6070mc

2nd generation

2nd generation

Cast-in cooling pipes

'Slim liner'

Bore-cooled

Cast-in cooling pipes

Figure 10.4 Cylinder liner designs

'Slim liner'

Bore-cooled

Figure 10.4 Cylinder liner designs

Cylinder cover: a solid steel component provided with bored passages for cooling water, a central bore for the exhaust valve, and bores for fuel valves, safety valve, starting valve and indicator valve.

Piston: an oil-cooled piston crown, made of heat-resistant chrome-molybdenum steel, is rigidly bolted to the piston rod to allow distortion-free transmission of the firing pressure. The piston has four ring grooves which are hard chrome plated on both upper and lower surfaces of the grooves. A cast iron piston skirt (with bronze sliding bands on the large bore engines) is bolted to the underside of the piston crown (Figures 10.5 and 10.6).

S-MC-Mk 5 S50/60/70MC-C and L70MC Mk 6

with high topland

S-MC-Mk 5 S50/60/70MC-C and L70MC Mk 6

with high topland

Figure 10.5 Piston/ring pack assembly MC vs MC-C engines

Piston rod: the rod is surface treated to minimize friction in the stuffing box and to allow a higher sealing ring contact pressure. The piston rod stuffing box provides effective sealing between the clean

Inconel layer for TCS and K-MC-C plants

Inconel layer for TCS and K-MC-C plants

New standard on 90-60MC

Piston skirt with lead Surface of O-ring bronze bands groove etc. N7 (smooth)

Figure 10.6 Piston assembly

New standard on 90-60MC

Piston skirt with lead Surface of O-ring bronze bands groove etc. N7 (smooth)

Figure 10.6 Piston assembly crankcase and the 'combustion area', and has a proven record of very low amounts of drainage oil.

Camshaft: the fuel injection pumps and the hydraulic exhaust valve actuators are driven by the camshaft. Cams are shrink-fitted to the shaft and can be individually adjusted by the high pressure oil method. Like its predecessors, the MC engine uses a chain drive to operate the camshaft and thus secures high reliability since a chain is virtually immune to foreign particles. It also enables the camshaft to be positioned higher, shortening the hydraulic connections to the fuel valves and the exhaust valves and, in turn, minimizing timing errors due to elasticity and pressure fluctuations in the pipe system.

Exhaust valve: hydraulic oil supplied from the actuator opens the exhaust valve and the closing force is delivered by a 'pneumatic spring' which leaves the valve spindle free to rotate. The closing of the valve is damped by an oil cushion on top of the spindle. The rotation force is provided by exhaust gas acting on vanes fitted to the valve stem. Extended service life from the valve is underwritten by Nimonic valve spindles and hardened steel bottom pieces, specified as standard on the large bore engines. The bottom piece features patented 'chamber-in-seat' geometry.

Fuel pump: larger engine models incorporate pumps with variable injection timing for optimizing fuel economy at part load; the start of fuel injection is controlled by altering the pump barrel position via a toothed rack and a servo unit. Individual adjustment can be made on each cylinder. Additionally, collective adjustment of the maximum pressure level of the engine can be carried out to compensate for varying fuel qualities, wear and other factors. Both adjustments can be effected while the engine is running. The pump is provided with a puncture valve which prevents fuel injection during normal stopping and shutdown.

Fuel oil system: the engine is served by a closed pressurized fuel oil system, with the fuel preheated to a maximum of 150oC to ensure a suitable injection viscosity. The fuel injection valves are uncooled. The fuel system is kept warm by the circulation of heated fuel oil, thus allowing pier-to-pier operation on heavy fuel oil.

Reversing mechanism: the engine is reversed by a simple and reliable mechanism which incorporates an angularly displaceable roller in the fuel pump drive of each cylinder. The link connecting the roller guide and the roller is self locking in the Ahead and Astern positions. The link is activated by compressed air which has proved to be a very reliable method since each cylinder is reversed individually. The engine remains manoeuvrable even if one cylinder fails: in such a case the relevant fuel pump is set to the zero index position.

Shaft generators: all MC engines can be arranged to drive shaft generators. The PTO/RCF (Renk constant frequency) system is MAN B&W Diesel's standard configuration for power take-offs from 420 mm bore models and upwards coupled to a fixed pitch propeller. The system is mounted on brackets along the bedplate on the exhaust side of the engine. The generator and its drive are isolated from torsional and axial vibrations in the engine by an elastic coupling and a tooth coupling mounted on a flange on the free end of the crankshaft. The drive comprises a three-wheel gear train. To ensure a constant frequency the planetary gear incorporates a hydraulic speed control arrangement which varies the gearing ratio. The frequency is kept constant down to 70 per cent of the main engine's specified maximum continuous rating speed, corresponding to 30 per cent of the engine's specified mcr power, making the system suitable for fixed pitch propeller installations.

The PTO/GCR (gear constant ratio) system is MAN B&W Diesel's standard solution for power take-off in plants featuring controllable pitch propellers. The system comprises a compact unit with a step-up gear coupled directly to the generator which is located above the elastic coupling.

Power turbines: larger MC engines (from 600 mm bore upwards) can be specified with a turbo compound system (TCS) which exploits exhaust energy surplus to the requirements of a high efficiency turbocharger to drive a power gas turbine (see Chapter 7). For engine loads above 50 per cent of the optimized power the gas turbine is mechanically/hydraulically connected to the crankshaft. Power is fed back to the main engine, thus reducing the total fuel consumption. The standard system, designated TCS/PTI (power take in), is delivered as a complete unit built on the engine. Also offered is a combined PTO/PTI unit embracing a power take off with associated generator and a TCS/PTI unit with a power turbine coupled to the crankshaft gear.

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Responses

  • mewael
    Why piston skirt is provided and why is bronzw sliding bands given on skirt?
    3 years ago

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