Pancyprian TS Marine Mech. II flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Mean indicated pressure

Average pressure acting on the piston during the working cycle; calculated from the indicator diagram area divided by stroke length. Used to compute indicated power: pmi x L x A x n x i.

Scavenging

Process of clearing burnt gases from the cylinder and filling it with fresh air in two-stroke engines. Uniflow, loop and cross scavenging differ in flow path and efficiency.

Compression ratio

Ratio of cylinder volume before compression to volume after compression. In slow-speed diesels typically 12-20:1; it must raise air temperature above fuel auto-ignition temperature.

Specific fuel consumption

Fuel mass flow divided by brake power, expressed in g/kWh. It measures engine efficiency; modern large two-stroke diesels achieve about 160-175 g/kWh.

Indicator diagram

Pressure-volume or pressure-crank angle diagram taken from a cylinder. It shows compression pressure, maximum firing pressure, injection timing and exhaust valve timing, allowing diagnosis of combustion faults.

Jerk-type fuel pump

Cam-driven plunger pump whose helix controls the spill point, setting injected quantity. The delivery valve with unloading volume prevents secondary injection and dribble at the injector.

Cylinder oil BN selection

Base number of cylinder oil must match fuel sulphur: about BN 40 for low-sulphur fuel below 0.5% and BN 70 for high-sulphur residual fuel, to neutralise sulphuric acid.

Starting air requirement

SOLAS requires compressed air capacity for at least 12 consecutive starts of a reversible engine, or 6 starts of a non-reversible engine, without replenishing the air receivers.

Reversing two-stroke engine

Direction change achieved by shifting the camshaft or reversing the fuel and exhaust cam arrangement, so injection and exhaust timing suit the new rotation direction.

Oil mist detector

Device monitoring crankcase atmosphere for oil mist, an early warning of overheated bearings or hot spots that could cause a crankcase explosion. It triggers an alarm and slows the engine.

NPSH

Net positive suction head: available NPSH must exceed required NPSH to avoid cavitation in a centrifugal pump. Cavitation causes noise, vibration, reduced head and impeller erosion.

Affinity laws

For a centrifugal pump, flow varies with speed, head with speed squared and power with speed cubed. Used to predict performance when speed or impeller diameter changes.

Purifier gravity disc

Ring dam in a centrifugal separator that sets the position of the oil-water interface. Correct selection depends on fuel density and temperature; wrong size causes water in oil or oil loss.

Steering gear SOLAS test

Main and auxiliary steering gear must move the rudder from 35 degrees one side to 35 degrees the other in not more than 28 seconds at maximum service speed.

LMTD

Log mean temperature difference between hot and cold streams in a heat exchanger. Heat transfer Q equals overall coefficient U times area A times LMTD; counterflow gives the highest value.

Emergency switchboard

Board fed from the emergency generator or battery, supplying essential services such as emergency lighting, steering gear, fire pump and radio. Automatic changeover within 45 seconds per SOLAS.

Insulation resistance test

Measurement with a megohmmeter at 500 V DC to verify insulation integrity of circuits and motors. Low readings indicate moisture, damage or contamination and require investigation before energising.

Reverse power protection

Generator protection that trips the breaker if the machine motoring occurs, for example after loss of prime mover. It prevents damage and protects the switchboard from abnormal current.

UMS operation

Unattended machinery space operation permitted by class rules when alarms, safety trips and fire detection are extended to the bridge and duty engineer's cabin, with periodic rounds.

Crankshaft deflection

Measurement of crankshaft web deflection at defined positions with the engine cold. Readings reveal bedplate distortion and bearing wear when compared with maker's limits and previous readings.

Vibration analysis

Condition monitoring technique identifying bearing defects, misalignment and unbalance from frequency spectra. Trend changes trigger inspection before failure, supporting planned maintenance.

Torque and stretch

Critical bolts such as connecting rod and cylinder cover bolts are tightened to a specified torque or by measuring stretch with a hydraulic tensioner, following the maker's procedure.

Non-destructive testing

Inspection methods including dye penetrant, magnetic particle, ultrasonic and radiography used to detect cracks in crankshafts, pistons, rods and welds without damaging the component.

Permit-to-work

Formal authorisation required before hot work, enclosed space entry, working aloft or electrical isolation. It records hazards, precautions, isolation and authorisation signatures.

Free surface effect

Reduction of metacentric height caused by liquid free to move in a partly filled tank. It is reduced by longitudinal subdivision and controlled by avoiding slack tanks.

Collision bulkhead

Watertight bulkhead forward of the engine room and cargo spaces, required by SOLAS, to limit flooding after a collision and preserve stability and buoyancy.

Damage control plan

Plan showing watertight compartment boundaries, closures, pumps and valves, posted on board and used to isolate flooding. Drills and records of damage control exercises are required.

Oily water separator

Equipment separating oil from bilge water, with a 15 ppm bilge alarm and automatic stopping device. Discharge is permitted only through this equipment outside special areas.

MARPOL Annex VI sulphur limits

Fuel sulphur limit is 0.50% m/m globally and 0.10% m/m in emission control areas. Changeover must be recorded; bunker delivery notes are retained three years.

Confined space entry

Entry into a space with restricted access and possible hazardous atmosphere requires permit, isolation, ventilation and testing for oxygen, flammable gas, hydrogen sulphide and carbon monoxide before entry.

STCW rest hours

Minimum rest is 10 hours in any 24-hour period and 77 hours in any 7-day period. It may be reduced to 6 hours in 24 hours if compensated; records must be kept.

Oil Record Book Part I

Record of machinery space operations including bilge water transfers, oily water separator use, sludge disposal and bunkering. Entries must be signed by the officer in charge and the master.