USCG Exam PracticeDiesel engine principles (motor propulsion)
A two-stroke diesel requires scavenging because:
- A. The compression ratio is too low to ignite fuel without pre-pressurized air
- ✓ There is no separate intake or exhaust stroke, so combustion products must be swept out by forced airCorrect
- C. The camshaft runs at half crankshaft speed and cannot open valves fast enough at high RPM
- D. Turbocharging alone cannot raise cylinder pressure to the level needed for compression ignition
Why B is correct
A two-stroke diesel completes all four events in one crankshaft revolution, leaving no dedicated intake or exhaust stroke. Fresh air must therefore be forced in above exhaust-manifold pressure to displace combustion products — a process called scavenging.
Cited:DOE-HDBK-1018 Vol.1 §1-2