Question 29 OSE02 - Assistant Engineer - OSV

The Correct Answer is B ### 2. Explanation of why Option B is correct: Option B is the correct statement because it accurately describes the functional division of labor in an Electronically Controlled Unit Injector (EUI) system, which is commonly used in modern marine diesel generator sets. * **Pressurization (Mechanical):** High-pressure fuel pumping is achieved by the **mechanically operated rocker arm** (driven by the engine camshaft). The rocker arm drives the unit injector plunger downwards, generating the extremely high injection pressures required for atomization. * **Timing and Metering (Electronic):** The **electronically controlled solenoid** regulates the injection process. The solenoid operates a spill port or valve. By controlling *when* the solenoid closes (starting the effective compression stroke) and *when* it opens (ending the effective stroke/spilling the pressure), the electronic control unit (ECU) dictates both the precise **timing** (start of injection) and the total volume of fuel injected (**metering**). ### 3. Explanation of why the other options are incorrect: **A) Pressurization and metering of the fuel is accomplished by the mechanically operated rocker arm, and the timing of the fuel is accomplished by the electronically controlled solenoid.** * *Incorrect:* Metering (fuel quantity) is primarily an electronic function in modern EUIs, achieved by controlling the duration the solenoid keeps the spill port closed. Assigning metering to the mechanical rocker arm is incorrect. **C) Pressurization of the fuel is accomplished by the electronically controlled solenoid, and the timing and metering of the fuel is accomplished by the mechanically operated rocker arm.** * *Incorrect:* This option completely reverses the roles. Pressurization is the mechanical function, and timing/metering are the electronic functions. The solenoid valve cannot generate the high pressures required for injection; it only controls the flow path. **D) Pressurization and timing of the fuel is accomplished by the mechanically operated rocker arm, and the metering of the fuel is accomplished by the electronically controlled solenoid.** * *Incorrect:* While pressurization is mechanical, the actual **timing** (start of injection) is determined by the moment the electronic solenoid closes the spill port. The rocker arm movement only makes pressure generation *possible*; the solenoid controls *when* that pressure is contained and injection begins. Both timing and metering are functions of the solenoid control.