06 04 02

Figure 22.26 Operating data from the 12V48/60B test engine to 11.9 kg/kW). The V12-cylinder 48/60B model, for example, develops 14 400 kW and weighs 181 tons, while its predecessor yields 12 600 kW from a weight of 193 tons. For the V18-cylinder engines, the reduction in weight is approximately 15 tons and the extra power around 2700 kW. The dimensions were also reduced: the height remains the same but the B-engine is 800 mm (15 per cent) narrower, thanks to a new exhaust system concept. A pair of 48/60B engines can thus be mounted closer together than before, giving an installation width saving of one metre. The turbocharger and two charge air coolers were combined to form a single module on the V-engine.

Internal refinements included an improved piston, with steel crown and nodular cast iron (or steel, if preferred) skirt. The cylinder head incorporates a re-shaped combustion chamber, no valve cages, an innovative rocker arm concept and a modified rocker arm cover. The connecting rod shank features optimized bearing shells, an increased oil clearance, reduced rotating masses and a strengthened bearing cover design.

Among the elements retained from the original design, with proven reliability in heavy fuel operation, were the stepped piston with chrome-ceramic first ring; exhaust valve with propeller (to ensure a clean and gas-tight seat); and MAN B&W's constant pressure charging system with exhaust gas wasting and bypass control.

IS (Invisible Smoke) variants of the 48/60 became available in early 2001 incorporating measures to achieve low Bosch smoke figures throughout the load range. The development was stimulated by requirements imposed on cruise ships in environmentally sensitive regions such as Alaska. The refinements—including a turbocharger optimized for lower loads, charge air preheating and a new cooled part-load fuel nozzle—can be applied to new engines and retrofitted

MAN B&W 48/60B engine data

Bore

Stroke

Speed

Output

Cylinders

Power range

Mean piston speed

Mean effective pressure

Maximum firing pressure

Specific fuel consumption*

Specific lube oil consumption

480 mm 600 mm

500-514 rev/min 1200 kW/cyl 6,7,8,9L/12,14,16,18V 7200-21 600 kW 10-10.3 m/s 25.8-26.5 bar 200 bar 173 g/kWh 0.6-0.8 g/kWh

* at 85 per cent mcr

(See Chapter 16 for details of 48/60B engine development procedure.)

to engines in service (see Chapter3/Exhaust Emissions and Control for details). MAN B&W favoured the fuel-water emulsion route to reduced smoke over direct water injection (Figure 22.27).

Smoke DWI - water injection

Smoke DWI - water injection

Figure 22.27 Smoke reduction from a 48/60 engine equipped with fuel-water emulsion (FWE) system

Figure 22.27 Smoke reduction from a 48/60 engine equipped with fuel-water emulsion (FWE) system

V40/50 ENGINE

A contender for ships valuing compact, high powered propulsion installations—notably the new breed of fast displacement-hulled RoPax ferries—was introduced by MAN B&W Diesel in 2001. The V40/50 series was evolved from group member SEMT-Pielstick's established 400 mm bore/500 mm stroke PC2.6B design (see chapter 25) and develops 750 kW/cylinder at 600 rev/min on a mean effective pressure of 23.9 bar. Outputs from 9000 kW to 15 000 kW are covered by V12, 14, 16 and 20-cylinder models, and a specific fuel consumption of 179 g/kWh at 85 per cent maximum continuous rating is claimed.

Improvements to the French designer's PC2 design were blended with MAN B&W Diesel's own proven medium speed engine features to yield a heavy fuel-burning model with a power/weight ratio of 9.311.6 kg/kW and a power/volume ratio of 71-75 kW/m3 (Figure 22.28). Measures were taken to enhance the service life and maintenance intervals of key components, as well as to reduce overhaul times. Beneficial here is the patented modular pulse converter (MPC) pressure charging system which features only one turbocharger. IMO requirements on NOx emissions can be met by internal engine measures alone but much lower values—reportedly below 4.5 g/kWh—can be achieved by fitting a Munters Humid Air Motor (HAM) system based

Man Crankshaft
Figure 22.28 Cross-section of V40/50 design

on seawater for humidifying the charge air (see Chapter 3/Exhaust Emissions and Control).

L27/38 AND L21/31 ENGINES

A new generation of smaller medium speed designs for propulsion and genset drives—the L27/38 and L21/31 series—extrapolated the principles of the successful L16/24 auxiliary engine (see MAN B&W Holeby in High Speed Engines chapter), including the twin camshaft configuration pioneered by the L32/40 series. The L27/38 series (Figure 22.29) was introduced in 1997 and the L21/31 series in 2000.

Figure 22.29 Cross-section of L27/38 engine, a larger version of the L21/31 design

The monobloc cast iron engine frame is designed for a maximum combustion pressure of 200 bar and direct resilient mounting. A static preloading of the casting is maintained by through-going main bearing tie rods and deeply positioned cylinder head tie rods, thus absorbing the dynamic loads from gas and mass forces with a high safety margin. All the rods are tightened hydraulically. Well supported main bearings carry the crankshaft with generously dimensioned journals. The combination of a stiff box design and carefully balanced crankshaft promotes smooth and vibration-free running. Large noise-dampening covers on the frame sides offer good access for inspection and overhaul. A 'pipeless engine' philosophy resulted in integrated oil ducts, with no water flowing through the frame; risk of corrosion or cavitation is thereby eliminated.

An innovation inherited from the L16/24 design, the front end box, is arranged at the free end of the engine. It contains connecting ducts for cooling water and lube oil systems as well as pumps (plug-in units), thermostatic valve elements, the lube oil cooler and automatic back-flushing lube oil filter. External pipe connections are arranged on the sides of the front end box to reduce engine length. A small optional power take-off is located on the forward side.

Less advanced but pursuing the same philosophy as the front end box, an aft end box is arranged at the flywheel end. This carries the turbocharger and incorporates a two-stage charge air cooler and integrated ducts for high and low temperature cooling systems. A regulating valve controls the water flow to the second stage of the cooler, adjusting to the operating conditions to secure an optimum charge air temperature.

High performance from the piston and ring pack depends on the cylinder liner geometry over the entire load range, the temperature in the TDC position of the top piston ring, and measures to avoid bore polishing. The liner is of the thick-walled high collar design, which protects the sealing between cylinder head and liner from the influence of engine frame distortions. Only the collar is water cooled, ensuring a stable geometry under variable load conditions. The temperature in the TDC position of the top piston ring is optimized to prevent cold corrosion, which is especially important in heavy fuel oil operation.

Years of experience with the flame ring concept successfully applied to the 28/32A and 23/30A engine series (see chapter 18/Alpha Diesel) was adopted for the L27/38 engine. The flame ring, inserted directly in the top of the cylinder, has a smaller inside diameter than the cylinder bore. The piston has a similar reduction in its top land diameter, allowing the flame ring to scrape away coke deposits and avoid bore polishing of the liner; optimum ring performance and low lube oil consumption over a long period are fostered.

Monobloc pistons in nodular cast iron had been state of the art for a number of years for applications imposing a maximum combustion pressure of around 160 bar. With pressures up to 200 bar, however, a monobloc piston was not suitable for the new engine generation. A

composite piston, with bore-cooled steel crown and nodular cast iron body, was therefore specified. The different barrel-shaped profile of the piston rings and the chromium-ceramic layer on the top ring target low wear rates and extended maintenance intervals.

The connecting rod is of the marine head-type, with the joint above the head fitted with hydraulically tightened nuts; the head remains on the crankshaft when the nuts are loosened for removal. A low overhaul height is secured. If engineroom space allows, the complete cylinder unit (cylinder head, water collar, liner, piston and connecting rod) can be withdrawn as a single assembly. A complete unit can thus be sent ashore for overhaul and replaced with a new or overhauled unit. The thin-walled main bearing shells are dimensioned for moderate bearing loads and a thick oil film. The crankshaft is a one-piece forged component provided with counter-weights on all crank webs (attached by hydraulically-tightened nuts) to yield suitable bearing loads and vibration-free running.

A combustion pressure of 200 bar and a mean effective pressure of 23.5 bar influenced the choice of nodular cast iron as the material for the four-stud cylinder head. The rocker arms for the two inlet and two exhaust valves are mounted on a single shaft supported in the casting. The cylinder segment charge air receiver is integrated in the casting, with the exhaust gas outlet arranged on the opposite side. This cross-flow design, together with flow-optimised inlet and outlet ducts, creates a swirl effect benefiting charge air renewal and combustion.

Inlet and exhaust valve spindles are armoured with heat-resistant hard metal on the seats. The exhaust valve spindles feature integrated propellers for rotation by the gas flow in order to equalize and lower the seat temperature, and to prevent deposits forming on the seat and on the water-cooled valve seat ring. The inlet valve spindles have valve rotators to minimize seat wear.

Two independent camshafts separate the functions of fuel injection and charge air renewal, one operating the injection pumps and one actuating the valve gear. Optimum adjustment of the gas exchange without influencing the injection timing is thus secured. Cam followers on the valve camshaft each actuate two valves via pushrods, rocker arms and a yoke.

A dedicated camshaft for fuel injection makes it possible to alter the timing, when required, for a low NOx emission mode while the engine is in operation; the engine can also be easily adapted for running on different fuel oil qualities. The injection pump has an integrated roller guide directly activated by the fuel cam (Figure 22.30). Pipe systems are virtually eliminated thanks to slide connections between the pumps, promoting easy assembly/disassembly and safety against

Figure 22.30 Fuel pump and injectorr of L27/38 engine

vibration and leakage. An uncooled injection valve contributes to simplicity of the injection system, which is designed for a pressure of 1600 bar; effective atomization is thus fostered even at part load operation with small injection volumes, contributing to a low exhaust smoke value. The complete injection equipment is enclosed behind easily removed covers. A fuel feed pump and filter are standard on propulsion engines.

The constant pressure turbocharging system incorporates a bypass connection from the turbocharger air outlet to the gas inlet side in order to increase the charge air pressure at part load. For certain operating conditions requiring high engine torque at reduced engine speed, a waste gate arrangement is incorporated in the exhaust system.

An entirely closed lube oil system eases installation and avoids the risk of dirt entering the lube oil circuit. A helical gear-type lube oil pump is mounted in the front end box and draws oil from the wet sump. The oil flows via a pressure regulator through the lube oil plate cooler and the automatic back-flushing filter; this solution eliminates the exchange of filter cartridges as well as the waste disposal problem. The back-flushing filter is drained to the sump and a purifier connected to maintain the lube oil in a proper condition. An integrated thermostatic valve ensures a constant lube oil temperature to the engine.

A cooling water system based on separate low temperature (LT) and high temperature (HT) systems is standard, both circuits cooled by freshwater (Figure 22.31). In the LT system, water is circulated by the LT pump through the second stage of the charge air cooler, the lube oil coolers for engine and gearbox, the HT cooler, through the

Figure 22.31 Cooling water system of the L27/38 engine, with the high temperature (HT) circuit on the left and low temperature (LT) circuit on the right

central cooler and via a thermostatic valve back to the LT pump. In the HT system, water is circulated by the HT pump through the first stage of the charge air cooler, the cooling water collar, cylinder heads and thermostatic valve, through the HT cooler and back to the HT pump. Almost 100 per cent of the heat removed from the HT system can be exploited for heat recovery. If required by the customer, a mixed LT/HT cooling system can also be arranged.

Engine speed is controlled by a mechanical or electronic governor with hydraulic actuator. All media systems are equipped with temperature and pressure sensors for local and remote reading. The number and type of parameters to be monitored are specified in accordance with (but not limited to) the classification society requirements. Shut-down functions for lube oil pressure, overspeed and emergency stop are provided as standard. The monitoring, control and safety system is arranged for compatibility with MAN B&W Diesel's CoCoS system for engine diagnosis, maintenance and planning, and spare parts handling (see below).

L21/31 and L27/38 propulsion engine data
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