How An Auxiliary Engine Starts By Air Motor?


Large Marine Engines are started using high pressure compressed air. The air is admitted into the cylinder when the piston is just past TDC and continued until just before the exhaust valve opens.

In air motor starting system, the engine is started by a starting air motor which is operated by compressed air. An article published in marine engineering online explain about starting air motor.

Here’s an excerpt from that. 

Steps To Start Auxiliary Engine

  1. Compressed air from air bottle reaches the auxiliary engine at 30 bar pressure.
  2. The air pressure is reduced to 6 bar with a reduction valve.
  3. A safety valve is also fitted in the line after reducing valve to protect the air starting system components. 
  4. Air then enters air starting valve (5) and wait there. 
  5. When ‘START’ button on the control panel is activated, starting solenoid valve (5) is opened to supply compressed air into the starting air motor (1). 
  6. Then, The pinion of the air starting motor is engaged with the gear rim of the engine flywheel. 
  7. As the pinion moves, relay valve (2) is supplied with air and it allows air to the starting air motor turbine wheel.
  8. Now air motor turns crankshaft of the engine. When the engine rotating speed reaches predetermined speed, fuel oil is injected into the combustion chamber. Then, starting of auxiliary engine is completed.
  9. After that, The pinion of the air starting motor is disengaged from the gear rim at predetermined speed.

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