How Compressed Air Helps in Starting a Diesel Engine of a Vessel

Do you know how diesel engines are started in ships? Equivalent in size to a four-story building, the main propulsion engine is started with the help of compressed air at a pressure of 30 bar. Where a ship gets its compressed air supply from?

Cruise Vessels
Air is a natural resource that is available in plenty and free of cost. It has a very important part in starting the engine of a vessel. Supply of compressed air is required to start diesel engines. This compressed air is passed on into the cylinders in the right order for the direction needed. A supply of compressed air is preserved in the air reservoirs present in the ships or ‘bottles’ for instant use. Usually, the stored compressed air facilitates up to 12 starts. The air system is engineered with interlocks to prevent starting if other parts of the engine are not in order.

The compressed air to the air receivers is supplied by air compressors. The compressed air is further passed on by a huge air pipe to a remotely operating automatic or non-return valve. Then it is supplied to the cylinder air start valve. Once the cylinder air start valve is opened, it will allow compressed air into the cylinder.

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Starting issues in a diesel engine of a vessel

Starting an engine during the colder months is really difficult. Besides, the lubricating oil that is used for running the engine remains in a very hot state and viscous. But the same oil gets very sticky and thickened when the engine is in stopped mode. The engine movement implies that the entire piston has to move up side and down within the engine cylinder which also comprises cold lubricating oil and gives much resistance. Using batteries is not a very practical idea because the power required to rotate such an engine is beyond imagination. It will require an army of batteries to get the result. In such a scenario, the role of the compressed air comes into action.

Role of compressed air:

  • Starting the main propulsion engine
  • Starting auxiliary diesel engine
  • Blowing vessels’ whistle
  • Cleaning and general service for engine room

The compressed air has a crucial role in ships. Every ship is equipped with a “The First Start” or “Dead-Start” mechanism. When the vessel is completely ‘dead’ i.e. no power or no machines are running and no compressed air in the reservoir to start the auxiliary diesel engine, then an alternative is kept in every vessel  to fill up the air bottle or reservoir to bring back the normal  and safe working condition of the ship. This is offered by either an “Emergency Air Compressor” run by an electric motor or a small diesel engine which gets its power supply from “Emergency Generator”.


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