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Bergen (Rolls-Royce)
Chapter | twenty three
Bergen (Rolls-Royce) The diverse shipbuilding and marine engineering interests of Norway’s Ulstein group for many years embraced the design and production of Bergen mediumspeed engines, now a key element of the UK Rolls-Royce group’s diesel interests. Two Bergen engine families for propulsion and genset applications—the 250 mm bore K-series which dates from the early 1970s, and the 320 mm bore B-series introduced in 1986—have been progressively upgraded and were joined in 2001 by a completely new design, the 250 mm bore C-series, developed in co-operation with Hyundai Heavy Industries of South Korea.
K-Series First introduced in 1971, the 250 mm bore/300 mm stroke K-engine was designed mainly to be a genset drive but numerous propulsion plant applications have been logged in tugs, offshore supply ships and fishing vessels. Engines are available as in-line three-to-nine-cylinder or V12-, 16- and 18-cylinder models covering an output range from 600 kW to 4010 kW at speeds of 720/750/ 825/900 rev/min. Design improvements introduced over the years have sought to maintain market competitiveness, the maximum brake mean effective pressure being raised from 20 bar to 22 bar to increase the output to 220 kW/cylinder. The later adoption of a ‘hot box’ arrangement for the fuel injection system followed a trend in larger engine designs. It provides the engine with cleaner lines and improves the working environment in the machinery room: temperatures are reduced and any fuel leakage from the injection system components is retained within the box. Other improvements have included a revised timing chain, sprockets and camshaft system to extend service life and accommodate a higher injection pressure. The valve stem rotators have been strengthened and the valve guides and guide seals improved to ensure better operational results running at 900 rev/min on heavy fuel. The provision of a carbon-cutting (or anti-polishing) ring at the top of the cylinder unit significantly reduced lube oil consumption and the amount of
615
616 Bergen (Rolls-Royce) insoluble deposits in the oil (hence extending filter life). The ring comprises a sleeve insert which sits between the top piston ring turning point and the top of the cylinder liner. It has a slightly smaller diameter than the bore of the liner, this reduction being accommodated by a reduced diameter piston top land. The main effect of the ring is to prevent the build-up of carbon around the edges of the piston crown which causes liner polishing and wear with an associated increase in lube oil consumption. A secondary function is a sudden compressive effect on the piston ring belt as the piston and carbon-cutting ring momentarily interface; this forces lube oil away from the combustion area and again helps to reduce consumption. The efficiency of the rings was such that Bergen found it necessary to redesign the ring pack to secure a desirable degree of oil consumption. The carbon-cutting ring, refined over a 2-year period, is now standard on all new Bergen engines, and numerous engines in service have benefited from retrofits.
B-Series The 320 mm bore/360 mm stroke B-series engine was conceived as a compact, heavy fuel-burning main engine and launched in 1986 with special features facilitating operation on lower price, poor quality fuel oils. The design’s tolerance of fuel quality has been demonstrated by an offshore rig installation running on crude oil direct from the well after degassing. A nominal rating of 360 kW/cylinder at 750 rev/min was initially quoted but some of the first engines sold were contracted at around 400 kW/cylinder, equivalent to a 10 per cent overload. An uprating in 1991/1992 took the output to 440 kW/cylinder at 750 rev/min which yielded a power band of 1870 kW to 3970 kW from in-line six-, eight- and nine-cylinder BR models. A decision to double the upper limit of the range—to 7940 kW—was announced in 1996 through the introduction of V12-, 16- and 18-cylinder models. These BV engines (see Section BV Engine) were planned to benefit from Bergen’s exhaust emissions reduction R&D by adopting faster fuel injection, a change in compression ratio and different valve timing to the existing in-line cylinder engines. The B-engine was reportedly the first of its size to feature a completely bore-cooled cylinder unit and combustion space (initially, a bore-cooled liner and head and, later, bore-cooled pistons). This arrangement yields good strength and stiffness combined with good temperature control, which is important in heavy fuel operation. Early in the engine’s development it was discovered that the temperature profile on the liner was not the optimum. The resulting design change, benefiting subsequent production engines, has reportedly proved effective in the long term for both propulsion and auxiliary power duties, even at medium load. A drawback to the original bore-cooling concept soon became apparent, however: the use of electrically driven cooling water pumps. Electrical black-outs could not be tolerated, and the fluctuation in cooling water flow away from the
B-series 617 optimum resulted in some cracking of liners. An early change therefore saw a switch to engine-driven pumps and the incorporation of a new strengthened liner design. In Arctic areas, it was also found that piston rings were vulnerable to poor ignition qualities and high temperature gradients, resulting, in some cases, in ring cracking. This problem was solved by optimizing the clearances and the layout of the ring pack. Other refinements following early installations included an improved bearing arrangement for the timing gears and, in line with other enginebuilders, a new fuel injection system was introduced in 1991 to counter an industry-wide problem of leakages. The complete injection system was enhanced by bigger pumps, better seals, larger nozzles and improved high-pressure pipes. The improvements coincided with the 1991/1992 decision to uprate the engine’s output to 440 kW/cylinder while retaining the same engine speed of 750 rev/min. Contributing to this power rise—and a brake mean effective pressure increase to 24.4 bar—was the first application of ABB’s VTR-4P high-efficiency turbocharger with a titanium compressor wheel, and a new type of composite piston with a bore-cooled forged steel crown and nodular cast iron skirt. A carboncutting ring (described above in the Section K-series) was introduced to the B-engine in 1994. The one-piece design cylinder block of nodular cast iron is arranged for an underslung crankshaft and features large crankcase doors. A receiver and supply ducts for oil and water are cast in. The centrifugally cast cylinder liner is bore cooled in the upper part only where cooling is needed; its running surface is specially treated to enhance wear resistance. The bore-cooled cylinder head is provided with a thick bottom for control of mechanical and thermal loads, and six holding bolts for good load distribution. Heavy fuel service is underwritten by exhaust valves with a Nimonic head and welded-on hard seat facing. A fully forged, continuous grain flow crankshaft has large diameter journals and pins for low bearing loads, and is fitted with hydraulically tightened counterweight bolts. The connecting rods are forged in alloy steel and machined all over, and feature an obliquely split big end with hydraulically tightened bolts. The tri-metal thin-walled bush bearings are formed from steel backed with lead/bronze bearing material and soft overlay. The two-piece piston is fitted with three compression rings and an oil scraper ring, all chromium plated to secure low wear. A L’Orange fuel injection system was developed for an injection pressure of 1400 bar (endurance tested at 1700 bar) with constant pressure unloading for cavitation-free operation at all loads and speeds. A Bergen-developed cleaning/lubricating system cleans the lower pump parts of heavy fuel residues and lubricates the moving parts, helping to reduce the risk of fuel rack sticking problems. An impulse turbocharging system based on ABB VTR..4 turbochargers is specified for six- and nine-cylinder engines, and a modified pulse converter
618 Bergen (Rolls-Royce)
Figure 23.1 A Bergen B32:40 engine in V12-cylinder form
system for the eight-cylinder model. Operation at low loads is fostered by elevated charge air temperatures through two-stage charge air cooling, high fuel injection pressures and optimized valve timing.
BV Engine The first BV engines—twin V12-cylinder models, each developing 5294 kW at 750 rev/min—were delivered in 1998 for powering a large anchor handling/ tug/supply vessel (Figure 23.1). The BV design is based on a single-piece engine block cast in GGG500 nodular iron carrying two banks of cylinders in a 55° V-configuration (Figure 23.2), an underslung crankshaft (Figure 23.3) and two camshafts; it also incorporates the charge air receiver between the cylinder banks. The camshafts are located outside each bank and housed in opensided recesses in the block, allowing the complete camshafts to be removed sideways. At the front of the block is an opening for the charge air cooler and another for the auxiliary gear drive; the timing gears are arranged at the rear of the engine. The whole structure is designed for firing pressures in excess of 200 bar. An advantage of the block material is that it can be repaired by welding in the event of accidental damage. A new cylinder liner design specified for the BV engines features a thicker upper wall section than the in-line cylinder BR models and a revised borecooling layout (Figure 23.4). The liner, rated for mean effective pressures up to
B32:40 engine 619
Figure 23.2 The BV engine block is a nodular iron casting
32 bar and peak pressures in excess of 220 bar, was subsequently standardized for all B-series engines. Small changes were made to the BV cylinder heads, mainly a new head gasket matching the redesigned liner. The two-piece piston is essentially the same as that used in the BR engines, with a nodular iron skirt and bore-cooled steel crown. The connecting rods were lengthened but the same bearings were used as before. Shorter fuel injection periods dictated strengthened camshafts to meet the increased loads, with a larger diameter both for the shaft and for the cam base circles. The fuel pumps are the same as those for BR engines but the fuel supply system was modified, chiefly by increasing pipe volumes and changing the layout to avoid cavitation and smooth out vibration caused by pressure pulses from the pumps. Twin turbochargers mounted above the two insert-type charge air coolers operate on the impulse system, the pipework enclosed in an insulated box between the cylinder banks. A choice of electronic governors is offered, operating in conjunction with a standardized hydro-mechanical actuator. All electrical transducers on the BV engine are linked to a common electrical rail, one on each side of the engine, in a neat layout enabling faulty transducers to be quickly changed.
B32:40 engine The B-series benefited from another rejuvenation in the shape of the longer stroke (400 mm) B32:40 design, offering an output of 500 kW/cylinder at 750 rev/min with a mean effective pressure of 24.9 bar. Production engines became available in the year 2000, supplementing the standard B-series in the programme. The B32:40 was initially offered in
620 Bergen (Rolls-Royce)
Figure 23.3 Crankshaft of the BV engine
six-, eight- and nine-in-line and V12-cylinder configurations to span a power band from 3000 kW to 6000 kW; outputs up to 9000 kW were planned by extending the V-cylinder programme. A new crankshaft design was incorporated to achieve the longer stroke and provide increased bearing areas, with new bearing technology addressing the larger bearing loads. Modified cylinder liners sought good control over temperatures at all points, and the piston/ring designs were also changed to minimize lube oil consumption and cylinder wear. The cylinder head design and material specification were refined to allow a small rise in the maximum combustion pressure and to handle the greater combustion air throughput from the upgraded turbocharging system. A new fuel injection system provided both an increase in capacity and a higher injection pressure. These changes contributed to a specific fuel consumption of 183 g/kW h at the rated speed of 750 rev/min and NOx emissions under the IMO limit. Improved reliability and maintainability were promised by a new pump-end module and turbocharger support structure.
B32:40 engine 621
Figure 23.4 BV engine cylinder liner with bore-cooled upper part, also applied to the in-line cylinder BR models
B32:40 Details Cylinder block: one-piece nodular cast iron design of rigid structure with underslung crankshaft, cast-in charge air manifold and large crankcase doors. The main bearing bolts are hydraulically tightened. Cylinder liner: centrifugally cast, bore-cooled design with a running surface treated to improve wear resistance; a carbon-cutting ring is incorporated at the top of the liner. Cylinder head: bore-cooled flame plate; six hydraulically tightened securing bolts to ensure even distribution; new cooled exhaust valve seat. Crankshaft: continuous grain flow forged; large diameter journals and pins; hydraulically tightened counterweight bolts. Connecting rod: forged of alloy steel and fully machined; obliquely split and serrated big end; hydraulically tightened big end bolts. Bearings: steel backed with Sn/Al bearing material. Piston: improved oil-cooled two-piece design; two compression rings and one oil scraper ring, all chromium plated. Fuel injection system: pumps designed for 2000 bar injection pressure; totally enclosed in heat-insulated compartment; constant pressure unloading for cavitation-free operation at all loads and speeds. Turbocharging system: multi-pulse converter system based on ABB TPL series turbochargers; easily removable insulation panels for inspection and maintenance.
622 Bergen (Rolls-Royce) Clean Design versions of the B32:40 engine were introduced for operators keen to minimize the environmental impact of their tonnage, the first B32:40V12P models to this specification being delivered in mid-2006 for offshore vessel projects. The challenge of reducing NOx emissions to 80 per cent below IMO Tier I requirements was met by Rolls-Royce without undermining power output or significantly increasing specific fuel consumption levels. Among the many refinements adopted were a revised piston bowl shape, along with modifications to the injector nozzles and other fuel system components, and turbocharger matching. Such changes reportedly avoided an increase in smoke output during part-load operation, which is a potential side effect of NOx reduction measures. A 10 per cent uprating announced in 2008 raised the maximum output to 550 kW/cylinder, the B32:40 series then spanning a power band from 3300 kW to 8800 kW.
C-Engine (C25:33L) A completely new design, the C25:33L, was launched in mid-2001 after a joint development project between Bergen and Hyundai Heavy Industries of South Korea, which markets and builds the engine as the HiMSEN H25/33. Flexibility in terms of power and speed ranges was a key development criterion to allow the 250 mm bore engine to target heavy fuel-burning gensets and smaller propulsion plants. Outputs from 1200 kW to 2700 kW at speeds from 720 rev/min to 1000 rev/min were initially covered by five- to nine-cylinder in-line models, with V-engines planned to double the power threshold. The C25:33L was expected eventually to replace the popular but ageing K-series, particularly in the genset market. The first four production engines (nine-cylinder models) were due for delivery in spring 2002 as the core of a diesel–electric propulsion plant for an offshore service vessel. In drawing up the design parameters, the stroke (330 mm) was determined by the piston speed which, in turn, was set by the desired time-between-overhauls of 15 000 h for the top end and 30 000 h for the bottom end, running on heavy fuel oil. The running speed was determined by the frequencies in genset applications, focusing on 900 rev/min to 1000 rev/min for 60 Hz and 50 Hz requirements. These ratings sought the best compromise between an industry preference for a moderate speed in heavy-duty gensets and the potentially lower price per kilowatt from a faster running set. The engines can also be supplied, however, for 720/750 rev/min operation. The C25:33L engine, Figure 23.5, is based on a compact and stiff nodular cast iron frame, with the charge air receiver, lube oil channel and coolant transfer channel incorporated in the casting to eliminate pipework. A continuous grain flow forged steel crankshaft with steel plate balance weights allowed the cylinder centre distance to be kept the same as the K-series engine in the interests of compactness and rigidity. Full power can be taken off at either end of the crankshaft, and an additional main bearing allows single-bearing alternators to be driven.
C-engine (C25:33L) 623
Figure 23.5 Primary modules of Bergen C25:33L engine
A key feature is the cylinder unit system, allowing a complete liner, piston, upper connecting rod, water jacket and cylinder head to be drawn as an assembly for servicing or exchange. The components are clamped together by the cylinder jacket and held down by four cylinder head bolts. A duct transfers air, exhaust and cooling water to and from the head, each cylinder unit being connected to its neighbour by quick-acting couplings to speed assembly and dismantling. The cylinder liner and water jacket combination is of the ‘open deck’ type, designed for intensive cooling and high strength without stress raisers in the critical top-end zone. The piston comprises a steel crown with three rings and a nodular cast iron skirt. An extended life and low controlled lube oil consumption are fostered by a chrome-ceramic piston ring coating, an anti-polishing ring at the top of the cylinder liner and special honing of the liner surface. A three-part connecting rod enables its upper part to be detached when drawing pistons without disturbing the big end bearing. One mechanical fuel pump is provided for each cylinder, with a simple two-step electronic timing feature controlled by the engine management system. (A common rail fuel system was not selected by Bergen because it was not seen as essential for the genset applications envisaged, nor as durable enough for unrestricted heavy fuel operation.) An impulse turbocharging system is based on an uncooled radial turbocharger which can be mounted at either end of the engine to suit the particular installation. A swift response to load changes, with minimal smoke emissions under rapidly changing load and
624 Bergen (Rolls-Royce) speed conditions, is fostered by the high-efficiency turbocharging, two-stage charge air cooling with electronic temperature control and a high-speed electronic governor. Ease of maintenance was addressed by providing good access to key components and a small number of hydraulic tools able to handle all the main bolts. Ancillaries are grouped in a front-end module accommodating pumps, charge air cooler, lube oil cooler and filters. The components are designed for plugging-in, with a minimum of joints avoiding leakages. Bergen C25:33 engine data Bore
250 mm
Stroke
330 mm
Speed
720–1000 rev/min
Output
220–300 kW/cyl
Cylinders
5, 6, 7, 8, 9L
Power range
1200–2700 kW
Mean effective pressure
22.6–24.7 bar
Mean piston speed
7.9–11 m/s
Firing pressure
190 bar
Specific fuel consumption
182–186 g/kW h
Output of the C25:33 design was raised by 10 per cent to 330 kW/cylinder in 2008, taking the upper rating to just under 3000 kW from the nine-cylinder model, and a Clean Design version introduced with emissions reduced to a minimum of 20 per cent less than IMO limits. The environmental improvement resulted from applying the Miller cycle in combination with an increase in compression ratio. To avoid smoke at low load and poor transient load behaviour in the low load range, which are negative consequences of the Miller cycle, the CD engines are equipped with variable valve timing (VVT) mechanisms. This enables the Miller cycle inlet valve timing to be turned off for low load running, with control of the VVT system exercised by the engine’s control logic. Advances in turbocharging technology, delivering higher pressure ratios, contributed to the power uprating in association with some changes in engine parameters.
GAS engines Growing availability of LNG for gas-fuelled vessels, particularly in Scandinavian and Baltic regions, stimulated Bergen to invest further in spark-ignited engines. The KV-G4 gas engine, now in Norwegian ferry service, was derived from the long-established 250 mm bore K-series medium-speed diesel design.
Gas engines 625 Introduced as a marine genset drive in 2002, it was released in 2004 as a variable speed engine for direct-mechanical propulsion. Design work on the spark-ignited 350 mm bore B-gas engine (B35:40) began in spring 2002, tapping experience with the successful 320 mm bore B-series diesel engine. A V12-cylinder prototype engine developing 5100 kW made its commercial debut in a Danish combined heat and power station in 2003 after a comprehensive test programme in Bergen. Orders booked in 2008 call for B35:40V12PG engines developing 5250 kW to power small roro/container vessels, the world’s first LNG-fuelled cargo tonnage. The B-gas engine series also offers V16- and V20-cylinder versions, taking the power band up to 9000 kW. Adding to the K-series and B-series gas engine portfolio, Rolls-Royce is developing a gas variant of the 250 mm bore C-series diesel design in six-, eight- and nine-cylinder versions. See also Chapter 2 for Bergen gas engines.
Bergen (Rolls-Royce) The diverse shipbuilding and marine engineering interests of Norway’s Ulstein group for many years embraced the design and production of Bergen mediumspeed engines, now a key element of the UK Rolls-Royce group’s diesel interests. Two Bergen engine families for propulsion and genset applications—the 250 mm bore K-series which dates from the early 1970s, and the 320 mm bore B-series introduced in 1986—have been progressively upgraded and were joined in 2001 by a completely new design, the 250 mm bore C-series, developed in co-operation with Hyundai Heavy Industries of South Korea.
K-Series First introduced in 1971, the 250 mm bore/300 mm stroke K-engine was designed mainly to be a genset drive but numerous propulsion plant applications have been logged in tugs, offshore supply ships and fishing vessels. Engines are available as in-line three-to-nine-cylinder or V12-, 16- and 18-cylinder models covering an output range from 600 kW to 4010 kW at speeds of 720/750/ 825/900 rev/min. Design improvements introduced over the years have sought to maintain market competitiveness, the maximum brake mean effective pressure being raised from 20 bar to 22 bar to increase the output to 220 kW/cylinder. The later adoption of a ‘hot box’ arrangement for the fuel injection system followed a trend in larger engine designs. It provides the engine with cleaner lines and improves the working environment in the machinery room: temperatures are reduced and any fuel leakage from the injection system components is retained within the box. Other improvements have included a revised timing chain, sprockets and camshaft system to extend service life and accommodate a higher injection pressure. The valve stem rotators have been strengthened and the valve guides and guide seals improved to ensure better operational results running at 900 rev/min on heavy fuel. The provision of a carbon-cutting (or anti-polishing) ring at the top of the cylinder unit significantly reduced lube oil consumption and the amount of
615
616 Bergen (Rolls-Royce) insoluble deposits in the oil (hence extending filter life). The ring comprises a sleeve insert which sits between the top piston ring turning point and the top of the cylinder liner. It has a slightly smaller diameter than the bore of the liner, this reduction being accommodated by a reduced diameter piston top land. The main effect of the ring is to prevent the build-up of carbon around the edges of the piston crown which causes liner polishing and wear with an associated increase in lube oil consumption. A secondary function is a sudden compressive effect on the piston ring belt as the piston and carbon-cutting ring momentarily interface; this forces lube oil away from the combustion area and again helps to reduce consumption. The efficiency of the rings was such that Bergen found it necessary to redesign the ring pack to secure a desirable degree of oil consumption. The carbon-cutting ring, refined over a 2-year period, is now standard on all new Bergen engines, and numerous engines in service have benefited from retrofits.
B-Series The 320 mm bore/360 mm stroke B-series engine was conceived as a compact, heavy fuel-burning main engine and launched in 1986 with special features facilitating operation on lower price, poor quality fuel oils. The design’s tolerance of fuel quality has been demonstrated by an offshore rig installation running on crude oil direct from the well after degassing. A nominal rating of 360 kW/cylinder at 750 rev/min was initially quoted but some of the first engines sold were contracted at around 400 kW/cylinder, equivalent to a 10 per cent overload. An uprating in 1991/1992 took the output to 440 kW/cylinder at 750 rev/min which yielded a power band of 1870 kW to 3970 kW from in-line six-, eight- and nine-cylinder BR models. A decision to double the upper limit of the range—to 7940 kW—was announced in 1996 through the introduction of V12-, 16- and 18-cylinder models. These BV engines (see Section BV Engine) were planned to benefit from Bergen’s exhaust emissions reduction R&D by adopting faster fuel injection, a change in compression ratio and different valve timing to the existing in-line cylinder engines. The B-engine was reportedly the first of its size to feature a completely bore-cooled cylinder unit and combustion space (initially, a bore-cooled liner and head and, later, bore-cooled pistons). This arrangement yields good strength and stiffness combined with good temperature control, which is important in heavy fuel operation. Early in the engine’s development it was discovered that the temperature profile on the liner was not the optimum. The resulting design change, benefiting subsequent production engines, has reportedly proved effective in the long term for both propulsion and auxiliary power duties, even at medium load. A drawback to the original bore-cooling concept soon became apparent, however: the use of electrically driven cooling water pumps. Electrical black-outs could not be tolerated, and the fluctuation in cooling water flow away from the
B-series 617 optimum resulted in some cracking of liners. An early change therefore saw a switch to engine-driven pumps and the incorporation of a new strengthened liner design. In Arctic areas, it was also found that piston rings were vulnerable to poor ignition qualities and high temperature gradients, resulting, in some cases, in ring cracking. This problem was solved by optimizing the clearances and the layout of the ring pack. Other refinements following early installations included an improved bearing arrangement for the timing gears and, in line with other enginebuilders, a new fuel injection system was introduced in 1991 to counter an industry-wide problem of leakages. The complete injection system was enhanced by bigger pumps, better seals, larger nozzles and improved high-pressure pipes. The improvements coincided with the 1991/1992 decision to uprate the engine’s output to 440 kW/cylinder while retaining the same engine speed of 750 rev/min. Contributing to this power rise—and a brake mean effective pressure increase to 24.4 bar—was the first application of ABB’s VTR-4P high-efficiency turbocharger with a titanium compressor wheel, and a new type of composite piston with a bore-cooled forged steel crown and nodular cast iron skirt. A carboncutting ring (described above in the Section K-series) was introduced to the B-engine in 1994. The one-piece design cylinder block of nodular cast iron is arranged for an underslung crankshaft and features large crankcase doors. A receiver and supply ducts for oil and water are cast in. The centrifugally cast cylinder liner is bore cooled in the upper part only where cooling is needed; its running surface is specially treated to enhance wear resistance. The bore-cooled cylinder head is provided with a thick bottom for control of mechanical and thermal loads, and six holding bolts for good load distribution. Heavy fuel service is underwritten by exhaust valves with a Nimonic head and welded-on hard seat facing. A fully forged, continuous grain flow crankshaft has large diameter journals and pins for low bearing loads, and is fitted with hydraulically tightened counterweight bolts. The connecting rods are forged in alloy steel and machined all over, and feature an obliquely split big end with hydraulically tightened bolts. The tri-metal thin-walled bush bearings are formed from steel backed with lead/bronze bearing material and soft overlay. The two-piece piston is fitted with three compression rings and an oil scraper ring, all chromium plated to secure low wear. A L’Orange fuel injection system was developed for an injection pressure of 1400 bar (endurance tested at 1700 bar) with constant pressure unloading for cavitation-free operation at all loads and speeds. A Bergen-developed cleaning/lubricating system cleans the lower pump parts of heavy fuel residues and lubricates the moving parts, helping to reduce the risk of fuel rack sticking problems. An impulse turbocharging system based on ABB VTR..4 turbochargers is specified for six- and nine-cylinder engines, and a modified pulse converter
618 Bergen (Rolls-Royce)
Figure 23.1 A Bergen B32:40 engine in V12-cylinder form
system for the eight-cylinder model. Operation at low loads is fostered by elevated charge air temperatures through two-stage charge air cooling, high fuel injection pressures and optimized valve timing.
BV Engine The first BV engines—twin V12-cylinder models, each developing 5294 kW at 750 rev/min—were delivered in 1998 for powering a large anchor handling/ tug/supply vessel (Figure 23.1). The BV design is based on a single-piece engine block cast in GGG500 nodular iron carrying two banks of cylinders in a 55° V-configuration (Figure 23.2), an underslung crankshaft (Figure 23.3) and two camshafts; it also incorporates the charge air receiver between the cylinder banks. The camshafts are located outside each bank and housed in opensided recesses in the block, allowing the complete camshafts to be removed sideways. At the front of the block is an opening for the charge air cooler and another for the auxiliary gear drive; the timing gears are arranged at the rear of the engine. The whole structure is designed for firing pressures in excess of 200 bar. An advantage of the block material is that it can be repaired by welding in the event of accidental damage. A new cylinder liner design specified for the BV engines features a thicker upper wall section than the in-line cylinder BR models and a revised borecooling layout (Figure 23.4). The liner, rated for mean effective pressures up to
B32:40 engine 619
Figure 23.2 The BV engine block is a nodular iron casting
32 bar and peak pressures in excess of 220 bar, was subsequently standardized for all B-series engines. Small changes were made to the BV cylinder heads, mainly a new head gasket matching the redesigned liner. The two-piece piston is essentially the same as that used in the BR engines, with a nodular iron skirt and bore-cooled steel crown. The connecting rods were lengthened but the same bearings were used as before. Shorter fuel injection periods dictated strengthened camshafts to meet the increased loads, with a larger diameter both for the shaft and for the cam base circles. The fuel pumps are the same as those for BR engines but the fuel supply system was modified, chiefly by increasing pipe volumes and changing the layout to avoid cavitation and smooth out vibration caused by pressure pulses from the pumps. Twin turbochargers mounted above the two insert-type charge air coolers operate on the impulse system, the pipework enclosed in an insulated box between the cylinder banks. A choice of electronic governors is offered, operating in conjunction with a standardized hydro-mechanical actuator. All electrical transducers on the BV engine are linked to a common electrical rail, one on each side of the engine, in a neat layout enabling faulty transducers to be quickly changed.
B32:40 engine The B-series benefited from another rejuvenation in the shape of the longer stroke (400 mm) B32:40 design, offering an output of 500 kW/cylinder at 750 rev/min with a mean effective pressure of 24.9 bar. Production engines became available in the year 2000, supplementing the standard B-series in the programme. The B32:40 was initially offered in
620 Bergen (Rolls-Royce)
Figure 23.3 Crankshaft of the BV engine
six-, eight- and nine-in-line and V12-cylinder configurations to span a power band from 3000 kW to 6000 kW; outputs up to 9000 kW were planned by extending the V-cylinder programme. A new crankshaft design was incorporated to achieve the longer stroke and provide increased bearing areas, with new bearing technology addressing the larger bearing loads. Modified cylinder liners sought good control over temperatures at all points, and the piston/ring designs were also changed to minimize lube oil consumption and cylinder wear. The cylinder head design and material specification were refined to allow a small rise in the maximum combustion pressure and to handle the greater combustion air throughput from the upgraded turbocharging system. A new fuel injection system provided both an increase in capacity and a higher injection pressure. These changes contributed to a specific fuel consumption of 183 g/kW h at the rated speed of 750 rev/min and NOx emissions under the IMO limit. Improved reliability and maintainability were promised by a new pump-end module and turbocharger support structure.
B32:40 engine 621
Figure 23.4 BV engine cylinder liner with bore-cooled upper part, also applied to the in-line cylinder BR models
B32:40 Details Cylinder block: one-piece nodular cast iron design of rigid structure with underslung crankshaft, cast-in charge air manifold and large crankcase doors. The main bearing bolts are hydraulically tightened. Cylinder liner: centrifugally cast, bore-cooled design with a running surface treated to improve wear resistance; a carbon-cutting ring is incorporated at the top of the liner. Cylinder head: bore-cooled flame plate; six hydraulically tightened securing bolts to ensure even distribution; new cooled exhaust valve seat. Crankshaft: continuous grain flow forged; large diameter journals and pins; hydraulically tightened counterweight bolts. Connecting rod: forged of alloy steel and fully machined; obliquely split and serrated big end; hydraulically tightened big end bolts. Bearings: steel backed with Sn/Al bearing material. Piston: improved oil-cooled two-piece design; two compression rings and one oil scraper ring, all chromium plated. Fuel injection system: pumps designed for 2000 bar injection pressure; totally enclosed in heat-insulated compartment; constant pressure unloading for cavitation-free operation at all loads and speeds. Turbocharging system: multi-pulse converter system based on ABB TPL series turbochargers; easily removable insulation panels for inspection and maintenance.
622 Bergen (Rolls-Royce) Clean Design versions of the B32:40 engine were introduced for operators keen to minimize the environmental impact of their tonnage, the first B32:40V12P models to this specification being delivered in mid-2006 for offshore vessel projects. The challenge of reducing NOx emissions to 80 per cent below IMO Tier I requirements was met by Rolls-Royce without undermining power output or significantly increasing specific fuel consumption levels. Among the many refinements adopted were a revised piston bowl shape, along with modifications to the injector nozzles and other fuel system components, and turbocharger matching. Such changes reportedly avoided an increase in smoke output during part-load operation, which is a potential side effect of NOx reduction measures. A 10 per cent uprating announced in 2008 raised the maximum output to 550 kW/cylinder, the B32:40 series then spanning a power band from 3300 kW to 8800 kW.
C-Engine (C25:33L) A completely new design, the C25:33L, was launched in mid-2001 after a joint development project between Bergen and Hyundai Heavy Industries of South Korea, which markets and builds the engine as the HiMSEN H25/33. Flexibility in terms of power and speed ranges was a key development criterion to allow the 250 mm bore engine to target heavy fuel-burning gensets and smaller propulsion plants. Outputs from 1200 kW to 2700 kW at speeds from 720 rev/min to 1000 rev/min were initially covered by five- to nine-cylinder in-line models, with V-engines planned to double the power threshold. The C25:33L was expected eventually to replace the popular but ageing K-series, particularly in the genset market. The first four production engines (nine-cylinder models) were due for delivery in spring 2002 as the core of a diesel–electric propulsion plant for an offshore service vessel. In drawing up the design parameters, the stroke (330 mm) was determined by the piston speed which, in turn, was set by the desired time-between-overhauls of 15 000 h for the top end and 30 000 h for the bottom end, running on heavy fuel oil. The running speed was determined by the frequencies in genset applications, focusing on 900 rev/min to 1000 rev/min for 60 Hz and 50 Hz requirements. These ratings sought the best compromise between an industry preference for a moderate speed in heavy-duty gensets and the potentially lower price per kilowatt from a faster running set. The engines can also be supplied, however, for 720/750 rev/min operation. The C25:33L engine, Figure 23.5, is based on a compact and stiff nodular cast iron frame, with the charge air receiver, lube oil channel and coolant transfer channel incorporated in the casting to eliminate pipework. A continuous grain flow forged steel crankshaft with steel plate balance weights allowed the cylinder centre distance to be kept the same as the K-series engine in the interests of compactness and rigidity. Full power can be taken off at either end of the crankshaft, and an additional main bearing allows single-bearing alternators to be driven.
C-engine (C25:33L) 623
Figure 23.5 Primary modules of Bergen C25:33L engine
A key feature is the cylinder unit system, allowing a complete liner, piston, upper connecting rod, water jacket and cylinder head to be drawn as an assembly for servicing or exchange. The components are clamped together by the cylinder jacket and held down by four cylinder head bolts. A duct transfers air, exhaust and cooling water to and from the head, each cylinder unit being connected to its neighbour by quick-acting couplings to speed assembly and dismantling. The cylinder liner and water jacket combination is of the ‘open deck’ type, designed for intensive cooling and high strength without stress raisers in the critical top-end zone. The piston comprises a steel crown with three rings and a nodular cast iron skirt. An extended life and low controlled lube oil consumption are fostered by a chrome-ceramic piston ring coating, an anti-polishing ring at the top of the cylinder liner and special honing of the liner surface. A three-part connecting rod enables its upper part to be detached when drawing pistons without disturbing the big end bearing. One mechanical fuel pump is provided for each cylinder, with a simple two-step electronic timing feature controlled by the engine management system. (A common rail fuel system was not selected by Bergen because it was not seen as essential for the genset applications envisaged, nor as durable enough for unrestricted heavy fuel operation.) An impulse turbocharging system is based on an uncooled radial turbocharger which can be mounted at either end of the engine to suit the particular installation. A swift response to load changes, with minimal smoke emissions under rapidly changing load and
624 Bergen (Rolls-Royce) speed conditions, is fostered by the high-efficiency turbocharging, two-stage charge air cooling with electronic temperature control and a high-speed electronic governor. Ease of maintenance was addressed by providing good access to key components and a small number of hydraulic tools able to handle all the main bolts. Ancillaries are grouped in a front-end module accommodating pumps, charge air cooler, lube oil cooler and filters. The components are designed for plugging-in, with a minimum of joints avoiding leakages. Bergen C25:33 engine data Bore
250 mm
Stroke
330 mm
Speed
720–1000 rev/min
Output
220–300 kW/cyl
Cylinders
5, 6, 7, 8, 9L
Power range
1200–2700 kW
Mean effective pressure
22.6–24.7 bar
Mean piston speed
7.9–11 m/s
Firing pressure
190 bar
Specific fuel consumption
182–186 g/kW h
Output of the C25:33 design was raised by 10 per cent to 330 kW/cylinder in 2008, taking the upper rating to just under 3000 kW from the nine-cylinder model, and a Clean Design version introduced with emissions reduced to a minimum of 20 per cent less than IMO limits. The environmental improvement resulted from applying the Miller cycle in combination with an increase in compression ratio. To avoid smoke at low load and poor transient load behaviour in the low load range, which are negative consequences of the Miller cycle, the CD engines are equipped with variable valve timing (VVT) mechanisms. This enables the Miller cycle inlet valve timing to be turned off for low load running, with control of the VVT system exercised by the engine’s control logic. Advances in turbocharging technology, delivering higher pressure ratios, contributed to the power uprating in association with some changes in engine parameters.
GAS engines Growing availability of LNG for gas-fuelled vessels, particularly in Scandinavian and Baltic regions, stimulated Bergen to invest further in spark-ignited engines. The KV-G4 gas engine, now in Norwegian ferry service, was derived from the long-established 250 mm bore K-series medium-speed diesel design.
Gas engines 625 Introduced as a marine genset drive in 2002, it was released in 2004 as a variable speed engine for direct-mechanical propulsion. Design work on the spark-ignited 350 mm bore B-gas engine (B35:40) began in spring 2002, tapping experience with the successful 320 mm bore B-series diesel engine. A V12-cylinder prototype engine developing 5100 kW made its commercial debut in a Danish combined heat and power station in 2003 after a comprehensive test programme in Bergen. Orders booked in 2008 call for B35:40V12PG engines developing 5250 kW to power small roro/container vessels, the world’s first LNG-fuelled cargo tonnage. The B-gas engine series also offers V16- and V20-cylinder versions, taking the power band up to 9000 kW. Adding to the K-series and B-series gas engine portfolio, Rolls-Royce is developing a gas variant of the 250 mm bore C-series diesel design in six-, eight- and nine-cylinder versions. See also Chapter 2 for Bergen gas engines.