A main propulsion diesel engine on your towing vessel produces gray to black smoke under virtually all load conditions as observed at the stack. The heavier the load on the engine, the darker the smoke becomes. What condition would most likely account for this?
• Relationship between diesel exhaust color and type of problem (fuel, air, oil, or water/steam) • How engine load and back pressure affect combustion and smoke color/intensity • Typical symptoms of oil burning vs water/steam in exhaust vs restricted exhaust flow
• For each choice, ask: would this problem usually make the exhaust look black/sooty, blue, or white? Which matches the question? • How would the smoke change as engine load increases for each condition—would it reliably get darker with more load? • Which condition directly affects how easily exhaust can leave the engine, and how would that influence combustion efficiency and smoke?
• Match smoke color (gray to black, heavier with load) with the most typical cause in diesel engines: fuel-rich/incomplete combustion vs oil burning vs water/steam. • Check which options would mainly introduce oil into the exhaust, which would introduce water, and which would change exhaust flow or pressure. • Eliminate any option that would more likely cause white steam or blue/oily smoke rather than sooty black smoke.
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