Maintaining the efficient and safe operation of a vessel’s main engine units is crucial for smooth sailing and ensuring the safety of all onboard. In certain circumstances, it becomes necessary to cut out the combustion on or to isolate one of the main engine units. This article will delve into the process of cutting out combustion and isolating the unit, discuss when it is necessary, highlight the factors marine engineers need to consider, and outline the essential precautions and measures to be taken. The extent of the work to be carried out depends, of course, on the nature of the trouble.

Understanding the Process of Cutting Out Combustion

When a marine engineer decides to cut out the combustion on a main engine unit, it means intentionally stopping the fuel injection into that particular unit. By doing so, the engine’s power output is reduced, and it ceases to contribute to the propulsion of the vessel. This process involves a systematic and controlled approach to ensure the safety and functionality of the remaining operational units.

When is it Necessary to Cut Out Injection on a Main Engine Unit?

There are several scenarios in which cutting out the injection on a main engine unit becomes necessary:

• • Technical Malfunctions: In the event of a malfunction or breakdown in one of the main engine units, cutting out the combustion allows the crew to isolate the faulty unit and prevent further damage. This ensures the vessel can continue its operations with the remaining functional engines. The technical malfunctions can be, for instance but not reduced to:
    • blow-by at piston rings or exhaust valve
    • bearing failures which necessitate reduction of bearing load
    • faults in the injection system.
  • Maintenance and Repairs: Routine maintenance and repair activities may require cutting out the combustion on a main engine unit. This allows the marine engineer to safely conduct necessary maintenance procedures, such as inspections, replacements, or repairs, without endangering the crew or vessel.
  • Fuel Economy and Efficiency: During periods of reduced power demand, such as when sailing at lower speeds or in calm waters, cutting out the combustion on one or more engine units can optimize fuel consumption and increase overall efficiency. This strategy helps minimize operating costs and extend the lifespan of the engines.

Process of Cutting Out Combustion on a Main Engine Unit

• • Initial Assessment: The marine engineer must conduct a thorough assessment of the engine to identify the specific unit requiring combustion cut-out. This includes analyzing performance data, monitoring alarm systems, and conducting visual inspections.

  • Preparing the Engine: Prior to cutting out combustion, the engineer needs to ensure the vessel is at a safe operating condition. This involves reducing the load on the affected unit and synchronizing the remaining engines, if required, for optimal performance.

  • Shutting Down Injection: Once the engine is prepared, the marine engineer can proceed with cutting out the injection on the designated unit. This is typically achieved by isolating the fuel supply, closing relevant valves, and activating the engine control system to cease fuel injection.

In case of camshaft type engine the injection can be cut out by lifting and securing the fuel pump roller guide. The entire procedure for cutting out the injection on one of the units is fully described in the engine manual.

Should the engine be kept running with the injection cut out for an extended period, the lubricating oil feed rate for the respective cylinder must be reduced to the minimum. If the piston and exhaust valve gear are still operational, do not shut down the piston cooling oil and cylinder cooling water on that particular unit.

In case of electronic controlled engines, cutting out the injection is more simpler as everything is done from the Engine Control Panel Unit.

You must be aware that with an injection pump cut out the engine can no longer be run at its full power.

Process of Combustion and Compression cut out. Piston still working in cylinder.

This measure is permitted in the event of, for instance, water is leaking into the cylinder from the cooling jacket/liner or cylinder cover.

The procedure is as follow:

• • Cut out the fuel pump by lifting and securing the roller guide.
  • Put the exhaust valve out of action and lock it in open position.
  • Shut-off the air supply to the exhaust valve, and stop the lube oil pumps. Dismantle and block the actuator oil pipe. Restart the lube oil pumps.
  • Close the cooling water inlet and outlet valves for the cylinder. If necessary, drain the cooling water spaces completely.
  • Dismantle the starting air pipe, and blank off the main pipe and the control air pipe for the pertaining cylinder.
  • When operating in this manner, the speed should not exceed 55% of MCR speed.

Note: The joints in the crosshead and crankpin bearings have a strength that, for a short time, will accept the loads at full speed without compression in the cylinder. However, to avoid unnecessary wear and pitting at the joint faces, it is recommended that, when running a unit continuously with the compression cut-out, the engine speed is reduced to 55% of MCR speed, which is normally sufficient to maneuver the vessel.
During maneuvers, if found necessary, the engine speed can be raised to 80% of MCR speed for a short period, for example 15 minutes.
Under these circumstances, in order to ensure that the engine speed is kept within a safe upper limit, the overspeed level of the engine must be lowered to 83 % of MCR speed.

Process of Combustion Cut Out. Exhaust Valve closed. Piston still working in cylinder.

This measure may be used if, for instance, the exhaust valve or the actuating gear is defective.

The procedure is as follow:

• • Cut out the fuel pump by lifting and securing the roller guide.
  • Put the exhaust valve out of action so that the valve remains closed (lift the guide or stop the oil supply and remove the hydraulic pipe).

Please note that, the cylinder cooling water and piston cooling oil must not be cut out.

Process of piston, piston rod, and crosshead suspended in the engine. Connecting rod out

This measure may be used if, for instance, serious defects in piston, piston rod, connecting rod, cylinder cover, cylinder liner and crosshead.

The procedure is as follow:

• • Cut out the fuel pump by lifting and fixing the roller guide.
  • Put the exhaust valve out of action so that the valve remains closed.
  • Dismantle the starting air pipe. Blank off the main pipe and the control air pipe for the pertaining cylinder.
  • Suspend the piston, piston rod and crosshead, and take the connecting rod out of the  crankcase.
  • Blank off the oil inlet to the crosshead.
  • Set the cylinder lubricator for the pertaining cylinder, to ‘ ‘zero’’ delivery.

Please note that, in this case the blanking-off of the starting air supply is particularly important, as otherwise the supply of starting air will blow down the suspended engine components.

Precautions and Measures for Cutting Out a Main Engine Unit

• • Safety Protocols: The utmost priority when cutting out a main engine unit is ensuring the safety of the vessel, crew, and engineers involved. Marine engineers must follow established safety protocols, wear appropriate personal protective equipment (PPE), and coordinate with the ship’s personnel to minimize risks during the procedure.

  • Communication and Coordination: Effective communication between the marine engineer, engine room crew, and bridge team is crucial. The bridge team must be aware of any changes in engine configuration to adjust vessel operations accordingly and maintain situational awareness.

  • Monitoring and Alarms: While cutting out combustion, continuous monitoring of engine parameters, alarms, and performance indicators is essential. Any unusual readings or abnormalities should be promptly reported and addressed to prevent further complications.

  • Documentation: It is vital to maintain comprehensive documentation throughout the process, including detailed reports of the engine condition, actions taken, and any observations made during the combustion cut-out. This information assists in analyzing the cause of the malfunction and aids in future maintenance planning.

In conclusion, cutting out the combustion on a main engine unit is a critical procedure that marine engineers may need to undertake to safeguard vessel operations and prevent further damage. Whether due to engine malfunction, contamination, or maintenance requirements, this process requires careful assessment, preparation, and adherence to safety protocols. By following the necessary precautions and measures, marine engineers can effectively isolate and address the issues affecting the main engine unit, ensuring the safety, efficiency, and reliability of the vessel’s propulsion system.

If you want to learn and get a “Diploma in Marine Diesel Engines”, please follow THIS LINK on Alison platform. The course is free and all you need to do is just to subscribe to their platform using the link above. This will be of a great help to me as well, as I will earn small commission. You can consider this as a reward for my effort to provide guidance and advices with regard to complex, challenging and rewarding marine engineering. 

If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World, Telegram Chief Engineer’s Log Chat or Instagram and will try to answer to all your queries. You can use the feedback button as well!

If you like my posts, please don’t forget to press Like and Share. You can also Subscribe to this blog and you will be informed every time when a new article is published.

Also you can buy me a coffee by donating to this website, so I will have the fuel I need to keep producing great content! Thank you!