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 ambient temperature
- 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, so injected fuel ignites spontaneouslyCorrect
- D. A glow plug provides continuous ignition energy throughout the power stroke
Why C is correct
A diesel is a compression-ignition engine: only air is compressed to roughly 300–500 psi, raising its temperature to about 1,000°F, which is above the fuel's auto-ignition point. Fuel injected at that point ignites without any spark. DOE-HDBK-1018 Vol.1 §1-1.
Cited:DOE-HDBK-1018 Vol.1 §1-1