USCG Exam PracticeDiesel engine principles (motor propulsion)
A diesel engine ignites its fuel charge without a spark plug because of which operating principle?
- A. Fuel is pre-heated by the exhaust manifold before injection
- ✓ Air compressed to roughly 300-500 psi reaches a temperature sufficient to auto-ignite the injected fuelCorrect
- C. A glow plug in each cylinder head raises air temperature during the compression stroke
- D. The high-pressure injection pump raises fuel temperature above its flash point before delivery
Why B is correct
A diesel compresses air alone to approximately 300-500 psi, raising its temperature to about 1000°F, which is above the auto-ignition point of the fuel. Finely atomized fuel injected near the end of compression ignites spontaneously from this heat of compression, requiring no spark plug or carburetor.
Cited:DOE-HDBK-1018 Vol.1 §1-1