BACKGROUNDER
In 1969 the first GE LM2500 aeroderivative marine gas turbine began operating aboard the United States Navy's G.T.S. Adm. Wm. M. Callaghan supply vessel. The ship sailed from Bayonne, New Jersey on a transatlantic voyage to Bremmerhaven, Germany. This novel installation sparked a renaissance in the marine industry that has forever changed the way ship propulsion systems are developed. Today, the LM2500 continues to enjoy the designation as one of the world's most popular gas turbines. GE has kept this aeroderivative gas turbine state-of-the-art through the continual infusion of technological enhancements. Significant enhancements have been made to the LM2500, including optimized compressor performance/efficiencies, high-pressure turbine temperatures and materials, and the single shank design with tapered airfoil that is more rugged than the original twin shank design. These technology enhancements have kept the LM2500 current and suitable for many marine programs yet to come.
LM2500 Marine Module
The LM2500 marine gas turbine consists of a compressor, combustor, high-pressure turbine, and free power turbine with associated accessories. The 16-stage compressor has variable inlet guide vanes (IGV), and in the first six stages there are variable stator vanes for improved stall margin and fuel efficiency. The combustor is a fully annular, straight-through-flow combustor with 30 fuel nozzles. The high-pressure turbine is a two-stage unit that selectively uses convection, impingement and/or filmcooling on blades and vanes.
The six-stage power turbine is a low speed, low stress turbine that is aerodynamically coupled to the gas generator and is driven by gas generator exit gas. The LM2500's modular construction, coupled with ports for borescope inspection of the internal components, offers simplified and reduced maintenance. The engine also has interchangeable modules, providing rapid assembly/disassembly, readily replaceable controls and accessories, ease of handling and quick gas turbine replacement. This modular construction also allows for easy, on-site maintenance.
Initial Applications
In December 1970 -- following on the heels of the first LM2500 marine gas turbine installation aboard the U.S. Navy's roll-on/roll-off cargo ship G.T.S. Adm. Wm. M. Callaghan -- GE was awarded another U.S. Navy contract to supply LM2500 engines for use aboard the Spruance (DD-963) class destroyers. The first of this class of destroyers was launched in 1973 -- making it the premiere all gas turbine ship - and thus cementing the U.S. Navy's commitment to gas turbine propulsion. GE went on to provide a total of 124 LM2500 gas turbines for 31 Spruance-class destroyers.
Technology Enhancements
In 1983, GE decided to uprate the LM2500, increasing the power rating 3% from 27,500 shaft horsepower (shp) to 29,500 shp at ISO conditions. In addition to an increased rating capability, improvement in heat rate was obtained with the LM2500 uprate. Higher exhaust temperature and mass flow for combined cycle and waste heat recovery applications were now available to industrial users.
A further uprate of almost 3% in power was put in place in the early 1990's. This uprate was accomplished by an aerodynamic enhancement, resulting in a significant improvement in combined exhaust diffuser and collector performance.
LM2500+
In 1995, GE began development and testing of the LM2500+ gas turbine, which offers 25% to 30% more power than the LM2500, and has a simple-cycle thermal efficiency in excess of 39%. The LM2500+ maximizes the LM2500 design commonality with technology advancement and features its forerunner's precedent setting 99.6% reliability.
The first application of the LM2500+ was in 1998 at an industrial cogeneration plant in Dordrecht, The Netherlands. In 2000, the inaugural marine uses of the LM2500+ occurred aboard the world's first gas turbine powered cruise ship -- Celebrity Cruises' Millennium -- and on the SNCM Corsaire 13000-class monohull fast ferry.
The LM2500+ has continued to achieve success in both the industrial and marine marketplaces, with a total of 200 LM2500+s operating worldwide -- 170 in industrial settings and 30 for marine applications. With its experience base solidified, the natural choice for the LM2500+'s initial military marine use was for U.S. Navy applications. In fact in August 2004, GE received U.S. Navy certification for the LM2500+ for 35,000 brake horsepower (bhp) for mechanical drive applications.
GE recently received U.S. Navy shock approval on the LM2500+ for use in connection with powering the U.S. Navy's LHD 8 and follow-on large-deck, multipurpose amphibious assault ships.
LM2500 Today
The LM2500 remains a popular choice for industrial as well as commercial and naval marine customers. In fact, 30 navies worldwide have selected the LM2500 for a variety of high-speed ship programs. GE has delivered more than 600 LM2500s to the U.S. Navy for a variety of combatant programs. The LM2500s power all of the U.S. Navy's surface combatant ships plus AOE supply ships and Sealift ships.
The LM2500 is part of the COmbined Diesel Or Gas turbine (CODOG) that powers the Office of Naval Research's X-Craft high-speed catamaran, christened in February 2005. The U.S. Coast Guard will use the LM2500 to drive its newest and largest multi-mission cutter under the Integrated Deepwater System program. The LM2500 will be incorporated into the integrated COmbined Diesel And Gas turbine (CODAG) propulsion system for the U.S. Coast Guard's new Maritime Security Cutter Large (WMSL).
Where To Go From Here
GE continues to invest in the LM2500 and its entire LM family of gas turbines, spending more than $350 million over the past decade on research and development.
For example, GE developed the LM2500+G4 gas turbine, which will have a 6% increase in airflow over the current LM2500+ model. Other changes include and redesigned IGV and re-staggered stage 0 blisk airfoils; increased high pressure compressor life design; and redesigned stage 2 high pressure turbine rotor for increased life.
Conclusion
The LM2500 has transformed the world's industrial power generation and marine propulsion markets. GE continues to enhance and update LM2500 gas turbine technology, keeping it state-of-the-art so that it remains the ideal choice for future marine programs.