Question 47 UFIV01 - Chief Engineer - UFIV

The Correct Answer is B **Explanation for B (Correct Answer):** The description of the injector shown as "figure 2" in illustration MO-0150 typically refers to a jerk pump or plunger-type fuel injection system, commonly associated with medium- and high-speed diesel engines. This design, pioneered by companies like Bosch, utilizes a spring-loaded needle valve (or pintle valve) which remains closed until the fuel pressure built up by the injection pump overcomes the spring force. Therefore, the injector itself is of the **closed type**. The *metering* (controlling the exact amount of fuel injected per cycle) and *timing* are achieved in the injection pump (not the injector nozzle itself) using a reciprocating plunger that has a **port and helix (or scroll) metering** system. The helix uncovers the spill port at a precise moment controlled by rotating the plunger via a rack, thus determining the effective pumping stroke and the amount of fuel delivered. **Explanation for A (Incorrect):** While the injector is of the closed type, it does not feature pressure-time metering. Pressure-time metering is characteristic of unit injectors (like those used in EMD engines) or common rail systems, where the duration of time the electronic solenoid valve is open (pulse width) determines the fuel quantity, influenced by system pressure. The mechanical plunger pump system described by port and helix metering is distinct from pressure-time metering. **Explanation for C (Incorrect):** The injector is **not** of the open type. An open-type injector would discharge fuel directly into the combustion space without a needle valve holding back the pressure, often leading to continuous dribbling or poor atomization. Modern high-pressure diesel engines almost universally use closed-type injectors (with a spring-loaded nozzle valve) to ensure sharp cut-off and proper atomization. **Explanation for D (Incorrect):** This option incorrectly states both key features. The injector is **not** of the open type, and the metering method used by the associated mechanical pump is the port and helix system, **not** pressure-time metering.