🔍 Key Concepts

• Difference between open and closed fuel injectors (look at the nozzle/needle arrangement in figure 2). • How port-and-helix metering works in a unit injector plunger compared with pressure-time metering. • The role of the rack and gear shown in figure 2 and what type of metering system they indicate.

💭 Think About

• Focus on the lower end of injector 2: does fuel flow freely to the cylinder until pressure builds, or is there a spring-loaded needle that must be lifted? How does that relate to open vs closed type? • Follow the fuel path around the plunger in figure 2. Do you see angled or helical grooves/ports in the plunger that rotate with the rack and gear, or a fixed orifice that would depend mainly on injection pressure and time? • Ask yourself: in which metering system does rotating the plunger via a rack change the effective stroke and therefore fuel quantity?

✅ Before You Answer

• Identify whether there is a spring-loaded needle valve at the tip (a key feature of one injector type). • Confirm whether the plunger in figure 2 has helical grooves/ports controlled by the rack and gear, or just a straight passage for pressure-time metering. • Before choosing, match both parts: injector type (open/closed) AND metering method (port-and-helix or pressure-time) to what you actually see in the illustration.