorporated in the engine design; this allowed advantage to be taken of the increase in maximum cylinder pressure resulting from the fuel injection retardation. The change caused a rise in NOx emission but of less than 3 per cent, and the resulting emissions were compliant with the IMO requirements; furthermore, most of the fuel consumption ‘lost’ by the injection retardation was restored. The increased compression ratio also improved starting on poorer quality fuels and curbed particulate and smoke emissions, particularly at part load. Ruston gained valuable experience with selective catalytic reduction (SCR) installations required to satisfy extremely low NOx emission limits dictated in special regions. The four 20RK270 engines powering the 110 m long fast monohull ferry Gotland exhaust via Siemens SINOx systems which reduce emissions to below 2 g/kW h—less than 20 per cent of the IMO standard.
RK270 engine details The bedplate is machined from a high-grade iron casting. Transverse diaphragms for each main bearing provide rigid support for the crankshaft, and angled joint faces ensure positive locking of the main bearing caps in the bedplate. The crankshaft is machined from a single-piece alloy steel forging with bolted-on balance weights. There is an integral forged coupling flange for the flywheel, and the camshaft drive gear is split to facilitate replacement. The main bearings are pre-finished, steel-backed shells with bimetal linings and are retained in the housing by caps drilled to direct oil to the bearings. The caps are located transversely in large registers in the bedplate and held in position by studs and nuts. The bearings are easily removable through the crankcase doors. The crankcase housing has transverse diaphragms between each cylinder to provide water compartments around the cylinder liners. It incorporates an integral air chest and is machined from a high-grade ductile spheroidal graphite iron casting. Explosion relief valves are fitted to the crankcase doors which allow easy access to the connecting rods and main bearings and to the camshaft and drive. Separate wet-type liners cast in alloy iron are flanged at their upper ends and secured by the cylinder heads. Cutting rings are fitted at the top of the liner to prevent the build-up of carbon on the piston crowns. The lower ends of the
RK270 engine details 631 liners are located in the crankcase and sealed by synthetic rubber rings. The liners are machined all over and the bore is hone finished to secure good piston/liner compatibility. A single camshaft for each cylinder bank is installed from the side of the engine and run in generously proportioned bearings. The camshafts are of modular construction with single-cylinder sections joined by bearing journals. Individual sections can be replaced with the camshaft in situ or the complete camshaft removed from the side. The final timing is adjustable through a slotted driven gear and hub assembly. The camshafts are driven by a train of hardened and ground steel spur gears from the crankshaft split gear. A two-piece piston, comprising a steel crown and an aluminium skirt, features a combustion bowl of the Hesselman design. Cooling oil is fed from the connecting rod through the small end bush and drillings in the gudgeon pin and piston body to the cooling gallery. The connecting rods are manufactured from steel forgings. The shell bearings are carried in obliquely split big ends, with the cap located by serrations on the joint face (a feature reducing the bending and shear loads across the joint). The stepped small end has a large diameter gudgeon pin with bronze bushings. A drilling through the shank of the connecting rod delivers oil for small end bearing lubrication and piston cooling. Individual cylinder heads are machined from iron castings which accommodate two inlet and two exhaust valves surrounding a central fuel injector. Both the air inlet port and the exhaust port are located on the same side of the cylinder head. The inlet port draws air from the integral air chest, and the exhaust port feeds into a manifold system mounted above the air chest. Each pair of valves is operated via short stiff pushrods and conventional rockers. The pushrods are driven from the side entry camshafts via roller cam followers. The fuel injection system features individual pumps directly operated from the camshaft, and injectors for each cylinder. Air motor starting is standard, using one or two motors operating via spur gears on the flywheel rim. A sensitive hydraulic governor is bevel driven from the camshaft. Over speeding is prevented by a separate safety trip mechanism which returns the control shaft to the ‘No-Fuel’ position. A digital electronic governor is available as an option. Auxiliaries are driven from the free end of the engine through a spring drive and spur gears. The standard arrangement embraces one water pump for the jacket water, one water pump for the charge air coolers and lubricating oil cooler circuits, a fuel lift pump and lubricating oil pumps. A secondary water pump may be fitted optionally. An extension shaft may be fitted to allow power to be taken from the free end of the engine. The lubricating oil system includes single or twin engine-driven pumps, full flow filtration, thermostat and oil cooler. The oil pressure is controlled by a single or double spring-loaded relief valve. The jacket cooling system is thermostatically controlled and includes an engine-driven water pump.
632 Ruston (MAN Diesel) The turbocharger(s) is mounted as standard at the free end of the engine, although a flywheel end location can be arranged if required.
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 RK270 model in this chapter). 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.
Figure 24.4 Ruston RK215 engine in V8-cylinder form
RK215 engine 633 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 claimed, 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° 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 l/min 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 feature 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
634 Ruston (MAN Diesel) 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 inline 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.
Ruston RK280 engine An advanced 280 mm bore RK280 medium-speed design developed by Ruston for fast commercial and naval vessel propulsion, introduced in 2001, was taken under the MAN Diesel umbrella and is now produced in Germany as the 28/33D series (see Chapter 22 for details).