BMW GT 101
A gas turbine would be much lighter than the 600 hp-plus class, gasoline-fueled reciprocating piston engines being used in the next-generation tanks, to that time primarily sourced from the Maybach firm for the Wehrmacht Heer's existing armored fighting vehicle designs, that it would considerably improve their power-to-weight ratio and thereby improve cross-country performance, and potentially outright speed.
On the upside, the use of inexpensive and widely available kerosene as fuel offset this disadvantage at least to some degree, so the overall economics of running the engines might end up being similar.
In order to use a turbine in the tank role, the design would need to use an advanced transmission and clutch that allowed the engine to run at a limited range of speeds, or alternately use some other method to extract power.
This design had a serious problem, however; when the load was removed, during gear shifts for instance, the power turbine was unloaded and could race out of control.
They were particularly interested in having the fuel injectors rotate along with the engine core, which could be expected to lead to much better mixing, with the additional benefit of reducing hot spots on the turbine's stators.
The best solution to the problem would have been to drive an electrical generator and use the power to drive motors for traction (a system Porsche had tried to introduce several times), but a serious shortage of copper by this point in the war — as well as its relatively poor quality throughout the war for electrical use, from copper ore resources that Germany could access — ruled out this solution.
Müller presented the new design on 14 September, and the Heereswaffenamt proved considerably more interested – the deteriorating fuel supply situation at this point may have been a factor as well.
Attention then turned to the Panther, which by this point in the war was to be the basis of all future tank production anyway (see the Entwicklung series for details).
The entire exhaust area extended out of the rear of the engine compartment into "free air", which made it extremely vulnerable to enemy fire, and it was realized this was not practical for a production system.
A new automatic transmission from Zahnradfabrik of Friedrichshafen (ZF) was built for the fitting, it had three clutching levels in the torque converter and twelve speeds.
While work on the GT 101 continued, Müller proposed another way to build the free-turbine engine that avoided the problems with his original designs.
Compressed air from the core's compressor, 30% of the overall airflow, was bled off through a pipe to a completely separate two-stage turbine with its own combustion chamber.
This avoided the overspeed problems of the original design; when load was removed, simply shutting off the airflow to the turbine would slow it down.
The only downside to the design was that the power turbine no longer had the huge spinning mass of the GT 101, and thus did not offer any significant flywheel energy storage.
2 design modified several sections of the original gas generator layout to shorten the compressor area and combustion chamber.
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.
