How to draw Indicator Diagram for a Slow Speed Marine Diesel Engine?

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We learnt about indicator diagrams in the previous article and the basic concepts associated with it. In this article we will learn the process of drawing actual indicator diagram for a slow speed marine diesel engine used for the main propulsion purposes. If you haven’t read that article, I strongly suggest that you go through it before reading this article so that you understand the procedure and the parts of the engine indicator mentioned in this article

Preparation for the Diagram

There are certain points which need to be kept in mind before plotting an indicator diagram in order to ensure that it gives a fairly true indication of the power generated. These points are listed in the bullet format as follows.

  • The propeller of the ship should be fully immersed in water
  • The ship should be at even keel and preferably fully laden
  • There are no strong winds present either against or in favour of the direction of motion of the ship. If winds are present the engine will either produce more power or will produce lesser power for the given speed because of the wind resistance or aid, as the case may be
  • The underside of the ship is pretty clean and is not fouled with underwater growth, otherwise the engine would develop more power for the given speed
  • The engine indicator is clean and properly lubricated so that friction does not cause an error in the reading
  • The writing pressure of the stylus against the inserted sheet of paper should neither be too low nor too strong. If it is strong it might tear the paper, while if it is too low it will not leave a strong impression
  • The cock should be clean so that all the pressure is made available to the piston of the engine indicator

Recording the Diagram

  • The engine indicator should be fastened to the cock and the cord on the instrument should be kept taut
  • While the cock is still in the shut position, the atmospheric pressure line should be traced
  • The indicator cock should be opened and the stylus should be pressed against the paper till the cycle gets imprinted after which the cock should be safely shut
  • The cord now needs to be removed and the indicator cock opened again and to be pulled with hand, the timing being such that the piston is at the top dead center at that time

Author’s Note

I know this description would be more helpful if accompanied by some video. I have requested videos from sources if I get hold of them will surely link them. If anyone has got such a clip just get in touch with me and I can link it here for everyone to see.