Question 22 UFIV02 - Assistant Engineer - UFIV

The Correct Answer is B **Explanation of why Option B is correct:** Unit Injectors (often referred to as Unit Pump Injectors, or Electronic Unit Injectors - EUIs, depending on the specific design shown in Illustration MO-0143, which is typical for modern medium/high-speed diesel engines like those found on a dredger) combine the high-pressure pump and the injector nozzle into a single unit. In modern electronic versions: 1. **Pressurization:** High pressure is achieved by a plunger that is mechanically actuated. This plunger is typically driven by a lobe on the engine's camshaft via a rocker arm system. The rocker arm applies the high force necessary to compress the fuel, creating injection pressure (often exceeding 2,000 bar). Therefore, the **mechanically operated rocker arm** accomplishes the **pressurization** of the fuel. 2. **Timing and Metering:** The start and end of the injection event, which dictate when the injection occurs (**timing**) and how much fuel is delivered (**metering**), are controlled precisely by an electronic signal opening and closing a solenoid valve (or control valve) located within the unit injector body. This **electronically controlled solenoid** manages the spill port, determining exactly when high pressure is trapped and released, thus controlling both the **timing and metering** of the fuel. Therefore, statement B accurately describes the functional split: mechanical power for pressure generation, and electronic control for precision timing and quantity. **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.** * This is incorrect because the metering (quantity of fuel) is primarily determined by the solenoid valve controlling the duration of the high-pressure phase, not solely by the mechanical rocker arm stroke. While the mechanical stroke provides the potential for injection, the electronic solenoid determines the actual quantity injected (metering) and the start of injection (timing). * **C) 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.** * This is incorrect because timing (when injection starts) is determined by when the electronic solenoid closes the spill port. If the rocker arm controlled the timing, the injection event would be fixed relative to the camshaft position, which contradicts the fundamental purpose of modern electronic control systems which allow variable and flexible injection timing. * **D) 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.** * This is fundamentally incorrect. Solenoids control the flow and timing; they do not possess the mechanical power required to generate the extremely high pressures necessary for modern diesel injection. The mechanical rocker arm handles the high-force pressurization, while the solenoid handles the timing and metering control.