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Recuperated intercooled gas turbine cycles offer efficiencies in the 40% and higher range at medium to high loads. Although these cycles offer better low-load efficiency than other gas turbine cycles, the idle and low-load fuel consumption are still not good enough for satisfactory vehicle operation. In addition, response time to sudden demands for power is slow. The multi-pressure gas turbine allows the combustion air to enter the cycle at a different point, reducing the mass flow and the rating of the gas turbine for efficient operation at low power. Yet, the full power of the gas turbine is available quickly for acceleration or hill climbing.

Microturbines are being successfully used in production hybrid electric buses. They are economically sound while demonstrating long life with dramatically reduced maintenance and emissions. However, to reach high production in a broad range of vehicles, certain improvements will be needed. These include lower first cost, much faster response time and higher efficiency into the 40% range at both full load and part load. This paper addresses these challenges and their solutions while using technology that mostly exists.

A 24 kW, 30% efficient gas turbine-driven generator set is being developed for hybrid electric vehicles. With the generator mounted on the same shaft as the compressor and the turbine, the rotor group is the only moving part other than the fuel pump. There are no engine-driven accessories. There is no oil as the rotor is mounted on air bearings. There is no water or antifreeze as the generator set is air cooled. Orientation can be vertical or horizontal. Emission levels on unleaded gasoline, methanol, M85, ethanol or natural gas are much less than ULEV standards using a lean premix combustor. They are one or two orders of magnitude less than ULEV standards using a catalytic combustor. This paper addresses some of the design and application factors considered in developing the hardware.

A 24 kW generator set driven by a gas turbine is being developed for hybrid electric vehicles. The gas turbine uses a catalytic combustor to reduce emissions to substantially less than ULEV standards. The turbine has no gear box no lubrication system and no engine-driven accessories. The manufacturing cost is relatively low. The result is an affordable, compact, light weight power package with low emissions that can extend the range of electric vehicles to equal or exceed those of conventional cars, trucks and buses.

A gas turbine-driven generator set is being developed as a range extender for a major automobile manufacturer's hybrid electric vehicle. The 24 kW continuous rating is sufficient to propel the automobile at maximum legal speed in the United States. For hill climbing and passing, 30 kW is available. A circumferential recuperator increases efficiency to 30% on unleaded gasoline. There is no gearbox since the permanent magnet generator is mounted on the gas turbine shaft. There is no lubrication system as the rotor group shaft runs on air bearings. The complete generator set with recuperator weighs 36 kg (80 lb). The OEM price will be under $1,000 in automotive quantities. Production units will have catalytic combustion to reduce emissions to less than those of an electric utility power plant. California regulatory authorities have indicated that this could permit a hybrid vehicle to be classed as “zero emission”.