Question 58 UFIV01 - Chief Engineer - UFIV
A Roots-blown, two-stroke cycle main propulsion engine on the fishing factory ship to which you are assigned is emitting excessive bluish-tinged smoke from the stack. Further investigation reveals excessive lube oil consumption. What condition would most likely account for this?
The Correct Answer is A **Why option A ("Worn blower rotor shaft seals") is correct:** The engine described is a two-stroke cycle engine utilizing a Roots blower for scavenging and charging air. Roots blowers operate by compressing air, and they often incorporate rotor shaft seals (similar to turbochargers or superchargers) to prevent the pressurized air from escaping and, critically, to prevent oil used for lubricating the blower's gears and bearings from entering the air stream. If these seals become worn, lubricating oil is drawn or forced into the scavenging air manifold, mixing with the combustion air. When this oil-laden air is subsequently burned in the cylinders, it results in excessive blue or bluish-tinged smoke (a classic sign of burning lubricating oil) and leads directly to excessive lube oil consumption. **Why the other options are incorrect:** * **B) Leaking fuel injector needle valve:** A leaking or "dribbling" fuel injector introduces excessive fuel that does not atomize properly. This would lead to incomplete combustion, typically resulting in **black smoke** (unburned carbon/soot), poor performance, and potentially high exhaust gas temperatures, but it would not directly cause excessive **bluish-tinged smoke** or excessive **lube oil consumption**. * **C) Restricted scavenging air intake ports:** Restricted ports reduce the amount of fresh air entering the cylinder to clear exhaust gases and provide oxygen for the next cycle. This leads to poor scavenging, incomplete combustion, and potentially **black or gray smoke** due to excess fuel relative to available air. While it impacts efficiency, it does not introduce lube oil into the combustion process. * **D) Restricted blower air intake filter:** A clogged filter restricts the total air mass flow into the engine. Similar to restricted scavenging ports, this results in an air-starved condition, leading to incomplete combustion and **black or gray smoke**. It does not provide a mechanism for lube oil to enter the combustion chamber.
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