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NAVY ENGINEERING BULLETIN MARCH 2003 13 information supplied by General Electric, and the PDE’s curve is for one diesel, developed from HMAS ARUNTA Steady Steaming Curves. FUEL CONSUMPTION COMPARISON Maintenance Benefits In comparison with the MTU 1163, the LM500 has a greater variety of Planned Maintenance (PM) tasks to complete, however the LM500s PMs take less time to complete, and have a greater interval between them. The longer intervals between PMs are not only for OLM tasks, but also includes ILM and DLM tasks. For example, the GT is required to complete an overhaul after approximately 15000-20000hrs (condition based) compared with the MTU 1163’s mandatory 12000hrs. Reliability Benefits The MTU 1163s are a relatively reliable diesel, and have proven dependable in the application on passenger ferries. However, a passenger ferry’s operational parameters are vastly different from that of a warship. The LM500 configuration will have a higher reliability compared with the PDE’s based on the figures released from both MTU and GE alone. The added reliability and commonality of parts, combined with the better maintenance package of the LM500 will also reduce the number and volume of stores required on board each vessel. Thus allowing more stores to be carried for other equipment and in turn possibly increases the ship’s independent operational time. The change to a gas turbine configuration will reduce the potential for support system failure, as the LM 500 has less associated ancillary equipment. The LM500, like the PDE, has a lube oil conditioning system, but it does not require systems such as engine coolant, seawater cooling, and control air. Systems such as the troublesome seawater cooling will no longer be required, thus negating any need for the respective maintenance requirements. Simplicity Benefits Whilst the LM500 has more exotic materials and complex construction requirements, the most important factor is that the design is simpler and has fewer parts than a piston arrangement engine. The MTU 1163 PDEs comprises approximately 320 major moving parts, while the LM500 has just 15. 1 The end result is that there are fewer parts, and fewer wearing surfaces, which in turn reduce the probability of a failure regardless of the reason. Cost Analysis The final comparison for the change are the cost benefits. It must be stressed that these calculations are only preliminary and the graphical representation is only to indicate the estimated value of the change. 2 Cost considered in the analysis included; fuel and oil consumption, breakdown maintenance 3 , and Planned Maintenance. All levels of maintenance (OLM, ILM, and DLM) were considered with their associated stores and labour costs. The calculation for the modification was based on only one ship being changed. It included the purchase of the gas turbine and production work required. It assumed that it was an in-service ANZAC, to ensure the greatest cost for changeover. 4 Final changeover cost, including set to work and documentation, is estimated at A$20 million per ship. Debits and incomes that were not considered in the cost analysis include; sale of the removed diesels and associated stores, RAN personnel man hours, current contract cancellation costs, and possible legal/public relation costs.
14 NAVY ENGINEERING BULLETIN MARCH 2003 GT Selection 19. The gas turbine selection, though preliminary, was made considering all gas turbine manufacturers available at the time of research. Each representative for the manufacturer was asked to supply information that could meet the following requirements: a. Produce 3600kW or be able to be electronically limited to 3600kW; b. Have an output shaft speed of between 300 and 1200rpm; c. Able to fit with the same dimensions as the PDEs; d. No increase in the hull noise signature; e. Be able to run on F76 and F44 fuel; and f. Able to integrate easily with the C&M System. 20. The LM500’s performance, fuel consumption characteristics, easily integrated control and monitoring method, cost and commonality of parts with the LM2500 meant that the LM500 was selected, thus enabling a physical review of the proposal. Modification Considerations 21. PDE Removal: The first step in the modification is the removal of the PDE, which already has a designated removal route, and redundant systems. The redundant systems to be removed include; Seawater system, PDE Enclosure, Control air, Lube oil circulation tanks, Lube oil replenishment system, Coolant recirculation system, PDE’s Local Operating Panel (LOP), and Drainage and dirty oil system. 22. Stability: The modification shall require the importing of approximately 11,000kg and export of 60,100kg. This fifty tonne difference does affect the ship’s stability by causing the centre of gravity to increase from 6m to 6.08m. Thus, would have little effect on the ship’s operation unless severe flooding was experienced. 23. Power transfer: The LM500 has an output of 4.4MW and a maximum operating shaft speed of 7000RPM. However, it has an incorporated gearbox that reduces the output shaft speed to that of the PDEs (300 – 1200RPM), enabling the LM500 to be connected directly to the existing Geislinger Coupling. 24. Intake and Exhaust: The LM500 has a greater air flow rate, but lower exhaust temp, than that of the PDEs. Calculations have shown existing intake plenums and exhaust trunkings are sufficient. 5 25. Control and Monitoring: This may seem to be one of the more complex obstacles in the modification, however it is relatively simple. The C&M Siemens display changes are a matter of simple programming changes, whilst the monitoring system changes will require connection of the LM500 ECM to the existing C&M wiring. The program will then have to be changed to ensure that the displays and control are corrected for the input/output voltages. However the engine power requirements are different, as the LM500 sets a PLA (not RPM as for the PDEs), and will therefore require trials to set PLA for shaft RPM. Integration Issues 26. Some of the perceived integration issues that could occur with the change include; an increased IR signature, and fuel consumption at lower speeds. Whilst gas turbines are renowned for a large heat plume during operation, this can be reduced by using a venturi effect to draw in ambient air. It could be safely predicted that the exhaust experienced after the modification will most likely not require any further reduction in IR signature, with the air-diluting duct already fitted to the ANZAC Class ships. 27. However a major flaw with the LM500 (or any gas turbine) is low load, or idle, fuel consumption compared with a diesel. As shown in the earlier figure. Conclusion 28. The proposal has clear benefits with operations, maintenance, reliability, support requirements, environmental issues and costs. Whilst the change to LM500s is a feasible project, both financially and practically, it is never likely to eventuate. The article was forwarded to inspire technical discussion, and encourage others to utilise their engineering prowess to see that some solutions are outside the square. Notes 1 Major parts are classified as items that are constantly cycling to keep the engine self-sustaining, such as rockers, shafts, pushrods, etc, but not dividing into their components or considering fuel racks, or variable stator vanes. 2 The cost analysis utilises information from PDE experience, and records obtained from serving ANZACs (AMPS). It also drew upon documentation and records supplied from GE regarding the LM500’s marine propulsion service, combined with current RAN gas turbine operating experience. 3 Even though each ship should not expect a prime mover to fail, one total failure for both the LM500 and PDE, requiring overhaul, was assumed to occur once in the life of the ship, and included in the cost analysis. This was done to enable an even comparison, noting that one PDE has already failed on HMAS ANZAC. 4 Calculations were completed with assistance from project managers, both RAN and private industry. The end production figure was then given a 25% increase for expansion of work, and rounded up to the nearest million dollars. 5 Calculations conducted by Author, iaw theories and formulas from Marks’ Standard Handbook For Mechanical Engineers (Tenth Edition), McGraw Hill.
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