USCG Exam PracticeDiesel engine principles (motor propulsion)
In a pump-line-nozzle fuel injection system, what causes the injector needle valve to open and admit fuel to the cylinder?
- A. A solenoid signal from the engine control unit
- B. Direct mechanical actuation by the camshaft at each cylinder
- ✓ High-pressure fuel from the injection pump lifting the needle valve against its springCorrect
- D. Fuel pressure in the common-rail accumulator reaching a set threshold
Why C is correct
In a pump-line-nozzle system, a jerk-type injection pump develops high pressure and sends it through a line to a spring-loaded injector; the needle valve opens when line pressure lifts it against the spring. Direct camshaft actuation describes the unit-injector system, and the common-rail accumulator describes a separate arrangement. (DOE-HDBK-1018 Vol.1 §1-3)
Cited:DOE-HDBK-1018 Vol.1 §1-3