Marine Engineering Maintenance and Operational Procedures Study Guide

Internal Combustion Engine Maintenance and Diagnostics

• Fuel Injection Timing and Pressure Equalization: When reducing the angle of fuel injection timing to equalize the maximum pressure ($P_z$) in the engine cylinders, the operating power of the engine must be more than $80\%$ and the maximum compression pressure ($P_c$) deviation must stay within permissible values.

• Cylinder Head Cracks: Cracks in the cylinder head of a marine diesel engine are most likely caused by blocked cooling ducts and/or spaces.

• Fuel Start Optimization: An optimal fuel start affects both thermal tension and specific fuel consumption.

• Injection Valve Pressure Settings: A high-pressure setting for the opening of the fuel oil injection valve causes an increase in fuel burned during the second phase of burning. Conversely, a low opening pressure reduces the fuel burned in the second phase but increases the fuel burned during the third and fourth phases of burning.

• Turbocharger (TC) Maintenance: TC bearings must be replaced every $12,000$ working hours, even if all operational parameters currently appear normal.

• Engine Sensitivity to Wear: Newer generations of engines are less sensitive to piston-cylinder group wear due to a higher stock of excess air ratio $\alpha$.

• Compression Pressure ($P_c$): This serves as an indirect diagnostic indicator of the technical condition of the engine. Current reference values are determined by maintaining the current value of the pressure in the scavenging manifold and using data from the engine bench test report, adjusted to standard conditions.

• Fuel Injection Pump Adjustments: Static adjustment and checking of the Main Engine fuel oil injection pump are performed using data from the engine instruction manuals provided by the manufacturer.

• Exhaust Gas Indicators:

  • Black smoke often indicates issues with high-pressure fuel oil supply, faulty engine fuel injectors, or overloaded cylinders.

  • High exhaust temperatures can be caused by a dirty turbocharger air filter or worn/broken piston rings.

  • Deviation of exhaust gas temperature between cylinders should be within $0.1\%$.

• Piston and Liner Maintenance:

  • Piston ring grooves must be meticulously cleaned to allow the rings to move freely, ensuring sufficient tightness and sealing of the cylinder-piston mechanism.

  • Damage to cylinder liners caused by cavitation is classified as vibrational cavitation.

  • Metal temperature for fuel valve sprayers should not exceed $180\,^{\circ}C$; higher temperatures lead to sediment accumulation and clogging of sprayer openings.

Fuel Oil Systems, Separation, and Filtration

• Fuel Separation vs. Filtration: Fuel separation cannot replace filtration.

• Clarification vs. Purification:

  • Clarification mode refers to the separation of mechanical impurities only from the fuel oil.

  • Purification mode is the process where both water and mechanical impurities are separated from the fuel.

• Water Seal: In a separator, the water seal refers to the interface in the bowl between the water and the oil.

• Fuel Change-Over Procedures: Switching between distilled (MDO) and heavy fuel oil (HFO) must be done at loads lower than nominal to avoid mechanical and thermal overloading. A rapid change-over can cause high-pressure pump plungers and injection valve nozzle needles to seize or jam.

• Heating Limitations: The steam pressure used for heating fuel oil must not exceed $0.7\,MPa$.

• Fuel Tank Management: To avoid spills during bunkering, tanks should not be filled above the level of the overflow tank bottom, and the pump station should be warned to reduce flow as the tank reaches capacity.

• Fuel Quality: The permissible water content of marine fuel shall not exceed $0.01$.

Steam Boilers and Systems

• Blowdown Procedures:

  • A lower blowdown is primarily intended to remove accumulated insoluble sludge from the lower manifold.

  • If a boiler must be emptied for inspection with sufficient time, the correct procedure is to let it cool naturally and then pump out the water.

  • The water gauge glass must be blown down periodically to check the operation of the stop cocks on the glass.

• Boiler Water Chemistry:

  • If the alkalinity $P = 450\,PPM$ calcium carbonate, the operator should blowdown the boiler and reduce the water treatment.

  • If salinity reaches $500\,PPM$, blowing is required, along with checking the condenser for leaks.

  • If pH is below $7$, increase the dosage of water treatment chemicals and re-analyze.

  • If pH is above $11$, perform a blowdown and partial water change until the range is normalized.

  • Samples for analysis are typically taken before blowdown and before adding chemicals.

• Boiler Efficiency and Operation:

  • Increasing superheated steam temperature by $10$ to $15\,^{\circ}C$ raises boiler efficiency by $1\%$.

  • The water economizer increases efficiency by utilizing exhaust gas; to raise feed water temperature by $1\,^{\circ}C$, it reduces exhaust gas temperature by $4\,^{\circ}C$.

  • Presence of Carbon Monoxide ($CO$) in the exhaust indicates incomplete combustion.

• Safety and Maintenance:

  • Safety valves must open whenever pressure exceeds the permissible operating pressure.

  • Low-temperature corrosion on heating surfaces in exhaust gas boilers is caused by the presence of Sulfuric Acid ($H_2SO_4$).

  • Scale is removed from boilers using the chemical digestion method.

Turbines and Condensate

• Preheating: The priority method for preheating ship steam turbines is using a dedicated steam conducting pre-heating system while turning the rotor with the assistance of the turning gear or flywheel mechanism.

• Operational Conditions:

  • If a turbine vibrates during acceleration, the load should be reduced until vibrations disappear, then acceleration can resume slowly after $5$ to $10$ minutes.

  • Noise inspections should be concentrated in the area of the bearings.

  • Condensate overcooling is considered a pure heat loss.

  • Oxygen content in the condensate water must not exceed a range of $0.05$ to $0.01\,mg/l$.

• Reversing: When a steam turbine is reversed, the back-steam pressure limit can be increased up to $1.5$ times.

Electrical Systems and Components

• Insulation Resistance: Normal insulation resistance for an operating electric machine is considered to be over $2\,M\Omega$. This is measured using a Megaohmmeter.

• Motors and Connections:

  • A three-phase asynchronous motor marked $230/380\,V$ should be connected in a Star configuration for a standard $380\,V$ voltage supply.

  • If an induction motor hums but does not turn, a common cause is a blown or burnt fuse in one of the phases.

  • Increasing the impedance in the rotor circuit of a running asynchronous motor with a wound rotor will cause the rotation speed to decrease.

• Generators:

  • In an asynchronous generator, doubling the current load causes the thermal load on stator coils to increase four times.

  • A DC generator may produce off-normal voltage if the brushes are offset from the neutral line.

• Batteries:

  • The compartment where batteries are charged must be well-ventilated because the gases discharged (Hydrogen) are highly explosive.

  • Normal charging current for a $12\,V$ $160\,Ah$ acid battery is $8$ to $16\,A$.

  • In alkaline batteries, the electrolyte density remains constant and does not depend on the state of charge.

Auxiliary Machinery and General Maintenance

• Pumps:

  • Ball bearings should be mounted to centrifugal pump shafts by heating the bearing in an oil bath first.

  • Operating a centrifugal pump for prolonged periods with a closed discharge valve leads to pump overheating.

  • Vortex, gear, or turbine pumps can be damaged if the discharge valve is closed while the motor is running.

• Crankshaft and Bearings:

  • Crankshaft deflection monitoring reveals the degree of misalignment of the main journals.

  • Pitting endurance is the primary metric for calculating roller bearings; they are selected based on dynamic load capacity ($1\,million$ revolutions without pitting).

  • White metal bearings turning black and hardening suggests water contamination in the oil.

• Air Compressors:

  • During starting, the purge valve should be open to ensure the motor does not struggle with high starting torque.

  • Water appearing in the crankcase oil of a water-cooled compressor usually originates from leaking O-rings on the cylinder liner.

• Maintenance Regulations:

  • Oil Record Book: Mandatory entries include fuel bunkering, oily water discharge, oil transfers between tanks, accidental discharges, and incineration of liquid waste.

  • Fresh Water Consumption: Planning for a voyage should guarantee $120$ to $160$ liters per person per day.

  • Marine Documents: Information regarding standard ambient environmental conditions for specific engines is found in the engine's technical documentation.