WI: Steam turbine development not cancelled

[wuzak]

In 1940 Junkers Moteren (Jumo) began the development of a steam turbine for use in multi-engine aircraft. The steam turbine ran on the bench in mid 1941 before being cancelled by the RLM in 1942 in favour of gas turbines.

There was interest from Messerschmitt in installing the steam turbine in the Me321 transport glider.

The specs for the Jumo steam turbine was 3000hp @ 8000rpm, prop shaft speed 950rpm, pressure 100atm, exhaust pressure 0.15atm. Weight 800kg, I assume just for the turbine and reduction gear.

Also in the same period the Technische Hochschule were developing a 4000hp steam turbine for aircraft use, but this too was cancelled in 1942.

In 1944 the Osermaschinen company was commissioned to develop a steam turbine for use with the Me264 long range bomber. The design requirements specified 6000hp @ 6000rpm for the turbine, a power to weight ratio for the entire installation of 0.7kg/hp and a sfc of 190g/hp/hr (0.42lb/hp/hr). There was to be two propellor options - a 5.3m (17ft 4.5in) diameter prop turning at around 500rpm, or a 2m (6ft 6in) diameter prop turning at 6000rpm.

The plan was to use 65% pulverised coal/35% liquid fuel while liquid fuel stocks were low, but to use 100% liquid fuel when sufficient quantities were available.

Parts of the turbine had been manufactured by the end of the war in Europe, but it had not run and the Me264 prototype that was to use it had been destroyed.

The advantages of steam turbines were:
Time between overhauls as much as 10 times that for piston engine (ie 4000-6000 hours tbo).
Constant power at varying heights.
Capacity for 100% overloading for extended periods (ie on a 3000hp engine you can go to 6000hp WEP, or on a 6000hp engine you could go to 12,000hp).
Full steam output in 5-10s (I presume from startup)
Not sensitive to low temperatures.
Simple control.
Poor quality fuels could be used

In comparison to the new gas turbines being developed the steam turbine promised to be much more fuel efficient.

On the downside, I don't think high pressure boilers would take too well to being hit by cannon shells, or even mg shells.

If the Junkers and the Technische Hochschule projects were not cancelled it may have been possible that they would have been available during 1943/1944.

With so many German designs perhaps not having the power required, and fuel shortages cutting into operations could steam turbines have provided a useful interim step between piston power and gas turbines?

Bearing in mind that gas turbines were relatively new, while steam turbines had been around in industry and shipping for the best part of half a century.

 

[wuzak]

Also, I believe that the rated power (ie 3000hp for the Jumo project) was also the maximum continuous power.

 

[davebender]

I wouldn't worry about resistance to enemy fire. A steel boiler is more bullet proof then an aluminum wing or fuselage.

Has anyone gotten such a power plant to work in an aircraft? That would tell us if the concept is technically practical.

 

[wuzak]

There was a steam powered aircraft in the 1930s, but that was a V2 piston engine.

The steam turbine would be closed loop so wouldn't need much extra water storage, whereas a steam pistin engine would need more make up water I would think (more leakage/loss).

Thinking about the boiler locations, for the Junkers project each turbine would have its own boiler and auxiliary systems mounted together in the wing.

For the later 6000hp Osermaschinen turbine there were to be four 1m diameter x 1.2m long/high boilers per turbine. One advantage that was mentioned was the ability to have components distributed throughout the airframe.

For the Me264 I would assume that only two of the 6000hp turbines would be required (V1 had 4 x 1200hp Jumo 211s - a total of 4800hp, and V2 had 4 x 1700hp BMW 801s - a total of 6800hp) - certainly the turboprop versions proposed had two 5000hp engines. That would mean locating 8 of the boiler units around the airframe.

I suppose two of the Junkers steam turbines at 3000hp each could do the job in an Me264 too, using the 100% overload capability to provide takeoff power and war emergency power. Even better if the alternative 4000hp units were available.

 

[fastmongrel]

The problem I can see is not the turbines or the boilers but the fact you are supplying very high pressure steam to the turbine. Also you need to run the used steam through a condenser to turn it back into feedwater the condenser also creates a vacuum to make the turbine work properly. So you have lots of piping carrying steam at 100 atm (1400 psi) and who knows what temperature possibly in 4 figures in a plane that shakes, rattles, twists and is prone to having holes suddenly appear in it. Also the condensers are very vulnerable they will have to be in the airflow like a radiator any leaks and you lose vacuum and your in trouble.

Everything will be incredibly hot and when I say hot I mean aluminium melting hot any leaks in the steam lines would cut through an aluminium wing like a gas cutting torch.

None of these problems would be insurmountable but remember this is late war Germany not well known for its quality control. A leaking oil line is a problem for a plane a bad joint in a 100 atm boiler and the boiler wouldn't just blow up the plane would go with it if you dont believe me google boiler explosions.

 

[wuzak]

The Junkers turbine was to run at 550°C.

Condensers could potentially be out of the airflow, using a radiator to transfer heat.

I have a diagram of the Junkers system, from Dieter Herwig and Heiz Rode, Luftwaffe Secret Projects, Ground Attack and Special Purpose Aircraft. The component labelling is in German. I will scan the pic and post it tomorrow.

 

[fastmongrel]

The Junkers turbine was to run at 550°C.

That temperature seems very low for a 100 atm system. Unless the boilers werent using superheaters which would seem to me to be very dangerous any water carry over is going to be fatal in the HP stage of the turbine.

 

[wuzak]

550°C is up there for temperature in a steam turbine.

Here is some data for steam at the specified temperature and pressure

Steam Pressure                                         100  atm
Steam Temperature                                      550  °C
Saturation Temperature                                 312  °C
Degrees Superheat                                      238  °C
Specific Enthalpy of Water (hf)                    1413020  J/Kg
Specific Enthalpy of Evaporation (hfg)             1309080  J/Kg
Specific Enthalpy of Superheated Steam (h)         3499570  J/Kg
Density of Steam                                   28.4626  kg/m³
Specific Volume of Steam (v)                     0.0351338  m³/kg
Specific Entropy of Water (sf)                     3368.61  J/kg.K
Specific Entropy of Evaporation (sfg)              2237.17  J/kg.K
Specific Entropy of Superheated Steam (s)          6748.84  J/kg.K
Specific Heat of Steam (cv)                         1833.7  J/kg.K
Specific Heat of Steam (cp)                        2505.54  J/kg.K
Speed of sound                                     674.232  m/s
Dynamic Viscosity of Steam                    0.0000310333  Pa.s
Isentropic Coefficient (k)                         1.27931
Compressibility Factor of Steam                   0.937066

Calculated using Superheated Steam Region - Steam Table : International site for Spirax Sarco

As you can see there is 238°C of superheat in the steam.

 

[tyrodtom]

You only have to look at some WW2 strafing films to see how vunerable boilers are to even .50 cal fire.

About 10 years later when the USA was researching nuclear powered aircraft, steam turbines would have been the power source in that case. They even had a B-36 with a reactor, but conventional power. But they couldn't get the weight of the reactor, and it's necessary shielding down enough.

 

[Siegfried]

If you were to ask an engineer how big a 100hp steam turbine would be he would tell you it would be about the size of an rugby or gridion football.
If you asked about the boiler the answer would be about the same size (eg a tube boiler.)
If you asked how big the condensor would be then you would have asked the key question: it would by far be the largest part.

The energy in the combustion gas of an piston or jet engine that could not be expanded further is simply dumped into the atmosphere. However the unutilised energy of the steam engine must be transfered via highly stressed condensor wall to the air. The radiator of an piston engine only gets rid of heat that was removed fom vital parts to keep them cool and strong ie about 30%.

The way around this is to increase the efficiency of the engine which can be done via opperating at as high a temperature as possible, this increases efficiency (See Carnot cycle) and means the radiator can be smaller as there is less heat to dispose of and what there is to dispose is quite hot and will conduct easily. Opperating at high temperatures (and 550C is very high) means special materials that don't corrode and suffer from hydrogen embrittlement. I believe 550C is supercritical?

They key is also where are the radiators/condensors going on this aircraft? Will evaporative skin cooling be used?

The advantage of this engine is that it can burn indifferent fuels, perhaps even granulated coke. The Bergius Hydrogenation syn fuel plants were big and efficient but hideously expensive to built due to the 700 atmospheres pressures.

The more capital affordable and much smaller (and disquisable) Fischer-Tropsch plants produced diesel, kerosene, waxes, lubricants and a mass of unususalbe or very low grade gasoline (about 30%) and were less efficient.

Having said that jet fuel was much easier to synthesise than even petrol or diesel and I tend to think that the jet engine solves a few problems for the German fuel situation anyway.

Conceivably this engine could work of granulated coal or the crap fuel from the syn fuel plants.

Saab-Valmet developed and series-produced the Saab 99 Petro car that ran on kerosene, turpentine or gasoline because during the 1970s fischer-tropsch still made a lot of kerosene. This is the Spark Ignition Hesselman engine. Today MTG (Methanol to Gasoline) is used to make petrol from coal or natural gas and Fischer-Tropsch is used only for diesel and kersosen (which is now extremely efficient). Topwards the end of the war the German FT plants were begining to produce low grade 77 octane Army gasoline.

 

[davebender]

German synthetic fuel plants provided all the high octane aviation gasoline. Lower octane fuel for German trucks, jet engines etc. was produced from petroleum at conventional oil refineries.

Your "crap fuel" is more likely to be produced in Ploesti or Galicia.

 

[wuzak]

You only have to look at some WW2 strafing films to see how vunerable boilers are to even .50 cal fire.

I would assume that the boilers for combat aircraft would have more protective armour than locomotives did.

About 10 years later when the USA was researching nuclear powered aircraft, steam turbines would have been the power source in that case. They even had a B-36 with a reactor, but conventional power. But they couldn't get the weight of the reactor, and it's necessary shielding down enough.

The nuclear powered aircraft was to use jet propulsion.

A turbojet was modified for this use - the compressor and turbine remained, but the combustion chambers were raplced by heat exchangers. The air would be compressed bythe compressor, then heat from the reactor transferred to the air in the heat exchangers, and the air would then expand through the turbine, which would drive the compressor, and exit out the back to create thrust.

The XB-36H carried an operating 1MW nuclear reactor. The B-36 was powered by 6 2.8MW R-4360s, yet was thought to be underpowered. A 1 MW reactor wasn't going to power the plane. What it did show is the viability of such an installation, and how th eradiation affected systems etc. IIRC the crew compartment was fully shielded, but the reactor was not.

 

[wuzak]

If you were to ask an engineer how big a 100hp steam turbine would be he would tell you it would be about the size of an rugby or gridion football.
If you asked about the boiler the answer would be about the same size (eg a tube boiler.)
If you asked how big the condensor would be then you would have asked the key question: it would by far be the largest part.

The energy in the combustion gas of an piston or jet engine that could not be expanded further is simply dumped into the atmosphere. However the unutilised energy of the steam engine must be transfered via highly stressed condensor wall to the air. The radiator of an piston engine only gets rid of heat that was removed fom vital parts to keep them cool and strong ie about 30%.

The way around this is to increase the efficiency of the engine which can be done via opperating at as high a temperature as possible, this increases efficiency (See Carnot cycle) and means the radiator can be smaller as there is less heat to dispose of and what there is to dispose is quite hot and will conduct easily. Opperating at high temperatures (and 550C is very high) means special materials that don't corrode and suffer from hydrogen embrittlement. I believe 550C is supercritical?

The exhaust steam exits the turbine at somewhat less than 550C - probably around 100C. I have a freebie steam turbine program which says that with 60% efficiency the exhaust temperature will be 71.2°C at 0.15 bar absolute, starting with inlet conditions of 500C and 100 bar (program limitations). The exhaust is still in superheat - about 17°C. This is because the steam exhausts into a partial vacuum.

The condenser's job is not to bring the water temp back down to ambient, but to convert it from steam to water.

They key is also where are the radiators/condensors going on this aircraft? Will evaporative skin cooling be used?

I doubt evaporative skin cooling would be used.

 

[barney]

The condenser's job is not to bring the water temp back down to ambient, but to convert it from steam to water.

Well, yes and no. To obtain proper vacuum the boiler water can't remain hot.

 

[Shortround6]

The 1st main question is the boilers. While many steam plants can produce tremendous amounts of "over load" power, they can only do it as long as the steam lasts. A bit like taking a hot shower with a small water heater. If you try to use hot water some where else( extra capacity) you run out pretty quick. Some steam plants (like locomotives) had a reserve of steam available in their fire tube boilers (water tank with flues from fire box going though it, holds a lot of water), some steam plants used water tube boilers (water is in the tubes surrounded by the fire/hot gases). Some small units (like Stanley Steamer autos) held only a quart or two of water in hundreds of feet of small tubing. The depended on the fire being able to generate steam as needed without much reserve. Much like a tankless water heater. If you demand more steam than the fire (boiler) can supply your extra power disappears pretty quick and in fact it may take some time to get back to "normal" power.

An airplane is not going to have the weight allowance to carry much in the way of excess steam generating capacity.

The entire steam system is vulnerable to gunfire/damage. Some damage or gunfire might only cause a small loss in performance, in other cases just a few rifle bullets could cause a major power loss. Steam plants are bulky, trying to armor them would be weight prohibitive.

 

[Siegfried]

There is not doubt a steam powered aircraft could be made to work fairly well.

Here is a youtube video of the Besler Steam aircraft.

View: https://www.youtube.com/watch?v=nw6NFmcnW-8

I should point out that Nathan Price, the man who almost invented the turbo-jet first started out developing a steam turbine that morphed into a turbojet.
http://en.wikipedia.org/wiki/Lockheed_J37

The question is how well would this steam aircraft work? The Technology the Germans were going to bring to bare would have been at a much higher
level than Besler/Doble could have in 1933.

@davebender: There is no doubt that the Germans could produced good fuel but there was a cost to producing high octane gasoline or high cetane diesel. There was also a lot of low grade byproduct that would best be used on suitable engines. Jumo 004 engine of the Me 262 actually flew missions direct of crude oil, refined by centrifugal impellor only and preheated before pumping into the tanks. The crude oil presumably being obtained from Germany's small natural supplies or distilled of bituminous coals.

I think a major problem was that the Bergius Hydrogenation plants, which were efficient and produced high grade fuel, had to be big and and thus were targets. The smaller fischer-tropsch plants did not yet produce much high grade gasoline. The "Geilenberg Plan" called for building plants underground as well as dispersal.

About 30% of the product of the FT plants was a low octane fuel of 42 RON while 30% was good quality diesel with the remained lubricants and waxes, pretty useless except for blending down. It seem that they were on a breaktrough however in direct production of gasoline.
The Progress of the Research Commission on Continued Development of the Gasoline Synthesis from CO and H2, Especially in the Direction of a Direct Synthesis of Isoparaffins. (SS6132-9798/42)

A steam power aircraft could relieve the pressure on supplies of high grade fuels. Given the quoted sfc of 190 grams per kilowatt hour which works out at a stunning 0.32 lbs/hp/hour it would be suited to long maritime patrol missions, raids on the USA and transfers of technology and strategic materials between Germany and Japan.

@wuzak

The heat rejection of 100C seems a little low to me, I suspect a higher temperature would improve heat transfer from the condenser to the atmosphere and thereby reduce its size considerably. There will be a cost in efficiency but weight and drag is a very important issue.

**********

The question for me are
1 What materials are to be used (I assume high chrome refractory steals)
2 What size the condensers, where to mount them.
3 What is the power to weight ratio?

A twin engine design is best from a structural point of view, I am inclined to put the turbine and boiler in the one nacelle while the condenser is in a turbofan engine like pod outboard of the wings where it can be designed to exploit the so called Meredith effect. Residual steam pressure can operate a small inductor fan to keep airflow up while the aircraft is stationary. Parts of the wing leading edge can be used for cooling and to provide a de-icing function. The engine would be smooth, vibration free which should keep weight of the propeller, gearbox and mountings down.

 

[davebender]

major problem was that the Bergius Hydrogenation plants, which were efficient and produced high grade fuel, had to be big and and thus were targets

IMO cost was a greater factor. Synthetic fuel plants are very expensive to build. The 1939 Gelsenberg hydrogenation plant cost 208 million RM to build. Over ten times the cost of the Genshagen DB601 engine factory constructed during 1936. More then a Bismarck class battleship cost to build during the late 1930s. With a price tag that high it's easy to understand why Goering didn't build a few more hydrogenation plants as part of the German 4 year economic plan.

 

[wuzak]

A steam power aircraft could relieve the pressure on supplies of high grade fuels. Given the quoted sfc of 190 grams per kilowatt hour which works out at a stunning 0.32 lbs/hp/hour it would be suited to long maritime patrol missions, raids on the USA and transfers of technology and strategic materials between Germany and Japan.

The sfc is listed as 190g/hp/hr, which equates to 0.42lb/hp/hr - which is more than competitive with piston engines of the era. In fact at that fuel consumption I believe the steam turbine would be at max power - having worse consumption at lower power. Max power in the big piston engines had far worse sfc - over 0.6lb/hp/hr on Merlins.

@wuzak

The heat rejection of 100C seems a little low to me, I suspect a higher temperature would improve heat transfer from the condenser to the atmosphere and thereby reduce its size considerably. There will be a cost in efficiency but weight and drag is a very important issue.

Most piston engines of WW2 ran at about 250°F/120°C. Wright field experimented with 300°F/150°C for the hyper program, but discovered that the reduction in radiator size was more than offset by the increase in oil cooler size.

Remember also that the condenser has to bring about a phase shift in the working fluid - ie from steam to water.

The question for me are
1 What materials are to be used (I assume high chrome refractory steals)
2 What size the condensers, where to mount them.
3 What is the power to weight ratio?

1. Unclear. It must be noted that the steam turbine had been in use for the best part of 50 years, and were heavily used in power production around the world and in Germany.

2. In the Junkers schematic the condenser would be part of the wing mounted system. Otherwise it is unclear. The condenser could also use a separate cooling circuit, so that it would not have to be in the airstream.

3. Power to weight of the system was to be 0.7kg/hp for the design intended for the Me264. That means 4200kg for 6000hp. The weight, I presume, includes all system requirements and fluids. How heavy would a piston engine or engines be for a max continuous power of 6000hp?

The Junkers was said to weigh 800kg. But I believe that only accounts for the turbine and the (weighty) reduction gear.

A twin engine design is best from a structural point of view, I am inclined to put the turbine and boiler in the one nacelle while the condenser is in a turbofan engine like pod outboard of the wings where it can be designed to exploit the so called Meredith effect. Residual steam pressure can operate a small inductor fan to keep airflow up while the aircraft is stationary. Parts of the wing leading edge can be used for cooling and to provide a de-icing function. The engine would be smooth, vibration free which should keep weight of the propeller, gearbox and mountings down.

I would consider mounting the boiler (or boilers) centrally in the fuselage, using it to feed two wing mounted steam turbines. As much as possible teh equipment could be kept in the fuselage. The returning steam could be used for de-icing as you suggestedd, being piped back along the leading edge.

I think fuselage mounting would offer the best chance of protecting the equipment from those pesky bullets.

 

[model299]

The nuclear powered aircraft was to use jet propulsion.

A turbojet was modified for this use - the compressor and turbine remained, but the combustion chambers were raplced by heat exchangers. The air would be compressed bythe compressor, then heat from the reactor transferred to the air in the heat exchangers, and the air would then expand through the turbine, which would drive the compressor, and exit out the back to create thrust.

The XB-36H carried an operating 1MW nuclear reactor. The B-36 was powered by 6 2.8MW R-4360s, yet was thought to be underpowered. A 1 MW reactor wasn't going to power the plane. What it did show is the viability of such an installation, and how th eradiation affected systems etc. IIRC the crew compartment was fully shielded, but the reactor was not.

In the summer of 1972, I spent 3 months in Idaho Falls, Idaho on a summer intern job at the AEC's LOFT project. (Loss Of Fluid Test)

The engineering offices were in town, but on occasion, we'd make field trips to the NRTS to take measurements, and perform other duties.

We rode a bus to the project site from the main gate. On the way there the first day, the group leader pointed at what appeared to be a short "train" in the distance, surrounded by a high security chain link fence. (A REALLY heavy duty one as I remember.) The "train" itself looked like it had been sitting there for some time, and in fact it had been.

He told us about this aircraft engine project, and said that they did manage to get one test unit functioning. The thing was mounted on a support platform that rode on a double wide set of railroad bogies. In other words, they used two sets of tracks side by side, (I guess it was sizeable.) and was moved about by the use of a remotely controlled locomotive. He said they were running tests one day, when things got out of control, and the unit suffered what amounted to a small "meltdown." He said they did manage to get things under control and get everything stabilised. They then built the high security storage area, used the locomotive to move the whole radioactive mess into it, sealed off the remaining fence, and there it sits to this day.

The monstrous hanger they built for the project (It was supposed to house 3 B-36 airframes, I believe.) was being used as an equipment storage building for the LOFT project. It was abolutely huge.

A book I have on the B-36 reported that the B-36 was indeed a bit underpowered due to the weight, and that the cockpit was eerily quiet in flight.

Needless to say, NO photography of any sort was allowed.

 

[Siegfried]

IMO cost was a greater factor. Synthetic fuel plants are very expensive to build. The 1939 Gelsenberg hydrogenation plant cost 208 million RM to build. Over ten times the cost of the Genshagen DB601 engine factory constructed during 1936. More then a Bismarck class battleship cost to build during the late 1930s. With a price tag that high it's easy to understand why Goering didn't build a few more hydrogenation plants as part of the German 4 year economic plan.

The Gelsenberg plant had a capacity of 300,000 tons of aviation fuel per anum.
http://www.fischer-tropsch.org/prim...Y/tech_rpt_217-45/Sources Report 217-45-2.pdf

Consider that if one was to supply 1 ton day to an aircraft one could operate only 1000 of them with this plant.

These production costs suggest to me that and Me 109 or FW 190 airframe was worth about RM 40,000 and the engine another RM 40,000.
German Production Costs

In other words about RM80,000.

If the Gelenberg Plant produced 300,000 tons per year for RM 200,000,000 investment we can say it cost RM 666 capital investment to produce 1 ton of fuel annually (about 3L/day)

One would realistically need to make 100 times this investment for a single tank or aircraft to give it enough fuel for daily opperation.

Thus about RM60,000 needs to be invested for each tank or aircraft. This is about the same price as that tank or aircraft.

The plants of course were improving in efficiency, yields and throughput greatly with new processes.

Critical were 'alkylation' the process by which the allies produced much of their 100/130 fuel (the German plants were started in 1940 but only coming on line in 1943) and catalytic cracking, which is how the US produced 100 octane. This latter process was not ideal for hydrogenation product and needed modification.

I it hadn't have been for the allied bombing campaign the output of gasoline, particularly high grades would have increased by 50%.