Question 42 MODE02 - Assistant MODU Engineer

The Correct Answer is A. **Explanation of Option A (Leak in a waste heat boiler tube):** A waste heat boiler (WHB) uses the hot exhaust gas from the engine to generate steam, typically by circulating water/steam through tubes exposed to the exhaust flow. The WHB is usually positioned upstream of the engine's turbocharger exhaust uptake (or sometimes bypassed around the turbocharger). If a tube in the waste heat boiler leaks, pressurized boiler water/steam will enter the exhaust gas stream. This water will then follow the path of the exhaust gas: 1. **Turbocharger Drains:** The exhaust gas, now carrying water, passes through the turbocharger turbine section. Due to cooling and condensation, some water will collect and drain from the turbocharger exhaust casing drains. 2. **Waste Heat Boiler Drains:** Since the leak originates within the WHB itself, water will also collect and drain directly from the WHB casing drains, especially if the leak is substantial or the boiler is in the drainage path. Therefore, a leak in a waste heat boiler tube is the only listed fault that can introduce water into the exhaust system before and/or within the path that feeds both the WHB drains and the turbocharger drains. **Why the Other Options are Incorrect:** * **B) Leak in a turbocharger exhaust casing:** A leak here (assuming it's a cooling water leak) would only affect the drains of the turbocharger itself, which is typically downstream of the WHB connection point. It would not introduce water into the main WHB structure or its drains. * **C) Leak from a turbocharger inlet casing:** The turbocharger inlet casing handles the combustion air (from the air cooler/scavenge manifold) before compression. Water leaking here would enter the combustion air stream or the scavenge space, potentially causing issues in the engine cylinders, but it would not introduce water into the **exhaust** gas path that leads to the WHB and turbocharger drains. * **D) Leak from a cylinder exhaust valve cage:** A leaking exhaust valve cage (usually containing cooling water) would introduce water directly into the cylinder exhaust manifold. This water would then flow through the turbocharger (and potentially to the WHB if the WHB receives exhaust flow directly from the manifold). While this would likely lead to water in the turbocharger drains, the location of the exhaust valve cage is typically well upstream of the WHB itself, meaning the water would not simultaneously exit from the dedicated waste heat boiler structure drains, making Option A a much stronger fit for the simultaneous drainage observation.