100+ Free SAMSA OICEW Practice Questions

Explanation: A two-stroke crosshead engine produces one power stroke per revolution of the crankshaft and features a diaphragm plate and piston rod stuffing box that completely isolates the crankcase from the combustion space. Trunk piston engines combine piston crown and skirt, transferring side-thrust directly to the cylinder liner walls. This design distinction prevents contamination of crankcase system oil by heavy fuel combustion residues in large two-stroke engines.

Explanation: P_indicated = IMEP * L * A * N * n. Area A = pi * (0.6)^2 / 4 = 0.28274 m^2. Stroke L = 2.0 m. IMEP = 1500 kPa. Cycles per sec N = 100 / 60 = 1.6667 Hz (since 2-stroke engine has 1 power stroke per rev). Number of cylinders n = 6. Power = 1500 * 2.0 * 0.28274 * 1.6667 * 6 = 848.23 kW per cylinder * 6 = 4,241 kW.

Explanation: A draw card (90-degree out-of-phase indicator diagram) expands the crank angle scale around TDC where pressure changes rapidly. This allows precise evaluation of maximum compression pressure (Pcomp), peak firing pressure (Pmax), fuel injection ignition delay, and rate of pressure rise. The standard power card compresses TDC events and is used instead to calculate mean indicated pressure.

Explanation: Variable Injection Timing (VIT) automatically advances injection timing as engine load decreases from 100% down to approximately 75-85% load. By advancing injection timing at partial load, Pmax is maintained near its rated maximum level, maximizing thermodynamic efficiency and reducing specific fuel oil consumption (SFOC).

Explanation: Fuel consumption per hour = 42,000 kg / 24 h = 1,750 kg/h = 1,750,000 g/h. BSFC = (Fuel consumption in g/h) / (Brake Power in kW) = 1,750,000 g/h / 10,000 kW = 175.0 g/kWh.

Explanation: Low-load operation causes cylinder liner surface temperatures to drop below the dew point of sulfuric acid (formed from sulfur in heavy fuel oil). Moisture and sulfur trioxide condense into liquid sulfuric acid, causing severe corrosive wear (cold corrosion). Low load also causes incomplete combustion, carbon buildup, and scavenge fire risks.

Explanation: The stuffing box contains upper sealing rings (held by garter springs) oriented upwards to prevent pressurized scavenge air and dirty oil sludge from passing down into the crankcase. Lower scraper rings face downwards to wipe system oil back into the crankcase.

Explanation: Black smoke across all cylinders indicates incomplete combustion due to a lack of air (rich air-fuel mixture). A fouled turbocharger air intake filter, dirty compressor blades, or fouled charge air cooler restricts charge air mass flow, elevating exhaust temperatures across all cylinders.

Explanation: Crankcase explosion relief valves feature a gauzed wire flame trap (flame arrester) that absorbs heat from escaping gases during an explosion, cooling the flame below its ignition temperature so it cannot ignite the surrounding engine room atmosphere. A non-return soft disc prevents fresh air from rushing back into the crankcase (which would cause a secondary explosion).

Explanation: High oil mist concentration indicates a severe hot spot (e.g. bearing failure) capable of igniting crankcase vapors. Opening crankcase doors immediately introduces fresh oxygen, triggering a devastating primary or secondary crankcase explosion. The engineer must inform the bridge, reduce engine speed or stop the engine, maintain lube oil circulation if safe, and wait at least 20-30 minutes for cooling before opening crankcase access doors.