100+ Free BD Marine Engineer Class 2 (Second Engineer) Practice Questions

Explanation: Scavenging pushes fresh air into the cylinder through the scavenge ports while the exhaust valve or ports are open, driving out the products of combustion so the next charge of air is as clean as possible. Efficient scavenging is essential for good combustion and full power development in a two-stroke engine, which has no separate exhaust stroke.

Explanation: In a trunk-piston engine the connecting rod is attached directly to the piston, so the extended piston skirt itself must bear against the cylinder liner to absorb the side thrust generated as the connecting rod angles during the stroke. This differs from large slow-speed crosshead engines, which use a separate crosshead and guide shoes to keep that side load off the liner.

Explanation: Surging occurs when the compressor operates to the left of its stable operating range on the performance map, typically at low engine load, fouled air filters, or a damaged blade, causing airflow to intermittently break down and reverse. The resulting pulsation produces heavy vibration and noise and can quickly damage the turbocharger's bearings and blading if not corrected.

Explanation: The delivery valve closes sharply as the pump plunger's helix uncovers the spill port, and its retraction piston relieves the line volume slightly, dropping pressure quickly so the injector needle snaps shut. This residual line pressure prevents fuel from continuing to dribble from the nozzle after the main injection, which would otherwise cause poor combustion and carbon deposits.

Explanation: Turning gear allows the crankshaft to be rotated slowly for jobs such as taking indicator cards, inspecting bearings, or positioning pistons for overhaul, without the engine actually firing. A mechanical or electrical interlock ensures the starting air valve cannot be opened while the turning gear is engaged, preventing the engine from starting and causing serious injury or damage.

Explanation: A developing hot spot, such as an overheating bearing, gradually raises local oil temperature until it forms a flammable oil mist inside the enclosed crankcase space. If that mist reaches an ignitable concentration and meets a further ignition source, often the same hot spot flaring up, it explodes; the crankcase relief doors are designed to lift and release the pressure wave, protecting the crankcase structure and personnel.

Explanation: Excess cylinder lubricating oil or fuel residues can accumulate as a combustible deposit in the scavenge space below the piston. If piston rings are worn, stuck, or broken, hot combustion gas can blow past them into the scavenge space and ignite that deposit, producing a scavenge fire that is often first detected by a rising scavenge space temperature alarm.

Explanation: Compression rings form a gas-tight seal between the piston and cylinder liner so that combustion pressure is not lost past the piston, and they also provide a metal-to-metal heat path that helps transfer heat from the hot piston crown into the cooler cylinder liner and jacket water. A worn or broken ring reduces compression, wastes power, and can allow blow-by gases into the scavenge space or crankcase.

Explanation: The governor continuously compares actual engine speed against the set speed and moves the fuel rack to increase or decrease fuel delivery as load changes, keeping speed steady. Many governors also include an overspeed trip function that shuts off fuel if speed rises to a dangerous level, protecting the engine from a runaway condition.

Explanation: If the liner surface temperature drops below the acid dew point of the combustion products, sulfuric acid formed from sulfur in the fuel can condense on the liner wall and cause cold corrosion. Conversely, running too hot increases thermal stress and can affect lubricating oil film stability, so the jacket cooling water outlet temperature is controlled within a specified band, often using a thermostatic valve.