Pancyprian TS Marine Mech. II key terms

The ratio of the cylinder volume at bottom dead centre to the volume at top dead centre. It sets the compression pressure and temperature that ignite the fuel in a diesel engine.

The process of clearing burnt exhaust gas from the cylinder and filling it with fresh air, using ports, valves or a uniflow arrangement. Effective scavenging is essential for good combustion and power output.

The average pressure that, acting on the piston through one complete cycle, would produce the measured shaft power. It is a standard way to compare the load and performance of engines of different sizes.

The power developed inside the cylinders, calculated from indicator diagrams or cylinder pressure readings. Comparing it with brake power gives the mechanical efficiency of the engine.

A pressure-versus-volume or pressure-versus-crank-angle plot of one cylinder cycle. It reveals combustion quality, peak pressure, timing faults and compression condition without dismantling the engine.

The crank angle at which injection begins relative to top dead centre. Too early raises peak pressure and knock; too late causes afterburning, smoky exhaust and higher exhaust temperature.

A nozzle and needle assembly that atomises fuel into the combustion chamber at high pressure. It must open at the set pressure, spray correctly and close without dribble or leakage.

The position reading of the fuel rack or pump control, indicating the quantity of fuel delivered per stroke. Comparing indices between cylinders helps detect imbalance or a faulty pump.

The temperature of gas leaving each cylinder or the main exhaust trunk. Uneven readings indicate poor combustion, injection faults, scavenge problems or a fouled turbocharger.

An exhaust-driven turbine driving a compressor that supplies air above atmospheric pressure to the engine. It uses otherwise wasted exhaust energy to increase power and efficiency.

A rotodynamic pump where an impeller throws liquid outwards, converting velocity into pressure. It suits large flows at modest heads and must be primed or self-priming before starting.

A pump that traps a fixed volume of liquid and forces it into the discharge each cycle, such as a gear, screw or reciprocating pump. It gives steady flow at high pressure and is self-priming.

Formation and collapse of vapour bubbles in a pump when local pressure falls below vapour pressure. It causes noise, vibration, reduced flow and progressive erosion of the impeller or casing.

The absolute pressure margin above the liquid's vapour pressure at the pump suction. Insufficient margin is the usual cause of cavitation and must be checked when pumps operate with hot liquids.

A safety device that opens automatically to release pressure when it exceeds a set limit. On positive displacement pumps and closed circuits it protects piping and equipment from overpressure.

A compact unit of corrugated plates forming channels where two fluids exchange heat without mixing. It offers high efficiency and can be opened for cleaning or plate replacement.

Accumulation of scale, sediment, biological growth or oil deposits on heat transfer surfaces. It reduces heat transfer and flow, raising temperatures and pressures, and is controlled by cleaning and water treatment.

A centrifugal machine that removes water and solid impurities from fuel by density difference at high rotational speed. Correct temperature and throughput are essential for efficient purification.

The flow rate at which a separator is operated. Running above the rated capacity shortens residence time and lets water and solids pass through with the cleaned fuel.

Continued oscillation of the rudder about the ordered position after a course change, caused by excessive gain or worn components. It wastes power and indicates a control system fault.

A steering mode where the rudder moves in proportion to the movement of the helm and stops when the commanded angle is reached. Non-follow-up mode instead runs the pump until the helm returns to centre.

A safety arrangement that prevents the engine from starting while the turning gear is engaged or the reversing gear is not correctly set. It protects personnel and machinery from serious damage.

A motor-driven device that slowly rotates the crankshaft for inspection, barring and maintenance. It must be disengaged before starting air is admitted to the engine.

The mechanism that changes the direction of rotation of a direct-reversing diesel engine by shifting camshaft or distributor positions. It must be fully in position before starting air is applied.

A device that samples crankcase atmosphere and alarms when oil mist concentration rises. It warns of a hot spot or incipient crankcase explosion, allowing the engine to be stopped in time.

Ignition of oil mist inside the crankcase, usually after a local hot spot vaporises oil. It can rupture doors and cause injury, so mist detection, relief valves and correct maintenance are vital.

A fire in the scavenge air space caused by oil accumulation ignited by hot blow-by or sparks. It is detected by high scavenge temperature and controlled by stopping fuel and applying smothering medium.

The empty space above the liquid surface in a tank, expressed as a measurement or percentage. It allows for thermal expansion and is used with sounding tables to calculate tank contents.

Loss of effective stability caused by liquid moving freely across a partly filled tank as the ship rolls. It raises the centre of gravity and can be reduced by pressing up or emptying tanks.

Measurement of liquid depth in a tank using a tape, float or gauge, converted to volume by calibration tables. It is used for fuel, ballast and water inventory and for detecting leaks.

Division of the hull into compartments by watertight bulkheads and closures. It limits flooding after damage and preserves buoyancy and stability, so doors and penetrations must be kept tight.

Organised actions to contain flooding, fire or structural damage, including closing watertight openings, isolating systems and reporting to the bridge. Drills prepare the crew to act quickly and correctly.

A mandatory record of oil transfers, machinery space bilge operations, sludge disposal and bunkering. Entries must be truthful, signed by the responsible officer and retained for inspection.

Equipment that reduces the oil content of bilge water before discharge overboard. It must be operated within the permitted outlet limit and any alarm or automatic stopping device must be working.

The part of the pollution convention covering prevention of pollution by oil, including discharge limits, equipment requirements and record keeping for machinery spaces and cargo areas.

A formal authorisation listing atmosphere tests, ventilation, isolation, standby personnel and rescue arrangements before entry into a tank or void. It ensures hazards are assessed and controlled.

The structured briefing between outgoing and incoming watchkeepers covering machinery status, running parameters, defects, ongoing work and standing orders. It ensures continuity and prevents missed hazards.

A class notation allowing periodic unmanned operation of the engine room, relying on automated monitoring, alarms and safety shutdowns. It demands tested alarms, fire detection and documented routines.

A timer-based alarm in the engine room that requires periodic resetting by the watchkeeper. If not reset within the set interval, it alarms on the bridge and elsewhere.

A structured schedule of inspections, servicing and overhauls based on running hours or calendar intervals, with records and defect tracking. It supports reliability, class compliance and defect follow-up.

Measuring parameters such as vibration, temperature, oil analysis and performance trends to detect developing faults. It allows maintenance to be planned before failure rather than at fixed intervals.

Measurement of the change in distance between crank webs as the shaft rotates, indicating bearing wear or hull deformation. Excessive deflection requires bearing adjustment and investigation.