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 lower temperatures.
- B. The fuel is pre-mixed with air in the intake manifold before entering the cylinder.
- ✓ Air alone is compressed to a temperature high enough to ignite the fuel spontaneously upon injection.Correct
- D. A glow plug heats the combustion chamber continuously during engine operation.
Why C is correct
A diesel compresses only air to roughly 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 from this heat of compression without any spark or pre-mixing device.
Cited:DOE-HDBK-1018 Vol.1 §1-1