Suppose your ship docking tug is equipped with 4-stroke diesel generator set drive engines fitted with the type of charge air blower show in Fig. "B" of the illustration. In terms of the pressure of the charge air entering the intake manifold, what statement is true? Illustration MO-0178
• Turbocharger operation – how exhaust gas energy drives the turbine, which in turn drives the compressor on the air side • Relationship between turbocharger speed and boost (charge‑air) pressure at the intake manifold • How engine load affects exhaust gas energy, turbocharger speed, and therefore intake‑manifold pressure
• Look at each choice and ask: when the engine is working harder and producing more exhaust, what happens to turbocharger speed and the air pressure going into the cylinders? • Consider whether turbocharger speed is directly tied to engine RPM, or more closely tied to how much fuel is being burned (engine load). • For a turbocharger like the one in Fig. B, would increased compressor/turbo speed logically raise or lower the pressure at the air outlet to the intake manifold?
• Identify which options say pressure increases vs decreases with speed and decide which trend matches how a compressor works. • Decide whether the controlling factor for turbocharger speed is engine RPM alone or engine load (fuel/exhaust energy). • Eliminate any option that claims intake pressure changes independently of engine load if that conflicts with how exhaust‑driven turbochargers behave.
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