LM2500 and LM2500

Derived from the GE military TF39 and commercial turbofan aircraft engines, the LM2500 marine gas turbine is a simple-cycle, two-shaft engine comprising a gas generator, a power turbine, attached fuel and lube oil pumps, a fuel control and speed-governing system, associated inlet and exhaust sections, lube and scavenge systems, and controls and devices for starting and monitoring engine operation. The four main elements (Figure 31.14) are:

• A 16-stage compressor, with an 18:1 pressure ratio; the first seven stages feature variable stators and inlet guide vanes promoting easy starting, good part-load performance, high efficiency and a high stall margin over the entire operating range.

• Fully annular combustor, with externally mounted fuel nozzles supporting liquid fuel combustion; virtually smokeless operation is assured through the complete power range even when burning heavy distillate fuels.

• Two-stage high pressure turbine, air cooled for a long life, which drives the compressor and accessory-drive gearbox.

Figure 31.14 Cutaway of GE Marine Engines' LM2500 aero-derived gas turbine showing (from left to right) the compressor, annular combustor, high pressure turbine and low pressure power turbine

Figure 31.14 Cutaway of GE Marine Engines' LM2500 aero-derived gas turbine showing (from left to right) the compressor, annular combustor, high pressure turbine and low pressure power turbine

• Six-stage low pressure power turbine; a low speed, low stress machine aerodynamically coupled to the gas generator and driven by its high energy release exhaust flow.

Lower installed and life-cycle costs per unit kW were sought from the LM2500+ derivative released in the late 1990s with a 25 per cent higher power rating than its precursor. An introductory rating of 27 600 kW was achieved with a thermal efficiency of more than 37 per cent; release at the design rating of 29 000 kW and a thermal efficiency of 38 per cent followed early sets in service demonstrating the traditional reliability and availability of the LM2500. The current rating is 30 200 kW with a thermal efficiency of 39 per cent. The design refinements applied to the LM2500+ focused on:

— The compressor rotor: air flow was increased by approximately 20 per cent; Stage 1 blades were redesigned to a wide chord configuration eliminating the mid-span dampers; an LM6000 rotor airfoil design was added to Stages 2 and 3; LM6000 stages were incorporated to improve compressor efficiency; and a new inlet guide vane assembly was specified.

— High pressure turbine rotor and stator: redesigned to reduce maintenance costs and new materials exploited for improved oxidation life; Stage 1 and 2 contours optimized for higher flows.

— Power turbine: redesigned in line with the higher output; Stage 1 and 6 blades optimized for aerodynamic efficiency; and the rotor strengthened for the higher torque and potential energy.

No changes were made to either the standard or dry low emissions (DLE) combustion system.

Only slightly longer and heavier than the LM2500, the LM2500+ offers dual-fuel capability (distillate and gas), rapid start-up and loading, variable speed operation and excellent part-load efficiency, GE claims.

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