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Critical Running

When running undercritical, significant varying torque at MCR conditions of about 100 150% of the mean torque is to be expected.

This torque (propeller torsional amplitude) induces a significant varying propeller thrust which, under adverse conditions, might excite annoying longitudinal vibrations on engine/double bottom and/or deck house.

The yard should be aware of this and ensure that the complete aft body structure of the ship, including the double bottom in the engine room, is designed to be able to cope with the described phenomena.

Overcritical running

The natural frequency of the one node vibration is so adjusted that resonance with the main critical order occurs about 30 70% below the engine speed at specified MCR. Such overcritical conditions can be realised by choosing an elastic shaft system, leading to a relatively low natural frequency.

The characteristics of overcritical conditions are:

•Tuning wheel may be necessary on crankshaft fore end

•Turning wheel with relatively high inertia

•Shafts with relatively small diameters, requiring shafting material with a relatively high ultimate tensile strength

•With barred speed range (EoD 4 07 015) of about ±10% with respect to the critical engine speed.

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Torsional vibrations in overcritical conditions may, in special cases, have to be eliminated by the use of a torsional vibration damper.

Overcritical layout is normally applied for engines with more than four cylinders.

Please note:

We do not include any tuning wheel or torsional vibration damper in the standard scope of supply, as the proper countermeasure has to be found after torsional vibration calculations for the specific plant, and after the decision has been taken if and where a barred speed range might be acceptable.

For further information about vibration aspects, please refer to our publications:

An Introduction to Vibration Aspects

Vibration Characteristics of Two-stroke Engines

The publications are available at www.mandiesel.com under ‘Quicklinks’ → ‘Technical Papers’

MAN B&W MC/MC-C/ME/ME-B/ME C/ME GI engines

MAN B&W ME/ME-C/ME-GI/ME-B engines

On the ME engines, the mechanical indicator system is replaced by a Pressure Analyser System for measurement of the cylinder combustion pressure.

The PMI pressure analyser systems measures the engine’s main parameters, such as cylinder pressure, scavenge air pressure, engine speed etc. enabling the engineer to run the diesel engine at its optimum performance.

This system gets its data from a high performance piezo electric pressure transducer which is to be

mounted on the indicator valve. The transducer is moved from one cylinder to another in order to complete measurements on all cylinders.

The crankshaft position is determined by means of the same trigger system as for the engine control system.

The PMI system compensates automatically for the twisting experienced by each section of the crankshaft due to the torque generated at different loads.

MAN B&W ME/ME C/ME GI/ME-B engines

MAN B&W ME/ME C/ME GI/ME-B engines

MAN B&W ME/ME C/ME GI/ME-B engines

MAN B&W ME/ME C/ME GI/ME-B engines

The shut down system must be electrically separated from other systems by using independent sensors, or sensors common for the alarm system but with galvanically separated electrical circuits, i.e. one sensor with two sets of electrically independent terminals. The list of sensors are shown in Table 18.04.04.

Attended Machinery Space (AMS)

The basic safety system for a MAN Diesel engine is designed for Attended Machinery Space and comprises the temperature sensors and pressure sensors that are specified in the ‘MAN Diesel’ column for shut down in Table 18.04.04.

These sensors are included in the basic scope of supply (option: 4 75 124) and are also included for UMS.

Unattended Machinery Space (UMS)

In the ‘Extent of Delivery’ an asterisk (*) marks items normally required for plants designed for UMS including the sensors for alarm and slow down, option: 4 75 127, but not those for shut down.

The shut down and slow down panels can be ordered as options: 4 75 610, 4 75 614 or 4 75 615 whereas the alarm panel is yard’s supply, as it normally includes several other alarms than those for the main engine.

For practical reasons, the sensors for the engine itself are normally delivered from the engine supplier, so they can be wired to terminal boxes on the engine.

The number and position of the terminal boxes depends on the degree of dismantling specified in the Dispatch Pattern for the transportation of the engine based on the lifting capacities available at the engine maker and at the yard.

Alarm, slow down and remote indication sensors

The International Association of Classification Societies (IACS) indicates that a common sensor can be used for alarm, slow down and remote indication.

A general view of the alarm, slow down and shut down systems is shown in Fig. 18.04.01.

Tables 18.04.02 and 18.04.03 show the requirements by MAN Diesel for alarm and slow down and for UMS by the classification societies (Class), as well as IACS’ recommendations.

The number of sensors to be applied to a specific plant for UMS is the sum of requirements of the classification society, the Buyer and MAN Diesel.

If further analogue sensors are required, they can be ordered as option: 4 75 128.

The slow down functions are designed to safeguard the engine components against overloading during normal service conditions and to keep the ship manoeuvrable if fault conditions occur.

The slow down sequence must be adapted to the actual plant parameters, such as for FPP or CPP, engine with or without shaft generator, and to the required operating mode.

MAN B&W ME/ME C/ME GI/ME-B engines