USCG Exam PracticeDiesel engine principles (motor propulsion)
In a pump-line-nozzle fuel injection system, what event causes the injector nozzle needle valve to open and admit fuel to the cylinder?
- A. The camshaft directly lifts the needle valve through a pushrod at the correct timing point
- B. An electronic solenoid energizes when the engine control unit commands injection
- ✓ High-pressure fuel from the jerk pump lifts the needle valve against its spring when line pressure is sufficientCorrect
- D. A common-rail accumulator releases stored pressure through a pilot valve to the nozzle
Why C is correct
DOE-HDBK-1018 Vol.1 §1-3 describes the pump-line-nozzle system as one in which a jerk-type injection pump develops high pressure and sends it through a line to a spring-loaded injector that opens when line pressure lifts the needle valve. Electronic solenoids and common-rail accumulators are features of different injection systems.
Cited:DOE-HDBK-1018 Vol.1 §1-3