Question 46

The Correct Answer is B. ### Explanation for Option B ("2"): Option B refers to position '2' in the illustration, which depicts a Fuel Injection Pump (FIP) barrel and plunger assembly. The operating principle shown is typically for a jerk-type pump, which regulates the amount of fuel delivered by varying the effective stroke of the plunger. * **Fuel Injection Begins:** Injection starts when the top edge of the plunger (the helix or scroll) first closes the inlet port (or spill port) on the pump barrel as the plunger moves upwards. In position **2**, the top edge of the plunger has just risen sufficiently to cover the inlet port. Once this port is covered, the fuel trapped above the plunger can no longer escape back to the fuel gallery. The pressure rapidly builds up due to the continuing upward movement of the plunger, opening the delivery valve and forcing fuel through the injector nozzle into the engine cylinder. Therefore, position 2 marks the start of the effective pumping stroke and the beginning of fuel injection. ### Explanation for Incorrect Options: * **Option A ("1"):** Position 1 shows the plunger at the lowest point of its stroke (Bottom Dead Center for the pump mechanism). Both the inlet port and the spill port are fully uncovered. Fuel is flowing freely into the space above the plunger (charging the pump). No pressure build-up or injection is possible here. * **Option C ("3"):** Position 3 shows the plunger further along its upward stroke. Injection is well underway, as the top edge is far above the inlet port. At this point, the effective pumping stroke is continuing, building maximum pressure. * **Option D ("4"):** Position 4 illustrates the end of the effective injection period (spill or termination of injection). The helix/scroll on the plunger has moved past the spill port, uncovering it. This allows the high-pressure fuel above the plunger to escape rapidly back into the fuel gallery, causing the pressure to drop immediately and ending the injection event.