USCG Exam PracticeDiesel engine principles (motor propulsion)
A diesel engine ignites its fuel charge without a spark plug because it relies on which principle?
- A. A glow plug preheats the combustion chamber before each injection event
- ✓ The heat generated by compressing air alone raises cylinder temperature above the fuel's auto-ignition pointCorrect
- C. A carburetor pre-mixes fuel and air to a ratio that ignites spontaneously at low compression
- D. A pilot flame in the prechamber initiates combustion at each power stroke
Why B is correct
A diesel compresses only air to roughly 300–500 psi, raising its temperature to approximately 1000°F, which exceeds the auto-ignition temperature of the injected fuel. No spark plug or carburetor is required.
Cited:DOE-HDBK-1018 Vol.1 §1-1