USCG Exam PracticeDiesel engine principles (motor propulsion)
In a diesel fuel injection system, what is the function of the injector nozzle needle valve?
- A. It meters the total quantity of fuel delivered per cycle by rotating against a helical land
- ✓ It opens when line pressure lifts it off its seat, admitting fuel to the spray holesCorrect
- C. It controls injection timing by advancing or retarding the camshaft position
- D. It maintains a constant fuel pressure in the common rail accumulator
Why B is correct
In a pump-line-nozzle system, the spring-loaded needle valve in the injector opens when fuel line pressure rises sufficiently to lift it, allowing fuel to pass through the precisely sized spray holes into the cylinder. DOE-HDBK-1018 Vol.1 §1-3.
Cited:DOE-HDBK-1018 Vol.1 §1-3