🔍 Key Concepts

• Function of a fuel injection nozzle needle valve in a diesel engine • What happens inside the cylinder if fuel continues to flow when it should be shut off • Difference between normal injection timing vs. leakage or dribbling from a nozzle

💭 Think About

• Think about what the needle valve is supposed to do during each injection event and what happens if it cannot close. • Consider whether a stuck-open needle valve would completely stop fuel delivery, change the timing only, or cause fuel to continue flowing when it should not. • Ask yourself where excess fuel from a nozzle normally goes and whether that path is designed for small control leaks or full injection flow.

✅ Before You Answer

• Review how the needle valve controls start and stop of injection in a pressure-type fuel injector. • Verify whether drain or return lines are sized for minor leakage or for full injection flow. • Check if a stuck-open needle would cause continuous dribbling into the cylinder versus normal, sharp injection at the correct time.