Question 5 OSE01 - Chief Engineer - OSV

The Correct Answer is A **Why option A ("Excessive carbon build-up on exhaust pyrometer probe of affected cylinder") is correct:** The data presented is contradictory: the exhaust temperature is significantly low, yet the compression and firing pressures are normal. If the cylinder were experiencing a major combustion issue (like a misfire or severe leak), the firing pressure would drop significantly, which is not the case here. If combustion is occurring normally (as evidenced by normal firing pressure), the actual exhaust gas temperature should be normal. Therefore, the discrepancy lies in the measurement itself. Excessive carbon or soot buildup on the tip of the exhaust pyrometer probe acts as an insulating layer, preventing the sensor from accurately measuring the true (hot) exhaust gas temperature, leading to a falsely low reading. **Why the other options are incorrect:** * **B) Excessive carbon build-up on air inlet ports or valves of affected cylinder:** Reduced air flow due to carbon buildup would lower the compression pressure and subsequently reduce the amount of fuel that can be burned efficiently, resulting in a drop in firing pressure and likely an increased exhaust temperature (due to afterburning or incomplete combustion, though sometimes a lower one if the load is severely restricted). This contradicts the reported normal pressure data. * **C) Leaking exhaust valve on affected cylinder:** A leaking exhaust valve causes a loss of gas during the compression and firing strokes. This would directly result in a noticeable drop in both compression pressure and firing pressure. Since the pressures are reported as normal, this condition is ruled out. * **D) Leaking fuel injector needle valve for affected cylinder:** A leaking injector (dribbling fuel) typically leads to poor atomization, delayed ignition, and incomplete combustion, often resulting in very high exhaust temperatures, increased thermal stress, and sometimes reduced firing pressure depending on the severity. It would not typically cause a low exhaust temperature while maintaining normal firing pressure.