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 (see Chapter 18) with the innovative high speed L16/24 series. The 160 mm bore/240 mm stroke design (Figure 30.8) 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 30.9); 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 30.8 Cross-section of MAN B&W Holeby L16/24 genset engine. Note the separate camshafts for the gas exchange valves (left) and fuel injection (right)
Figure 30.9 MAN B&W Holeby L16/24 engine. All main support ancillaries are grouped in a single front-end box for ease of access

the outer frame forming a stiff shell with minimal vibration (Figure 30.10). 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 30.10 Noise emission and vibration from the MAN B&W Holeby L16/24 engine are minimized by the inner frame, outer shell and cover arrangement

Inner Frame Outer Shell Cover

Figure 30.10 Noise emission and vibration from the MAN B&W Holeby L16/24 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 cross-flow 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 fitted 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 30.8). 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 valve 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 air pressure. If the engine is operating at low-load condition the temperature 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 (see Chapter 22).

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

(Figures 30.11, 30.12 and 30.13) 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 30.11 MAN B&W Holeby 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 (see Chapter 22).

Bushes for charge Removal of air and cooling cylinder unit

Bushes for charge Removal of air and cooling cylinder unit

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