A turbocharged, two-stroke cycle main propulsion diesel engine on your fishery research vessel is emitting gray to black smoke excessively from the stack. Upon comparing the measured air box pressure against a reference engine which is producing a clear stack, the measured air box pressure is determined to be too low. Which of the following conditions would most likely be the cause for the relatively low air box pressure?
⢠Relationship between turbocharger performance, scavenge air (air box) pressure, and exhaust flow on a two-stroke diesel ⢠How restrictions on the air side vs restrictions on the exhaust side affect boost pressure and smoke ⢠Where carbon or physical restrictions would most directly reduce air flow into the cylinders on a two-stroke, turbocharged engine
⢠Ask yourself: Which component, if restricted, would MOST DIRECTLY lower the amount of air actually reaching the cylinders (and thus the air box pressure)? ⢠Consider what happens to turbocharger speed and boost pressure if the exhaust flow to the turbine is restricted versus if the air flow after the turbo is restricted. ⢠Think about how each listed restriction would show up as symptoms: would it mainly cause higher temperatures, more exhaust back pressure, less boost, or less effective scavenging of the cylinders?
⢠Verify which component is downstream of the turbo compressor and directly feeds the scavenge/air box on a two-stroke engine. ⢠Check which restriction would primarily cause high exhaust back pressure without directly choking scavenge air ports or air box pressure. ⢠Confirm which option would most logically produce low air box pressure AND heavy gray/black smoke due to poor scavenging and low excess air.
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