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The use of graphical dynamic system simulation software is becoming more popular as economic demands require reducing time and cost of development and troubleshooting equipment. Nuclear power plants pose unique problems in this regard because installed equipment must be available to support the plant safety function, so it is not available to support qualification testing of new designs or troubleshooting in the case of equipment malfunction. Commercial design processes have similar constraints due to the high cost of prototype development. This paper discusses recent successes in using modular system simulation software to support the implementation of improved speed control governors installed on emergency diesel generators. The original governors are to be replaced as part of an overall control system upgrade.

Cylinder head cracking has been an engine development problem since the first high Performance diesels were designed and manufactured in the early 20th century. Valve bridge cracking is a common failure mode that is very dependent on engine application and operating conditions. Cracking failures cause increased engine maintenance and downtime, costly part replacement and in rare cases catastrophic engine failure. Cylinder head cracking continues to be problematic for modern diesel engines as peak firing pressures increase to meet exhaust emissions legislation and BMEPs increase for improved power density. The root cause of cylinder head cracking is often difficult to diagnose due to large number of design, manufacturing and engine operational variables involved. This paper summarizes the methods, results and conclusions of a study to determine the root cause of cracking in cylinder heads of large diesel engines used for standby power generation in nuclear plants.

This paper describes the root cause investigation of cracking in cylinder liners installed in ALCO 251 diesel engines in nuclear standby service. The results of the investigation identify conditions which contribute to cracking of the upper cylinder liner flange. It is demonstrated that the cracks are initiated via high cycle fatigue, but that most cracks will arrest. A cylinder liner with an arrested crack of this type would be expected to continue to provide reliable service. For worst case conditions, low-cycle thermal fatigue may cause crack growth to continue beyond the normal arrest point, ultimately causing catastrophic failure of the cylinder liner flange. Several corrective actions are identified to preclude the cracking of replacement cylinder liners. These corrective actions are applicable to all operators of ALCO 251 diesel engines.