Power plants

still need to add fuel injection, DG components, misc, and tests

What are the main hazards of the ME?

Starting air line explosion, crankcase explosion, and scavenge fire

What are the components of a crankcase explosion?

Oil vapour, hotspot, and oxygen from stuffing box leak

What are the sources of hotspots in a crankcase?

Bearings with not enough clearance, hot gases blow-by, and a hot piston

What are the sources of oil vapour in a crankcase explosion?

LO vapour or LO contaminated by FO vapour

What are the mechanics of a crankcase explosion?

Hot spot, fuel vapour, vapour goes to cooler area and gets denser, air-vapour ratio gets explosive, hotspot ignites vapour then rapid pressure build

How can a crankcase explosion be prevented?

Avoiding hot spots with proper engine maintenance and operation or detecting vapours early with a detector

What are the warning and prevention devices for a crankcase explosion?

Oil mist detector, crankcase exhauster fan, and crankcase pressure relief door

What to do if there is risk of a crankcase explosion?

Inform Chief/bridge/duty engineer, reduce RPM, ensure crankcase area is clear, stop the engine if possible, and inpect the crankcase

What are the components of a scavenge fire?

Cylinder/Fuel/Crankcase oil, gas blow-by, and scavenge air

What can cause the components of a scavenge fire?

Crankcase oil (leaky stuffing box ring), gas blow-by (bad piston rings), and excessive scavenge air

What are signs of a scavenge fire?

Scavenge/Exhaust temps increase, turbo-charger surging, power/speed drops, and overheating signs on covers

What to do if there is a scavenge fire?

Reduce speed, change over to diesel, cut-out fuel to cylinder, increase cylinder LO, and shut scavenge space drains

What to do if scavenge fire does not go out?

Stop the engine, engage the turning gear, and flood scavenge space with CO2

How to prevent a scavenge fire?

Keep under-piston space clear, open scavenge drains regularly, maintain proper liner lubrication, piston rod stuff box, and cylinder conditions

What are the components of a starting air line explosion?

Compressor LO causing deposits in lines, leaking start air valve/quick air line opening, and compressed air

How to prevent a start air line explosion?

Drain air bottle regularly, open air line valves slowly, and maintain start air line/valves and compressor lubricator

What are the safety devices for a start air line explosion?

Relief valve, bursting disc, fusible plug, and flame trap

How can opening the start air line valves quick cause an explosion?

The rush of air can cause a spark in the lines

What is a sign of a high likelyhood of a start air line explosion?

A hot start air line

What is the funcion of a crankshaft?

To transform the reciprocating motion of the pistons into rotary motion

What is a crankshaft made of?

Crank throws, which consist of 2 webs, 1 pin, and 2 journals (draw)

What are the main forces on a crankshaft?

Static, compression, combustion, inertia, centrifugal, vibration, hull deflection, and prop reaction

What are sources of crankshaft stress?

Static + dynamic loads, and misalignment

What are static loads on a crankshaft?

Weight of the running gears, and hoop stress from shrink fitting

What are dynamic loads on the crankshaft?

Working cycle, torsional vibration, and axial vibration

What is the working cycle loads on a crankshaft?

Flucctuation forces from gas pressure, inertial forces of moving parts, and centrigual forces at the cranks

What are crankshaft stresses from?

Bending (tensile/compressive/shear stress) and twisting (torsional shear stress)

What are the types of crankshaft construction?

Single piece, fully built, semi-built, and welded

What are the advantages of a single piece/solid forged crankshaft?

Continous grain flow, higher fatigue strength (10-20%), no shrink fitting so no hoop stress/raisers, compact, and lighter

What are the disadvantages of a solid forged crankshaft?

Extremely rigid, less tolerance to misalignment, and difficult to repair

What is a fully built crankshaft?

A crankshaft where the webs, journals, and crankpins are all forged/cast seperately and webs are shrunk onto journals/crankpins

What is a semi-built crankshaft?

A crankshaft with the webs and crankpin forged/cast in one piece and shrunk onto the journals

What are the advantages of a semi-built crankshaft?

Continuous grain flow through webs/pins increases fatigue strength, webs are smaller and lighter than fully built, flexible with deflection, and can be rapaired

What are the disadvantages of a semi-built crankshaft?

Hoop stress from shrink fitting, no CGF in journal and web, overstressing risk if shrinkage allowance is low and slippage if high, and it is heavy

What is a welded crankshaft?

A crankshaft welded at the journals using submeged arc narrow gap welding

What are the advantages of a welded crankshaft?

Reduced engine dimensions and web thickness, longer journals with lower bearing loads, higher natural frequencies from higher stiffness, and lighter

What is the shrink fitting process?

The holes in the webs are smaller than the pins, so the webs are heated to 400 C or pins are cooled with N2 and the webs/pins are slotted together

What is used for gripping in shrink fitting?

A cermet coating on the journals to have efficient grip

What is the shrinkage allowance on crankshafts?

1/550 - 1/700 of the pin diameter

How can stress in a crankshaft be limited?

Semi-built or welded crankshafts, generous fillet radii, cold rolling fillets, correct firing sequence, and proper balancing

What are desirable properties for a crankshaft material?

High UTS, ductility, wear/corrosion resistance, and high fatigue strength

What does the flywheel do?

It stores enegery and supplies it the prop shaft (flywheel = aft end, damper = fore end)

What are the causes of crankshaft misalignment?

Distortion/Crack in bedplate cross girder, loose chocks, loose tie bolts, excessove/uneven tie bolt tightening, deformation of foudation, or main bearing wear

What is the order from crankshaft to prop shaft?

Crankshaft → (fly wheel → (4-stroke gearbox)) → thrust shaft → inter shaft → prop shaft

What are causes of slippage or twisting of the crankshaft?

Fluid filled cylinders when starting, running gear seizure, bearing failure, turning gear engaged, sudden engine stop, engine overloading, overspeeding, or prop fouling

What are the factors that affect deflection readings?

Crankshaft stiffness, position of dial gauge, bedplate condition, crankcase temp, trim of ship, ship loading condition, and pretension of tie bolts/holding down bolts/chocks

What are the main benefits of a turbocharger?

It increases the fuel efficiency of the engine by increasing the scavenge air volume and removes waste heat from the exhaust

How does a turbocharger work?

It is driven by exhaust gases of the engine and doesn’t work on start up so the combustion air is supplied by the aux blowers until its at RPM (10-15k)

What is the flow of inlet air for an engine?

Atm → Blower → Cooler → Scavenge → Exhaust manifold → SCR → Turbine → EGB → Stack

What and where are the types of bearing in a turbocharger?

Ball bearings are on the outside of the casing with seperate lubrication and plain bearings are on the inside on the ME lubrication

What does the impeller of a turbocharger do?

It moves air axially and releases it radially

What does the volute casing of a turbocharger do?

Converts air KE into pressure and directs air

What do nozzle rings do?

Generate KE in the exhaust gases and guide them to the rotor

What does the inducer in a turbocharger do?

Guides air to flow centrally to the impeller

What does the exhaust casing on a turbocharger do?

Guides the exhaust and has a cooling arrangment

What do the turbine blades in a turbocharger do?

Convert heat into KE or rotational energy

What do the filter and silencer in a turbocharger do?

Filter traps dirt at the air inlet and the silencer reduces the noise at higher RPM

How is the turbine side of a turbocharger cleaned?

At low RPM with water

How is the blower side of a turbocharger cleaned?

At high RPM with water or grit

What properties does turbocharger LO need?

Resistant to high temps, good visocity index, non-reactive to parts, good load carrying capacity, low pour point, high flash point, and corrosion resistant

What is a high viscosity index?

The ability to maintain viscosity at high temperatures

Why and where does turbocharger surging happen?

On the blower side and is cause by backflow due to high scavenge pressure resulting in rapid RPM drop

How can turbocharger surging be prevented?

Cleaning blower inlet filters, proper maintenace, soot blowing for boiler/EGB, and using indicator card to maintain performance

Why does turbocharger surging happen?

Improper power distribution between cylinders, sudden drop in ME speed, dirty impeller blades, bad weather, choked inlet filter, or fouling in the nozzle rings

What does shafting do?

It transmits power + thrust, supports the prop, and withstands running loads/vibrations

What are the parts of a shafting system?

Crankshaft, thrust shaft, inter shaft(s), tail shaft, couplings, flanges/muff couplings, and tapered shank fitted bolts

What are the parts of a shafting system supported by?

Crankshaft (main bearing), thrust shaft (journal bearing), inter shaft(s) (inter bearing), and tail shaft (stern tube bearing)

How are shafts connected?

By flanges with tapered shank fit bolts, morgrip bolts, or muff couplings

What are the characteristics of morgrip bolts?

They are hydraulic, easy to instal and remove, and cost effective

What is a benefit of a muff coupling?

The tail shaft can be removed without the prop

What is a thrust block?

A component that transfers fore+astern prop thrust into the hull, limits axial movement, and reduced dfferential expansion issues

What is the construction of a thrust block?

The casing is in two bolted halves, bolted to the hull, lubricated with pressurized LO from the ME, and is either an independent or intergral part

What are additional components that the thrust shaft has?

A thrust collar and integral flanges for bolting

What is the order for a thrust arrangment?

Shaft → collar → pad → block → tanktop → hull

What is the arrangment of the thrust pads?

They are fitted fore and aft of the thrust collar, and are white metal lined with a radial ridge for the pads to tilt on

How is shaft thrust absorbed?

The thrust on the collar is balanced by oil pressure under the pads and is transmitted to the hull via that housing

What are the types of shaft bearings?

Aftermost tunnel bearing and all others

What is the aftermost tunnel bearing?

The bearing that counteracts the prop mass and take vertical upward thrust at the fore end of the tail shaft

What makes the aftmost tunnel bearing different from other bearings?

The aftmost bearing has a top and bottom bearing shell while other only have bottom since they just support shaft weight

How are shaft bearings cooled and lubricated?

Cooling is by water circulation through a tube cooler and lubrication is from a bath with a throw ring both in the casing bottom

What do intermediate shafts do?

Connect the thrust shaft to the prop shaft (either one or multiple)

What types of bearings are the intermediate shafts supported by?

Plain or tilting pad bearings

What is a sleeve coupling?

Also called a muff coupling, they are alternatives to a flange coupling for the tail shaft and allow for the outboard removal tail shaft

What is the construction of a muff coupling?

Two steel sleeve, thin inner one is slightly larger than the shaft and the outer side is tapered to match to the outer sleeve

What is done to instal a muff coupling?

When in position the outer sleeve is hydraullically driven onto the inner sleeve and oil is simultaneously injected between them

What is a stern tube?

A metal tube welded to the hull that houses the prop shaft, and the most vulnerable area for flooding and pollution

What are the advantages of an oil lubricated stern tube?

Better lubrication, less wear, don’t need a liner, can handle a larger prop, good sealing, stable, and reliable

What are the disadvantages of an oil lubricated stern tube?

Need a fore + aft seal (common fail point), risk of oil pollution, biodegradable oil is expensive, LO condition needs to be monitored, higher cost, and risk of SW contamination

How are the stern tube seals attached to the shaft?

A housing with the seal rings is clamped onto the bush, keeping water out and letting the shaft rotate

What are the two seals for oil lubricated stern tubes?

External aft for oil/water and internal fore for oil

What types of seal does oil lubricated use?

Radial face, lip face, or a combo of both

What is a lip face seal?

A seal of rings with protruding edges held in contact with the shaft

What is a face seal?

Also called a mechanical seal

What makes Thordon bearings different?

They lubricate with water

What are common seal failure reasons?

Loss of garter spring tension, liner scoring, LO contamination, improper cooling, high differential pressure, and excessive vibration

What are the main purposes of a stern tube bearing?

Keep SW out of the machinery space and support the prop/tail shaft

Why are there two gravity tanks for stern tube lubrication?

Which is used depends on the draft of the ship, since lower means it needs to counter higher water pressure

What are the disadvantages of a fully-built crankshaft?

No CGF, slippage if shrink allowance is too high, over stressing if shrink allowance is too low, and hoop stress from shrink fitting

What are the advantages of a fully-built crankshaft?

Easy to repair parts, webs are smaller and lighter than solid forged, and flexible to conform to bearing deflections

What are the disadvantages of a welded crankshaft?

Stiffer than semi/fully-built, weak points from missed flaws, and expensive