Question 18 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is B ### Explanation for Option B ("2") **B (Position 2)** corresponds to the engine running under no load at idle RPM. 1. **Principle of Metering:** Diesel fuel injector pumps (specifically, jerk pumps or distributor pumps utilizing a plunger) meter fuel by rotating the plunger. This rotation changes the alignment of an angled helical groove (the control helix) relative to the spill port (or release port) in the barrel. 2. **Effective Stroke:** The effective stroke is the distance the plunger travels from the moment it covers the inlet port until the moment the control helix aligns with the spill port, causing the pressure to drop and injection to cease (spill). 3. **Idle Requirement:** Running at idle RPM under no load requires the absolute minimum amount of fuel needed to overcome internal friction and maintain rotation. 4. **Conclusion:** Position '2' shows the plunger rotated slightly beyond the "stop" position. This slight rotation results in a **very short effective stroke**, delivering the minimal charge of fuel necessary for idle operation. ### Why Other Options Are Incorrect * **A (Position 1):** This position typically represents the **"Stop"** or **"Zero Delivery"** position. In this setting, the plunger is rotated so that the helix uncovers the spill port immediately upon the beginning of the upward stroke, resulting in no fuel delivery. * **C (Position 3):** This position represents an intermediate rotation, resulting in a **medium effective stroke**. This amount of fuel delivery would correspond to the engine operating under **partial load** or higher cruising RPM, far exceeding the requirement for idle. * **D (Position 4):** This position typically represents the maximum rotation possible, resulting in the **longest effective stroke**. This delivers the maximum fuel charge, corresponding to the engine running at **full load and maximum power**.