DieselShip

 

High speed engines

 

High speed four-stroke trunk piston engines are widely specified for propelling small, generally specialized, commercial vessels and as main and emergency genset drives on all types of tonnage. The crossover point between high and medium speed diesel designs is not sharply defined but for the purposes of this chapter engines running at 1000 rev/min and over are reviewed.

Marine high speed engines traditionally tended to fall into one of two design categories: high performance or heavy duty types. High performance models were initially aimed at the military sector, and their often complex designs negatively affected manufacturing and maintenance costs. Applications in the commercial arena sometimes disappointed operators, the engines dictating frequent overhauls and key component replacement.

Heavy duty high speed engines in many cases were originally designed for off-road vehicles and machines but have also found niches in stationary power generation and locomotive traction fields. A more simple and robust design with modest mean effective pressure ratings compared with the high performance contenders yields a comparatively high weight/power ratio. But the necessary time-between-overhauls and component lifetimes are more acceptable to civilian operators.

In developing new models, high speed engine designers have pursued essentially the same goals as their counterparts in the low and medium speed sectors: reliability and durability, underwriting extended overhaul intervals and component longevity and hence low maintenance costs; easier installation and servicing; compactness and lower weight; and enhanced performance across the power range with higher fuel economy and reduced noxious emissions.

Performance development progress over the decades is highlighted by considering the cylinder dimension and speed of an engine required to deliver 200 kW/cylinder (Figure 1). In 1945 a bore of 400 mmplus and a speed of around 400 rev/min were necessary; in 1970 typical medium speed engine parameters resulted in a bore of 300 mm and a speed of 600 rev/min, while typical high speed engine parameters were 250 mm and 1000 rev/min to yield 200 kW/cylinder.

 

Figure 1 Cylinder dimensions and speeds for medium and high speed engines delivering 200 kW / cylinder (1945, 1970 and 1995). (Reference Wartsila)

Today, that specific output can be achieved by a 200 mm bore high speed design running at 1500 rev/min.

Flexible manufacturing systems (FMS) have allowed a different approach to engine design. The reduced cost of machining has made possible integrated structural configurations, with more functions assigned to the same piece of metal. The overall number of parts can thus be reduced significantly over earlier engines (by up to 40 per cent in some designs), fostering improved reliability, lower weight and increased compactness without compromising on ease of maintenance. FMS also facilitates the offering of market-adapted solutions without raising cost: individual engines can be optimized at the factory for the proposed application.

A widening market potential for small high speed engines in propulsion and auxiliary roles encouraged the development in the 1990s of advanced new designs for volume production. The circa- 170 mm bore sector proved a particularly attractive target for leading European and US groups which formed alliances to share R&D, manufacture and marketing—notably Cummins with Wärtsilä Diesel, and MTU with Detroit Diesel Corporation.

High speed engine designs have benefited from such innovations as modular assembly, electronically controlled fuel injection systems, common rail fuel systems and sophisticated electronic control/ monitoring systems. Some of the latest small bore designs are even released for genset duty burning the same low grade fuel (up to 700 cSt viscosity) as low speed crosshead main engines.

Evolving a new design

An insight into the evolution of a high speed engine design for powering fast commercial vessels is provided by MTU of Germany with reference to its creation of the successful 130 mm bore Series 2000 and 165 mm bore Series 4000 engines, which together cover an output band from 400 kW to 2720 kW.

MTU notes first that operators of fast tonnage place high value on service life and reliability, with fuel economy and maximized freight capacity also important. In the fast vessel market, conflicting objectives arise between key parameters such as low specific fuel consumption, low weight/power ratio and extended engine service life. If one parameter is improved, at least one of the others is undermined. The engine designer’s aim is therefore to optimize co-ordination of the parameters to suit the application.

Knowledge of the anticipated service load profile is vital for determining the specific loads that must be addressed during the engine design stage so that the required maintenance and major overhaul intervals can be established. Load acceptance characteristics and performance map requirements have a strong influence on turbocharging and the maximum possible mean pressures.

Specifying performance map requirements is simultaneously connected with the selection of the lead application, in this case high speed tonnage. The maximum possible mean pressures are determined on the basis of the power-speed map requirements of various vessel types (for example, air cushion, hydrofoil and planing hull types) and the form of turbocharging (sequential or non-sequential, single or two-stage). With increasing mean pressures (higher power concentration), the weight/power ratio of the engine can be improved.

The maximum mean piston speed is derived from a service life requirement (time-between-overhaul) and the target for the weight/ power ratio. With increasing mean piston speed, a greater power concentration in a given volume is achieved, thus improving the weight/ power ratio. For fast vessel engines, mean piston speeds of 11–12 m/ s and mean effective pressures up to 22 bar (single-stage turbocharging) or 30 bar (two-stage turbocharging) are typical. Figure 2 shows the correlations of four-stroke engines for determining bore diameter, stroke and speed. The output per cylinder (Pe) is known from the power positioning of the proposed new engine, and the maximum mean pressure and maximum mean piston speed have already been established. The required minimum bore diameter (D) can thus be determined.

 

Figure 2 C alculation of power output

The appropriate stroke (s) is determined using the specified stroke/ bore ratio (s/D). If large s/D ratios are selected, a large engine height and width results (V-engine); small s/D ratios are associated with somewhat reduced fuel efficiency. For relevant MTU engines with good weight/power ratios, the stroke/bore ratio lies within a range of 1.1 to 1.25. The engine speed appropriate to the established stroke I determined via the resulting mean piston speed. Engine speed is an important factor for the customer as the size of the gearbox required is based on the speed and torque.

The peak firing pressure or peak firing pressure/mean pressure ratio is the most important factor influencing the specific effective fuel consumption. For high efficiency, MTU suggests, peak firing pressure/mean pressure ratios of around 8 should be targeted. With the mean pressure already specified, the peak firing pressure can be established. If, for example, a mean pressure of 22 bar (single-stage turbocharging) is selected, the peak firing pressure should lie in the 160–180 bar range. For two-stage turbocharged engines with correspondingly high mean pressures, peak firing pressures of above 200 bar must be targeted. With two-stage turbocharging, the potential for fuel consumption reduction can be increased using charge air cooling.

CATERPILLAR

A wide programme of high speed engines from the US designer Caterpillar embraces models with bore sizes ranging from 105 mm to 170 mm. The largest and most relevant to this review is the 170 mm bore/190 mm stroke 3500 series which is produced in V8-, V12- and V16-cylinder versions with standard and higher B-ratings to offer outputs up to around 2200 kW. The engines, with minimum/maximum running speeds of 1200/1925 rev/min, are suitable for propelling workboats, fishing vessels, fast commercial craft and patrol boats. Genset applications can be covered with ratings from 1000 kVA to 2281 kVA.

The series B engines (Figure 3) benefited from a number of mechanical refinements introduced to take full advantage of the combustion efficiency improvement delivered by an electronic control system. Electronically controlled unit fuel injectors combine high injection pressures with an advanced injector design to improve atomization and timing. Outputs were raised by 17 to 30 per cent above earlier 3500 series models.

 

Figure 3 Caterpillar 3512B engine with electronic control system

A special high performance variant of the V16-cylinder 3500 series model was introduced to target niche markets, the refinements seeking increased power, enhanced reliability and lower fuel and lubricating oil consumptions without undermining durability. This Phase II high performance version of the 3516 has an upper rating of 2237 kW at 1925 rev/min. It was released for fast passenger vessels with low-load factors with a standard maximum continuous rating of 1939 kW at 1835 rev/min and a ‘two hours out of 12’ rating of 2088 kW at 1880 rev/min. Optional higher ratings up to 2205 kW at 1915 rev/min can be specified for cooler climate deployment, with revised turbocharger, fuel injector and timing specifications.

Key contributions to higher performance came from high efficiency ABB turbochargers, a seawater aftercooler to supply colder air to the combustion chambers, larger and more aggressive camshafts, and a new deep crater piston design. The fuel is delivered through strengthened unit injectors designed and manufactured by Caterpillar to secure injection pressures of 1380 bar.

An optimum air-fuel mixture which can be burned extremely efficiently is fostered by the combination of a denser air intake andmthe high injection pressure. The reported result is a specific fuel consumption range at full load of 198–206 g/kWh with all fuel, oil and water pumps driven by the engine. Modifications to the steel crown/aluminium skirt pistons and rings lowered lubricating oil consumption to 0.55 g/kWh.

A particularly desirable feature for fast ferry propulsion is underwritten by the high efficiency combustion and low crevice volume pistons which help to eliminate visible exhaust smoke at all steady points along the propeller demand curve. The rear gears were widened and hardened to serve the higher pressure unit injectors. New gastight exhaust manifolds with bellow expansion joints and stainless steel O-rings improved engineroom air quality by eliminating exhaust gas leaks.

A longer-stroke variant of the Cat 3500 series B engine was introduced after marine field tests undertaken from early 1998, these 3512B and 3516B models offering as much as 13 per cent higher powers than their standard counterparts, with respective maximum commercial ratings of 1380 kW and 1864 kW at 1600 rev/min. Seven per cent mprovements in power-to-weight ratio and fuel economy were reported, along with lower emission levels than the standard engines. The higher output was achieved by enlarging the cylinder displacement (increasing the stroke by 25 mm) and without raising cylinder pressure or undermining bearing life or the durability of other key components.

A new single-piece forged crankshaft has more mass and is made from a stronger steel alloy than before to handle the higher loads. The connecting rods are longer and feature stronger shaft geometry; and a more robust rod pin end enhances the durability required for the increased piston speeds and higher inertia loads. The pistons are of the same two-piece design proven in standard Cat 3500 series B engines, a steel crown and aluminium skirt securing high strength and reduced weight. The engine footprint of these more powerful variants remained unchanged; only the dimensions of the higher capacity aftercooler and turbochargers were increased.

All Caterpillar 3500 series-B engines are controlled by a microprocessor-based electronic control module (ECM). Information is collected from engine sensors by the ECM which then analyses the data and adjusts injection timing and duration to optimize fuel efficiency and reduce noxious exhaust emissions. Electronic control also supports onboard and remote monitoring capabilities, the ECM reporting all information through a two-wire Cat Data Link to the instrument panel. The panel records and displays faults as well as operating conditions. An optional Customer Communications Module translates engine data to standard ASCII code for transmission to a PC or via satellite to remote locations.

Caterpillar’s Engine Vision System (EVS) is compatible with the high performance 3500 series-B engines and the company’s other electronically controlled engines. The EVS displays engine and transmission data, vessel speed, trip data, historical data, maintenance intervals, diagnostics and trouble-shooting information. Up to three engines can be monitored simultaneously, the system transferring between the vision display and individual ECMs via the two-wire data link.

An upgrade announced in 2002 introduced the 3500B series II engines with enhancements to their electronic control, monitoring, display and cooling systems as well as new derating and operating speed options designed for specific applications. New electronics included the latest Caterpillar ADEM III control system, allowing more engine parameters to be controlled and monitored, with more accuracy and fault-reporting capability. A new ‘programmable droop’ capability allows precise governor control for load-sharing applications. A combined cooling system, rather than two separate circuits, became an option. A higher maximum continuous rating of 2000 kW from the 3516B series II engine was offered to yield more power and bollard pull capacity for larger harbour tugs; the higher rating also addressed some types of ferries and offshore service vessels.

CUMMINS

The most powerful own-design engine in Cummins’ high speed programme, the KTA50-M2 model, became available from early 1996 (Figure 4). The 159 mm bore/159 mm stroke design is produced by the US group’s Daventry factory in the UK in V16-cylinder form with ratings of 1250 kW and 1340 kW for medium continuous duty and 1030 kW and 1180 kW for continuous duty applications. The running speeds range from 1600 rev/min to 1900 rev/min, depending on the duty; typical applications include fishing vessels, tugs, crewboats and small ferries.

 

Figure 4 Cummins’ largest own-design engine, the KTA50-M2 model

The KTA50-M2 engine benefited from a new Holset turbocharger, low temperature after-cooling and gallery-cooled pistons. Cummins’s Centry electronics system contributes to enhanced overall performance and fuel economy, providing adjustable all-speed governing, intermediate speed controls, dual power curves, a built-in hour meter and improved transient response. Diagnostic capabilities are also incorporated.

DEUTZ

A long tradition in high speed engine design is maintained by Deutz of Germany (formerly Deutz MWM) whose current programme is focused on the 616 and 620 series with an upper output limit of 2336 kW for propulsion and genset drives. Other high speed engines produced under the Deutz banner cover a power range down to 14 kW.

The 616 series is a 132 mm bore/160 mm stroke design covering propulsion plant applications from 320 kW to 1360 kW at speeds up to 2300 rev/min by V8-, 12- and 16-cylinder models (Figure 5).

Figure 5 V12 cylinder block of Deutz 616 engine

The 170 mm bore/195 mm stroke 620 series design also embraces V8, 12 and 16-cylinder versions covering a power band from 829 kW to 2336 kW at speeds up to 1860 rev/min for propulsion duty (Figure 6). Good exhaust gas exchange and optimum combustion with minimal emissions are fostered by cross-flow cylinder heads and four valves per cylinder, while a relatively high compression ratio promotes excellent cold-start characteristics and low fuel consumption. High pressure fuel injection further contributes to these operating qualities. Correct swirl under both low load and full load conditions is secured by the boost pressure-controlled throttle of the HALLO-Swirl system, a variable swirl-supporting air intake system. Outputs from 1035 kW to 3600 kW at 1000 rev/min are delivered by six, eight and nine in-line and V12- and V16-cylinder versions of the 240 mm bore/280 mm stroke 628 series, which can be operated on heavy fuels (RMK 35) as well as marine diesel oil.

 

Figure 6 V16 cylinder version of Deutz 620 series engine

GMT

Grandi Motori Trieste (GMT) of Italy—now part of the Wärtsilä Corporation—focused its high speed engine developments on a 230 mm bore design offered in several versions for commercial and naval propulsion applications as well as for genset drive duties (Figure 7). A heavy fuel-burning model was available for unifuel machinery installations while a non-magnetic version could be specified for minehunters.

The series was produced in standard (B230) form with a stroke of 270 mm and in BL230 long stroke (310 mm) form, later versions benefiting from improved cooling and turbocharging arrangements for higher outputs at speeds up to 1200 rev/min. The B230 had a rating of 210 kW/cylinder and the BL230 a rating of 225.5 kW/cylinder. Both types were produced in in-line four to V20-cylinder configurations.

A two-stage turbocharged version with variable compression ratio, the BL 230 DVM, developed 283 kW/cylinder at 1050 rev/min on a mean effective pressure of 25.1 bar to provide a compact plant for corvettes and frigates. The V20-cylinder model delivered 5660 kW.

 

Figure 7 GMT BL230 engines in a genset installation

A BL230P version was developed for operation on heavy fuel up to IFO 500 with a maximum speed of 1000 rev/min and a power rating— 190 kW/cylinder—lower than the gas oil-fuelled models. Its special features included: composite pistons with forged steel crowns and plasma-coated rings in the first groove for wear resistance; Nimonic A material exhaust valves; valve rotators; cooled fuel injection valves; and oversized fuel injection pumps for enhanced atomization and combustion. Other variants in the engine programme targeted natural gas and LPG burning installations.

A highly rigid cast iron main structure for the 230 mm bore engine incorporates the water, oil and air manifolds, virtually eliminating external pipes and fostering compactness. Camshafts, oil cooler, oil, water and fuel pumps, and filters are arranged for accessibility; and pistons and connecting rods are withdrawable from the top.

GMT’s high speed portfolio also included the A210 series, the 210 mm bore/230 mm stroke design developing 170 kW/cylinder at 1500 rev/min on a mean effective pressure of 16.2 bar. A programme embracing V6- to V20-cylinder models covered output demands up to 3400 kW. A special version designed for submarine propulsion—the compact and lightweight A210SM—benefited from anti-noise, shock and vibration characteristics. An ability to operate in severely inclined positions was also addressed, along with ease of access for maintenance.

ISOTTA FRASCHINI

A family of high speed engines from Isotta Fraschini, part of Italy’s Fincantieri group, is headed by the 170 mm bore/170 mm stroke 1700 series which is available in different versions for light, medium and heavy propulsion duties in commercial and military vessels, as well as for genset drives. A non-magnetic variant was developed for mine warfare vessels.

The 1700 series embraces V8, 12 and 16-cylinder models, all with a 90-degree configuration arranged on a high tensile alloy iron crankcase and featuring a direct fuel injection system and four valves per cylinder. Recent upgrades raised the power output, the largest model—the V1716 T2—now offering up to 2595 kW at 2100 rev/min, compared with its previous maximum rating of 2350 kW at the same speed.

MAN B&W HOLEBY

In 1995 MAN B&W Diesel’s genset engine specialist Holeby Diesel of Denmark supplemented its popular L23/30H and L28/32H medium speed auxiliary prime movers with the innovative high speed L16/24 series. The 160 mm bore/240 mm stroke design (Figure 8) was conceived as a new generation 1000/1200 rev/min engine dedicated to genset drives and capable of operating on an unrestricted load profile on heavy fuel up to 700 cSt/50°C viscosity. The programme embraces five-, six-, seven-, eight- and nine-cylinder models covering a power range from 450 kW to 900 kW.

The main problem in burning heavy fuel oil in small high speed engines is ignition delay. Smaller quantities of the volatile, easily combustible hydrocarbon fractions are present in such fuels than in lighter diesel fuels. The L16/24 designers addressed the problem by adopting a number of measures to achieve excellent heavy fuel combustion even at part- and low-load operation: a higher injection pressure (1500 bar), a higher opening pressure for the fuel valve, smaller nozzle hole diameters in the valve, and a higher compression ratio (15.5:1). The maximum combustion pressure is 180 bar. Another contribution came from a cylinder head design refined to improve the swirl of fuel in the combustion chamber.

Support-function components were traditionally distributed around the engine block and connected with externally mounted supply pipes. The practice was reversed for the L16/24 engine: all support elements— oil and water pumps, coolers, filters, and safety and regulator valves— are arranged in a single front-end box for ease of accessibility and maintenance (Figure 9); and the supply channels are cast into the block for maintenance-free operation. Virtually all the engine’s internal supply lines are channelled through the cooling water jacket and cylinder head. The arrangement considerably simplifies the overall design, reducing the overall number of components by some 40 per cent compared with earlier engines. The front-end box system components can be exchanged using clip-on/clip-off couplings without removing any pipes.

High rigidity was sought from a monobloc cast iron engine frame whose elements are all held under compressive stress. The frame is designed to accept an ideal flow of forces from the cylinder head down to the crankshaft and to yield low surface vibrations from the outer shell. Two camshafts are located in the frame: the camshaft for the inlet/exhaust valves is arranged on the exhaust side in a very high position; and the fuel injection camshaft is on the service side of the engine.

Covers in the frame sides offer access to the camshafts and crankcase; some of the covers are arranged to act as relief valves. There is no cooling water in the frame. The framebox is designed to minimize noise emission, the inner frame absorbing all the engine forces and

Figure 8 Cross-section of MAN B&W Holeby L16/24 genset engine. Note the separate

 

Figure 9 MAN B&W Holeby L16/24 engine. All main support ancillaries are grouped

the outer frame forming a stiff shell with minimal vibration (Figure 10). The main bearings for the underslung crankshaft are carried in heavy supports by tie-rods from the intermediate frame floor and secured by bearing caps. The caps are provided with side guides and held in place by studs with hydraulically tightened nuts. The main bearing features replaceable shells which are fitted without scraping. Both engine and alternator are mounted on a rigid baseframe that acts as a lubricating oil reservoir. Specially designed engine mounts reduce noise and vibration.

The centrifugal cast iron cylinder liner, housed in the bore of the engine frame, is clamped by the cylinder head and rests on its flange on the water jacket; it can thus expand freely downwards when heated during engine operation. The liner is of the high flange type, the height of the flange matching the water-cooled area to give a uniform temperature pattern over the entire liner surface. The liner’s lower part is uncooled to secure a sufficient margin for cold corrosion at the bottom end. There is no water in the crankcase area. Gas sealing between liner and cylinder head is effected by an iron ring. The liner

 

Figure 11 Noise emission and vibration from the MAN B&W Holeby LI6/24 engine are minimized by the inner frame, outer shell and cover arrangement

is fitted with a slip-fit-type fire ring at its top to reduce lubricating oil consumption and bore polishing.

The cast iron cylinder head, with integrated charge air receiver, is made in one piece and incorporates a bore-cooled thick-walled bottom. It has a central bore for the fuel injection valve and a four-valve crossflow configuration with a high flow coefficient. The valve pattern is turned about 20 degrees to the axis to achieve an intake swirl promoting optimized combustion. The head is hydraulically tightened by four nuts acting on studs screwed into the engine frame. A screwed-on top cover for the head has two main functions: oil sealing the rocker chamber and covering the complete top face of the head.

Air inlet and exhaust valve spindles are of heat-resistant material and their seats armoured with welded-on hard metal. All the spindles are fitted with valve rotators to ensure an even temperature on the valve discs and to prevent deposits forming on the seatings. The cylinder head is provided with replaceable valve seat rings of heat-resistant steel, and the exhaust valve seat rings are water cooled. The seating surfaces are hardened to minimize wear and prevent dent marks.

The valve rocker arms are actuated through rollers, roller guides and pushrods. The roller guides for the inlet and exhaust valves are mounted in the water jacket part. Access for dismantling is provided by a side cover on the pushrod chamber. Each rocker arm activates two spindles via a spring-loaded valve bridge with thrust screws and adjusting screws for valve clearance. The valve actuating gear is pressure feed-lubricated from the centralised lubricating system, through the water chamber part and from there into the rocker arm shaft to the rocker bearing.

The oil-cooled pistons comprise a nodular cast iron body and forged steel crown with two compression rings and one scraper ring fitted in hardened grooves. The different barrel-shaped profiles of the compression rings and their chromium-plated running surfaces aim to maximize sealing and minimize wear. The piston has a cooling space close to the crown and the ring zone which is supplied with oil from the engine lubricating system. Heat transfer, and thus cooling, is promoted by the shaker effect stimulated by the piston movement.

Oil is supplied to the cooling space through channels from the oil grooves in the piston pin bosses. Oil is drained from the space through ducts located diametrically to the inlet channels. The piston pin is fully floating and kept in position in the axial direction by two circlips.

The die-forged connecting rod has a big end with a horizontal split and bored channels to transfer oil from the big end to the small end. The big end bearing is of the tri-metal type coated with a running layer. The bearing shells are of the precision type and can therefore be fitted without scraping or any other adaptation. The tri-metal small end bearing is pressed into the connecting rod. The bush is provided with an inner circumferential groove and a pocket for distributing oil in the bush itself and for supplying oil to the pin bosses.

A one-piece forged crankshaft with hardened bearing surfaces is suspended in underslung, tri-metal main bearings coated with a running layer. To attain a suitable bearing pressure and vibration level the crankshaft is equipped with counterweights which are attached to the shaft by two hydraulic screws. At its flywheel end the crankshaft is itted with a gearwheel which, through two intermediate wheels, drives the twin camshafts. Also mounted here is a coupling flange for the alternator. At the opposite (front) end is a gearwheel connection for the lubricating oil and water pumps.

Lubricating oil for the main bearings is supplied through holes drilled in the engine frame. From the main bearings the oil passes through bores in the crankshaft to the big end bearings and thence through channels in the connecting rods to lubricate the piston pins and cool the pistons.

Separate camshafts for the inlet/exhaust valves and the fuel pump facilitate adjustment of the gas exchange settings without disturbing the fuel injection timing (Figure 8). Likewise, it is possible to adjust fuel injection without disturbing gas exchange parameters. The resulting flexibility allows engine operation to be adjusted and optimized for fuel economy or low NOx emissions. The camshafts are mounted in bearing bushes fitted in bores in the engine frame. The valve camshaft is arranged in a very high position on the engine exhaust side to secure a short and stiff valve train and reduce moving masses. The fuel injection camshaft is arranged on the service side of the engine.

Both camshafts are structured in single-cylinder sections and bearing sections in such a way that disassembly of individual cylinder sections is possible through the side openings in the crankcase. The camshafts and governor are driven by the main gear train at the flywheel end of the engine, rotating at a speed half that of the crankshaft. The lubricating oil pipes for the gearwheels are equipped with nozzles adjusted to apply lubricant at the points where the gearwheels mesh.

All fuel injection equipment is enclosed securely behind removable covers. Each cylinder is individually served by a fuel injection pump, high pressure pipe and injection valve with uncooled nozzle. The injection pump unit, mounted on the engine frame, comprises a pump housing embracing a roller guide, a central barrel and a plunger. The pump is activated by the fuel cam and the volume injected controlled by turning the plunger. The fuel injection valve is located in a valv sleeve in the centre of the cylinder head, its opening controlled by the fuel oil pressure and closure effected by a spring.

The high pressure fuel pipe is led through a bore in the cylinder head surrounded by a shielding tube. The tube also acts as a drain channel to ensure that any leakage from the fuel valve and the high pressure pipe is drained off.

A lamda controller ensures that all injected fuel is burnt, countering the internal engine pollution and increased wear that might otherwise result from genset step loading.

A constant pressure turbocharging system embraces an MAN B&W NR/S turbocharger purpose-designed for the L16/24 engine, charge air cooler, charge air receiver and exhaust gas receiver. The charge air cooler is a compact two-stage tube unit deploying a large cooling surface.

A patented ‘intelligent’ cooling water system was designed to secure an optimized temperature across the engine operating band from idling to full load. The system, which accepts fresh water within the 10–40°C temperature range, has one inlet and one outlet connection. Its two pumps, in combination with thermostatic valves, continuously regulate cooling water temperature to achieve the optimized operating condition. Since charge air from the turbocharger never falls below the dew point there is no danger of water condensation in the cylinders.

The cooling water system comprises a low temperature (LT) system and a high temperature (HT) system, each cooled by fresh water. The LT circuit is used to cool charge air and lubricating oil. The HT circuit cools the cylinder liners and heads, fostering optimized combustion conditions, limiting thermal load under high load conditions, and preventing hot corrosion in the combustion area. Under low load, the system is designed to ensure that the temperature is high enough for efficient combustion and that cold corrosion is avoided.

Water in the LT system passes through the low temperature circulating pump which drives the water through the second stage of the charge air cooler and then through the lubricating oil cooler before the water leaves the engine together with the high temperature water. The amount of water passing through the second stage of the charge air cooler is controlled by a three-way valve dependent on the charge airpressure. If the engine is operating at low-load condition the emperature regulation valve cuts off the LT water flow, thus securing preheating of the combustion air by the HT water circuit in the first stage.

The HT cooling water passes through the high temperature circulating pump and then through the first stage of the charge air cooler before entering the cooling water jacket and the cylinder head. It then leaves the engine with the low temperature water. Both LT and HT water leaves the engine via separate three-way thermostatic valves that control the water temperature.

All moving parts of the engine are lubricated with oil circulating under pressure, the system served by a lubricating oil pump of the helical gear type. A pressure control valve built into the system reduces the pressure before the filter with a signal taken after the filter to ensure constant oil pressure with dirty filters. The pump draws oil from the sump in the baseframe, the pressurized oil then passing through the lubricating oil cooler and the filter. The oil pump, cooler and filter are all located in the front box. The system can also be provided with a centrifugal filter. Lubricating oil cooling is carried out by the low temperature cooling water system, with temperature regulation effected by a thermostatic three-way valve on the oil side (see above). The engine is equipped as standard with an electrically driven prelubricating pump.

The L16/24 engine is prepared for MAN B&W Diesel’s CoCoS computerized surveillance system, a Microsoft Windows-based program undertaking fully integrated monitoring of engine operation, maintenance planning, and the control and ordering of spares. The four CoCoS software modules cover engine diagnosis, maintenance planning, spare parts catalogue, and stock and ordering

Each cylinder assembly (head, piston, liner and connecting rod) can be removed as a complete unit for repair, overhaul or replacement by a renovated unit onboard or ashore. Replacing a cylinder unit is accomplished by removing the  covers and high pressure fuel injection pipe, and disconnecting a snap-on coupling to the exhaust gas pipe. The only cooling water connections are to the cylinder unit as there is no cooling water in the baseframe. Inlet and outlet cooling water passes between cylinder units via bushes which are pushed aside in disassembling a unit. The charge air connections are dismounted in the same way. The four hydraulically fastened cylinder head nuts and the two connecting rod nuts (all six are of the same size) are then removed, allowing the 200 kg unit to be withdrawn from the engine.

 

Figure 11 MAN B&W Holey L16/24 engine: preparing for cylinder unit removal

The design principles of the L16/24 engine were later applied to the larger L27/38 and L21/31 medium speed engines, respectively introduced in 1997 and 2000 for both genset and propulsion applications

 

Figure 12 MAN B&W Holeby L16/24 engine: preparing for cylinder unit removal

MITSUBISHI

Fast ferry propulsion business potential stimulated the development in the early 1990s of the Mitsubishi S16R-S engine by the Japanese group’s Sagamihara Machinery Works. The higher performance V16- cylinder model was evolved from the established S16R design which had been in production since 1989 as a general purpose marine engine. A constant pressure turbocharging system based on a newly developed turbocharger and a revised fuel injection system contributed to a 20 per cent rise in the power output. The 170 mm bore/180 mm stroke design has a maximum continuous rating of 2100 kW at 2000 rev/min with overload ratings up to 2300 kW.

The weight was reduced to 89 per cent of the original engine, primarily through the adoption of aluminium alloy components optimized in size for the duty. An overall weight of 5500 kg underwrites a power-to-weight ratio of 2.62 kg/kW.

 

Figure 13 MAN B&W Holeby L16/24 engine: removing a complete cylinder unit

MTU

A portfolio of high performance high speed designs with an upper output limit of 9000 kW is offered by MTU (Motoren- und Turbinen- Union) of Germany, which was created in 1969 when Daimler-Benz and MAN consolidated the development and production of relevant engines from MAN and Maybach Mercedes-Benz. MTU Friedrichshafen became part of the Deutsche Aerospace group in 1989, and is now a DaimlerChrysler company.

Series 396

Addressing lower power demands, MTU’s Series 396 engine is long established as a propulsion and genset drive, the 165 mm bore/ 185 mm stroke design delivering up to 2560 kW at 2100 rev/min from V90-degree configuration 8-, 12- and 16-cylinder models (Figure 14). Engines are available in three different versions:

• TB04, with external charge air cooling (intercooler in raw water circuit).

 

Figure 14 MTU 16V 369 TE94 engine with split-circuit cooling system

• TC04, with internal charge air cooling (intercooler in engine coolant circuit).
• TE04, with internal charge air cooling (intercooler in engine coolant circuit; split-circuit coolant system).

TE split-circuit cooling system: the Series 396 engine—and other MTU designs—can be supplied with the TE split-circuit coolant system with a power-dependent sub-circuit to cool the combustion air. Optimum performance is fostered throughout the engine’s power range: at idling speed the air supply is heated to achieve complete fuel combustion; in the medium power and full load range conditions are optimized for high output while keeping thermal stress on engine components at a low level.

Coolant flow from the engine is split in two. Approximately twothirds of the flow passes through a high temperature (HT) circuit and returns directly to the engine inlet, while the remainder is fed into a thermostatically controlled low temperature (LT) circuit. During engineidling or low-load operation the thermostat allows heated coolant to bypass the recooler on its way to the intercooler in order to warm up the combustion air and prevent white smoke in the exhaust.

An annular slide valve in the thermostat remains in its initial positionuntil increasing power raises the coolant temperature, causing the wax pellet in the thermostat to expand. Gradual closing of the bypass line now directs the coolant stream through the recooler. As a result, coolant entering the intercooler is at a low temperature which, in turn, underwrites a high combustion air volume and, consequently, maximum engine power. After flowing through the intercooler and the oil heat exchanger, ‘cold’ coolant rejoins the uncooled HT circuit, thereby cooling the total volume flow before it re-enters the engine.

Sequential turbocharging is exploited for propulsion engines required to deliver high power in the lower and medium speed ranges. The system incorporates two or three turbochargers with automatic on/ off control as a function of engine speed, power demand and turbocharger maximum efficiency. In addition to increased torque the system yields reduced fuel consumption and lower exhaust temperatures.

Cylinder cut-out (no fuel injection into selected cylinders) is adopted for engines operating under varying speed conditions (low idling speed). The system enhances combustion at idle, thus shortening the warm-up phase and avoiding white smoke from unburnt fuel, and generally contributing significantly to environmental compatibility.

Series 595

A power range from 2000 kW to 4320 kW at 1500–1800 rev/min is covered by the 190 mm bore/210 mm stroke Series 595 engine, introduced in 1990 in V12- and V16-cylinder versions for propulsion and genset applications (Figure 15).

Contributing to a compact design yielding power-to-weight ratios of under 3 kg/kW and a power-to-space ratio of 250 kW/m3 (including all ancillaries) are the following features: a V72-degree cylinder configuration with all ancillaries arranged for space saving within the engine contour; nodular cast iron crankcase extending below the crankshaft centreline to maximize rigidity; crankshaft with hardened main and connecting rod bearing radii, designed to withstand firing pressures of up to 180 bar; individual fuel injection pumps designed for injection pressures of up to 1500 bar; plate-type coolant heat exchanger integrated with the engine; split-circuit coolant system; and two-stage sequential turbocharging system with charge air cooling for boost pressures of up to 4.8 bar. The turbocharging sequencing is electronically controlled.

Components requiring regular servicing are located to provide good access at the engine’s auxiliary power take-off end. Maintenance is also smoothed by the modular arrangement of functionally interlinked components, plug-in connections and the omission of complex

 

Figure 16 V16-cylinder MTU Series 595 engine

pipework, hose couplings and cabling. A new electronic control system (ECS) was purpose-developed by MTU for the Series 595 engine to provide information for the operator, promote easier operation and enhance safety, reliability and economy. The safety functions embrace engine and plant monitoring, overload protection, diagnostics, automatic start-up and load control.

Series 1163

The highest power outputs from the MTU programme were offered for many years by the Series 1163 engines (Figure 16). The 230 mm bore/280 mm stroke design is produced in V60-degree configuration 12-, 16- and 20-cylinder versions delivering up to 7400 kW at 1300 rev/min for commercial and naval propulsion installations. The key elements of the design are summarized as:

 

Figure 16 MTU Series 1163 engine in V20-cylinder form

Crankcase: nodular cast iron structure with access ports on both sides and a flange-mounting facility for alternators or other driven machinery; a welded sheet steel oil pan is provided.

Cylinder liner: replaceable, wet-type centrifugally cast.

Cylinder head: cast iron component arranged with two inlet and two exhaust valves, all equipped with Rotocap rotators, a centrally located fuel injector separated from the rocker area, and a decompression valve.

Valve actuation: by two camshafts, roller tappets, pushrods and rocker arms. Valve clearance adjustment is performed via two screws located in the rocker arms.

Crankshaft: a single-structure forged component finished all over and featuring bolted-on counterweights; axial crankshaft alignment is effected by a deep-groove ball bearing.

Bearings: thin-walled, two-piece, replaceable steel-backed tri-metal sleeve bearings for the crankshaft and connecting rod, with crossbolted bearing caps.

Connecting rods: forged and finished all over and grouped in pairs to serve two opposite cylinders.

Piston: composite-type with light alloy skirt and bolted-on steel crown, cooled by oil spray nozzles; three compression rings are fitted in the crown, with one oil control ring between crown and skirt; all rings replaceable after piston crown removal.

Fuel injection: direct injection by individual pumps and via short high pressure lines; pump replacement requires no readjustment; gear-type fuel delivery pump; two duplex fuel filters; cylinder cut-out facility available (see under Series 396 engine section).

Governor: hydraulic MTU unit mounted on the gearcase, with the linkage between governor and fuel injection pumps accommodated in the gearcase and camshaft space. Engine shutdown solenoids act on the fuel rack; in addition, independent emergency air shut-off flaps are arranged to block the engine’s air supply.

Lubricating oil system: self-contained forced feed system, with oil flow progressing through gear-type pumps, heat exchanger and filters to the engine lubrication points. Oil for piston cooling is tapped off after the heat exchanger and filters; the engine-mounted oil heat exchanger is integrated in the engine coolant circuit (Series 1163-02 model) or raw water circuit (Series 1163-03 model).

Cooling system: two-circuit system; closed engine coolant circuit using two centrifugal pumps; thermostatic control; recooling provided by raw water heat exchanger or fan cooler.

Turbocharging: the Series 1163-02 model exploits pulse charging based on two turbochargers (one turbocharger for the 12-cylinder engine) with intercoolers incorporated in the raw water circuit. The Series 1163-03 model exploits constant pressure turbocharging with two-stage air compression and interstage cooling; four or five charger groups (depending on the application) are under sequential

turbocharging control; the constant pressure exhaust manifold is located in the V bank, and charge air pipework mounted externally; high pressure (HP) and low pressure (LP) intercoolers are incorporated in the raw water circuit. For start-up and low-load operation the Series 1163-03 model features a charge air preheater, fed with engine coolant, in each HP intercooler outlet. Coolant jackets for the exhaust manifolds and turbocharger turbines of this model secure reduced heat rejection.

Like the Series 595 engine, the Series 1163 design features inboard high pressure fuel injection lines and the enclosure of all hot exhaust components in water-cooled and gas-tight casings: valued for unmanned enginerooms by helping to reduce the possibility of fire in the event of fuel or lubricating oil leakages. A triple-walled insulation design also maintains surface temperatures well within the limit of 220°C dictated by classification societies, as well as considerably reducing radiant heat in the engineroom.

Sequential turbocharging (output-dependent control of the number of turbochargers deployed) fosters high torque at low rev/min (wide performance band) and hence good acceleration. Optimization during sea trials, with assistance from an electronic control system, can eliminate black smoke emissions.

An uprated Series 1163 engine for fast ferry propulsion benefits from:

• An improved fuel injection system to optimize consumption and exhaust emissions reductionA higher cylinder head fatigue strength, thanks partly to bore cooling.
• Improved power and torque characteristics achieved by modifying the two-stage sequential turbocharging system.
• Adaptation and optimization of the turbochargers to match the increased cylinder output (325 kW).
• Intelligent electronic engine management.

Series 8000 engine

MTU’s thrust in commercial and naval propulsion sectors was strengthened in 2000 with the introduction of its most powerful-ever engine, the advanced 265 mm bore Series 8000 design (Figure 17). Innovative fuel injection, turbocharging and electronic management systems proven on earlier MTU engines are exploited, while a new modular power unit-based structure helps to ease maintenance and minimise life-cycle costs.

The Series 8000 engine was conceived with the aim of consolidating the company’s position in the market for fast ferries and extending opportunities to mainstream commercial arenas, such as cruise liners. Outputs up to 9000 kW for naval vessels and megayachts were initially sanctioned from the V20-cylinder model which launched the series, with an 8200 kW rating at 1150 rev/min approved for high speed commercial tonnage. A potential for firing pressures up to 230 bar underwrites future power rises, projected after successful long term testing of engines in service. Extension of the programme with V12 and V16 models was planned to allow the series to target power demands down to 5000 kW; and in-line cylinder and heavy fuel-burning versions were anticipated for large workboat propulsion applications. The first four production 20V 8000 engines were installed as a megayacht propulsion plant, subsequent orders calling for units to power a large catamaran fast ferry, frigates and naval supply vessels.

 

Figure 17 MTU Series 8000 engine in V20-cylinder form. Note the fuel pumps (lower right) for the common rail injection system

A V48-degree cylinder configuration contributes to a narrow engine (1.9 m wide), well suited for fast catamaran and monohull ferries where machinery space is at a premium. The specific power output related to volume and weight is reflected in figures of 200 kW/m3 and just over or under 5 kg/kW, depending on the application.

Common rail fuel injection, proven on MTU’s 1996-launched 165 mm bore Series 4000 engine , allows all injection parameters affecting combustion to be independently controlled; these include such variables as the timing, period and pattern of injection as well as the injection pressure. Independent control fosters reduced fuel consumption and exhaust emission levels across the entire engine power curve. The common rail system also benefits engine noise and vibration levels, substantially lowering them at idling and mid-range running speeds compared with conventional systems.

Two high pressure fuel pumps mounted at the free end of the engine develop pressure levels of up to 1800 bar. The fuel is pumped through double-walled delivery lines arranged longitudinally down the engine and directed to the cylinders via distributors into individual accumulators. The accumulators are large enough to prevent any drop in pressure before the fuel injector when maximum fuel quantities are being injected, and to prevent pressure oscillations in the system.

The fuel is injected via electronically-controlled injectors arranged centrally in the cylinder head. Experience gained from numerous Series 4000 engines in service moulded the common rail system created by L’Orange for the new larger engine, which is detailed in Chapter 8/Fuel Injection. Considerable scope for further development of the system promised further advances in fuel economy, emission levels and noise reduction in future production engines.

The Series 8000 design’s sequential turbocharging system had been successfully applied by MTU to its Series 396, 538, 595 and 1163 engines for many years to secure a large performance map width. First fitted on production models in 1982, the system marries a series of individual turbochargers that can be switched in and out while the engine is running to match the load. High brake mean effective pressures can thus be sustained even at low engine speeds. Among the merits cited for the sequential turbocharging system are excellent acceleration and substantially lower fuel consumption and smoke emission levels at low and medium power rates. Additionally, in twinengine plants with common transmission and fixed pitch propellers or waterjets, the system can be run on one engine virtually up to its rated power. Quadruple MTU ZR 265 turbochargers are specified for the single-stage turbocharging system serving the 20V 8000 engine, Figure 18.

Both common rail fuel injection and sequential turbocharging systems contribute to a claimed specific fuel consumption of below 195 g/ kWh across a broad power range, and less than 190 g/kWh at the most economical points. These figures are achieved while maintaining NOx emissions within IMO limits. Smoke indices are reportedly <0.4 Bosch throughout the entire engine performance map and <0.2 Bosch at full load.

Electronics are increasingly exploited by engine designers, MTU addressing the full potential from the conceptual stage of the Series 8000. The resulting MDEC (MTU Diesel Engine Control) engine management system allows all functions and parameters to be precisely monitored and controlled for optimum effect. The system also incorporates the basic functions for trend analysis and diagnostics, and the facility for integrating the engine in a comprehensive control and monitoring package for the entire propulsion system as well as other ship systems. MTU offers these advanced options in the shape of its RCS (remote control system) and MCS (monitoring and control system) products.

Figure 18 Thermodynamic model of the MTU 20V 8000 M70 engine and its sequential

Structurally, the Series 8000 is the first MTU engine to feature modular ‘power units’, which can be quickly removed and replaced, Figure 19. Each integrated module comprises:

• A cylinder head, including valve gear, fuel injector, exhaust Tpiece and coolant line segment.
• Cylinder liner.
• Piston and connecting rod.
• Spacer (for channelling coolant to the upper section of the liner and to the coolant pipes).

Each power unit is attached to the crankcase by four hydraulicallytightened stud bolts which have to withstand the high ignition pressures but do not perform a sealing function. A good seal is effected by securing the cylinder liner directly to the cylinder head from below with 24 bolts. By separating the functions of sealing and retention, MTU explains, wider design scope was created for optimizing the channels, valve gear and cylinder head cooling.

High design rigidity and endurance strength were sought from the transverse-flow nodular grey cast iron cylinder head. Its exhaust ports and particularly the inlet ports are said to yield excellent flow coefficients which establish the fundamental conditions for fuel economy and low

 

Figure 19 All the cylinder components of the MTU Series 8000 engine are combined in a functional module termed a 'power unit' for ease of withdrawal and replacement

emission levels. Circularity of the cylinder liner when the engine is running is sustained by the 24 evenly-spaced bolts around its perimeter and by which it is attached to the cylinder head. That circularity underwrites highly efficient sealing by the piston rings and, combined with a special liner honing process developed by MTU, promotes smooth running and durability. The high sealing efficiency of the rings and liners is also the basis for the ‘exceptionally low blow-by levels’ demonstrated by the Series 8000 engine, the designer reports. This significantly extends the life of the lubricating oil by reducing the amount of dirt escaping past the rings.

A robust nodular cast iron crankcase extending well below the centreline of the crankshaft is described as particularly rigid, the structure offering large inspection ports to ease checking and maintenance. Integrated in the crankcase are large lateral charge air ducts to the cylinders, the central bore for the camshaft operating the valve gear, and a centrally located main oil gallery. The cylinder liner is cooled only in its upper region and the crankcase is therefore completely coolant free.

Wide, cross-bolted bearing caps retain the crankshaft with its Bolton counterweights. Both big end and crankshaft main bearings are of the micro-groove type, and the latter can be replaced in-situ. Other key elements of the running gear are fully machined connecting rods with diagonally-split big ends, and composite pistons comprising a forged steel skirt (for the first time in an MTU engine) bolted to a steel crown carrying two compression rings and an oil control ring. The pistons are cooled by nozzles spraying cooling oil.

Exceptional engine rigidity imparted by the power unit concept, and consequently low-wear characteristics, were expected to help keep lube oil consumption at a constantly low level throughout the period between major overhauls. Confidence in a promised overhaul interval of up to 24 000 running hours—depending on the engine’s load profile and power rating—was supported by trials during which the test engines were subjected to an extremely severe alternating load sequence as well as continuous operation at full and overload powers. Minimizing the number and complexity of necessary interfaces, the pumps for engine coolant, raw water, fuel (high and low pressure) and lube oil, as well as the associated filters and oil coolers, are mounted on the engine. The electronic MDEC engine management unit is also arranged here. Locating all these components together as a ‘service block’ on the free end of the engine fosters accessibility and simplifies integration of the engine with the ship’s systems. Installation work is further reduced by an engine mounting concept proven with the Series 1163 engine in many high speed ferries, the torsionally resilient, offset-accommodating shaft couplings and a special arrangement of the air intake and exhaust connections.

Engine starting is effected by an air starter, the sequence incorporating an initial slow-turn phase which allows engine functioning to be quickly checked without having to open the decompression valves. This is followed immediately by the main starting sequence.

Contributing to trouble-free, low maintenance operation are: an automatic oil filter and two oil centrifuges in the secondary oil circuit (an indicator filter is fitted in the return line of the automatic filter for monitoring purposes); fuel filter cartridges with paper elements that can be replaced while the engine is running; and an engine coolant filter. The circulation systems are also fitted with running-in filters which trap any dirt that has found its way into the engine fluids during the installation process.

Adopted from previous MTU engines is the TE cooling system. Raw water never comes into contact with the engine components and the inlet temperature of the coolant at the engine can be controlled to suit the operating conditions. At low ambient temperatures and/or low engine loads, for example, the recooler is bypassed so that the coolant remains at a high temperature and heats up the combustion air. ‘White smoke’ emissions produced by cold engines can thus be eliminated. At full power, however, the system provides highly efficient cooling and creates the optimum conditions for combustion, both in terms of fuel economy and NOx emission levels, according to MTU.

MTU 20V 8000 engine data

 

MTU/DDC designs

An alliance formed by MTU in 1994 with Detroit Diesel Corporation (DDC) resulted in the creation of two advanced high speed designs for joint marketing by the German/US partners, the Series 2000 and Series 4000 engines, which were launched in 1996. MTU was responsible for the basic design development of both engines and the variants for propulsion applications.

Series 2000

The Series 2000 design, with a 130 mm bore/150 mm stroke, is based on the Mercedes-Benz 500 commercial vehicle engine (Figure 20). Models with V90-degree 8, 12 and 16 cylinders cover a propulsion band from 400 kW to 1343 kW, while genset drive applications start from 270 kW. The most powerful version, intended for yachts, has a maximum speed of 2300 rev/min. A single-stage turbocharging system is specified as standard but, when special requirements regarding power band width and acceleration characteristics are dictated, Series 2000 engines can benefit from MTU’s sequential turbocharging system. Fuel injection, adapted from the commercial vehicle engine, is a solenoid valve-controlled pump/fuel line/injector system, each cylinder having its own separate injection pump.

 

Figure 20 MTU V16-cylinder Series 2000 engine

Marine versions are fitted with MTU’s TE twin-circuit cooling system (detailed above in the Series 396 engine section) which fosters an optimum temperature for all operating conditions: intake air can be heated at idling speeds or at partial throttle and cooled at full throttle.

Series 4000

A number of notable design and performance features were highlighted by MTU for the 165 mm bore/190 mm stroke Series 4000 engine whose designers focused on high reliability and ease of maintenance without compromising compactness (Figures 21 and 22). A propulsion power band from around 840 kW to 2720 kW at 2100 rev/ min is covered by the V90-degree 8-, 12- and 16-cylinder versions.

 

Figure 21 MTU Series 4000 engine in V16-cylinder form

Testing confirmed fuel economy figures that reportedly set a new standard for compact engines in the design’s performance class and speed range. A specific fuel consumption of 194 g/kWh was considered exceptional for an engine with a power-to-weight ratio of between 2.7 and 3.5 kg/kW.

A key contribution, along with a high peak firing pressure potential, is made by the common rail fuel injection system—an innovation in this engine category—whose development was carried out in conjunction with MTU’s specialist subsidiary company L’Orange:

The system, which allows infinite adjustment of fuel injection timing, volume and pressure, embraces a high pressure pump, a pressure accumulator, injectors and an electronic control unit. The tasks of pressure generation and fuel proportioning are assigned to different components: pressure generation is the job of the high pressure pump while metering of the fuel relative to time is the job of the injectors.

 

Figure 22 Cross-section of MTU Series 4000 engine

The flexibility of the common rail system across the engine power band enables it to deliver the same injection pressure (around 1200 bar) at all engine speeds from full rated speed down to idling (Figure 23). The high pressure fuel pump and electronically controlled injectors are fully integrated in the electronic control system. Peak pressures with the common rail system are around 20 per cent lower than with conventional systems, reducing stress on the high pressure components. The pump is also simpler and its plunger has no helices. Since the pressure-relief requirement of conventional systems is eliminated the mechanical effort is reduced, further enhancing fuel economy.

 

Figure 23 Performance of common rail fuel injection system of MTU’s Series 4000 engine

One fuel rail is provided for the injectors and their respective solenoid valves on each bank of cylinders. The fuel pressure is generated by the high pressure pump driven via a gear train at the end of the crankcase. The electronic system controls the amount of fuel delivered to the injectors by means of the solenoid valves, while the injection pressure is optimized according to the engine power demand. Separate fuel injection pumps for each cylinder are thus eliminated, and hence the need for a complicated drive system for traditional pumps running off the camshafts. A reduced load on the camshaft and gearing system is therefore realized, and the removal of the mounting holes for separate injection pumps enhances the rigidity of the crankcase.

Maximum strength and optimized rigidity were sought from the crankcase, with integration of the main lubrication and coolant circulation channels reducing the number of separate components (Figure 24). The crankshaft, machined all over and with bolted-on counterweights, is designed to withstand maximum combustion pressures of up to 200 bar. Wear-resistant sleeve bearings contribute to longer service intervals. The cylinder head design, with integrated coolant channels and stiffened base, also addresses a 200 bar pressure. Provision is made for two inlet and two exhaust valves, and a fuel injector located in the centre of the head (Figure 25).

 

Figure 24 The crankcase of MTU's Series 2000 (right) and Series 4000 engines

 

Figure 25 The four-valve heads of MTU's Series 2000 engine (right) and Series 4000 engine (left) with central injector

A piston comprising an aluminium skirt and a bolted-on steel crown is provided with chrome-ceramic coated rings which, in combination with the plateau-honed cylinder liner, foster low lubricating oil consumption and an extended service life. An optimized combustion chamber shape and the bowl of the composite piston promote low fuel consumption and low emission levels.

Exhaust and turbocharging systems on the Series 4000 engine benefit from established MTU practice. A triple-walled exhaust system, withman outer water-cooled aluminium casing, ensures that the surface temperatures do not exceed permissible levels at any point while also securing gas tightness. Heat dissipation via the cooling system is reduced. The exhaust pipework is positioned centrally between the V-cylinder banks. The turbochargers are mounted in a water-cooled housing. A sequential turbocharging system is exploited to deliver high torque at low engine speeds. A wide power band at high fuel economy is also claimed, along with excellent acceleration capabilities without black smoke emission.

A split-circuit cooling system for the engine and intake air complements the sequential turbocharging system. It acts as an ‘intelligent’ cooling system to maintain engine coolant, lubricating oil and intake air at an optimum temperature for all operating conditions. When the engine is idling or running at low load the temperature of the intake air is raised in order to ensure smooth and complete combustion without generating white smoke emissions. On the front end of the engine is an integral service block providing ease of inspection and maintenance of the seawater cooler, oil cooler, oil filter, oil centrifuge and fuel filter. The turbochargers and charge air coolers are located at the flywheel end.

Access openings in the crankcase are said to be large enough to allow all running gear servicing to be performed without removing the engine, even under restricted machinery space conditions. The application-tailored service block integrated in the auxiliary power take-off end also simplifies routine maintenance tasks. A variety of ancillary mounting options enable the engine to be matched to specific customer requirements.

Early indication of necessary maintenance, based on the actual duty profile, is provided by an electronic engine management system designed to foster reduced downtime periods and lower servicing costs. A time-between-major-overhauls of 18 000 hours was anticipated by MTU.

NIIGATA

The FX series from Niigata Engineering was completed in 1996 with a 205 mm bore model to complement the established 165 mm and 260 mm high speed engines in a programme developed for fast commercial and military vessel propulsion. The resulting 16FX, 20FX and 26FX models offer maximum continuous outputs from 1000 kW to 7200 kW in commercial service, with slightly higher ratings available for naval propulsion. The 16FX engine is produced in in-line eight, V12- and V16-cylinder versions running at 1950 rev/min, the V20FX in V12 and V16 versions running at 1650 rev/min, and the V26FX (Figure 26) in V12-, 16- and 18-cylinder versions running at 1300 rev/min.

 

Figure 26 Cross-section of Niigata V26FX engine

Compact and highly rigid engines were sought by the Japanese designer from a monobloc structure fabricated from nodular cast iron, with the extensive use of light alloy elements contributing to a modest overall weight. Engine width was minimized by adopting a V60-degree cylinder bank and overall length reduced by minimizing the distance between cylinders while maintaining the required bearing width.

A one-piece nodular cast iron piston was specified for the V16FX engine, but the higher mechanical and thermal stresses imposed by the cylinder pressure parameters of the V20FX ‘Blue Arrow’ engine influenced the selection of a component with a steel crown and aluminium skirt for the larger design. A bore cooling-type oil gallery structure on the crown reduces the temperature of the piston at higher mean effective pressures. Higher cylinder pressures also foster increased piston blow-by, calling for a high sealing capability and wear resistance from the piston rings. A chromium-ceramic coated top ring contributes to these properties, while an anti-polishing ring in the top of the cylinder liner yields a lower lube oil consumption rate.

An output ceiling of 7200 kW at 1300 rev/min from the Niigata high speed engine portfolio is provided by the 18-cylinder version of the 260 mm bore V26FX design. A monobloc frame of high tensile strength ductile cast iron and the use of light alloy parts where appropriate contribute to rigidity and light weight from a compact envelope.

Miller system for 32FX

The potential of the 32FX design was demonstrated by a development project to create a lightweight, high performance 320 mm bore medium speed engine series with a weight/power ratio of 4 kg/kW yielding outputs from around 8000 kW to 13 000 kW. Using the established 32CX engine as a basis, Niigata reportedly achieved a rating of 769 kW/cylinder at 1030 rev/min from the 32FX variant.

High output achieved by traditional development routes, Niigata explains, is accompanied by an increase in mechanical load attributable to the higher maximum pressure. Coping with the increased loading normally dictates the specification of thicker and hence heavier components. Thermal loads also rise, resulting in elevated NOx emissions. Reducing the compression ratio to maintain Pmax at a normal level, however, lowers efficiency and undermines overall performance and starting capability.

Given these constraints, Niigata opted for the Miller system to keep the Pmax and temperatures in the combustion chamber at a normal level, and reduce NOx emissions, while increasing the brake mean effective pressure. The system is designed to reduce charge air temperature and pressure before compression (thus lowering the combustion temperature) by subjecting the charge air in the cylinder to adiabatic expansion.

Miller systems come in two variants: an advanced closure timing, which closes the intake valve before bottom dead centre; and a delayed closure timing, which closes the intake valve after BDC. Based on an engine performance simulation analysis, Niigata selected the advanced closure timing route for the 6L32FX engine, adopting a closing timing of 10 degrees before BDC in contrast to the 35 degrees after BDC applied in the 6L32CX engine (Figure 27).

 

Figure 27 P-V diagram for Miller system (Niigata)

In the Miller system, with the intake valve closed before BDC at the normal boost pressure, the exhaust temperature rises as the intake air volume is reduced. This effect makes it necessary to increase the boost pressure to achieve the targeted output, which lowers the exhaust temperature. Securing a higher boost pressure than that obtainable with single-stage turbocharging called for the adoption of a two-stage system in which the low pressure and high pressure turbochargers are connected in series with two intervening air coolers (Figure 28).

 

Figure 28 Two-stage turbocharging system (Niigata)

Applying the Miller system in conjunction with two-stage turbocharging—low pressure and high pressure turbochargers connected in series with two intervening coolers—secured the desiredn goal of a power rate of 38.2 (3.09 Mpa brake mean effective pressure ¥ 12.4 m/s mean piston speed) at 110 per cent maximum load— claimed to be the highest of any engine in the circa-320 mm bore class. In addition, the NOx emission level with the Miller cam was 20 per cent lower than with a conventional cam, equating to 5.8 g/kWh compared with the IMO limit of 11.2 g/kWh at 1030 rev/min in E3 mode. Fuel consumption with a conventional cam was lower than with the Miller cam at low loads (which could anyway be improved by using a variable geometry cam) but it rose rapidly at higher loads and exceeded the Miller cam at a load of around 75 per cent.

Supporting the performance boost, Niigata also investigated new materials for key components to enhance engine reliability and reduce weight, notably: a ceramic-sprayed bimetal cylinder liner; tri-alloy intake valves and pushrods; and sodium-sealed and Waspaloy Inconel 718 exhaust valves. The ceramic-sprayed coating was applied to the sliding part of the liner surface to improve resistance to abrasion and seizure.

PAXMAN (MAN B&W)

Over 60 years experience in high speed diesel design was exploited by Paxman Diesels in creating the VP185 engine, launched in 1993 to join the UK-based company’s established 160 mm bore Vega and 197 mm bore Valenta series (Figure 29), which respectively offered specific outputs of 107 kW/cylinder and 206 kW/cylinder. The new 185 mm bore design was introduced initially in V12-cylinder form with outputs up to 2610 kW and complemented in 1998 by a V18- cylinder version extending the power limit of the series to 4000 kW at a maximum speed of 1950 rev/min. Paxman became a member of Germany’s MAN B&W Diesel group in mid-2000.

In designing the 12VP185 engine (Figure 30), Paxman sought improvements in compactness and lightness over its earlier models, goals dictating a smaller swept volume, slightly higher ratings and a review of piston speeds. The first parameter to be fixed was the stroke which was set at 196 mm; this, linked to a crankshaft speed of 1800 rev/min, gave a mean piston speed of 11.8 m/sec for continuous duty. An improved speed platform for marine applications was derived, the edge of which is bounded by a maximum speed of 1950 rev/min with a mean piston speed of 12.8 m/sec.

The cylinder bore was fixed at 185 mm which, coupled with a design maximum mean effective pressure of 25.3 bar, delivered a maximum power of 2610 kW at 1950 rev/min from the V12-cylinder configuration: a rating primarily targeting high speed military and commercial marine

 

Figure 29 Paxman V16-cylinder Valenta engine

markets, as well as megayacht propulsion. An unrestricted rating of 2180 kW at 1800 rev/min is quoted (at 45°C air and 32°C sea water conditions) for continuous marine duties (for example, fast ferry propulsion) where the engine’s high torque capability over a broad speed range is considered especially attractive for hydrofoil service.

The 18-cylinder VP185 model offers a maximum output of 4000 kW at 1950 rev/min, a 3300 kW continuous power rating for fast ferries and patrol craft, and 3000 kW at 1770 rev/min for unrestricted marine duty.

A smaller bore and stroke than the Valenta design, combined with a switch from a 60-degree cylinder bank angle to a 90-degree configuration, achieved a layout which was short and with a width under 1.5 m while providing an adequate platform for the charge air system mounted above the engine. The 90-degree bank angle itself also lowered the profile of the charge air system to foster space efficiency (Figure 31).

A higher mean effective pressure normally leads to a lower compression ratio which in turn promotes poor starting characteristics,

 

Figure 30 Paxman 12VP185 engine. Note the compact turbocharging arrangement along the top

 

Figure 31 Cross-section of Paxman VP 185 engine

reduced thermal efficiency and possible exposure to ignition delay damage. Some of these problems can be addressed by the use of intercylinder charge air transfer arrangements but Paxman decided to adopt a compression ratio in excess of 13:1. The resulting VP185 engine was claimed to be simple and easy to start under cold conditions, with good thermal efficiency and the potential to satisfy low NOx emission limits. The combination of high boost levels and compression ratios demands a robust construction but Paxman sought to avoid a heavy and cumbersome engine by securing robustness within a small and hence a stiff envelope.

The reciprocating assembly of the engine was designed for high strength and rigidity in handling a high maximum cylinder pressure and securing high reliability with a long lifetime. The backbone is a compact crankcase cast in high strength spheroidal graphite iron to provide a stiff and solid support for the underslung crankshaft. Crankcase doors along each side of the engine give access to the connecting rod large ends for in situ servicing and piston removal.

The crankshaft is a fully machined steel forging, fully nitrided to yield strength and durability. It is secured by main bearing caps which are drawn internally against the deep-fitting side faces of the crankcase by high tensile set screws and hydraulically tensioned main bearing studs. Such a configuration, the designer asserts, delivers good strength and stiffness characteristics to the bottom end of the crankcase and provides solid support for the crankshaft. A generous overlap between the crankpin and main bearing journals adds to stiffness and strength. Both main and big end bearings are of steel-backed aluminium–tin type with thrust washers controlling axial location. The crankshaft is provided with a viscous torsional damper totally enclosed within the gearcase.

Connecting rods of side-by-side design are forged in high tensile steel, fully machined and ferritic nitro-carburised. The large end is obliquely split to allow the rod to pass through the cylinder liner and the joint faces are serrated. The one-piece nodular cast iron pistons incorporate a large oil cooling galley above the ring belt, oil being supplied by accurately aligned standing jets mounted in the crankcase. The pistons run in wet cylinder liners made of centrifugally cast high grade iron.

The cast iron cylinder heads are designed to withstand the high firing pressures with an internal configuration ensuring maximum flame face stiffness and high cooling efficiency. They incorporate two exhaust valves, two inlet valves and a centrally mounted unit fuel injector (combined pump and injector) which is fixed with a single screw. The valves and injectors are actuated through a pushrod arrangement from a single large diameter camshaft mounted centrally in the vee of the engine. The stiffness of the actuating system reportedly achieves valve control similar to that of an overhead camshaft, while the specially designed unit injectors yield very high rates of fuel injection with clean cut-off, contributing to low NOx generation and good fuel efficiency. The fuel cam design was based on an optimized width for long life and a large base circle, coupled with high rates of lift to secure the key injection characteristics.

A maximum injection pressure of 1400 bar promotes good combustion characteristics with low emissions and fuel consumption. The unit injector is rack controlled, the rack itself being controlled by a linkage operated from twin shafts in the centre vee of the engine. The shafts in turn are coupled to the governor via an overspeed protection assembly which closes the fuel racks independently of the governor in the event of the engine overspeeding.

A safety merit of the unit injector (which combines fuel pump and injector in one unit) is that it eliminates the need for high pressure fuel pipes. Low pressure fuel oil is delivered to the injectors by a geardrive ift pump mounted on the main gearcase. The fuel is fed to a sub-assembly—comprising cooler, filter (duplex optional), reservoir and solenoid-operated shut-off valve—mounted high at the free end of the engine for convenient access.

A single camshaft reflects the policy adopted by the designers of minimizing the number of components. This, allied to the 90-degree cylinder bank angle, allowed the camshaft gear to mesh directly with the crankshaft gear and so eliminate the need for idlers in a critical area and reduce the component count even further.

Charge air is delivered by a ‘valve-less’ two-stage turbocharging system designed for simplicity and ease of maintenance. Preliminary explorations of single-stage high pressure ratio turbocharging showed poor low speed torque characteristics due to surge limitation, along with poor acceleration and load acceptance. Sequential turbocharging was considered but the necessary valve gear and associated control system conflicted with the primary aim of keeping the engine as simple as possible, Paxman explains. Another factor was that few turbocharger designs in the smaller size range were capable of meeting the pressure ratio required.

A two-stage turbocharging arrangement with intercooling and aftercooling was finally adopted for the VP185 engine, based on six Schwitzer automotive-type turbochargers with broad and stable operating characteristics: four turbochargers provide low pressure charge air and two provide the high pressure air.

Inlet air compressed in the low pressure turbochargers is fed through a raw-water intercooler to the compressors of the high pressure turbochargers; high pressure air is then passed through the jacket water aftercooler into the air manifolds on either side of the engine.

The high pressure stage exploits a pulsed exhaust system to give good low-end performance without recourse to complex valve systems associated with sequentially turbocharged configurations. The turbocharging system’s high air/fuel ratios, coupled with high pressure/ high rate fuel injection, address low NOx emission requirements. A highly responsive performance with good engine torque characteristics is reported throughout the speed range, Figure 32.

 

Figure 32 Performance map for Paxman 18VP185 engine

All six turbochargers are mounted in the walls of a water-cooled gas-tight casing, the turbine sides arranged on the inside and the compressors on the outside. The rotating assembly and compressor casing of each turbocharger form a cartridge which can be replaced quickly without the need for lifting gear and without disturbing the rest of the engine. The exhaust manifolds feature sliding joints and, like the turbochargers, are housed in water-cooled gas-tight aluminium casings; together with the turbocharger enclosure, they form a single, cool gas-tight shell around the hot parts of the engine. The casings foster low radiant and convective heat losses from the engine.

The gear train is mounted at the engine’s free end and the camshaft gearwheel meshes directly with the crankshaft gearwheel. Auxiliary drives are provided for the externally mounted lubricating oil and jacket water pumps, the governor, overspeed governor and fuel lift pump; further auxiliary power take-off capability is incorporated for different applications. The PTO at the free end will accept either gear-driven or belt-driven pumps and alternators. The VP185 is supplied as a complete assembly with engine-mounted jacket water and lubricating oil heat exchangers to simplify installation procedures. A choice of air, electric or hydraulic starting systems is available.

Marine engine versions are controlled by a Regulateurs Europa digital Viking 2200 governor and 2231 actuator with the option of ball head back-up. Multiple Schwitzer turbochargers in a passive two-stage configuration with intercooling and aftercooling were retained for the V18-cylinder model, albeit with an increased number of sets. Three high pressure turbochargers each expand into a pair of similar low pressure turbochargers, giving a total of nine turbochargers. Unlike the 12VP185 engine, the turbochargers are packaged in groups of three (one HPtwo LP), each group having its own water-cooled gas-tight housing.

The hot turbine volutes are fixed to the inside of each housing, with the rest of the turbocharger, the ‘cartridge’, plugged in from the outside: an arrangement which enables the turbochargers to be replaced quickly. The hot exhaust manifold pipes are similarly housed in their own water-cooled gas-tight casings, so eliminating unwanted heat and gas around the engine (an important safety aspect).

SEMT-PIELSTICK

The Paris-based designer SEMT-Pielstick fields three long-established high speed programmes, the PA4, PA5 and PA6 series. The PA4 is produced in 185 mm and 200 mm bore versions (both having a stroke of 210 mm) and features a variable geometry (VG) pre-combustion chamber; and the PA5 is a 255 mm bore/270 mm stroke design.

Development has benefited the 280 mm bore PA6 design, introduced in 1971 with a stroke of 290 mm and a maximum continuous rating of 258 kW/cylinder at 1000 rev/min. The output was raised to 295 kW/ cylinder in 1974 and to 315 kW/cylinder in 1980. Extensive service experience in naval vessels moulded progressive refinements over the years, including the creation of a BTC version in 1980 which yielded 405 kW/cylinder at 1050 rev/min through the adoption of a reduced compression ratio together with two-stage turbocharging. This PA6 BTC model was released in 1985 with a higher output of 445 kW/ cylinder. The series was extended in 1983 by a longer stroke (350 mm), slower speed PA6 CL variant with a rating of 295 kW/ cylinder at 750 rev/min.

A sequential turbocharging system (STC) was introduced to the 290 mm stroke engine in 1989, this PA6 STC model developing 324 kW/cylinder at 1050 rev/min. Performance was enhanced in a 330 mm stroke B-version from 1994, an STC system and a cylinder head with improved air and gas flow rates contributing to a nominal maximum continuous rating of 405 kW/cylinder at 1050 rev/min. A maximum sprint rating of 445 kW/cylinder at 1084 rev/min equates to an output of 8910 kW from the V20-cylinder PA6B STC engine which targets high performance vessels.

At the nominal mcr level the V12-, 16- and 20-cylinder models, respectively offer 4860 kW, 6480 kW and 8100 kW for fast ferry propulsion, and are released for sustained operation at these ratings. The weight/power ratio of the 20PA6B STC model at 8100 kW is 5.2 kg/kW (Figure 33).

 

Figure 33 SEMT-Pielstick V20-cylinder PA6B STC engine with sequential turbocharging system. A rating of 8100 kW is offered for fast ferry propulsion

PA6B STC design

High rigidity without compromising overall engine weight is achieved by a stiff one-piece crankcase (Figure 34) of nodular cast iron specially treated for shock resistance, with transverse bolt connections between both crankcase sides through the underslung-type bearing caps. Integrated longitudinal steel piping supplies lubricating oil to the main bearings.

 

Figure 34 SEMT-Pielstick PA6B STC crankcase

Large dimension main journals yield a particularly large bearing surface and conservative pressures which underwrite prolonged bearing life, as do the large surface area connecting rod bearing shells. The alloy steel one-piece forged crankshaft (Figure 35) has high frequency hardened crankpins and journals, and is bored to feed lubricating oil to the connecting rods.

 

Figure 35 SEMT-Pielstick PA6B STC crankshaft

A nodular cast iron cylinder head was configured to achieve improved air and gas flow rates for the PA6B STC version. The composite piston (steel crown and aluminium skirt) is fitted with five rings. The forged steel connecting rod is fitted with large surface bearing shells to yield high durability under high firing pressures. Special low wear characteristics were sought from the centrifuged cast iron material specified for the cylinder liner (Figure 36). The camshaft is formed from several sections for ease of dismantling.

 

Figure 36 SEMT-Pielstick PA6B STC cylinder liner

Operational flexibility and power output are fostered by the singlestage sequential turbocharging system which is based on two turbochargers and delivers a large combustion air excess at partial loads. Supercharging is effected by one turbocharger for engine loads up to 50 per cent of the nominal power, its effort boosted by the second identical turbocharger at higher loads. Switching from single to twin turbocharger mode is performed automatically by opening two flap valves. Engine performance at prolonged low load is improved with respect to fuel consumption, smoke emission, fouling resistance and transient performance. Additionally, engine utilization is expanded towards the high torque/low rev/min area.

Developing the high performance derivative

Refining an established engine for high speed vessel propulsion duty must focus on achieving a lighter and more powerful package within a more compact envelope, while also enhancing operating flexibility. The resulting PA6B STC design was released with a nominal maximum continuous rating of 405 kW/cylinder at 1050 rev/min, and a sprint rating of 445 kW/cylinder at 1084 rev/min (Figure 37).

SEMT-Pielstick’s development goals aimed to:

 

Figure 37 Cross-section of SEMT-Pielstick PA6B STC engine

• Increase the power rating by 25 per cent.
• Use an operating field allowing operation following a double propeller law.
• Maintain, and if possible reduce, the specific fuel consumption.
• Reduce the weight/power ratio and enhance engine compactness.
• Reduce installation costs.
• Retain the maximum number of existing components.

Power can be raised in two ways: by increasing the brake mean effective pressure and by increasing the piston speed. Increasing piston speed can be effected by increasing the rev/min and by lengthening the, stroke. Increasing the rev/min was not attractive because of a need to maintain an acceptable synchronized speed for land power plant applications but also because of these drawbacks: increased specific fuel consumption; higher wear rate; and higher noise levels. Raising piston speed by lengthening the stroke is considered preferable because it reduces specific fuel consumption and fosters optimum performance at starting and low load (the compression ratio is secured without resorting to a combustion chamber that is too flat). This route was therefore selected but with the piston speed limited to 11.5 m/s (representing an increase of 14 per cent with a stroke of 330 mm). To reach the required power rating, the brake mean effective pressure had to be increased by 10 per cent; this was achieved by adopting high performance turbochargers. Attaining the desired specific fuel .consumption called for the maximum cylinder pressure to be raised to 160 bar.

Coping with these new parameters dictated redesigning some key components. The existing cylinder head, for example, was incompatible with the targeted specific fuel consumption level. This was partly because its mechanical strength was insufficient in relation to the necessary peak combustion pressure, and partly because the pressure loss through the inlet and exhaust ports would be unacceptable in relation to the intervening gas flow dictated by the increased power. A new cylinder head was therefore designed with a reinforced bore-cooled fire plate and incorporating inlet and exhaust ports with large dimensions. In addition, cooled seats were specified for the inlet valves as well as the exhaust valves to maximize seat reliability and avoid risks of burning.

A redesigned connecting rod was also necessary to address the increased peak compression pressures and the inertia efforts linked to the lengthening of the stroke. The bevel cut design of the original component was abandoned in favour of a straight-cut rod to avoid weak points, such as the bevel cut serrations and the threading anchorage in the shank. Piston cooling by jet replaced the traditional oil supply through the connecting rod from the crankpin, simplifying machining and allowing the bearing shell grooves to be eliminated and yield these benefits: increasing capacity of the bearing shells; stopping cam wear of the crankpin (differential wearing of the pins between the side areas of the plain bearing shell and the central area; that is, the area including the groove); and cutting out the risk of cavitation erosion on the bearing shells at the end of the grooves. The new connecting rod is 10 per cent lighter than its bevel cut forerunner. The weight reduction, along with an improved bearing shell capacity, partly compensates for the increased inertia efforts.

Temperature measurements on the jet-cooled piston head indicated similar levels to those of the original piston, and even lower in some areas. Critical points of the piston were modified to cope with the higher peak combustion pressure: a spherical shape was given to the support spot face used for the piston head/skirt tightening spacers; and the radius under the skirt vault was increased.

Crankshaft dimensions were modified to target the same reliability from the component as before, despite the increased stroke and peak combustion pressure. Finite element analyses of the crankwebs and hydrodynamic calculations led to an increase in the journal diameter from 230 mm to 250 mm, and in the crankpin diameter from 210 mm to 230 mm.

High performance turbochargers were necessary to secure the brake mean effective pressure increase with the required efficiency, a model from MAN B&W’s then new NA series—the NA 34S—being selected to meet the performance and compactness parameters. Sequential turbocharging was applied, based on the principle of reducing the number of turbochargers in operation as the engine speed and load fall. The speed of the turbochargers still operating consequently rises and significantly larger quantities of air are thus delivered to the engine.

A simple system was adopted using only two turbochargers, one being switched off at below approximately 50 per cent of the nominal engine power rating. This is effected by closing two flap valves located at the compressor outlet and at the turbine inlet of one of the turbochargers. The designer cites the following benefits from the PA6 engine’s sequential turbocharging (STC) system:

• High torque and power ability at reduced engine speed.
• A gain in fuel economy at low and part loads.
• Capability to run the engine at very low loads for extended periods with minimal fouling (the light deposits can be cleaned out by running for half an hour at 50 per cent load).
• Invisible smoke emissions over a wide working range.
• Reduced exhaust temperature.
• Lower thermal stresses in the combustion chamber components at part loads.

A higher output rating naturally reduced the engine’s weight/power ratio but other measures were pursued to trim overall weight. The scope for using aluminium alloy was explored for all components where operating stresses (particularly thermal) and class rules allowed, leading to the engine supports, turbocharger support, air manifolds (after the air cooler), lube oil and water cooler support, and lube oilfilter support being designed in cast aluminium. Studies assessed other components for which aluminium could not be considered, either to use alternative materials with higher mechanical properties and so reduce thickness, or simply to optimize existing shapes and thicknesses. As an example, specifying high yield point steel sheet for the manifolds connecting the turbocharger to the air cooler allowed a reduction in thickness from 10 mm to 4 mm. The lube oil sump plate was also modified by reducing the material thickness.

A 10 per cent reduction in the original engine weight, along with the increased power output, contributed to a weight/power ratio of 4.8 kg/kW, including all ancillaries. In parallel with the weight trimming studies, SEMT-Pielstick focused on reducing the overall dimensions of both engine and ancillaries.

A key element here is the combi-cooler, integrating one lube oil and one freshwater plate cooler circulated by a common seawater system (Figure 38). The combi-cooler’s support is used as the rear plate of the cooler and includes as-cast part of the connections to the high temperature freshwater and lube oil systems. Its front plate incorporates as-cast the connections to the low temperature freshwater

 

Figure 38 Fresh and seawater circuits integrated on the PA6B STC engine

loop and the water thermostatic valve. The main self-cleaning lube oil filter is incorporated axially in a cast support located under the combicooler, and includes the lube oil thermostatic valve as well as the centrifugal oil filters.

Such solutions fostered compactness, a simple pipeless configuration and good access to the main subjects of maintenance. Integration of the ancillaries on the engine further eases shipboard installation procedures. All pumps (water, oil, fuel make-up), as before, are driven by the engine upon which is also mounted the fuel filter.

A potential for burning an intermediate fuel oil grade such as IF30 was addressed in the development programme, and reflected in the specification of cooled valve seats and exhaust valve rotators. The 75°C temperature necessary to reach an adequate viscosity for its injection can be derived by taking heat from the engine’s high temperature freshwater system. In such installations, however, the engine is derated to 360 kW/cylinder and the time-between-overhauls is reduced.

WÄRTSILÄ

The medium speed specialist Wärtsilä added high speed designs to its four-stroke engine portfolio with the acquisition in 1989 of SACM Diesel of France. The Finnish parent group saw the market potential for a new generation engine blending the best features of high and medium speed designs for continuous duty applications, resulting in the 1994 launch of the Wärtsilä 200 series (Figures 39 and 40).

The 200 mm bore/240 mm stroke engine is produced by Wärtsilä France for propulsion and genset drive applications, with an output band from 2100 to 3600 kW at 1200 or 1500 rev/min covered by V12, 16- and 18-cylinder models. High reliability in continuous duty (defined as 24 hours a day operation with an annual running period of over 6000 hours) was sought from an engine structure and main components designed for a maximum cylinder pressure of 200 bar. Wärtsilä’s medium speed engine technology was exploited to achieve a high power density, low emissions and fuel consumption, and ease of maintenance.

A multi-functional connection piece or ‘multi-duct’ located between the cylinder head, engine block and exhaust manifold has the following duties:

• Combustion air transfer from charge air receiver to cylinder head.
• Introduction of an initial swirl to the inlet air for optimal part load combustion.

 

Figure 39 Wärtsilä W200 engine

• Exhaust gas transfer to the exhaust system.
• Cooling water transfer from the cylinder head to the return channel in the engine block.
• Insulation/cooling of the exhaust transfer port.
• Support for the exhaust manifold and insulation.
• Inclined face towards the cylinder head facilitates easy removal/ remounting of the cylinder head. The exhaust gas piping and insulation box, supported by the multi-duct, stay in place when the head is removed.

The nodular cast iron engine block (Figure 41) is designed for maximum stiffness with a V60-degree configuration optimizing balancing and hence limiting vibration. Bolted supports dictate only four to six fixing points, and provision is made for elastic mounting. The locations of the camshaft drive (integrated in the flywheel end of the block) and the air receiver channel (in the middle of the vee-bank and also integral with the block) reflect solutions adopted in Wärtsilä medium speed engines. Arranging the oil lubrication distribution

 

 

Figure 40 Wärtsilä W200 engine. The original automotive-type turbochargers shown here were later replaced by ABB or Holset models

through a channel in the middle of the vee, however, was a new idea. The areas of the block that support the camshafts and fuel injection pumps are designed for high strength to accept the forces created by the high injection pressures. Large openings on both sides of the block facilitate access for inspection and maintenance.

The cylinder unit also benefited from solutions validated in other Wärtsilä designs, notably: a plateau-honed cast iron cylinder liner incorporating an anti-polishing ring at the top to eliminate bore polishing; a composite piston (steel crown and aluminium alloy skirt) with a three-ring pack (two hard chromium-plated compression rings and one spring-loaded oil scraper ring) and optimized cooling; and Wärtsilä’s patented piston skirt lubrication system. The piston is lubricated by an oil jet, which also supplies oil to the cooling gallery in the piston top.

 

Figure 41 The nodular cast iron block of the Wärtsilä W200 engine incorporates fluid

The forged high tensile steel connecting rods are fully machined and balanced for low vibration running, and designed to facilitate oil lubrication to the small-end bearings and pistons. The big end has a diagonal split with serration teeth. Two stud screws are hydraulically tensioned and can be accessed through the inspection doors at the engine sides. An off-set split makes its possible to overhaul the piston and connecting rod assembly through the cylinder liners.

The strong 220 mm diameter forged high tensile steel monobloc crankshaft (Figure 42) has gas-nitrided surfaces for added safety and a high degree of balancing from two bolted counterweights per crank throw. The generous diameters of both crankpin and journal achieve a large bearing surface while allowing a reduced cylinder spacing ratio (1.5 times the bore) to minimize engine length and weight. The crankshaft is fitted with counterweights and fully balanced, and the oil seal can be changed without removing the crankshaft. The running surfaces of the crankpin and main journal are hardened, and the connecting rod big end bearings and main bearings are of the CuPb type.

 

Figure 42 The Wärtsilä W200 engine crankshaft has gas-nitrided surfaces

Supporting the loads generated by the high injection pressure, the well-dimensioned camshafts are formed from modular sections bolted together, each section serving two or three cylinders; the sections can be removed axially from the engine block. The cams are surface hardened for wear resistance. Located on both sides of the engine block, the camshafts are driven by timing gearwheels arranged inside the engine block at the flywheel end.

Among the measures designed to ease inspection and maintenance are: cylinder heads hydraulically tightened with four stud screws on the cylinder block; and connecting rod big ends and main bearing caps fastened by two hydraulically tightened studs.

Fuel injection starts slightly before TDC so that combustion takes place during the beginning of the expansion phase in lower temperatures. The combination of a high compression ratio (16:1) and late fuel injection fosters low NOx generation without raising fuel consumption since the engine’s injection period at 1500 rev/min is sufficiently short. Applying this low-NOx principle requires the engine to be able to inject fuel late in the cycle and over a short duration without undermining performance: high pressure capacity injection equipment is therefore dictated. The engine is released for operation on marine diesel oil (ISO 8217, F-DMX to FDMB).

Individual fuel injection pumps are integrated in the same cast multi-housing (Figure 43) as the inlet and exhaust valve tappets

 

Figure 43 The fuel injection pump of wartsila's W200 engine is integrated in the multi-housing

and the inlet and outlet fuel connections, and can be removed directly without touching the housing or any piping. The coated pump plungers are designed for pressures up to 2000 bar and for a high flow capacity. Fuel is injected into the cylinder through a nitrided eight-hole nozzle designed to yield optimal performance in combination with the combustion bowl and swirl level, and to ensure good resistance to wear and thermal loads. The feeding parts are optimized to eliminate the risk of cavitation. Injection timing is adjusted from the camshaft drive. The injection pumps are equipped with pneumatic emergency stop pistons which are activated to switch the fuel racks to the 0- position by a signal from the engine overspeed detector or safety stop contacts.

An important contribution to engine performance is made by the cooling water system which can be divided into low temperature (LT) and high temperature (HT) circuits with separate outlets and inlets for the HT and LT sides, or configured as a single circuit with an HT outlet from the engine and return to the LT side. The cooling system comprises: a preheating module; double-impeller cooling water pump for LT/HT circuits; thermostatic valves and LT/HT water mixing; charge air cooler; lube oil cooler; seawater pump (optional); and cooling circuitry mostly incorporated in the engine block casting. The external system normally comprises a plate-type heat exchanger for cooling the engine water and another smaller plate-type unit for fuel cooling.

The LT system cools both the charge air and the lubricating oil; the charge air and oil coolers are placed in parallel to achieve maximum cooling efficiency. Increased engine component reliability is reported due to the low lubricating oil temperature (70°C after cooler), and reduced NOx emissions due to the cold charge air temperature (60°C after cooler). The HT system cools the engine block and also the first stage of the charge air when optional maximized waste heat recovery on the HT line is specified.

The main elements of the lubricating oil system (Figure 44) are: a wet oil sump; lube oil pump module (comprising engine-driven oil pump and electrically-driven pre-lubrication pump); lube oil module, (comprising thermostatically controlled lube oil cooler and main filters); centrifugal filter; distribution channels integrated in the engine block; oil jet nozzles for piston cooling and lubrication; and instrumentation. Pre-lubrication can be controlled automatically or manually.

 

Figure 44 Lubricating system of W200 engine

Integration of lubricating oil, fuel oil and cooling equipment in modules mounted on the engine achieves a significant reduction in external connections: only two for water, two for fuel oil and one for starting air. The lubricating oil filters can be changed one by one, even while the engine is running, using a three-way valve to interrupt the oil flow to the filter chamber. The chamber is drained externally by a tap and cleaned without risk of contaminating the lubricating oil system. The system is equipped with a bypass centrifuge filter, located to facilitate ease of maintenance while the engine is running. The washable cell-type air filters are mounted on top of the engine and fixed with a quick clamping arrangement.

The lubricating oil pump, electrically driven pre-lubricating pump, cooling water pump, fuel pump and optional priming fuel pump, and seawater pump are all mounted externally at the free end of the engine. The fuel pump is placed on the same shaft as the lubricating oil pump. The twin water pump for both LT and HT cooling water circuits has only one shaft for both circuits; this means fewer gearwheels need checking and less changing of bearings and sealings. The prelubricating pump can also be used for draining the oil sump.

An engine flywheel housing of multi-functional design supports starters and turning gear, and conveys fluids between the different modules. The starting motor is of the pneumatic type, operating effectively even at low pressure.

Marine versions of the W200 engine were originally turbocharged with four automotive-derived turbochargers but these were later replaced by ABB or Holset marine models. The 12V200 models now feature twin turbochargers arranged at the free end of the engine.

The 1500 rev/min engines in service suffered some failures in 1998– 99 owing to lube oil circuit problems and material issues, but design refinements and an improved manufacturing process eliminated the main causes. Lubricating circuit performance was upgraded by a better oil filter module design and main lube oil pump, allowing ‘fail-safe’ cartridge replacement and a constantly clean and air-free oil flow. The connecting rod big-end assembly was thoroughly re-engineered to secure the highest reliability. The engine top overhaul period for 1500 rev/min engines (50 Hz gensets) was extended from 12 000 hours to 18 000 hours in 2002.

ZVEZDA

St Petersburg-based Zvezda’s portfolio includes the interesting ChN 16/17 high speed radial engine formed from 160 mm bore/170 mm stroke cylinders. Seven-cylinder aluminium monobloc banks are grouped in a star-configuration to create 42-cylinder or 56-cylinder engines (using either six or eight banks) with a steel tunnel-type crankcase.

An integral reversible gearbox or hydraulic transmission is available for parallel operation with gas turbines. Another variant offered is a 112-cylinder power unit comprising two 56-cylinder engines driving via a common reversible gearbox. Among the merits of the concept claimed for fast vessel propulsion is a weight/power ratio of less than 2 kg/kW.

 

Figure 45 Cross-section of Zvezda radial engine

Technically more modest, the V12-cylinder ChN 18/20 engine is a 180 mm bore/200 mm stroke design based on twin six-cylinder aluminium monobloc banks. The design has benefited from a stronger crankcase and high alloy steel crankshaft and connecting rods underwriting outputs up to 1100 kW at 1600 rev/min. Both engine types feature direct fuel injection and turbocharging with or without intercooling.

AUTOMOTIVE-DERIVED ENGINES

Marinized automotive-derived high speed engines are popular for small craft propulsion and genset drives on larger ships, where their ruggedness and reliability (based on numerous truck applications) are appreciated.

Swedish truck engine specialist SCANIA launched its most powerfulever marine engine in 2001, the DI16M design replacing the longestablished DI14M series. The new 16-litre engine exploits an extra two litres of displacement in a package that is both shorter and lower than its forerunner (Figure 46). Increased torque and lower emissions are also delivered by the DI16M, a twin-turbocharged V8-cylinder design offered with commercial power ratings from 338 kW to 590 kW at speeds from 1800 rev/min to 2200 rev/min. The highest rating addresses light duty applications such as patrol boat propulsion; ratings from 440 kW to 590 kW (medium duty/high power commercial) serve pilot, police and rescue vessels; and the lower output range is applied for heavy duty commercial propulsion (tugs, workboats, fishing vessels).

 

Figure 46 Scania DI16M engine

The DI16M was the first Scania marine engine to use electronic unit injectors (EUI) and the company’s new S6 fully electronic engine management control module. EUI allows fuel injection timing to be adjusted to suit all engine running conditions, from cold start to idling and throughout the power range. The system fosters improved power output, fuel economy and emission control, with reduced exhaust smoke.

Based on Scania’s 16-litre truck engine, the 127 mm bore/154 mm stroke DI16M shares the same separate four-valve cylinder heads, cylinders and valve mechanism as its smaller sibling, the DI12M. New composite pistons feature aluminium bodies and steel crowns to handle the high combustion pressure. The engine measures 1.25 m long ¥ 1.178 m wide ¥ 1.15 m high overall, and has a dry weight of 1500–1600 kg, depending on its equipment.

Low emissions were also high priority for another Swedish specialist, VOLVO PENTA, when designing its 16-litre TAMD 165 automotivebased marine engine. The in-line six-cylinder model benefits from an upgraded fuel injection pump and a new injector as well as a new charge air cooling system, which reduces the inlet air temperature byaround 10°C compared with earlier engines. New pistons and rings reportedly reduce lube oil consumption by 50 per cent. High reliability and low noise and vibration were also targeted, relevant measures including the cast iron engine block, trapezoidal connecting rods and a crankshaft with seven main bearings.

Volvo Penta’s in-line six-cylinder D12 series is available with four power ratings—from 450 kW to 515 kW—for light duty and special light duty commercial applications. Contributing to increased power with lower emissions and fuel consumption, as well as higher reliability, are unit fuel injectors, a new electronic diesel control (EDC) system, an extremely rigid cylinder block and a seven-bearing crankshaft. Fuel is injected at a high pressure (1800 bar) through eight-hole nozzles to foster an efficient fuel/air mix. Precise control of injection is secured by the unit injectors and the EDC system, which receives continuous data from five sensors, determines the torque created by each cylinder and compensates for any difference.