Question 28 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is D **Explanation for why Option D is correct:** Large marine diesel engines, especially V-type engines found in tugs and similar vessels, are typically equipped with multiple turbochargers. The most common configuration involves using one turbocharger for each cylinder bank (or side) of the engine. This configuration (Two turbochargers used, one for each cylinder bank) achieves several goals: 1. **Efficient Exhaust Gas Collection:** It simplifies the routing and reduces the length of the exhaust manifolds leading to the turbine inlet for each bank. 2. **Optimized Pulsation:** It allows the turbocharger to efficiently utilize the exhaust pressure pulses generated by the firing order of that specific bank of cylinders. 3. **Reduced Exhaust Back Pressure:** By utilizing appropriately sized turbochargers—one per bank—the design ensures that the exhaust gas flow is handled efficiently, minimizing back pressure against the pistons during the exhaust stroke, which improves engine efficiency and performance. **Explanation for why other options are incorrect:** * **A) Two (2) turbochargers are used and configured in series for a two-staging effect to boost charge air pressure.** While two-stage (series) turbocharging is used on some high-performance modern engines, it is not the primary or defining feature of a typical twin-turbo V-engine setup shown in standard illustrations. Usually, the two turbochargers operate in parallel, not series, with one serving each bank. * **B) Four (4) turbochargers are used, two for each cylinder bank, to reduce exhaust back pressure.** Using four turbochargers (two per bank) is possible in very high-output or specialized engines (e.g., sequential twin-turbo setups), but it is a complex and less common configuration for the baseline illustration of a typical marine diesel. The standard configuration for a V-engine with twin turbos uses only two total (one per bank). * **C) Four (4) turbochargers are used and configured in series for a four-staging effect to boost charge air pressure.** Four-stage turbocharging is excessively complex, rarely (if ever) seen, and would provide marginal benefit compared to the immense cost and design difficulty. If four turbochargers were present, they would likely be configured in a parallel arrangement for maximum flow, not series.