You are analyzing the data used for trend analysis for a two-stroke main propulsion diesel engine on your river push boat. Although the engine has yet to experience a safety shutdown on high crankcase pressure, over time the crankcase pressure (which normally runs in a vacuum) has gradually become less negative. Which of the following failures would most likely be responsible for this condition?
• How crankcase pressure is created and why a healthy crankcase often runs slightly in vacuum on a large diesel • What kinds of problems allow combustion gases to get past the piston and into the crankcase (blow-by) • The difference between a local external air leak at the crankcase and an internal leak path from the cylinders into the crankcase
• Which of these failures would increase the amount of gas entering the crankcase volume from inside the engine, gradually reducing the vacuum over time? • For each option, ask yourself: does this mainly affect the combustion chamber, the fuel system, the exhaust side, or the crankcase sealing, and how would that influence crankcase pressure readings? • Which failure is most commonly associated with increased blow-by in diesel engines, and would that be a slow trend or an immediate large change?
• Be clear on what a "less negative" crankcase pressure means: the pressure is moving closer to atmospheric from a vacuum, not going deeper into vacuum • Identify which component directly controls sealing between the combustion space and the crankcase during operation • Consider which fault would produce a gradual trend in crankcase pressure rather than a sudden step-change or a symptom seen elsewhere first (like exhaust temperature or visible external oil leaks)
No comments yet
Be the first to share your thoughts!