USCG Exam PracticeDiesel engine principles (motor propulsion)
A diesel engine ignites its fuel charge WITHOUT a spark plug because:
- A. A glow plug pre-heats the fuel before it enters the cylinder
- ✓ Compressing air alone raises cylinder temperature to approximately 1000°F, above the fuel's auto-ignition pointCorrect
- C. A carburetor mixes fuel and air at a ratio that allows spontaneous combustion
- D. The camshaft-driven injector creates a high-voltage arc across the nozzle tip
Why B is correct
A diesel compresses only air to roughly 300–500 psi, raising its temperature to about 1000°F. Finely atomized fuel injected near top dead center ignites spontaneously from this heat of compression; no spark plug or carburetor is required.
Cited:DOE-HDBK-1018 Vol.1 §1-1