Power plants

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?

Clean under-piston space clear and drained, 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?

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

What causes misalignment in a crankshaft?

Bearings not being on the same level from wear, lack of support, or hull deformation

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 witht he 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 is 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 → (flye wheel → (4-stroke gearbox)) → 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 is the main benefit of a turbocharger?

It increases the fuel efficiency of the engine by increasing the scavenge air volume

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