🔍 Key Concepts

• Operation of fuel injector needle valves in diesel engines • Difference between opening force vs. closing force on a differential needle valve • What role spring force and fuel pressure play in injector operation

💭 Think About

• Think about what initially lifts the needle off its seat and what later reseats (closes) it when injection ends. • Consider which of the options provides a reliable and repeatable closing force every cycle, independent of cylinder pressure. • Ask yourself: in normal diesel injector design, which force is usually pre‑set and adjustable to control the injector opening/closing characteristics?

✅ Before You Answer

• Verify which force is used to hold the needle on its seat before injection starts. • Confirm which factor among the choices can be precisely calibrated during injector setting and testing. • Eliminate any forces that mainly act outside the injector body rather than directly on the needle valve.