Detail

Marine auxiliary engines are manufactured keeping in mind the rigorous environment they will be installed and operated in, along with maintaining the continuity of operation to provide uninterrupted power supply to various ship systems. The ignition and combustion of the fuel is converted by the engine to work. The engine consists of a fixed cylinder and a moving piston. The expanding combustion gases push the piston, which in turn rotates the crankshaft.

Shipboard power is generated using a prime mover and an alternator working together. For this an alternating current generator is used on board. The generator works on the principle that when a magnetic field around a conductor varies, a current is induced in the conductor. The generator consists of a stationary set of conductors wound in coils on an iron core. This is known as the stator. A rotating magnet called the rotor turns inside this stator producing magnetic field. This field cuts across the conductor, generating an induced EMF or electro-magnetic force as the mechanical input causes the rotor to turn. The magnetic field is generated by induction (in a brushless alternator) and by a rotor winding energized by DC current through slip rings and brushes.

There are two kinds of engines: the spark ignition gasoline engine and the compression ignition diesel engine. Most of these are four-stroke cycle engines, meaning four piston strokes are needed to complete a cycle. The cycle includes four distinct processes: intake, compression, combustion and power stroke, and exhaust. In a spark ignition engine, the fuel is mixed with air and then inducted into the cylinder during the intake process. After the piston compresses the fuel-air mixture, the spark ignites it, causing combustion. The expansion of the combustion gases pushes the piston during the power stroke. In a diesel engine, only air is inducted into the engine and then compressed. Diesel engines then spray the fuel into the hot compressed air at a suitable, measured rate, causing it to ignite.The Power Distributed on board a ship needs to be supplied efficiently throughout the ship. For this the power distribution system of the ship is used. A shipboard distribution system consists of different components for distribution and safe operation of the system. They are as follows:

• Ship Generator consisting of prime mover and alternator

 

• Circuit breakers which act as a switch and in unsafe condition can be tripped to avoid breakdown and accidents

 

• Fuses as safety devices for machinery

 

• Transformers to step up or step down the voltage

 

• When supply is to be given to the lighting system, a step-down transformer is used in the distribution system

 

• In a power distribution system, the voltage at which the system works is usually 440v

 

• There are some large installations where the voltage is as high as 6600v

 

• Power is supplied through circuit breakers to large auxiliary machinery at high voltage

 

• For smaller supply fuse and miniature circuit breakers are used

 

• The distribution system is three wires and can be neutrally insulated or earthed

 

• Insulated system is more preferred as compare to earthed system because during an earth fault essential machinery such as steering gear can be lost

Few points to be noted about power on board are: AC, 3 phase power is preferred over DC as it gives more power for the same size. 3 phases is preferred over single phase as it draws more power and in the event of failure of one phase, other 2 can still work.

The reduction in the number of auxiliary engines will not only result in fuel saving but primarily a reduction in auxiliary maintenance and will allow better engine performance. It must be stressed that in emergency situations, the possibility of a blackout must not delay the decision to shut down dangerous machinery. When the vessel is in confined waters the above should not apply as enough auxiliary engines should be run to provide an ample supply of power to cope with any such emergency.

In contrast to main diesel engine, auxiliary engines are generally 4-stroke, medium speed, medium size, trunk piston engine. They have high rotations, power to weight ratio is less. they have more moving parts. They are highly efficient but less powerful. Their turning movement is not uniform and a heavier flywheel required. They are non-reversible and maneuvering is done by other means. They have cheaper parts, require more maintenance and generally make more noise.