Question 23 OSE02 - Assistant Engineer - OSV

The Correct Answer is B **Explanation of why Option B is correct:** In a typical diesel engine fuel system, especially one utilizing mechanical injection pumps and injectors (which the context of an illustration referencing items like "leak off" and "injection pump return" usually implies, or even in modern systems where these lines still exist): * **Item "11" is a high-pressure fuel line:** This line connects the output of the high-pressure fuel pump (or injection pump) directly to the fuel injector. This fuel must be at extremely high pressure (thousands of psi/bar) to overcome the compression pressure in the cylinder and atomize correctly. * **Item "13" is the common injector leak off line (or drain line):** Not all fuel pumped to the injector is injected. A small amount of fuel is used to cool and lubricate the injector needle valve assembly, and some inevitably leaks past the close tolerances. This leaked fuel (and sometimes air/vapor) is collected via a small, low-pressure return line (the leak off line) and routed back to the fuel tank or the low-pressure side of the system. Since this line often connects multiple injectors, it is a "common" line. * **Item "15" is the injection pump return line:** Fuel pumps (both high-pressure and low-pressure components) often require constant circulation for cooling and to purge air/vapor from the system. This excess, low-pressure fuel is returned directly from the injection pump unit (or a pressure regulating valve on the pump) back to the service tank via this return line. Therefore, the identification in Option B is accurate based on standard diesel engine fuel system architecture. **Explanation of why the other options are incorrect:** * **A) Item "11" is a low-pressure fuel line...**: This is incorrect. Line 11 connects the pump to the injector and must carry fuel at injection pressure, making it a high-pressure line. * **C) Item "11" is a high-pressure fuel line... Item "15" is the injection pump supply line.** This is incorrect. Item 15 is identified as the return line (carrying excess fuel/leakage *away* from the pump). The supply line would bring filtered fuel *to* the injection pump from the service tank. * **D) Item "11" is a high-pressure fuel line... Item "13" is the common rail supply line...**: This is incorrect. If the system used a common rail, Item 13 would be the leak-off/drain line. A "common rail supply line" would be the main high-pressure line feeding the central fuel manifold (the common rail) from the pump, not the low-pressure drain line connecting the injectors.