Main Engines Flashcards
What gauges and alarms are on your main engine?
Onboard we have temperature gauges that read oil, coolant, charge air, thrust bearing, cylinder exhausts and gearbox.
We then have pressure gauges for oil, coolant, fuel, raw water, crankcase and stern tube flow.
All these are fitted with high and low alarms that will alarm and slow then main engines down. Then there are high high and low low alarms which will then shut an engine down to protect from further damage .
What alarms will shut down the main engine?
- Low Low oil pressure
- Low fuel Pressure
- High High Coolant temperature
- Low low coolant pressure
- Overspeed
- High High exhaust gas temp
- High high thrust block temperature
What monitoring devices and safety devices?
- Temperature sensors
- Pressure sensors
- Level sensors
- Overspeed sensor
- Fuel leakage
- Oil Mist
- Interlocks
- Position sensors
- Slow downs
- Shut downs
- Quick closing valves
How does a speed sensor work and how do you know how fast your engine is going?
Magnetic Induction Sensors: These sensors use a magnetic pickup coil to detect changes in magnetic field strength caused by passing ferrous targets, such as teeth on a gear or a toothed wheel attached to the rotating component. As the target passes by the sensor, it induces a voltage signal in the coil, which is then processed to determine the speed of rotation.
To know how fast your engine is going, you rely on a tachometer, which is an instrument that displays the engine speed in revolutions per minute (RPM). The tachometer receives the speed signal from the speed sensor and converts it into a readable display.
What could create a high exhaust temp reading?
- Incomplete combustion from a poor air to fuel ratio, possibly a leaking injector.
- Restricted exhaust from a build up of soot in the DPFs
- Overloading from bad weather, damaged propellor or a line around the propeller.
- Cooling issues from a leak, blockage, or trapped air pockets.
- Airflow restrictions from blocked filters or not enough air flowing into the engine room.
- Poor fuel quality due to water not being removed.
How would you remove a cylinder head on the main engine?
- Check manufactures manual for a step by step procedure
- Organise Classification to come onboard for an inspection if possible
- Shutdown main engine
- Inform the bridge of the situation and request to stop all engines
- Inspect the issue
- Fault find it is an internal failure
- Lock the shaft using the shaft break
- Call all engineers for assistance
- Have a toolbox talk to create a plan
- Get classification spares and tools
- Request a permit and risk assessment
- Inform bridge
- Isolate battery switch and tag out
- Engage safety interlocks
- Isolate fuel, water and exhaust valves
- Take oil and coolant samples
- Drain coolant
- Remove fuel lines
- Remove wiring
- Remove air filter
- Remove inlet and exhaust manifold
- Remove rocker cover
- Remove tie down bolts
- Remove injectors
- Inspect cylinder head, exhaust ports and valve seating
- Inspect rockers and push rods
- Reinstall all of the above
- Check over work
- Open water and exhaust valves
- Remove interlocks
- Open indicator cocks and engage turning gear
- Turn on batteries and turn the engine 2 turns. Making sure everything id free to turn.
- Bleed off fuel until fuel is at each injector.
- Call bridge and inform you are ready to test
- Remove shaft break.
- Once started close the indicator cocks and stop after a minute
- Check oil and coolant levels, as well for any leaks
- If all is good sign off and record in the PMS and E.R Logbook
- Close permit.
Draw an air start system and describe its components?
See onenote
How does a cylinder start valve work?
It works by compressed air making its way to the automatic valve. Here it will wait while until the start signal is activated and the turning gear interlock is de-energised.
Air can now travel to the manifold via the non return valve and into the air start valve. At the same time air is sent to the distributor to which ever piston is on the firing stroke.
This is know as the pilot air and will act against a piston to compress a spring which also opens the valve head into the cylinder and allowing the main start air to enter.
Once the engine has achieved a certain speed the pilot air will shut off and stop combustion being able to travel back into the air system.
What are the dangers of air start systems?
- It is high pressure, normally around 30 Bar
- Overpressurizing the cylinder can cause damage to the engine.
- If there is oil carry over there is a risk of explosion or a fire.
- High pressure air can generate a lot of heat also causing a fire.
How would you assess the power of your main engine?
The method I have seen the most on yachts is bringing the manufacture onboard for a sea trial and they will plug a laptop in. We will communicate with the bridge going through different power ranges and they will collect all the data which can then be converted live into a readable outcome.
Bigger 2 stroke engines have the option of using a PV Diagram which by using an indicator drum and a plotting card can produce a graph showing compression pressure, peak pressure and engine power known as a draw card.
or a power card shows power output verse RPM, fuel consumption or torque.
What type of maintenance do we do?
Onboard we aim for all maintenance to be planned maintenance which can be broken down into Calendar based, Running Hour based or condition based.
We always try to avoid unplanned maintenance.
What are the normal clearances for intake and exhaust valves?
Intake is around 0.25mm and exhaust is around 0.30mm but varies from engines.
Why are Intake and Exhaust valve clearances different?
It is to allow clearance when the exhaust valve expands from heat due to the combustion process.
How would you set injector height clearances?
By using an Injector Height tool. They come in 3 sizes
What types of common main engine faults are there?
- Fuel contamination from water, diesel bug or foreign objects blocking filters and reducing fuel pressure.
- Worn fuel injectors causing poor combustion and overheating
- Lub oil contamination from fuel, water and foreign objects causing sludge or a reduce in lubrication leading to engine wear
- Fowling in the sea chests and coolers from marine growth, causing a drop in raw water pressure and cooling effect
- Dead batteries or weak batteries or a faulty charging system
- Loose connections over time from the vessel vibrating causing sensor failures or incorrect readings.
- Blocked DPFs from operating at low rpms causing a build up of soot and rising exhaust temperatures and pressures
Why is the Engine Room Log book so important?
- By keeping a record an engine room log can build a record of events, temperatures, pressures and levels.
- This can then be used for trends and for future voyage planning
- It is also evidence to classification, flag and port state that you are following regulations like performing test and drills. It can cover the engineer legally if an issue was to occur.
- It can be used to record breakdowns.
On older 4 stroke main engine, how would you determine compression on cylinders with engine running?
By taking the peak pressure of each cylinder, as the engine isn’t common rail so each injector needs to be individually adjusted and balanced as they wear differently.
How do you assess engine performance?
On 4 strokes it can be assessed by the common rail pressure, computer softwares, indicators on the fuel pump, peak pressures and performance logs.
2 strokes it can be assessed by draw cards and cam followers.
How often would you check Main Engine Safety devices?
Onboard we check them before every major crossing and once a year on our PMS.
What is overspeed trip and How would you test overspeed trip?
Overspeed trip will shut the engine down in the event of overspeed, protecting the engine in the event of failure of the governor or loss of load.
To test I would refer to the MTU Manual which would involve adjusting the set point to a much lower speed. Then turning the engine on and waiting for it to get to the new set point and shut the engine down.
Once the test is completed, return the overspeed trip to original set point.
What would you do in the event of bottom end failure on one of your engines whilst underway?
- Organise Classification to come onboard for an inspection if possible
- Check manufactures manual for a step by step procedure
- Shutdown main engine
- Inform the bridge of the situation and request to stop all engines
- Inspect the issue
- Fault find it is an internal failure
- Lock the shaft using the shaft break
- Call all engineers for assistance
- Have a toolbox talk to create a plan
- Get classification spares and tools
- Request a permit and risk assessment
- Inform bridge
- Isolate battery switch and tag out
- Engage safety interlocks
- Isolate fuel, water and exhaust valves
- Take oil and coolant samples
- Drain oil and coolant
- Remove oil and fuel filters
- Remove fuel lines
- Remove wiring
- Remove air filter
- Remove inlet and exhaust manifold
- Remove rocker cover
- Remove tie down bolts
- Remove injectors
- Inspect cylinder head, exhaust ports and valve seating
- Inspect rockers and push rods
- Remove sump pan
- Remove bottom end bolts
- Remove pistons and inspect the cylinder linear
- Take linear measurements using a microammeter. Taking top, middle and bottom readings.
- Inspect piston skirts and gulden pin
- Inspect oil control ring, scrapper ring and compression ring
- Inspect ring channels for a build up of carbon
- Measure butt clearances on the rings
- Inspect piston crown
- Inspect bottom end bearing
- Inspect cam shaft
- Replace the bottom end bearing and other damaged parts
- Refer to manual for correct torque of the tie down bolts
- Reinstall all of the above
- Check over work
- Refill with new oil and coolant
- Bleed off air in jacket water
- Open water and exhaust valves
- Remove interlocks
- Open indicator cocks and engage turning gear
- Turn on batteries and turn the engine 2 turns. Making sure everything id free to turn.
- Bleed off fuel until fuel is at each injector.
- Call bridge and inform you are ready to test
- Remove shaft break.
- Once started close the indicator cocks and stop after a minute
- Check oil and coolant levels, as well for any leaks
- If all is good sign off and record in the PMS and E.R Logbook
- Close permit.
Explain a thrust block failure scenario?
- Oil failure
- Bearing Failure
- Alignment increased wear
- Foreign objects scoring
- Water contamination
What is the difference between a 2 stroke and a 4 stroke?
The operating cycle of the 2 are different. With a 2 stroke it will have a power stroke per every rotation where as a 4 stroke has a power stroke per every 2 rotations.
2 strokes tend to have an inlet port rather than an inlet valve while 4 strokes will have inlet and exhaust valves.
2 strokes have a greater power to weight ratio but a 4 stroke is a lot more fuel efficient and produce lower emissions.
List some air start safety devices
- Bursting disk to stop combustion coming back into the system
- Turning gear interlock, stopping air being supplied while turning gear is engaged.
- Relief valve on the air receiver to counter overpressurizing
- Air receiver drain valve to remove any water in the system
- SOLAS require a minimum 6 starts per engine
