GT 103
Much of the poor fuel economy of the gas turbine in the traction role was due to the hot exhaust, which essentially represented lost energy. In order to reclaim some of this energy, it is possible to use the hot exhaust to pre-heat the air from the compressor before it flows into the combustion chamber, using a heat exchanger. Although not common, these recuperators are used in a number of applications today.
W. Hryniszak of Asea Brown Boveri in Heidelberg designed a recuperator that was added to the otherwise unmodified GT 102 design to produce the GT 103. The heat exchanger used a rotating porous ceramic cylinder fit into a cruciform duct. Air from the gas generator's exhaust entered the duct outside the cylinder at 500 Celsius and blew around the cylinder, heating it and then exhausting at about 350 C. The ceramic cylinder rotated slowly in order to avoid overheating the "hot" side. Compressed air flowing into the power turbine was piped through the middle of the cylinder, entering at about 180 C and exiting at about 300 C.
This meant that 120 C of the 800 C final temperature of the air did not have to be provided by the fuel, representing a fairly substantial savings. Estimates suggested an improvement of about 30% in fuel consumption. It was also suggested that a second heat exchanger could be used on the gas generator engine core, saving another 30%. This reduced fuel use by half overall, making it similar to the original gasoline engine. These estimates appear unreasonable in retrospect, although General Motors did experiment with these systems throughout the 1960s and 70s.
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