Question 63 OSE01 - Chief Engineer - OSV

The Correct Answer is B. ### Explanation for why option B ("2") is correct Option B (Position 2) corresponds to the moment when fuel injection begins. In the diagram, the fuel injector pump (likely a jerk pump type, as indicated by the components) operates by the plunger moving upwards. Injection begins when the top edge of the plunger covers the **spill port (or inlet/delivery port)**, trapping the fuel in the chamber above the plunger. * **Position 1:** The plunger is at the bottom of its stroke (Bottom Dead Center - BDC). The spill port is fully uncovered, allowing fuel to fill the chamber. * **Position 2:** The plunger has moved up, and its top edge has just covered the spill port. This marks the moment that compression begins and the pressure rapidly increases, causing the delivery valve to lift and the fuel to be injected through the nozzle. This point is known as the **effective stroke beginning**. ### Explanation for why the other options are incorrect * **Option A (1):** This position shows the plunger at the bottom of its stroke (BDC). The spill port is open, and the pump chamber is filling with fuel. No injection is occurring. * **Option C (3):** This position shows the plunger farther up its stroke. Injection has been occurring since Position 2. In this diagram series, Position 3 typically illustrates the point where the control helix/scroll edge uncovers the spill port, marking the moment injection **ends** (spill point). * **Option D (4):** This position shows the plunger near the top of its stroke (TDC), significantly past the point of injection termination (spill). Injection has already started (at 2) and stopped (at 3). This position often represents the maximum lift position after injection has completed, or sometimes it is used to show the relationship between the helix and the port at the maximum fuel delivery setting.