Oral engine questions Flashcards
How does an oil mist/oil mist explosion occur?
Oil mist may form when high pressure fuel oil, lubricating oil, hydraulic oil, or other oil is sprayed through a narrow crack, or when leaked oil connects with a high temperature surface, vaporizes, and comes in contact with low air temperature.
Action on oil mist detector alarm.
Specific actions will depend on the engine, the vessel and the Company’s
emergency procedures. General principles include:
Raise the ALARM
The alarm will automatically reduce engine load or shut down engine;
If the alarm cannot be verified as false, the engine must be shut down as soon
as possible;
Machinery spaces to be evacuated and preparations for fire/explosion made
(crew to Muster);
Situation to be monitored to note if further alarms occur of if an explosion
occurs;
After a set time period (such as 20 minutes), a small party of engineers to re-enter the machinery space;
Engine and bilges to be checked for evidence of explosion door(s) lifting;
A quick general external inspection of engine to be made, using a heat gun to
check for excessive temperatures;
One team to finish isolating the engine – starting air off, turning gear in,
indicator cocks open, isolate lube oil pumps;
OMD to be checked to see if alarm is still active;
Note the crank chamber which raised the alarm;
Carefully open the crankcase door furthest from the noted crank chamber –
loosen dogs and pop the door using a long block of wood or pole, do not stand
in front of door;
Look for evidence of hot spot/issue
o use heat gun, (do not enter the crank chamber as it is a confined space);
o run/overheated bearings;
o debris in sump;
o scored/overheated piston rod;
o dry/scuffed bottom of cylinder (blow by);
o compression test for piston ring failure;
o inspect camshaft drive arrangements;
o check pressure and temperature and alarm records of monitoring system;
OMD to be cleaned, serviced and tested;
If no evidence of issues; conduct engine trials:
o Start engine, but have on idle/low load and run for a brief time (5 minutes);
o Monitor OMD;
o Shut down engine and reinspect;
o If no issues, slowly run up engine to acceptable load – run engine for
longer periods of time, and gradual increases of load, shutting down and
inspecting engine at intervals
How do you inspect the engine after an OMD shut down, and what are you looking for?
After a set time period (such as 20 minutes), a small party of engineers to reenter the machinery space;
Engine and bilges to be checked for evidence of explosion door(s) lifting;
A quick general external inspection of engine to be made, using a heat gun to
check for excessive temperatures;
One team to finish isolating the engine – starting air off, turning gear in,
indicator cocks open, isolate lube oil pumps;
OMD to be checked to see if alarm is still active;
Note the crank chamber which raised the alarm;
Carefully open the crankcase door furthest from the noted crank chamber –
loosen dogs and pop the door using a long block of wood or pole, do not stand
in front of door;
Look for evidence of hot spot/issue
o use heat gun, (do not enter the crank chamber as it is a confined space);
o run/overheated bearings;
o debris in sump;
o scored/overheated piston rod;
o dry/scuffed bottom of cylinder (blow by);
o compression test for piston ring failure;
o inspect camshaft drive arrangements;
o check pressure and temperature and alarm records of monitoring system;
OMD to be cleaned, serviced and tested;
You find a bottom end bearing cap is blue, the bearing wiped and the crankpin scored. How do you repair?
. Consult with the Master
. Check lube oil flow to find the original fault
. Replace the crankpin bearing
. Repair and clean the crankpin scores with sand paper
. Test the bearing clearance
. Reassemble and test by gradual
. Start engine, but have on idle/low load and run for a
brief time (5 minutes);
. Monitor OMD
. Shut down engine and reinspect;
. If no issues, slowly run up engine to acceptable load –
run engine for longer periods of time, and gradual
increases of load, shutting down and
inspecting engine at intervals.
. Depending on the repair, you may need to inform the
master that the engine is cleared for full load or it may
need to be run on part load until further repairs are
carried out.
What monitoring do you have on your engine?
Examiner wanted more that the NSCV minimum standard.
NSCV Essential monitoring
All engines essential for the safe operation of the vessel shall be fitted with
instrumentation to enable critical engine parameters to be monitored from a
continuously manned control station. On vessels with an unmanned
machinery space, the instrumentation shall be located adjacent to the
steering position. Subject to the requirements of the engine manufacturer,
the following instrumentation should be provided:
a) Engine lubricating oil pressure.
b) Engine jacket cooling water outlet temperature.
c) Engine gearbox lubricating oil pressure.
d) Charging rate of generator or state of battery charge.
e) Rotational speed (in the case of propulsion machinery).
NOTE: In addition to the above instrumentation, Clause 6.7.7 requires a rudder
position indicator for certain vessels.
How do you test lube oil pressure alarms?
State the process for testing the low lubricating oil pressure alarm/shut down on a diesel engine.
1. Locate and read and understand the procedure
2. Complete a risk assessment and include the
Master and a time that suits the vessel operation.
3. Obtain the correct tooling
4. Follow the below diagram
5. Isolate the engine LOTO, and test the isolation
6. Make sure valve 2 is closed and tamper proof tag
is in place and remove the blanking plug 3
7. Check calibration certificate of valve 4
8. De isolate the engine and start up
9. Check engine oil pressure at gauge 4
10. Once the engine has oil pressure and at operation
temperature
11. Remove tamper proof tag (TPT) from valve 1 and
close valve 1
12. Remove TPT from valve 2 and slowly open valve 2
while recording the pressure on gauge 4
13. Record the pressure at gage 4 when the low oil
pressure alarm activates
14. Continue to release oil pressure at valve 4 until
the engine shuts down and record the pressure
at gauge 4
15. It the switch at 5 works correctly then review the
risk assessment and isolate the engine and test
the isolation
16. close valve 2 and replace the TPT, refit the plug at
3.
17. Open valve 1 and refit the TPT
18. De isolate and recommission the engine
19. Record the findings on the work order and engine
room log
20. Review the procedure.
Give a basic description of a governor and how it works.
a) The fuel rack is controlled by the speed control, setpoint, as the speed measuring unit weights through out with centrifugal force against the speeder spring this lifts the pilot valve up and draining some oil away from the servo piston and the spring will move the fuel rack to decrease the RPM. If the weights move in due to the engine slowing down the pilot valve will allow oil to flow into the servo piston raising the fuel rack to increase the RPM.
How to test the engine overspeed
On the 3512 caterpillar mechanical Woodwood governor, hold the fuel rack after the governor, over by hand, increasing the RPM to the 1900 RPM overspeed setpoint.
document and record the findings in the PMS.
What is the purpose of under piston splash lubrication?
To cool the piston and provide liner/piston lubrication. This could also provide lub oil to the gudgeon pin bearing.
How does oil circulate in and around your engine?
. Sump . Pump . Relief valve . Oil cooler . Filters . Check valve . Crankshaft and Connecting rod bearings . Aux drives . Camshaft . Piston cooling . Top end lube, ie rockers and push rods . Turbo bearings . Back to the sump
What is scavenge fire ?
Carbonized lube oil, unburnt fuel oil and carbon from the residual products of the combustion spaces are accumulated in the scavenge spaces with the running of the engine. Under certain faulty running condition of the engine, these may ignite causing a fire in the enclosed scavenge space, known as scavenge fire.
Causes of Scavenge Fire
. Blow past of combustion products caused by leaky,
sticky or broken piston rings, worn out liner, faulty
cylinder lubrication, or insufficient axial clearance of
the piston rings.
. Overheated piston dissipates heat to the under piston
area caused by faulty atomization and injection
pressure, faulty fuel pump timing, loss of compression,
engine overload, failure of coolant circulation or
insufficient cooling due to formation of scale.
. Blow back of exhaust gases caused by exhaust back
pressure or deposits on exhaust ports, fouling of grid
before turbine inlet, fouling of turbine blades, choking
of EGB or economiser gas outlet.
. Presence of fuel oil in the scavenge spaces due to
defective fuel injectors, incorrect pressure setting of
injectors or fuel particles landing on the cylinder liner
due to excessive penetration.
. Excessive cylinder lubrication which is drained down
to scavenge spaces.
. Oxygen is plenty during engine operation.
. Fouled scavenge manifold.
Indication of Scavenge Fire
. Engine revolution drops as the power generation in
the affected cylinder is reduced.
. Unstable operation of Turbo charger and may cause
surging.
. Exhaust temperature of the affected cylinder
increases, as the cylinder is not receiving fresh air.
. Black smoke with exhaust due to incomplete
combustion in that unit.
. Discharging of spark, flame or smokes through drain
cocks from scavenge air boxes.
. Rise of pressure and temperature of air in the air box
below the piston.
. Visible evidence of fire if a transparent window is
fitted.
. Cooling water outlet temperature of the affected unit
is increased.
. Action to be Taken
. Inform bridge and reduce the speed.
. Cut of fuel supply to the affected unit and shut off
valves.
. Cylinder lubrication is increased.
. Coolant flow through jacket and piston is maintained.
. Drains to be shut to prevent flow of spark in engine
room.
. Keep clear of scavenge space relief valve to prevent
human injury.
. Fire should be extinguished after some time. If the fire
spread in the other scavenge spaces along with the
scavenge manifold, then –
Inform bridge and stop the engine
Stop fuel oil booster pump
Open indicator cocks, engage turning gear and turn engine to prevent engine seizure
Normal engine cooling and lubrication are maintained
Scavenge air duct flap valve before engine is to be shut
Release the smothering gases (Steam or CO2) to extinguish fire
Before opening scavenge door ventilate the space thoroughly if CO2 is released.
Inspection after Scavenge Fire
Intense fire can cause distortion and may upset piston alignment
Check by turning the engine and watch movement of piston in the liner, check for any occurrence of binding at part of stroke (Binding indicates misalignment of piston)
Check spring on scavenge space relief device, if the device was near the set of fire
Piston rod packing spring also should be checked, which may have become weakened by overheating
Check piston rings and liner for any distortion or reddish burning mark
Check diaphragm and frame near affected part
Check guides and guide shoes
Check tension of tie bolts
Prevention of Scavenge Fire
Clean scavenge space and drain at regular intervals
Keep scavenge space drain open at regular intervals
Excess cylinder lubrication must be avoided
In case of timed lubrication, the time has to be checked as per PMS
Piston rings must be properly maintained and lubricated adequately
Piston rod stuffing box must be maintained to prevent oil ingress in the scavenge space.
Prolong engine or any cylinder over loading to be avoided
Cylinder liner wear must be within admissible limits
Scavenge Space Protection Devices
Electrical temperature sensing device fitted within the trunking, which will automatically sound an alarm in the event of excessive rise in local temperature.
Pressure relief valves consisting of self closing spring loaded valves are fitted and should be examined and tested periodically.
Fixed fire extinguishing system may be CO2, Dry Powder or Steam.
Starting Air Line Explosion
- This is mainly due to the accumulation of oil due to carry-over of oil from the starting air compressors. A defective start air valve on the cylinder head provides heat if it leaks back into the start air line
- Causes of starting air line explosion on ships
. The main cause of starting airline explosion is the
leaking starting air valve or jamming at open position
of the valve.
. Initially, the oil which is discharged from the air
compressor to starting air line system, it will deposit as
a thin moist film on the internal surface of the pipes
but not ready to combustion.
. If starting air valve leaked or jammed at open position,
hot gas or flame may enter the starting air manifold,
vaporize the oil and set the fire to oil mist and greasy
matters, which generally deposit on the surface.
. At that condition, mostly arrival first start for
manoeuvring time, high pressure compressed air
coming into contact with the fire and may cause
explosion. - Prevent starting the air line explosion
. Ensure that all safety devices fitted are working
correctly
. Draining of the air bottle is carried out every watch
. Auto drain to be checked for proper functioning
. Air compressor is well maintained to avoid oil carry
over
. The oil separator at discharge of the compressor is
working efficiently
. The starting air manifold pipe to be cleaned and
check for paint deformation which will indicate
overheating of the pipe
. Starting air valve to be overhauled regularly to avoid
leakage
. Starting air valve seat to be inspected and lapped - Safety devices on starting air line
. Spring loaded safety valve or bursting disc. (if bursting
disc fitted, no need of relief valve)
. Flame trap. (At Joint where manifold to each cylinder
starting line)
. Starting air line drain valve. (Inlet of automatic air
starting valve)
. Turning gear interlock
. Reversing interlock
What is exhaust gas economiser (EGE) fire and how it occur ?
- A flame appear at the economizer coil during running of main engine at sea while the EGE is put into service with circulation water passing through the coils, it is called economizer fire.
. It is actually cause by soot fire at the economizer coils.
For the economizer coils fire, heat is already
presented due to passing the gases of main engine.
. Air is available due to excess supply of scavenging air
into the unit combustion chamber.
. Thick deposit of unburnt fuel, carbon residue (soots)
are sticking at the economizer coils .
. Soots are formed from incomplete combustion and
use of low grade fuel and high carbon content fuel.
. At the manoeuvring time, the more incomplete
combustion may occur and at that time leaving flue
gas velocity is very low, thus unburnt fuel can be
adhering on the economizer coils.
. A flame is produced when air and fuel are
proportionally mixed in the sufficient heating
temperature. - What are the indications of EGE fire ?
. Smoke smell will get from the economizer.
. Over heat at economizer body ( external casing of
uptake.)
. Heavy smoke and sparks will emit from the funnel.
. Sudden unexpected increase in uptake gas
temperature ( Abnormally high stack pyrometer
reading)
. Flame visible in the smoke indicator. - How to prevent EGE fire on ships ?
. To get complete combustion of fuel, maintain the main
engine (ME) in optimum combustion condition.(
governor, fuel injection pump, fuel injection valve, fuel
injection timing, fuel condition, air cooler,
turbocharger, do not run too long ME with slow speed)
Regular open up & cleaning smoke side of economiser depending upon soot accumulation. (water washing)
. Regular soot blowing operation. Check & maintain
soot blowing equipment.
. Regular overhaul boiler burner, correct air fuel ratio &
damper. - What are the actions to be taken during economizer
fire ?
. Inform to the bridge and chief engineer. Take the
permission to stop main engine.
. Gradually slowdown the ME and then stop.
If fire fighting equipment is fitted, it should be brought
into operation.
. Cool down the economizer by means of boundary
cooling.
. Circulation pump must be run but, if large amount of
water lost it must be stopped.
. There is no heat source and fire is out.
. When economizer fire occurs never do soot blow to
economizer.
. It can cause hydrogen fire and melt down the coils
stack. It can cause deformation and tube bulking
because intensive heat and high thermal stress
formed at economizer coils. - What are the actions to be taken after economizer fire ?
. Cool down to ambient temperature.
. Open the economizer cover.
. Clean inside parts of the economizer.
. Check the any defective coil and repair for temporary
used by welding or plugging the tubes. - How to effectively fight the economiser fire ?
. Slow down the engine.
. Shut off oil burners, draught fans, dampers & air
register.
. Raise water level full and blow down continuously so
as to maintain good flow of water.
. Reduce boiler pressure by easing gear.
. Spray water on the external casing of the uptake to
cool the affected area.
. A few times starting and stopping of main engine
should be done to blow out collected soots at the
uptake. - What is self perpetuating fire or hydrogen fire on
ships ?
. When the fire causes the metal itself burning at about
700 °C, if steam smothering soot blowing system or
water jetting system have been attempted, the big
hydrogen fire may result.
. The applied steam dissociates into hydrogen and
oxygen and accelerating the fire.
. Once such a fire has started, resulting two kind of fires
may take place simultaneously, one kind, iron burning
in steam, and the other, the hydrogen burning in an air
exothermic way.
. This combined fire being self supporting and lasting
until the supply of steam is exhausted.
. The primary objective of dealing the fire is to cool the
surface and burning material as quickly as possible.
