Question 19 3AE01 - Third Assistant Engineer

The Correct Answer is D. **Explanation for Option D (aftercooler) being correct:** Based on standard engineering practices and common marine/industrial engine diagrams (like those often depicted in technical illustrations designated as "MO-xxxx"), an item labeled "R" in a typical illustration showing the air intake and cooling components of a large engine (especially if it's turbocharged and uses forced induction) is frequently pointing to the **aftercooler** (or charge air cooler). The aftercooler is positioned immediately after the turbocharger's compressor stage and before the intake manifold. Its primary function is to cool the compressed, hot air coming from the turbocharger, making the air denser and improving combustion efficiency. Visually, it typically appears as a heat exchanger component situated prominently in the intake path. **Explanation for why other options are incorrect:** * **A) exhaust manifold:** The exhaust manifold handles hot exhaust gases leaving the cylinders. It would be located on the opposite side of the engine or positioned near the cylinder head outlets, not in the low-temperature intake air path where an aftercooler is found. * **B) air filter:** The air filter is always located upstream, at the very start of the intake system (before the turbocharger). The item labeled "R" (the aftercooler) is located far downstream in the high-pressure side of the intake system. * **C) non-return scavenge valve:** While valves are critical components, a scavenge valve is typically associated with two-stroke engine scavenging systems or lubrication/drainage systems. It is not a major heat exchange component in the main high-pressure intake air path, which is the role and likely location of the aftercooler.