GT 101
Encyclopedia
The German Army
's development division, the Heereswaffenamt (Army Ordnance Board), studied a number of gas turbine
engines for use in tank
s starting in mid-1944. Although none of these were fitted operationally, the GT 101 (GT for "Gas Turbine") reached a production quality stage of development and was considered for installation in the Panther tank
. Several designs were produced over the lifetime of the program, including the GT 102 and GT 103.
divisions, proposed the use of a gas turbine for armored vehicle engines. A gas turbine was so much lighter than the 600 hp-class engines being used in the next-generation tanks that it would considerably improve their power-to-weight ratio
and thereby improve cross-country performance, and potentially outright speed. There were problems with the gas turbine in this role, however.
In the case of a jet engine the hot exhaust from the turbine is used directly for thrust, but in the case of a traction engine any heat flowing out the exhaust was essentially wasted power. The turbine exhaust was much hotter than that from a gas engine, and turbine engines would thus have terrible gas mileage compared to traditional designs. On the upside, the use of inexpensive and widely available kerosene
offset this disadvantage at least to some degree, the overall economics of running the engines might end up being similar. Given the extreme problems the Germans had with fuel supplies late in the war, use of low-grade fuels, no matter how much of it, was actually seen as a major advantage, and the primary reason the Heereswaffenamt eventually became interested in the design.
Another problem was that the gas turbine engine only works well near a particular design operating speed, although at (or near) that speed it can provide a wide variety of output torque
. More specifically, turbines offer very little torque at low operating speeds, which is much less an issue with a traditional piston engine. In order to use a turbine in this role, the design would need to use an advanced transmission and clutch that allowed the engine to run at a more limited range of speeds, or alternately use some other method to extract power.
At first the Army was uninterested, and Müller turned to the design of an advanced turbosupercharger for BMW
(it is unclear if this design saw use). When this work was completed in January 1944 he once again turned to the traction engine designs, and eventually met with the Heereswaffenamt in June 1944 to present a number of proposed designs for a 1,000 hp unit.
Another problem was that the Heereswaffenamt was seriously concerned about the quality of the fuels they could find. Unlike the aviation role where it was expected the fuel would be highly refined, it was considered likely the Army would end up with lower quality fuels that could expected to contain all sorts of heavy contaminants. This led to the possibility that the fuel would not have time to mix properly in a traditional design, leading to poor combustion. 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 stator
s. Unfortunately Müller's design did not appear to be able to be adapted to use these injectors, and the design was eventually rejected on 12 August.
had tried to introduce several times), but a serious shortage of copper
by this point in the war ruled out this solution. Instead some sort of hydraulic transmission was to be used, although not initially specified. Additionally, the new design included the rotating fuel injectors in the combustion chamber
that the Heereswaffenamt was interested in. 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.
Oddly, they then suggested that any engine core developed for this role should also be suitable for aviation use, which led to the abandonment of the rotating injectors after all, and eventually to the use of a modified BMW 003 core. The basic layout had to be modified with the addition of a third bearing near the middle of the engine to help absorb shock loads, and a third turbine stage was added to the end of the engine to take off more power. Unlike the earlier design, the power-take off could be placed anywhere (not just off the free turbine stage) and was in fact moved to the front of the engine in order to make the design as compatible as possible with existing engine compartments. The basic design was completed in mid-November, and assigned the name GT 101.
Originally they had intended to mount the new engine in the Tiger tank
, but although the engine was smaller than the engine it replaced, it was too long to fit in the Tiger's engine bay. 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). For experimental fitting, Porsche provided one of the prototype Jagdtiger
hulls.
Fitting of the GT 101 in the Panther hull took some design effort, but eventually a suitable arrangement was found. The engine exhaust was fitted with a large divergent diffuser to lower the exhaust velocity and temperature, which also allowed for a larger third turbine stage. 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. The transmission also included an electrical clutch that cut off the engine completely at 5,000 rpm, below which the engine produced no torque on the output. At full speed, 14,000 rpm, the engine itself also acted a huge flywheel, which greatly improved cross-country performance by allowing some of the engine's speed to be dumped into the transmission to pull the tank over bumps.
In terms of performance the GT 101 would have been surprising effective. It would have produced a total of 3,750 hp, using 2,600 hp to operate the compressor and thus leaving 1,150 hp to power the transmission. The entire engine assembly weighted 450 kg (922 lb), not including the transmission. In comparison, the existing Maybach HL230 P30
it replaced provided 620 hp yet weighted a comparatively huge 1,200 kg. With the Maybach the Panther had a specific power of about 13.5 hp/ton, with the GT 101 this would improve to 27 hp/ton, outperforming any tank of WWII by a wide margin (for instance, the T-34
was 16.2 hp/tonne). For other reasons, essentially wear and tear, speeds would be deliberately limited to those of the gasoline-powered Panthers. The only downsides were poor torque at low power settings, and a fuel consumption about double that of the Maybach, which presented problems in finding enough room for fuel tankage.
The basic idea of the GT 102 was to completely separate the power turbine from the engine itself, using the later as a gas generator
. The core engine was run hot enough to power itself and nothing more, no power was taken from the core to drive the tank. 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. This also meant that the core could be run at full speed while the power turbine ran at low speed, providing significantly improved low-speed torque. 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.
Since the turbine section of the core engine was no longer being fed all of the air from the compressor, it could be built smaller than in the GT 101. This made the engine shorter overall, allowing it to be installed transversely in the upper portion of the Panther's engine compartment, in the wider area above the tracks. The power turbine was then fit into the empty space below, mounted at a right angle to the engine. This positioned it in-line with the normal transmission, which was located at the front of the vehicle, driving it via a power shaft. The mounting was considerably more practical than the GT 101, and entirely "under armor" as well. Although the GT 102 had fuel economy about equal to the GT 101, the mounting left considerably more empty room within the engine compartment in the space formerly used by the engine cooling system that could be used for new fuel cells, doubling the overall fuel capacity to 1,400 liters and thus providing equal range to the original gasoline engine.
Most of the design work for the GT 102 was compete by early 1945, and the plans were to have been delivered on 15 February (along with final designs for the GT 101). It appears the plans were not delivered, likely due to the deteriorating war condition.
by operating the first stage close to Mach 1
. With these reductions in length the engine could be fit lengthwise in the engine compartment, allowing the space above the tracks to be used for fuel storage, as they had originally.
. Although not common, these recuperator
s 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.
German Army
The German Army is the land component of the armed forces of the Federal Republic of Germany. Following the disbanding of the Wehrmacht after World War II, it was re-established in 1955 as the Bundesheer, part of the newly formed West German Bundeswehr along with the Navy and the Air Force...
's development division, the Heereswaffenamt (Army Ordnance Board), studied a number of gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....
engines for use in tank
Tank
A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...
s starting in mid-1944. Although none of these were fitted operationally, the GT 101 (GT for "Gas Turbine") reached a production quality stage of development and was considered for installation in the Panther tank
Panther tank
Panther is the common name of a medium tank fielded by Nazi Germany in World War II that served from mid-1943 to the end of the European war in 1945. It was intended as a counter to the T-34, and to replace the Panzer III and Panzer IV; while never replacing the latter, it served alongside it as...
. Several designs were produced over the lifetime of the program, including the GT 102 and GT 103.
Origins
As early as mid-1943 Adolf Müller, formerly of Junkers and then Heinkel-Hirth's jet engineJet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
divisions, proposed the use of a gas turbine for armored vehicle engines. A gas turbine was so much lighter than the 600 hp-class engines being used in the next-generation tanks that it would considerably improve their power-to-weight ratio
Power-to-weight ratio
Power-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources...
and thereby improve cross-country performance, and potentially outright speed. There were problems with the gas turbine in this role, however.
In the case of a jet engine the hot exhaust from the turbine is used directly for thrust, but in the case of a traction engine any heat flowing out the exhaust was essentially wasted power. The turbine exhaust was much hotter than that from a gas engine, and turbine engines would thus have terrible gas mileage compared to traditional designs. On the upside, the use of inexpensive and widely available kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...
offset this disadvantage at least to some degree, the overall economics of running the engines might end up being similar. Given the extreme problems the Germans had with fuel supplies late in the war, use of low-grade fuels, no matter how much of it, was actually seen as a major advantage, and the primary reason the Heereswaffenamt eventually became interested in the design.
Another problem was that the gas turbine engine only works well near a particular design operating speed, although at (or near) that speed it can provide a wide variety of output torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
. More specifically, turbines offer very little torque at low operating speeds, which is much less an issue with a traditional piston engine. In order to use a turbine in this role, the design would need to use an advanced transmission and clutch that allowed the engine to run at a more limited range of speeds, or alternately use some other method to extract power.
At first the Army was uninterested, and Müller turned to the design of an advanced turbosupercharger for BMW
BMW
Bayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...
(it is unclear if this design saw use). When this work was completed in January 1944 he once again turned to the traction engine designs, and eventually met with the Heereswaffenamt in June 1944 to present a number of proposed designs for a 1,000 hp unit.
Preliminary design
Müller's first detailed design was a simple modification to a traditional jet engine, the core engine being based on the Heinkel HeS 011. In this design a separate turbine and power take-off shaft was bolted onto the exhaust of the engine core, the hot gases of the engine powering the turbine, and thus the tank. Since the engine core was entirely separate from the power take-off, torque was available immediately because the core could be left running at full speed while generating small amounts of power, the gases being "dumped". 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. Either the power turbine had to be braked during these periods, or the gas from the engine core had to be dumped.Another problem was that the Heereswaffenamt was seriously concerned about the quality of the fuels they could find. Unlike the aviation role where it was expected the fuel would be highly refined, it was considered likely the Army would end up with lower quality fuels that could expected to contain all sorts of heavy contaminants. This led to the possibility that the fuel would not have time to mix properly in a traditional design, leading to poor combustion. 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 stator
Stator
The stator is the stationary part of a rotor system, found in an electric generator, electric motor and biological rotors.Depending on the configuration of a spinning electromotive device the stator may act as the field magnet, interacting with the armature to create motion, or it may act as the...
s. Unfortunately Müller's design did not appear to be able to be adapted to use these injectors, and the design was eventually rejected on 12 August.
GT 101
Müller then turned to designs that removed the separate power turbine and instead required some sort of torque-maintaining transmission. 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 PorschePorsche
Porsche Automobil Holding SE, usually shortened to Porsche SE a Societas Europaea or European Public Company, is a German based holding company with investments in the automotive industry....
had tried to introduce several times), but a serious shortage of copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
by this point in the war ruled out this solution. Instead some sort of hydraulic transmission was to be used, although not initially specified. Additionally, the new design included the rotating fuel injectors in the combustion chamber
Combustion chamber
A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...
that the Heereswaffenamt was interested in. 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.
Oddly, they then suggested that any engine core developed for this role should also be suitable for aviation use, which led to the abandonment of the rotating injectors after all, and eventually to the use of a modified BMW 003 core. The basic layout had to be modified with the addition of a third bearing near the middle of the engine to help absorb shock loads, and a third turbine stage was added to the end of the engine to take off more power. Unlike the earlier design, the power-take off could be placed anywhere (not just off the free turbine stage) and was in fact moved to the front of the engine in order to make the design as compatible as possible with existing engine compartments. The basic design was completed in mid-November, and assigned the name GT 101.
Originally they had intended to mount the new engine in the Tiger tank
Tiger I
Tiger I is the common name of a German heavy tank developed in 1942 and used in World War II. The final official German designation was Panzerkampfwagen Tiger Ausf. E, often shortened to Tiger. It was an answer to the unexpectedly formidable Soviet armour encountered in the initial months of...
, but although the engine was smaller than the engine it replaced, it was too long to fit in the Tiger's engine bay. 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
Entwicklung series
The Entwicklung series, more commonly known as the E- series, was a late-World War II attempt by Germany to produce a standardised series of tank designs. There were to be standard designs in six different weight classes, from which several specialised variants were to be developed...
for details). For experimental fitting, Porsche provided one of the prototype Jagdtiger
Jagdtiger
Jagdtiger is the common name of a German tank destroyer of World War II. The official German designation was Panzerjäger Tiger Ausf. B. The ordnance inventory designation was Sd. Kfz. 186. It saw service in small numbers from late 1944 to the end of the war on both the Western and Eastern Front...
hulls.
Fitting of the GT 101 in the Panther hull took some design effort, but eventually a suitable arrangement was found. The engine exhaust was fitted with a large divergent diffuser to lower the exhaust velocity and temperature, which also allowed for a larger third turbine stage. 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
Automatic transmission
An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...
from Zahnradfabrik of Friedrichshafen (ZF) was built for the fitting, it had three clutching levels in the torque converter
Torque converter
In modern usage, a torque converter is generally a type of hydrodynamic fluid coupling that is used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load...
and twelve speeds. The transmission also included an electrical clutch that cut off the engine completely at 5,000 rpm, below which the engine produced no torque on the output. At full speed, 14,000 rpm, the engine itself also acted a huge flywheel, which greatly improved cross-country performance by allowing some of the engine's speed to be dumped into the transmission to pull the tank over bumps.
In terms of performance the GT 101 would have been surprising effective. It would have produced a total of 3,750 hp, using 2,600 hp to operate the compressor and thus leaving 1,150 hp to power the transmission. The entire engine assembly weighted 450 kg (922 lb), not including the transmission. In comparison, the existing Maybach HL230 P30
Maybach HL230
The Maybach HL230 is a water-cooled 60° 23 liter V12 gasoline engine designed by Maybach. It was used during World War II in heavy German tanks, namely the Panther, Jagdpanther, Tiger II, Jagdtiger , and later versions of the Tiger I and Sturmtiger...
it replaced provided 620 hp yet weighted a comparatively huge 1,200 kg. With the Maybach the Panther had a specific power of about 13.5 hp/ton, with the GT 101 this would improve to 27 hp/ton, outperforming any tank of WWII by a wide margin (for instance, the T-34
T-34
The T-34 was a Soviet medium tank produced from 1940 to 1958. Although its armour and armament were surpassed by later tanks of the era, it has been often credited as the most effective, efficient and influential design of World War II...
was 16.2 hp/tonne). For other reasons, essentially wear and tear, speeds would be deliberately limited to those of the gasoline-powered Panthers. The only downsides were poor torque at low power settings, and a fuel consumption about double that of the Maybach, which presented problems in finding enough room for fuel tankage.
GT 102
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. In December 1944 he presented his plans, which were accepted for development as the GT 102.The basic idea of the GT 102 was to completely separate the power turbine from the engine itself, using the later as a gas generator
Gas generator
A gas generator usually refers to a device, often similar to a solid rocket or a liquid rocket that burns to produce large volumes of relatively cool gas, instead of maximizing the temperature and specific impulse. The low temperature allows the gas to be put to use more easily in many...
. The core engine was run hot enough to power itself and nothing more, no power was taken from the core to drive the tank. 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. This also meant that the core could be run at full speed while the power turbine ran at low speed, providing significantly improved low-speed torque. 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
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...
energy storage.
Since the turbine section of the core engine was no longer being fed all of the air from the compressor, it could be built smaller than in the GT 101. This made the engine shorter overall, allowing it to be installed transversely in the upper portion of the Panther's engine compartment, in the wider area above the tracks. The power turbine was then fit into the empty space below, mounted at a right angle to the engine. This positioned it in-line with the normal transmission, which was located at the front of the vehicle, driving it via a power shaft. The mounting was considerably more practical than the GT 101, and entirely "under armor" as well. Although the GT 102 had fuel economy about equal to the GT 101, the mounting left considerably more empty room within the engine compartment in the space formerly used by the engine cooling system that could be used for new fuel cells, doubling the overall fuel capacity to 1,400 liters and thus providing equal range to the original gasoline engine.
Most of the design work for the GT 102 was compete by early 1945, and the plans were to have been delivered on 15 February (along with final designs for the GT 101). It appears the plans were not delivered, likely due to the deteriorating war condition.
GT 102 Ausf. 2
In order to further improve the fit of the GT 102 in the Panther, the GT 102 Ausf. 2 design modified several sections of the original gas generator layout to shorten the compressor area and combustion chamber. These were somewhat longer in the GT 102 than they would have been in a comparable aircraft engine in order to allow for better mixing with lower quality fuels. The Ausf. 2 returned these to their original dimensions, and instead re-introduced the rotating fuel injectors from the original pre-GT 101 designs. The compressor was further reduced in length by reducing it from nine to seven stages, but retained the original compression ratioCompression ratio
The 'compression ratio' of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity...
by operating the first stage close to Mach 1
Mach 1
Mach 1 can refer to:* The speed of sound* M.A.C.H. 1, a comic strip* Mach 1, a novel by Allen Adler* Mach 1 Racing, a former NASCAR team...
. With these reductions in length the engine could be fit lengthwise in the engine compartment, allowing the space above the tracks to be used for fuel storage, as they had originally.
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 exchangerHeat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
. Although not common, these recuperator
Recuperator
A recuperator is a special purpose counter-flow energy recovery heat exchanger positioned within the supply and exhaust air streams of an air handling system, or in the exhaust gases of an industrial process, in order to recover the waste heat...
s are used in a number of applications today.
W. Hryniszak of Asea Brown Boveri
Asea Brown Boveri
ABB is a Swiss-Swedish multinational corporation headquartered in Zürich, Switzerland, and best known for its robotics. ABB operates mainly in the power and automation technology areas. It ranked 143rd in Forbes Ranking ....
in Heidelberg
Heidelberg
-Early history:Between 600,000 and 200,000 years ago, "Heidelberg Man" died at nearby Mauer. His jaw bone was discovered in 1907; with scientific dating, his remains were determined to be the earliest evidence of human life in Europe. In the 5th century BC, a Celtic fortress of refuge and place of...
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
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
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
General Motors
General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
did experiment with these systems throughout the 1960s and 70s.