BTEB Diploma in Marine Engineering Examination flashcards

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

Brake mean effective pressure

The average pressure that would produce the measured brake power over the working stroke; calculated from brake power, engine geometry and speed, and used to compare engine loading.

Specific fuel consumption

Fuel mass burned per unit of brake energy produced, usually in g/kWh. Lower values indicate a more efficient engine and are compared at the same load and calorific value.

Scavenge air

Fresh air supplied by the blower or turbocharger to clear burnt gas from the cylinder and fill it for the next cycle. Its pressure must exceed exhaust pressure in uniflow two-strokes.

Crankshaft deflection

A measurement of the gap between crank webs at fixed positions, used to detect bedplate misalignment, bearing wear or hull deformation that could overstress the shaft.

NPSH available

The absolute pressure head at the pump suction above vapour pressure. If it falls below the pump's required NPSH, cavitation damages the impeller and reduces flow.

Pump affinity laws

For a centrifugal pump at constant impeller diameter, flow varies with speed, head with speed squared and power with speed cubed. These laws guide speed control and throttling decisions.

Fuel oil viscosity control

Fuel viscosity at the injector is held near 10–15 cSt by heaters. Too high causes poor atomisation and pump overload; too low causes leakage and poor combustion.

Fresh water generator

A vacuum evaporator using engine jacket water heat. Low pressure lets seawater boil near 40–60 °C, and the distillate is used as boiler feed and domestic water.

Block coefficient

The ratio of the underwater hull volume to the product of length, breadth and draught. It indicates hull fullness and affects resistance and required propulsion power.

Tonnes per centimetre

The mass in tonnes that must be loaded or discharged to change mean draught by one centimetre. It equals waterplane area times water density divided by 100.

Metacentric height

The distance between the centre of gravity and the transverse metacentre. A positive value gives stable equilibrium; too large a value causes rapid, uncomfortable rolling.

Collision bulkhead

The foremost watertight transverse bulkhead, located between 0.05L and 0.08L from the forward perpendicular, limiting flooding if the bow is damaged.

Insulation resistance test

A DC megger test of a circuit or machine to earth. Readings below about 1 MΩ indicate moisture or damaged insulation and require investigation before energising.

Generator droop

The deliberate fall in frequency or voltage as load increases, allowing paralleled generators to share kW and kVAr stably without fighting each other.

4–20 mA loop

A current signalling standard where 4 mA represents zero and 20 mA full scale. A broken wire reads below 4 mA, so faults are detected rather than hidden.

PID control

A controller combining proportional action on present error, integral action to remove steady offset, and derivative action to damp fast changes, tuned for stable response.

Carnot efficiency

The maximum possible efficiency of a heat engine between two reservoirs, equal to one minus the cold absolute temperature divided by the hot absolute temperature.

Dryness fraction

The mass fraction of saturated vapour in a wet steam mixture. It is found from enthalpy data or a throttling calorimeter and affects turbine efficiency and erosion.

Diesel cycle efficiency

Efficiency of constant-pressure heat addition cycle, depending on compression ratio, cut-off ratio and specific heat ratio. Higher compression ratio and lower cut-off improve efficiency.

Reynolds number

A dimensionless ratio of inertial to viscous forces, equal to velocity times diameter divided by kinematic viscosity. It determines laminar or turbulent flow regime.

Log mean temperature difference

The effective temperature driving force in a heat exchanger, calculated from the two terminal differences. It is higher for counterflow than parallel flow arrangements.

Overall heat transfer coefficient

The combined conductance of a heat exchanger path, including both film coefficients, wall conduction and fouling resistances. Its reciprocal is the total thermal resistance.

Galvanic corrosion

Corrosion caused by contact between dissimilar metals in an electrolyte, where the less noble metal becomes anodic and dissolves. Insulation or cathodic protection prevents it.

Sacrificial anode

A block of zinc or aluminium alloy bolted to the hull or sea-water spaces. It corrodes preferentially, protecting the steel until it is consumed and replaced.

Tempering

Reheating hardened steel to a temperature below the transformation range to reduce brittleness, relieve internal stress and achieve the required toughness and hardness.

Cutting speed

The surface speed of the workpiece relative to the tool, equal to pi times diameter times rpm divided by 1000 in m/min. It controls tool life and finish.

MIG welding

Metal inert gas welding uses a continuously fed consumable wire electrode and a shielding gas. It suits semi-automatic production welding of steel and aluminium.

15 ppm alarm

Oil filtering equipment must include a 15 ppm bilge alarm and an automatic stopping device. It prevents discharge of oily bilge water above the MARPOL Annex I limit.

NOx Tier III

The strictest MARPOL Annex VI nitrogen oxide emission limit for new engines, applying in designated emission control areas and requiring selective catalytic reduction or equivalent measures.

Fire triangle

The three elements needed for combustion: fuel, oxygen and heat. Removing any one extinguishes fire, which is the basis of all firefighting tactics.

First-angle projection

A drawing convention where the object lies between the observer and the projection plane, so the top view appears below the front view in the layout.

Section modulus

A geometric property equal to the second moment of area divided by the distance from the neutral axis to the extreme fibre. It links bending moment to maximum stress.