USCG Exam PracticeDiesel engine principles (motor propulsion)
What is the primary reason a diesel engine does not require a spark plug or carburetor?
- A. Diesel fuel has a lower flash point than gasoline and ignites at atmospheric pressure
- B. The fuel is pre-mixed with air in the intake manifold before entering the cylinder
- ✓ Air alone is compressed to a temperature above the auto-ignition point of the fuel, causing spontaneous ignitionCorrect
- D. A glow plug continuously heats the combustion chamber to sustain ignition
Why C is correct
A diesel is a compression-ignition engine: air alone is compressed to roughly 300–500 psi, raising its temperature to about 1000°F, well above the fuel's auto-ignition point. Injected fuel ignites spontaneously from this heat, requiring neither spark plug nor carburetor. (DOE-HDBK-1018 Vol.1 §1-1)
Cited:DOE-HDBK-1018 Vol.1 §1-1