The Role Of Compressed Air In Starting Marine Diesel Engines

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The Role Of Compressed Air In Starting Marine Diesel Engines

If you are constantly travelling through sea, it is a good idea to learn as much as you can about the marine diesel engine you use.

For example, do you know how the marine diesel engine starts? The primary propulsion engine is started using compressed air. The air is typically compressed at a pressure of 30 bars.

 

You understand that ships are powered through mini power plants that have all the facilities. Industrial ships also have a compressed air chamber that makes a number of on-ship activities possible.

The number of air compressors could be anywhere between 4 and 10 on a single ship, depending on its size.

The air compressors take suction from the engine room which is already under pressure. The compressors then compress the air in multiple stages and fill up larger air containers. The amount of compressed air depends on the size of the compressor, onboard requirements and plenty of other factors.

Starting The Auxiliary Engine

Starting an auxiliary engine using compressed air usually depends on the engine size. Many marine diesel engines may also be started using air motors or electricity. However, compressed air is still commonly used.

Before proceeding, a series of checks need to be conducted:

  • Lubricating the oil sump level
  • Disengaging the gear
  • Checking turbocharger oil levels
  • Checking diesel pump
  • Checking rocker arm tank level
  • The air valves in the compressed air line are then opened towards the engine

The air from the main air container reaches the starting valve. As soon as the pilot air makes its way to the air distributor, there is a slight tapping. As soon as the engine rotates, it causes the camshaft to rotate which then rotates the air distributor cam.

The cam is specifically designed according to the firing order for distributor rotation and pushing the pilot air ahead. The air then makes its way to the starting valve, eventually letting in the main air into the primary combustion chamber. The piston is pushed down as the air is compressed at 30 bar.

Ultimately, this rotates the crankshaft, allowing the engine to start working at the lowest RPM, creating the ideal conditions for fuel injection. As soon as the engine starts using fuel, the main air supply is shut off. This is how compressed air is used to start a marine diesel engine.

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