Wartsila

The medium speed specialist Wartsila 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 Wartsila 200 series (Figures 30.39 and 30.40).

The 200 mm bore/240 mm stroke engine is produced by Wartsila 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. Wartsila'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 30.39 Wartsila 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 30.41) 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 Wartsila medium speed engines. Arranging the oil lubrication distribution

Figure 30.40 Wartsila 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 Wartsila 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 Wartsila'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 30.41 The nodular cast iron block of the Wdrtsild W200 engine incorporates fluid channels

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 30.42) 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 30.42 The Wartsila 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 (see Chapter 27) 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 F-DMB).

Individual fuel injection pumps are integrated in the same cast multi-housing (Figure 30.43) as the inlet and exhaust valve tappets

Figure 30.43 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 (70oC after cooler), and reduced NOx emissions due to the cold charge air temperature (60OC 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 30.44) 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 30.44 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 pre-lubricating 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 199899 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.

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