Oil Mist Detector Alarm: Actions to be taken and what to do or not

Oil Mist Detector Alarm: Actions to be

taken and what to do or not

Oil Mist Detector is equipment which monitors the environment inside a

crankcase space of an internal combustion engine and thus tells the

engineer, in case of formation of any type of explosive vapors occurring in

the crankcase of engine. This is a preventive step avoiding crankcase

explosion taking place. Here is the step by step procedure, to be followed in

case of an alarm.

What Causes Oil Mist Detector Alarm

This piece of equipment is needed to monitor the environment inside the

crankcase. Oil vapors of lube oil are constantly formed inside crankcase and

they possess a hazard of crankcase explosions. So, to avoid that, OMD (Oil

Mist Detector) will keep taking samples of air, from the connected space at

an interval of 1.5 sec to 2 seconds. Then after this it will measure it with the

standard value, plus the values from other units as well. If the

reading is out of limit, alarm comes in.

Measures to be taken After Oil Mist Detector Alarm

Following is the step by step procedure for the same:

1) First thing, first, accept the alarm from the panel.

2) Inform the bridge and chief engineer and side by side initiation of Slow

Down the engine.

3) Press Engineers alarm, to call the required manpower for the same.

4) Check that alarm which has come is true or not. Just reset it and see if it

comes again. Sometimes, false alarms also come in engine room.

5) Next step is to increase the lubrication of the main engine, by starting the

standby lubrication pump.

6) As soon as bridge gives you command for stopping engine, you are ready

to stop it. Bridge can also do that, depending on the situation.

7) Indicator cocks of the units needs to be opened.

8) This will be followed by one man engaging the turning gear and start

turning the engine. This is a counter measure to avoid piston getting stuck.

9) In the mean time, this is happening; other manpower can keep the fire

extinguishers ready. Lubrication should be kept on all the times.

10) As a precautionary measure, make sure that nobody is standing near or

close to the crankcase relief door. As pressure relieve by them can be too

much, which may prove fatal.

11) When the alarm has gone, you can switch off the lube oil pump. With

the back of your hand, feel the crankcase door. If they are cool, then we can

proceed further, otherwise wait for them till the time, they are cooled. You

may also look for any sign of paint color change on the doors.

12) When it is cooled down to normal temperature, open the crankcase door.

Two, three ventilation blower are to be kept for ventilating the crankcase

space.

13) Now it is time to go inside and make few checks. But before that, make

sure that, the light that you are using is flame proof. Also, you boiler suit is

clean and free of any oil. Both the sleeves needs to be rolled down, as there

might be hot surface inside.

14) Check for any sign of local hot spot. Try to see for any sort of metal

particles etc. Rectify the same.

15) Now again start the lube pump and see the flow.

Note: This was all, which you need to do, during an OMD alarm. The

procedure might differ from people to people, as different people have

different approaches. This is just a general approach.

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Internal Combustion Engines Nomenclature, Performance Parameters and Power Ratings

Internal Combustion Engines Nomenclature,Performance Parameters and Power Ratings

Know about all the engine performance parameters like IHP, BHP Volumetric

Efficiency and also about MCR, astern output etc. These are the basic terms that you

need to know when you are studying the Internal Combustion Engine.

Internal Combustion Engines Nomenclature

Cylinder Bore (d) – The nominal inner diameter of the working cylinder is called

as cylinder bore. It is denoted by the letter ‘d’ and is usually expressed in mm.

Piston Area (A) – The area of circle of diameter equal to the cylinder bore is called

as piston area. It is denoted by the letter ‘A’ and is expressed in cm .

Stroke (L) – The nominal distance through which piston moves between successive

reversals of its direction of motion is called the stroke. It is denoted by the letter ‘L’

and is usually expressed in mm.

Stroke to Bore Ratio (L/d) – This ratio is an important parameter in classifying

the size of engine.

If d < L it is called under square engine

If d = L it is called square engine

If d > L it is called as over square engine.

Dead Centre – The position of working piston and the moving parts which are

connected to it, so when the piston motion is reversed at the either end of the stroke

is called the dead centre. There are two dead centres in an engine. They are Top Dead

Centre and Bottom Dead Centre.

Top Dead Centre (TDC) – It is the dead centre when the piston is farthest from

the crank shaft. It is denoted as TDC for vertical engines and Inner Dead Centre

(IDC) for horizontal engines.

Bottom Dead Centre (BDC) – It is a dead centre when piston is nearest to the

crankshaft. It is denoted as BDC for vertical engines and Outer Dead Centre (ODC)

for horizontal engines.

Displacement or Swept Volume (Vs) – The nominal volume swept by the

working piston when travelling from one dead centre to other is called the

displacement volume. It is denoted by Vs and expressed in cubic centimeter (cc). Vs

= A x L

Cubic capacity or engine capacity – The displacement volume of a cylinder

multiplied by number of cylinders in an engine will give cubic capacity or engine

capacity.

Clearance Volume (Vc) – The nominal volume of combustion chamber above the

piston when it is at top dead centre is known as clearance volume. It is denoted by Vc

and expressed in cubic centimeter (cc).

Compression Ratio (r) – It is ratio of total cylinder volume when piston is at

bottom dead centre to the clearance volume.

It is denoted by letter ‘r’(Total cylinder volume =Swept volume + clearance volume)

Hence, r = Vc + Vs / Vc = 1 + Vs / Vc

As compression ratio increases the thermal efficiency increases but it also leads

higher peak pressure and temperature. The upper limit of compression ratio is

therefore fixed by strength of cylinder, bearing and other parts whose stresses are

determined by peak values of mechanical and thermal loading. Large marine engines

use compression ratio of 1214 whereas medium speed engines use compression ratio

of 16. Life boat diesel engine which needs good starting ability even in cold climate

have compression ratio of 20.

Internal Combustion Engine Performance

Parameters

Indicated Thermal Efficiency – Indicated thermal efficiency is the ratio of

energy in indicated power ( i.e. output generated in the cylinder) to input fuel energy

in appropriate units. Indicated Power is measured by taking indicator diagram from

engine cylinder. Brake Thermal Efficiency Brake thermal efficiency is the ratio of

energy in the brake power ( i.e. output available at the driving shaft of engine) to

input fuel energy in appropriate units. Brake Power can be measured by using

hydraulic dynamometer.

Mechanical Efficiency – Mechanical efficiency is defined as ratio of brake

power (delivered power) to the indicated power ( power provided to the piston ).

Volumetric Efficiency – Volumetric efficiency is ratio of volume of air drawn in

the cylinder (at normal temperature and pressure) to the swept volume. It is one of

the important parameters which decides the performance of four stroke engines.

Four stroke engines have distinct suction stroke and therefore the volumetric

efficiency indicates the breathing ability of the engine. It must be noted that the

availability of air and its utilization determines the power output of the engine. In a

naturally aspirated four stroke engine the volumetric efficiency is between 85% to

90%

Mean Effective Pressure – It is that theoretical constant pressure which may

be assumed to act on piston during its power stroke. It is equal to the average

pressure inside the cylinder of an IC engine based on calculated or measured power

output

ip = pimLAnK / 60 x 1000 then

pim = 60000 x ip / LAnK where

ip = indicated power (kW)

pim = indicated mean effective pressure ( N/m2)

L = Length of stroke (m)

A = Area of the piston (m2)

N = Speed in RPM

n = Number of power strokes

N/2 for 4 stroke engine and N for 2 stroke engine

K = Number of cylinders

Another way of specifying indicated mean effective pressure pim is from engine

indicator diagram (p–V diagram). In this case pim = Area of indicator diagram /

length of indicator diagram..

Mean Piston Speed (sp) – It is an important engine parameter and is defined

as sp = 2LN where L = stroke and N = RPM. It is often a more appropriate parameter

than crank shaft speed for correlating engine behavior as a function of speed.

The above expression which is a part of power equation suggests that power can

simply be increased by increasing m.p.s. However it can be done only the limitations

imposed by following factors:

1) Increase in m.p.s increases mechanical stresses on bearings, bearing bolts and

other moving parts. It also increases inertia forces and peak turning moments.

2) Increase in m.p.s also decreases service life of reciprocating and rotating pairs of

engine components. (Though speed is not the only criteria for wear when working

conditions involve higher temperatures and pressures with lubrication being in the

thin film region speed needs to be limited for greater reliability and safety. )

3) Beyond certain speed scavenge efficiency drops sharply and this lowers engine

output. At higher m.p.s. resistance of gases to flow in and out of cylinder increases

and scavenge efficiency drops.

Mean Piston Speed Classification based on it:

Low speed- 4.5 m/s to 7 m/s

Medium speed -7m/ s to 10 m/s

High speed -10m/s to 15 m/s

Specific Fuel Consumption (sfc) – The fuel consumption characteristics of an

engine are generally expressed in terms of specific fuel consumption in gms / kWhr.

It is an important parameter that reflects how good the engine performance is. It is

inversely proportional to the thermal efficiency of engine. Fuel consumption is

measured by carrying out a test which subjects engine to a constant rated load for

half an hour and consumption of fuel by engine is measured by suitably located fuel

flow meters. The test is repeated and average value taken as sfc.

Scavenge Efficiency – The ratio of volume of air (at normal temperature and

pressure) contained in cylinder at the start of compression to the volume swept by

the piston from top edge of the ports to the top of its stroke is called as scavenge

efficiency.

Air Charge Ratio -The ratio of volume of air (at normal temperature and

pressure) contained in cylinder at the start of compression to the swept volume of

piston is called as air charge ratio. It is also referred to as air mass ratio or air supply

ratio. This term has now more or less replaced the terms scavenge efficiency and

volumetric efficiency.

Air Charge Ratio – In four stroke engines for naturally aspirated engines air

charge ratio is about 0.85 whereas for highly super charged engine it is 4 or above it.

In two stroke engines the value is about 0.85 for engines have ported scavenge and

exhaust and it is up to 2.5 for supercharged engines.

Internal Combustion Engine Power Ratings

Maximum Continuous Rating (MCR) – The maximum continuous rating

signifies the maximum output at which the engine can run safely and continuously.

This output forms the basis of calculation for the strength of engine.

Normal or Standard Rating – The normal of standard rating signifies the

output at service speed. The service speed is that speed which is regarded as

economical for efficiency and corresponds to thermal and mechanical load best

suited from maintenance point of view.

Overload Rating – The overload rating signifies the extent of overload that can be

safely exerted on the engine for a short period.

Astern Output – It signifies the maximum output while going astern.

So these are the terminology that we use for the Internal Combustion Engine.

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Main Engine Exhaust Valve Parts, Working and Overhaul Procedure

Main Engine Exhaust Valve Parts, Working andOverhaul Procedure

Marine Diesel Engine now a days employs the hydraulic mechanism of

opening and closing the exhaust valve. Just like other machineries, it also

requires maintenance from time to time. Let’s have a look at its working and

maintenance.

Main Engine Exhaust Valve Parts

Hydraulic Pipe

Hydraulic Oil Cylinder

Air Cylinder

Spindle and vanes

Exhaust Valve Housing

Working of Main Engine Exhaust Valve

Pressurized hydraulic oil is used to open the exhaust valve, against the air

spring pressure of 7 bars. The timing of this hydraulic oil is as per the opening

timing of the exhaust valve. So, we have a benefit of changing the timing of

opening of exhaust valve, if we are using the hydraulic system.

Below is the diagram of Exhaust Valve

So, at the top, we have the hydraulic operated servo piston and at the bottom

we have the air operated piston. When hydraulic pressure is relieved, the air

pressure brings the exhaust spindle back to close position.

Overhauling Of the Exhaust Valve

1)First thing first, that the people who will work during the overhaul having

been given instructions as per the work profile.

2) After making sure that proper tools and spares are onboard, unit isolation

can be carried out.

3) Open the hydraulic nuts using the hydraulic jack .

4) After it place the valve on a wooden platform carefully. First thing to take

out is the oil cylinder of the exhaust valve. After that retaining ring for the

spindle will be removed with use of special tool.

5) Also, after this, air piston arrangement is removed.

6) Now we have opened everything. We will put main consideration on

Spindle Bushing, Spindle and the Exhaust valve seating surface, as these are

the places where the actual wear and tear takes place.

Checking the Exhaust Valve Spindle Bushing

In the diagram below you can see what you have to check. You can use the

dial gauge to measure the clearance.

Checking the Bottom Seat Surface

Checking with the help of template, you can check whether clearances are in

the right limit or not. Before putting the template, it is wise to remove any type

of carbon being deposited on the seat.

Small dents, that cannot hamper the sealing of seat, should be avoided for

any repair. But yes, if there are tends and erosion, that are damaging the

sealing between the exhaust valve spindle and the seat, then some grinding is

necessary.

Outer seating needs to be lapped smoothly, with the help of special tool

shown below. The lapping needs to be one half turn clockwise and half turn

anti clockwise.

Checking Exhaust Valve Spindle Seating Surface

Manufacturer of the engine provides the standard template for the

measuring the clearance of the spindle face. If it is not satisfactory, you can

grind it.

Secondly, with the help of template, you can also, check the amount of burn

off on valve face.

Sometime, you need to grind the face, to remove the black carbon depositing

on it, so that you can get the actual surface to measure on.

You also need to check the trueness of the spindle shaft. This can be done by

putting the one end of the shaft on rolling point and on the other end you can

fit the dial gauge. Any difference will tell, whether shaft is true or not.

After doing all the checks and putting necessary spares, it is time to box back

the exhaust valve. This exhaust valve overhaul was for the MAN B&W engine.

So for other engines, things might vary. So this was all from this article ‘Main

Engine Exhaust Valve Overhaul’.

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Every Day checks in Engine Room Rounds from Funnel to Tunnel on Ship

Every Day checks in Engine Room Rounds

from Funnel to Tunnel on Ship

When a duty engineer is taking rounds, half of the problems or troubleshooting can

be done by them, if they check the items below given properly. This is for a specific

ship, so some things can vary, but mostly things will be same. This piece of

information gives idea to the engineer as what they have to and what not to.

This is also useful when the engine room is being put in to UMS operations.

Everyday Routine checks in Engine Room of a Ship Checks onFunnel Casing

Funnel exhaust lines for leaks / vibrations.

Fire dampers / remote cylinder for leaks.

the soot blower sealing air fan

F – Deck Level

funnel exhaust lines for leaks / vibrations.

lift machinery room ( starboard Side )

Battery room exhaust fan.

D – Deck Level.

The Air Handling Unit Room.

The amp’s for the accommodation blowers.

C – Deck Level

the emergency generator room and make sure the e/g is in auto.

the diesel oil tank level.

Exhaust Boiler Deck Level

Funnel exhaust lines for leaks / vibrations .

Reduction steam pressure controller for leaks.

Feed water valves for leaks.

The soot blowers.

Expansion tank level

Engine control room deck

Engine room crane secured

Air condition unit for control room ps. Temperatures – pressures – internal leaks –

water inlet /outlet

Workshop : all electrical tools switches to be off. Air condition switched off and

water tight doors closed.

Bow thruster & stern thruster panel – lamp test – hrs. Meter amp meter when

running.

Air condition & provision compressor’s pressure’s, oil level, cooling water pressure,

‘v’ belt tension, freon level.

The HP,LP drum water levels. And fill the chemical dosing tanks for hp & lp.

Cylinder daily tank level.

Hot water pre heater unit with pumps, leaks – noise – in / outlet pressures –

temperatures.

Calorifier heater panel, power source – temperature – pressures – pumps for leaks

and noise.

Engine Room Control Room Checks

Main switchboard – lamps amp.meters – earth lamps – hrs. Meters – 220 volt feed

panel –440 volt feed panel syncro. Panel – generator running kw- meters and amp

meters.

24 volt ups panel, output voltage / amps. – charger 1 –2.

All parameters. Alarm interlock list and manual mode list

Main cabinet for maneuvering system.

Fire alarm panel / disconnections.

Main Engine Top Floor

Air drier for working /control air : pressure lamps pressure.

Service air reservoir : pressure – drain – leaks.

Service air compressors 1 and 2 : pressures – temperatures – lamps internal leaks –

oil level.

Manually drain both service and main air bottles.

Main air compressor oil level

The level and temperature of feed filter tank.

Fresh Water Generator

Sewage plant

Aux. Boiler for proper operation

Sterilizer

Re-hardening filter pressure

M/e units

Vibration level at platform : for loose brackets

High pressure pipe for any leakages.

M/E turbocharger blower pressure drop oil Flow signs of leaks vibration

M/E top bracing

High Pressure Pumps auto backwash filter unit

Generator Room Checks

Sump level of both generators

A/e ' s for any sign of leakages

Purifier room exhaust fan for any abnormal noise or vibration

Priming pumps

No. 3 a/e sump level.

For any signs of leakage.

Emergency Maneuvering Platform

And feel m/e under piston doors

Hps unit for leakages

Local pressure gauges and rpm indicator

Hps auto backwash filter unit control panel

Hps pump motor amperage

Air cooler pressure drop and inlet outlet temperatures

Central Cooler Deck Level

central Fresh Water cooler

vacuum condenser

f.w hydrophore

m/e aux blower power panel

vacuum pumps and cooling water tank level

central cooling f.w pumps

water mist system always to be in auto

Purifier Room Checks

Drain water from hfo settling and service tanks

HFO settling and service tank temperatures

F.O heaters

Purifiers and purifier feed pumps

Fuel supply pumps and circulating pumps

Boiler F.O pump

F.O auto backwash Filter

Bottom Platform

L.O auto backwash filter

Bilge levels

S.W pumps and ballast water pumps for leakages

Turbocharger l.o pumps and l.o coolers

And m/e crankcase door

M/e l.o pumps and l.o coolers.

Thrust bearing temperatures

Scavenge drain tank level

Shaft earthing device

MGPS unit

Dosing pumps

Stern tube pumps and fwd seal pumps and cooler

Air sealing system for stern tube.

Stern thruster unit for any leakages

Hydraulic power pack for remote control valves-oil Level

Steering Gear Room

Steering system for any leakages tank levels

Greasing pump and grease level in tank

Vibration compensator for any abnormality.

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Marine Engineering Practice Series which deals in questions related to the troubleshooting of the ship machinery etc.

Marine Engineering Practice Series whichdeals in questions related to the troubleshootingof the ship machinery etc.

How will you come to know that EGB is leaking?



Abnormal decrease in Cascade tank water level

White smoke from funnel

Less production of Steam

Exhaust Gas temperature going low.

Rise in the level of soot collecting tank

How to check leakage in lube oil cooler shell and tubetype?

Tube leakage can result from corrosion. This can be checked for, or identified,

by having the shell side of the cooler circulated while the cooling water is shut

off and the end covers removed. Any seepage into the tubes will indicate the

leak. It is also possible to introduce fluorescent dyes into the shell side liquid:

any seepage will show under an ultraviolet light as a bright green glow.

Leaking tubes can be temporarily plugged at each end or removed and

replaced with a new tube.

Main Engine Crankcase inspection and what all checksto be done?

1) After the engine shutdown. Open doors after half hour

2) Start from the bottom. Check for any sign color change of lube oil. Search

for any metal particles etc.

3) Look towards the main bearing and see if any metal paste or particles are

coming.

4) Bottom bearing clearance can be checked here.

5) Then we can take clearance crank bearing.

6) Check for any loose bolts.

7) Check on crank pin for any signs of crack.

8) Check the condition of crosshead guides and their clearances.

9) Piston Rod needs to be checked for any signs of scoring or deep scratches.

10) Run the lubrication pump to see the flow of oil.

Pre bunkering and During Bunkering SafetiesPre bunkering:

1) High level Alarm of all fuel tanks has been checked.

2) Pre Bunker meeting has been carried out.

3) The required amount of SOPEP kit is placed near the bunker manifold.

4) All the deck scuppers have already been checked and plugged.

5) Flag on the Ships is hoisted.

6) Emergency phone numbers are displayed at desired location.

7) Bunker hose is in good condition and properly tightened.

During Bunkering

1) Mooring ropes and distance bunker barge from ship is well maintained.

2) Check on both sides, that no oil is visible on water.

3) Time to time sounding of tanks, manually.

4) At the end of bunkering, blow air from the bunkering hose to clean it.

What Inspections to be carried out in a Dry Dock of aShip?

1) Propeller inspections like cavitations and drop

2) Rudder, hull

3) All the sea outlet valves

4) Condition of Sea chest

5) All the Cathodes condition

6) Condition of Thrusters if any

What is the composition of inert gas in terms of

Percentage?

2-4%of Oxygen

.2-.4% of Sulphur dioxide

12-14%Carbon dioxide

80% Nitrogen

Function of Inducer, impeller, diffuser and volute

casing in Turbocharger

Function of inducer is to have sockless air flow at the entry of turbocharger.

Inducer is to convert the pressure energy into kinetic energy. Volute Casing as

name suggest, the air will come, and will get rotary motion through the

impeller of the blow and will be forced forward towards the diffuser. Diffuser

helps in converting the K.E at the inlet to P.E at inlet.

Reasons for oil coming out from water side in purifierand remedy?

1) Gravity disc problem

2) Sludge bowl not closing problem

3) Incorrect Rpm

4) Too much feed flow to the purifier.

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