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Maritime Forum

TOPIC: Reversing of Main Engine

Reversing of Main Engine 24 Mar 2017 07:44 #4757

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(a) Describe three methods of reversing a main engine.

(b) Explain what is meant by lost motion.
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Reversing of Main Engine 08 Jun 2017 00:36 #4842

For reversing the Main engine first the engine has to be started in reverse firing order, this is achieved by the changing the cam direction in the mechanical pilot air distributor of the main engine, which is done by the engine's pneumatic system on receiving the appropriate Signal from Engine order telegraph operated from the ship's wheelhouse.

a) Three methods of reversing the main engine After the engine is started on air in reverse order as mentioned it can be run on fuel by following either of the three methods as following:-
1} Reversing the firing order of the fuel pump:- It means the sequence in which the fuel is injected to each unit of the Main engine is reversed by its cam drive (it could have a separate cam for each cylinder for reverse firing order or the cam has special heart shape which when rotates in reverse direction due to running of engine in reverse direction due to air will work for reverse firing order) or electrical signal(as in the modern electronic engines)
2} Reversing the Actuation of the exhaust valves:- In this method the actuation of the valve opening and closing is reversed, only. This method is old and can run the engine safely in reverse order for small RPMs only.
3} Reversing the Fuel pump and Exhaust valve actuation: This is the most commonly used system where above mentioned both methods are applied.

b) The lost motion is the turning of the cam by an angle with respect to the cam shaft (In this there is a small servomotor put inside the cam shaft which shifts the cam in its axis)so that when the cam shaft is rotating in the reverse direction the cams would be pushing the roller of the fuel pumps in different firing order or alternatively both the shapes are forward and reverse directions are combined together as a heart shaped cam.
Last Edit: 08 Jun 2017 00:52 by anandgardener.
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