HomeEngineering Knowledge GeneralMain Engine Operational and maintenance Guide

Main Engine Operational and maintenance Guide

The main Propulsion system is Like the heart of the ship. there are a couple of engine manufactures in the world such as Man B &W, Sulzar, Catapiller. these fuel-powered two-stroke engines we can divide into two categories,

  1. MC engines
  2. ME engine

In this guide, we are discussing MC engines. for an active seaworthy ship, it’s crucial to do proper maintenance and the crew should be well familiar with the system.

Failure to do so can cause main engine failure and the Ship and the crew could face serious troubles. As a part of the engine room team regardless of your rank, it’s crucial to know your main engine components, associated systems, safety devices, and its operation.

Let’s start with the Safety of the main engine

What are the  Main Engine safety devices?

  • Turning gear interlock

This interlock prevents the engine from turning when the turning gear is engaged.

  • Reversing interlock

Reversing interlock prevents starting air turns the engine to the opposite direction while it’s running.to change the cam direction you have to stop the main engine completely

  • Crankcase relief door

The crankcase Relief door is there to prevent building excessive pressure inside the crankcase and to prevent suck air to the chamber from the atmosphere.

  • Cylinder head relief valve

The cylinder head relief valve prevents being damage to the cylinder head and liner in case of build excessive pressure such as the event of hydraulic lock.

  • Scavenge manifold relief valve

As the name suggests it’s preventing building excessive pressure in scavenge manifold.

  • OMD

Oil mist detector is there to monitor oil mist level in the crankcase which could lead to crankcase fire

  • Emergency stop button

The main engine can be stopped suddenly using an emergency stop in case of emergency

  • Starting airline safety including bursting disc, flame trap, relief valve, and Non-Return valves

Protects air staring system from malfunctioning

 What are the Main Engine Shut Down Events?

  • Low LO inlet pressure to camshaft and piston cooling
  • Low LO pressure to the main bearing and thrust bearing
  • T/C LO inlet pressure low
  • Thrust bearing very high temperature
  • Over speed of the engine which activates shut down at 107 % MCR (maximum continuous rating)
  • Exhaust valve spring air low pressure

What are the Main Engine slow down Events?

  • High LO inlet temperature
  • No flow of Cylinder lube oil
  • High piston cooling outlet temperature
  • Piston cooling oil non-flow
  • High main bearing temperature
  • A high crankpin bearing temperature
  • High cross-head bearing temperature
  • High thrust bearing temperature
  • High T/C bearing oil temperature
  • High JCW outlet temperature
  • Low JCW inlet pressure
  • High scavenge air receiver temperature
  • High exhaust gas temperature after cylinder
  • Control air low pressure
  • Exhaust gas economizer high temperature
  • Low fuel oil pressure
  • OMD alarm

Crankcase Explosion

What Is a Crank Case explosion

For an explosion of this type to happen inside the crankcase, there must be a hotspot and a presence of oil mist with satisfying conditions. inside the crankcase, there are many moving metallic parts with direct links to each other. if by some fault a hot spot develops in such place and it reaches 200’c, the oil flashing on it will vapourize. this Vapour will circulate the crankcase to its coolest part where it will condensate into white oil mist. when the concentration of this mist reaches 50mgl-1 it is at its lowest explosion limit. under operating conditions, at a temperature at 850’c, this oil mist will ignite causing Primary Explosion

Secondary explosion

The secondary explosion is that explosion that might happen in the crankcase after the primary explosion. when the primary explosion happens all the flame and gas are vented due to high pressure inside. when the pressure drop below 1 bar(atmospheric pressure) this will create a vacuum causing air to flood inside the crankcase resulting in another flammable mixture to be developed resulting in a secondary explosion.

Safety of Crankcase

  • Oil mist detector
  • C/C oil must be of high flashpoint
  • C/C door should be of robust construction
  • Crankcase breather
  • Smothering gas connection
  • Crankcase relief valve

Colors of Smoke

  • The white color indicates the presence of water vapor in the fuel.
  • Blue-colored smoke indicates the presence of lubricating oil in the smoke.
  • The dark black color indicates inefficient combustion or the lack of air. It could also be due to scavenging fire or economizer fire or boiler problems.

Causes of Black Smoke

The air-related problems in marine diesel engines may be due to the following reasons:

  • The turbocharger air filter is choked.
  • The turbocharger turbine blades are fouled and damaged; therefore it is giving insufficient air to the engine.
  • The turbocharger inlet grid in the exhaust manifold is choked, and therefore the turbocharger is running at low speed.
  • The compressor blades are dirty or damaged.
  • The scavenge ports of the engine may be dirty and choked.
  • The scavenge valves may be faulty or damaged.
  • The nozzle ring of the turbocharger is soiled.
  • The engine room blowers are not supplying sufficient air as the filters are choked.

The fuel-related problems that could cause black smoke are as follows

  • A low temperature of the fuel causing poor atomization and penetration.
  • The fuel injectors may be dripping causing after-burning.
  • The timing of the fuel pumps may be wrong.
  • The holes of the fuel injectors may have become large by wear.
  • Incorrect spring pressure of the fuel injectors.
  • Wrong grade of fuel or low fuel quality.
  • Incorrect valve lift of the fuel injection valves.
  • Unbalanced engine. Thermal and power balancing needs to be done.
  • Overloaded engine due to governor malfunction.
  • Some units may not be firing leading to overloading of the other units.
  • Scavenge fire has taken place

Finding the Source of Black Smoke

  • The engine must be checked for overloading and the exhaust temperatures of the individual units must be checked. The difference in temperature of the individual unit and the average temperature must not exceed 50 degrees C.
  • The engine must be checked for scavenging fire and the under-piston temperature must be checked of all the units.
  • The fuel racks of all the fuel pumps must be checked and must be within limits.
  • The air filter of the turbocharger blower must be checked for choking.
  • The turbocharger speed must be checked and the temperature drop across the turbocharger must be checked.
  • The fuel temperature must be checked and it must be within the range 120 to 140 degrees C for heavy fuel oil.
  • In the case the problem is only due to a particular cylinder, the units must be cut off one by one and for about two-three minutes any change in exhaust must be observed.

Reasons for Main engine Knocking 

  • Early ignition causes an abnormally high peak pressure in the cylinder at about the top of the piston stroke. A heavy shock load will be transmitted to the running gear and bearings with a corresponding knocking sound. It may cause due to Incorrect fuel pump timing, broken or wrongly set injector springs, incorrect fuel condition, and overheating of parts inside the cylinder.

  • Overload or unbalanced engine
  • If fuel oil has a lesser cetane number the fuel will have a very long ignition delay period. When the ignition delay period is high the fuel-injected will not have undergone combustion and by this time the fuel-air mixture starts to accumulate and it will undergo combustion after a long delay and there will be a huge shock wave as all the fuel droplets will undergo combustion at the same time.
  • Cold start of the engine. Because low working temperature does not allow vaporization of fuel in time and promotes a long delay period.
  • Piston cooling oil temp. high or insufficient cooling
  • Excessive bearing clearance of running gear
  • Clearance between piston and liner increased

Action to prevent Engine Knocking

  • Correct fuel timing
  • Correct fuel rack position
  • Injector overhauling or renewed
  • Use good quality fuel
  • Maintain the correct working temperature of the engine. Before starting warm up the engine.

Single unit

  • Excessive bearing clearance of running gear
  • Clearance between piston and liner increased
  • The piston may be striking cylinder head at TDC
  • Piston ring may be striking against the worn ridge at cylinder liner top
  • Early ignition: This will cause an abnormally high peak pressure in the cylinder at about the top of the piston stroke. A heavy shock load will be transmitted to the running gear and bearings with a corresponding knocking sound.
  • Incorrect fuel pump timing, broken or wrongly set injector springs, incorrect fuel condition, and overheating of parts inside the cylinder.

Reasons and actions for all unit and single unit exhaust temperature high and low

Exhaust temp. Low in all unit

  • Low load of the engine
  • High scavenge air pressure and low scavenge air temperature allows more supply of scavenging air which promotes optimum combustion of fuel oil and no unburnt fuel remains
  • Early ignition results in high thermal efficiency and reduced exhaust temperature
  • Fuel timing has been advanced due to wrongly set fuel pump, incorrect fuel injector timing.
  • Fuel oil booster pump pressure low
  • Fuel regulating shaft stuck at minimum position
  • Fuel oil filter chocked or dirty
  • Water content in fuel

Reasons for Exhaust temperature Low in Single unit

  • Faulty pyrometer.
  • Scavenge air pressure high.
  • Scavenge air temperature low
  • Fuel oil high-pressure pipe leaking
  • Faulty fuel injector, needle stuck up in the injector
  • Fuel timing has been advanced due to wrongly set fuel pump, incorrect fuel injector timing.
  • Fuel regulating shaft stuck at minimum position

Action

  • Inform bridge
  • If possible, increase the rpm
  • Check scavenge air temperature, if it is too low adjust by opening SW recirculating valve
  • Check fuel oil for water content
  • Check fuel oil filter if differential pressure high then change over to stand by filter and clean the dirty one
  • Check pressure regulating valve
  • Check fuel rack position
  • Check fuel oil injector and check whether the needle is stuck up or not
  • Check for any steam leakage from the heater

Exhaust temp. high in all unit

  1. Insufficient supply of scavenging air
  2. High scavenge air temperature due to faulty air cooler
  3. In case of late ignition, power is lost since the fuel is not burned correctly to transmit power at the most effective part of the stroke. Combustion may continue during the expansion stroke and may be incomplete, giving loss in energy produced, high exhaust temperature, and smoke.
      • excessive injector spring setting,
      • poor atomization,
      • high viscosity or poor quality fuel,
      • incorrectly timed fuel pump,
      • ow compression pressure due to chocked scavenge port, the air is escaping past piston during compression
  • Engine overload due to hull fouling, propeller obstacle, or bad weather
  • Scavenge fire
  • Early opening of the exhaust valve
  • Fouling of T/C
  • Poor quality of fuel used and improper purification
  • Fuel regulating shaft stuck at maximum position

Exhaust temp. high in one unit

  • Faulty pyrometer
  • Leaky exhaust valve
  • Early opening of the exhaust valve will cause a loss in power since pressure is released too soon (due to the loss of heat energy in the combustion chamber, this energy will increase exhaust temperature).
  • Specific unit’s scavenge port dirty, so less amount of scavenging air is delivered thus scavenge pressure low
  • Scavenge fire in a specific unit
  • In case of late ignition, power is lost since the fuel is not burned correctly to transmit power at the most effective part of the stroke. Combustion may continue during the expansion stroke and may be incomplete, giving loss in energy produced, high exhaust temperature, and smoke.
      • excessive injector spring setting,
      • poor atomization,
      • high viscosity or poor quality fuel,
      • incorrectly timed fuel pump,
      • low compression pressure due to chocked scavenge port, the air is escaping past piston during compression

Action

  • Inform bridge
  • Check and adjust scavenge air pressure and temperature
  • Check and adjust fuel viscosity, injector, pump.
  • Check fuel regulating shaft position
  • Reduce RPM if bad weather exists.

Reasons For Abnormal Smoke in exhaust

  • Overloaded running condition
  • Scavenge fire
  • Increase fuel temperature or fuel viscosity
  • After burning
  • Contaminated fuel
  • Too low turbocharge RPM
  • Injector fuel not atomizing the fuel completely
  • Compression pressure too low due to leaky piston ring or exhaust valve

Exhaust Valve Leaking

  • Deposit on valve and valve seat
  • Mechanical impact
  • Incorrect valve seat material
  • Hot corrosion (accelerated oxidation at high temperature) and cold corrosion (sulphuric acid condensation)
  • Damage of spring
  • Insufficient tappet clearance
  • Presence of sodium and vanadium in fuel to a high extent

Indication of Piston Running Hot

  • Piston coolant temperature will be high.
  • Knocking sound due to early ignition.
  • The jacket temperature will be high for the affected unit.

Reasons for overheated Pistons

  • Overloading the engine
  • Poor circulation of piston cool oil.
  • Due to high piston coolant temperature.
  • Fuel impingement causes local overheating of the crown.
  • Insufficient scavenge air supply
  • Poor cylinder lubrication

Cause of exhaust valve burning

When burning of HFO of high viscosity which contains sodium and vanadium, deposits on the valve seat, which at high temperature becomes strongly corrosive, strictly compounds as a result valve will be burned and wear down

Causes of jacket water temperature high

  • Cooler malfunctioning
  • Air getting entry into cooling water system
  • Piston running hot
  • Overload engine
  • Crack in liner and cylinder head
  • Insufficient venting of the expansion tank
  • Clogging of cooling water pipe system
  • The trouble of cooling water pump
  • Cooler bypass valve more open

Causes of jacket water temperature low

  • Engine running on low load
  • Low SW temperature
  • High SW pressure
  • Leakage of cooling water system
  • Water leakage of pump joint
  • Cooler bypass opened a minimum

Fuel injector

  • The first screw slacken the compression nut, check nut
  • Remove spring and spindle
  • Unscrew the cap nut
  • Take out the nozzle, needle valve, and dowel pin
  • Cleaned, inspect, and renewed if necessary
  • Lapped the nozzle holder surface and nozzle
  • Checked the dowel pin
  • Inspected spring for distortion
  • Cleaned atomized hole
  • Box up back

Injector check after Overhaul 

  •  Atomizing hole cleaning
  •  Nozzle and needle valve lapping
  • Nozzle holder and nozzle contact surface lapping
  • Spring inspected
  •  Adjust needle valve opening pressure

The function of Tie Bolt

  • To keep the whole engine structure under compression.
  • Reduce the bending stress being transmitted to the transverse girder.
  • To provide proper alignment of running gear, which prevents fretting.
  • Provide fatigue strength.
  • The firing pre. force directly transmitted to the main bearing and engine frame through tie rod.
  • Transmit the gas forces which act on the cyl. Liner.
  • To prevent unbalanced loads from being transmitted to the welds.

Effect of running Engine With Loose Tie Bolts

  • Misalignment of the main bearing and another sliding surface
  • Other tie-bolt will be overloaded to leading to failure
  • There is a possibility of fatigue failure
  • Fretting corrosion will occur.
  • Noise and vibration levels will increase.
  • The cyl. The beam would flex and lift at the location.

What Are The Reasons For Broken Tie Bolts 

  • Overstressed bedplate of cyl. block.
  • Misalignment.
  • Over tightened.
  • Vibration.
  •  Compression in the locality of the missing bolt.
  •  Overload.
  • Very high gas load transmitted to tie-bolt.

 

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