Free Practice Questions for GASM Uzakyol Başmühendisi

Explanation: Scavenge air relief valves are critical statutory safety devices installed on the scavenge manifolds of large two-stroke crosshead engines. In the event of a scavenge fire or violent pressure surge caused by the ignition of unburnt cylinder lubricating oil and carbon deposits, they lift rapidly to relieve overpressure and prevent trunking rupture. They reseat immediately under spring force to stop atmospheric oxygen from entering and sustaining the fire.

Explanation: For a two-stroke engine, power per cylinder is given by P = P_mi * L * A * n. Cylinder cross-sectional area A = (pi / 4) * (0.60)^2 = 0.282743 m^2. Stroke length L = 2.40 m, and rotational frequency n = 100 / 60 = 1.6667 rev/s. Power per cylinder = 1,800,000 Pa * 2.40 m * 0.282743 m^2 * (100 / 60) s^-1 = 2,035,752 W = 2,035.75 kW. For 6 cylinders, total indicated power = 6 * 2,035.75 kW = 12,214.5 kW, which rounds to 12,215 kW.

Explanation: SFOC is calculated as fuel mass flow per unit power: SFOC = (1,750 kg/h * 1,000 g/kg) / 10,000 kW = 175.0 g/kWh. Brake thermal efficiency eta_b = Work output / Heat input = P_b / (m_f * LHV). Work output per hour = 10,000 kW * 3,600 s = 36,000,000 kJ. Heat input per hour = 1,750 kg * 42,700 kJ/kg = 74,725,000 kJ. Thus, eta_b = 36,000,000 / 74,725,000 = 0.48177 = 48.2%.

Explanation: In MAN B&W ME-C electronically controlled engines, the camshaft is replaced by hydraulic cylinder units (HCUs). The FIVA (Fuel Injection Valve Actuation) valve or ELFI (Electronic Fuel Injection) proportional valve is driven by the engine control system (ECS). It modulates high-pressure hydraulic servo oil (200-300 bar) to actuate the fuel oil pressure booster piston, precisely governing injection timing, pressure profile, and fuel quantity per stroke.

Explanation: In WinGD RT-flex common rail engines, the ICU (Injection Control Unit) is mounted adjacent to each cylinder. It contains electro-hydraulic rail valves controlled by the WECS (Wärtsilä Engine Control System) that meter fuel from the high-pressure fuel rail (approx. 1,000 bar) to the injectors. The ICU features an internal free-floating piston and position transmitter that provides precise volumetric feedback of fuel injected per cycle.

Explanation: Turbocharger surge occurs when the operating point on the compressor performance map crosses the surge line. When the mass airflow through the compressor falls too low relative to the downstream receiver pressure (often due to fouled scavenge ports, fouled air coolers, sudden engine load reduction, or exhaust pulse mismatches), the compressor blades stall aerodynamically. Air then surges backward through the impeller until downstream pressure drops, whereupon normal flow restarts, setting up a destructive cyclic pulsation.

Explanation: On a standard power indicator card, the piston is moving very slowly near top dead center (TDC), so the pressure changes during combustion are compressed into a narrow vertical spike. By shifting the indicator drive 90 degrees out of phase, the indicator drum moves at its maximum linear velocity when the engine piston is at TDC. This spreads out the pressure trace around TDC, allowing precise visual and quantitative evaluation of compression pressure (Pcomp), ignition delay, rate of pressure rise (bar/degree), and peak firing pressure (Pmax).

Explanation: A light-spring indicator diagram uses a highly flexible spring (with a low spring scale such as 1 mm = 0.1 bar) fitted with a protective stop to prevent damage during high-pressure combustion. Its sole purpose is to magnify the low-pressure gas exchange process near the bottom dead center (exhaust blowdown, scavenging period, and air inlet pressure). It immediately detects fouled exhaust ports, high exhaust backpressure, late exhaust valve opening, or inadequate scavenge pressure.

Explanation: Crankshaft web deflection gauges measure the distance between adjacent crank webs as the shaft is turned through one revolution. When the webs open out at the bottom (B reading greater than T reading), the crank pin is bowed downward, meaning the main bearings supporting that throw are lower than the adjacent bearings. This indicates excessive wear of the main bearing shells, loose holding-down bolts, or local sagging of the ship's double bottom structure.

Explanation: In high-efficiency ultra-long-stroke engines, peak cylinder pressures exceed 180-200 bar, which raises the sulfuric acid dew point to 140-160 degrees Celsius. When liner wall temperatures fall below this dew point, condensed water reacts with sulfur trioxide (SO3) from fuel combustion to form corrosive sulfuric acid (H2SO4). Mitigation requires selecting a cylinder lubricating oil with a matching Base Number (BN) and feed rate to neutralize the acid, combined with load-dependent jacket water preheating (e.g. jacket temperature control at 85-90 degrees Celsius) and scavenge air temperature optimization.