Jump to content


Photo

Viability of the steam turbine as an aircraft power plant?


  • Please log in to reply
114 replies to this topic

#1 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 21 October 2011 - 05:03

As I have previously mentioned in this forum, during WW2 there were a few projects for designing a steam turbine for aviation use.

The first of these was started by Junkers Moteren (Jumo) in 1940. The turbine ran on the test bench in 1941, but the project was shelved in 1942 in favour of gas turbines.

The specs for the Jumo turbine were:
Power - 3000hp
Turbine speed: 8000rpm
Propellor Speed: 950rpm
Weight: 800kg (I presume this only applies to the turbine itself and the reduction gearing, not the boiler and other required equipment).
Intake Pressure: 100atm
Intake Temperature: 550°C
Exhaust Pressure: 0.15atm

A further steam turbine design was also being undertaken by Professor Lösel and Dipl-Ing Pauker at the Technische Hochschule. This was to be rated at 4000hp. Not much in the details for this turbine, except that the turbone would be roughly 1/2 the length and 2/3 the height of the Jumo 213 aero engine (ie about 1225mm long x 565mm high). It was also cancelled in 1942.

Steam turbines re-emerged in 1944 when Messerschmitt were looking for suitable engines for their long range Me264 "Amerika bomber". The first prototype Me264 flew with 4 x 1250hp Jumo 211s, taken straight from the Junkers Ju88, and the second prototype used 4 x 1750hp BMW 801 radials. Both were considered underpowered. The original concept called for 1750hp Daimler-Benz DB603s, but these were in short supply.

Various alternatives, including mixing piston engines and jet engines, turboprops and turboprop and jet combinations were investigated. Steam turbines were also investigated, with Professor Lösel's Osermaschinen company being asked to design and manufacture a suitable steam turbine.

The specificatiosn for the engine were:
Power: 6000hp
Turbine speed: 6000rpm
Propellor RPM: either 400-500rpm using a 5.3m diameter prop or 6000rpm using a 2m diameter prop.
Power to weight: 0.7kg/hp = 4200kg (I presume this is for the complete installation).
Specific Fuel Consumption: 190g/hp/hr = 0.42lb/hp/hr

Due to the shortages of aviation fuels in Germany in late 1944 it was thought that the steam turbine could use a 65% pulverised coal/35% petrol fuel mix until sufficient quantities of petrol were available. Many of the components had been manufactured prior to VE day, but the turbine had not run.

The advantages of the steam turbine (compared to piston engines) were thought to be:
Constant power at all altitudes.
Capacity for 100% overloading, even for extended periods.
Full steam output achieved in 5-10s.
Not sensative to low temperatures.
Long life and simple servicing requirements.
Simple and quick control.

The expected life of the steam turbine was between 4000 and 6000 hours between overhauls, as compared with less than 500 for most high powered piston engines - Merlins were less than 300 for some versions.

I would presume that the rated powers of these turbines were for continuous use. The Jumo 213 was rated at 1750hp at takeoff and at rated altitude, but this was a 3-5 minute rating. Continuous rating was less. The Jumo 213 weighed 940kg dry, not including radiator and oil cooler.

The similar Daimler-Benz DB603 was also rated to 1750hp, and 920kg dry. It's maximum continuous power was 1500hp (from Wiki: DB603. Two DB603s, therefore, should be able to produce the same continuous power as the Jumo steam turbine (ie 3000hp) for 1840kg (without coolers). If the power to weight of 0.7kg/hp was achieved for the Jumo turbine it would weight approximately 2100kg.

One of the obvious disadvantages to using a steam turbine in a combat aircraft is its susceptibility to battle damage - particularly the condenser and boilers.

How big would the condenser have to be for the 3000hp unit? Would it be much larger than for a piston engine(s) with 3000hp continuous power, whose coolant would be at about 120°C?

The 100% overloading would mean a normal 3000hp unit would produce 6000hp? What would limit the time for its use? How would this be achieved - extra steam mass flow/consumption?


The first US gas turbine/jet project, the Lockheed L1000/J37 also began from a steam turbine project Wiki: Lockheed J37.

In 1930 Nathan C. Price joined Doble Steam Motors, a manufacturer of steam engines for cars and other uses. Over the next few years he worked on a number of projects and starting in autumn 1933 began working on a steam turbine for aircraft use. The engine featured a centrifugal compressor that fed air to a combustion chamber, which in turn fed steam into a turbine before exiting through a nozzle, powering the compressor and a propeller. The engine was fitted to a test aircraft in early 1934, where it demonstrated performance on par with existing piston engines but maintaining power to higher altitudes due to the compressor. Work on the design ended in 1936 after Doble found little interest in the design from aircraft manufacturers or the Army.


The Besler brothers demonstrated a steam powered aircraft in 1933.
Besler steam plane

But this used a 2 cylinder piston engine rather than a turbine.

Advertisement

#2 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 21 October 2011 - 05:38

Some pictures.

Junkers 3000hp turbine and reduction gear
Posted Image

Junkers 3000hp turbine wing installation diagram
Posted Image

Size comparison between a 4000hp steam turbine and a Junkers Jumo 213 piston aero engine
Posted Image

Images from Dieter Herwig and Heinz Rode, Luftwaffe Secret Projects: Ground Attack & Special Purpose Aircraft

Edited by Wuzak, 22 October 2011 - 03:55.


#3 Vanishing Point

Vanishing Point
  • Member

  • 1,093 posts
  • Joined: June 09

Posted 21 October 2011 - 14:05

It might have been the figures for the actual weight required for the whole system including fuel,water,boiler,and pipework that stopped the idea from literally getting off the ground and the turbines inherent lack of any throttle response that kept steam turbines where they belong in ships.I'd bet landing the thing would have been fun.

#4 Charles E Taylor

Charles E Taylor
  • Member

  • 175 posts
  • Joined: December 07

Posted 21 October 2011 - 16:14

Aircraft Steam Engines.


I have always been impressed by this Steam Aircraft Engine.
Here


Hypergolic fuels? yes, but fantastic specifics, nearly 20Kn thrust from a 180kg engine.



Charlie

#5 MatsNorway

MatsNorway
  • Member

  • 2,069 posts
  • Joined: December 09

Posted 21 October 2011 - 17:17

I only care about the power to weight ratio of the system.

Got any numbers on that?

Edited by MatsNorway, 21 October 2011 - 17:17.


#6 Charles E Taylor

Charles E Taylor
  • Member

  • 175 posts
  • Joined: December 07

Posted 21 October 2011 - 18:48

The Numbers


I only care about the power to weight ratio of the system.

Got any numbers on that?


It is difficult to compare Thrust with Horsepower, but for visualisation.... at 375MPH 1.0lb of thrust equates to ~ 1.0bhp. You can see more about this Here


So 4000+ Horspower from an engine of 396lbs (180kg) at a speed of 375mph. Emitting Steam....... Very impressive!



Walter HWK 109-509

Variants

A-0: Pre-production model, manufactured from May 1943. The thrust of this engine was regulated between 300 kp (2.9 kN) and 1500 kp (14.7 kN (3,300 lbf)).

A-1: The first series production engine was used in the Messerschmitt Me 163 B from August 1944. The thrust here was adjustable between 100 kp (1 kN) and 1600 kp (15.7 kN (3,500 lbf)).

A-2: Version for the Messerschmitt Me 163B-1a. Weighing only 100 kg (220 lb) complete, this engine consisted of two main assemblies, the forward assembly comprising the turbine housing, the fuel pumps geared to the turbine shaft, the control box, a pressure-reducing valve and the electric starter motor, with the aft assembly made up of the combustion chamber, connected to the fore unit by a cylindrical tube containing pipes which carried fuel to the individual jets. The thrust was adjustable between 200 kp (2 kN (450 lbf)) and a maximum of 1700 kp (16.7 kN (3,800 lbf)).

B-1: Increased performance version of the A-1. This engine had a second, "cruising" combustion chamber just below the main combustion chamber, with an additional thrust of 300 kp (2.9 kN (650 lbf)). This auxiliary chamber proved necessary due to the actual T-Stoff consumption of the main unit, at nearly 5 kg/s, exceeding estimates by 100%. Thrust adjustable between 100 kp (1 kN (220 lbf)) and 2000 kp (19.6 kN (4,400 lbf)).

C-1: Based on the uprated version of the A-2. The main combustion chamber gave between 400 kp (3.9 3.9 kN (880 lbf)) and 2000 kp (19.6 kN (4,400 lbf)), auxiliary chamber 400 kp (3.9 kN (880 lbf)). To be used in the Me 263 (Ju 248).

D-1: Variant of the C-1 for use in the Bachem Ba 349. Engine designed to be recovered by parachute, along with the entire rear section with empennage.




Charlie


#7 J. Edlund

J. Edlund
  • Member

  • 1,295 posts
  • Joined: September 03

Posted 21 October 2011 - 19:51

How big would the condenser have to be for the 3000hp unit? Would it be much larger than for a piston engine(s) with 3000hp continuous power, whose coolant would be at about 120°C?


Rankine cycle steam turbines require much larger condensors than piston engines require radiators. With a piston engine most of the heat rejection is performed by the exhaust, of the heat released perhaps 40% is rejected with the exhaust. With a gas turbine, all the heat leave with the exhaust and the bypass air.

Lets say you've got a steam turbine operating with an efficiency of 40%, then 60% of the heat have to be rejected by the condensor. That figure should be about four times that of a piston engine radiator. For maximum efficiency the temperature of the fluid leaving the condensor also needs to be as low as possible, that's why steam turbines usually operate with seawater as the coolant. Say you got a maximum temperature of 550 degC, then you got a temperature difference of 530 degC if you can cool the fluid down to 20 degC, but only 430 degC with a temperature of 120 degC. That is going to hurt the efficiency of the steam turbine. What is also going to hurt the efficiency is the requirement of a high power to weight and power to volume ratio, that means you're probably limited to high pressure steam turbines. Stationary plants use both high pressure and low pressure turbines, giving a high expansion of the steam and a high efficiency, something that both add volume and weight.

It's however possible to operate a gas turbine by adding heat to the gas by a heat exchanger, if adding heat directly can't be done for some reason.

#8 Bloggsworth

Bloggsworth
  • Member

  • 7,479 posts
  • Joined: April 07

Posted 21 October 2011 - 19:53

How would it work if the plane was inverted? Would the green lobby insist that they used smokeless fuel? Would The Clean Air Act allow them to land at Heathrow or City Airport? I wouldn't fancy shovelling coal while under attack...

#9 J. Edlund

J. Edlund
  • Member

  • 1,295 posts
  • Joined: September 03

Posted 21 October 2011 - 20:40

How would it work if the plane was inverted? Would the green lobby insist that they used smokeless fuel? Would The Clean Air Act allow them to land at Heathrow or City Airport? I wouldn't fancy shovelling coal while under attack...


No one is shovelling coal, the coal is made into a fine powder which is burned. The powder can also be used as a slurry if blended with a liquid.

#10 Grumbles

Grumbles
  • Member

  • 326 posts
  • Joined: September 09

Posted 21 October 2011 - 21:23

...For maximum efficiency the temperature of the fluid leaving the condensor also needs to be as low as possible...


I don't understand this bit J. Why would you want the fluid from the condensor to be cold if you're just going to heat it up again anyway?




#11 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 21 October 2011 - 22:37

I don't understand this bit J. Why would you want the fluid from the condensor to be cold if you're just going to heat it up again anyway?


To gain the maximm efficiency/power from the system.

The Junkers system diagram shows a surface cooler and a condenser.

I doubt the systems proposed in WW2 got anywhere near exhaust temperatures of 20°C.

Is it necessary to cool the water much, or is the main requirement to change the steam back to water?

#12 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 21 October 2011 - 22:41

It might have been the figures for the actual weight required for the whole system including fuel,water,boiler,and pipework that stopped the idea from literally getting off the ground and the turbines inherent lack of any throttle response that kept steam turbines where they belong in ships.I'd bet landing the thing would have been fun.


Throttle response was a major problem for gas turbines of teh WW2 era.

But in an aircraft propelled by constant speed propellers throttle response would be less of an issue - they are designed to be used at contsant engine speeds.

#13 Greg Locock

Greg Locock
  • Member

  • 4,536 posts
  • Joined: March 03

Posted 21 October 2011 - 23:14

presumably the nuclear powered bombers would have used steam turbines as well.



#14 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 21 October 2011 - 23:34

presumably the nuclear powered bombers would have used steam turbines as well.


No. They were to use jet propulsion.

#15 Kelpiecross

Kelpiecross
  • Member

  • 903 posts
  • Joined: October 10

Posted 22 October 2011 - 02:08

Some pictures.

Junkers 3000hp turbine and reduction gear
Posted Image

Junkers 3000hp turbine wing installation diagram
Posted Image

Size comparison between a 4000hp steam turbine and a Junkers Jumo 213 piston aero engine
Posted Image

Images from Dieter Herwig and Heinz Rode, Luftwaffe Secret Projects: Ground Attack & Special Purpose Aircraft


I can't open the pictures - all I get is a red "x". Why is this? - nobody else seems to be complaining about lack of pictures.

#16 gruntguru

gruntguru
  • Member

  • 5,367 posts
  • Joined: January 09

Posted 22 October 2011 - 03:08

I don't understand this bit J. Why would you want the fluid from the condensor to be cold if you're just going to heat it up again anyway?

The condenser temperature is equal to the boiling point of water at the condenser pressure (which is also the turbine outlet pressure). So, if the condenser temperature is 20 deg C the turbine outlet is at 2.3 kPa, if the condenser temp is 100*C, the turbine outlet pressure is 101.3 kPa (atmospheric pressure). Clearly with an extra atmosphere of backpressure, the turbine efficiency and power will be a lot lower.

#17 bigleagueslider

bigleagueslider
  • Member

  • 861 posts
  • Joined: March 11

Posted 22 October 2011 - 03:19

The father of the Lear Jet (Bill Lear) had a fondness for steam engines:

http://wizbangblue.c...-got-to-own.php

#18 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 22 October 2011 - 03:20

Anybody else not see the pictures?

#19 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 22 October 2011 - 03:56

Fixed.

Advertisement

#20 Grumbles

Grumbles
  • Member

  • 326 posts
  • Joined: September 09

Posted 22 October 2011 - 07:40

The condenser temperature is equal to the boiling point of water at the condenser pressure (which is also the turbine outlet pressure). So, if the condenser temperature is 20 deg C the turbine outlet is at 2.3 kPa, if the condenser temp is 100*C, the turbine outlet pressure is 101.3 kPa (atmospheric pressure). Clearly with an extra atmosphere of backpressure, the turbine efficiency and power will be a lot lower.


Thanks GG that makes sense.



#21 Tony Matthews

Tony Matthews
  • Member

  • 17,499 posts
  • Joined: September 08

Posted 22 October 2011 - 15:41

How would it work if the plane was inverted? Would the green lobby insist that they used smokeless fuel? Would The Clean Air Act allow them to land at Heathrow or City Airport? I wouldn't fancy shovelling coal while under attack...

You'd need a fireman to do the occasional riddling, too...

#22 desmo

desmo
  • Tech Forum Host

  • 13,074 posts
  • Joined: January 00

Posted 23 October 2011 - 02:41

Fixed.


Not. The images don't have permission set to be hotlinked to. If you're seeing them in the post, they are probably coming from your browser cache. The board used to allow users server space to upload images to here but that unfortunately was discontinued.


#23 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 23 October 2011 - 08:08

Posted Image

Posted Image

Posted Image

Do they now?

#24 gruntguru

gruntguru
  • Member

  • 5,367 posts
  • Joined: January 09

Posted 23 October 2011 - 09:31

Can see them now. Wonderful images they are too.
Back to viability - the main issue now is the absence of a market for such technology. Gas turbines have completely displaced reciprocating engines in high power propellor applications. Their efficiency is high in aero applications where exhaust thrust can be utilised. Packaging efficiency, frontal area and power to weight would all be far superior to the steam turbine.

Alternative heat sources like nuclear would also be better off using air cycle (gas) turbines in fan-jet or prop-jet configuration depending on aircraft speed.

Edited by gruntguru, 23 October 2011 - 09:31.


#25 Tony Matthews

Tony Matthews
  • Member

  • 17,499 posts
  • Joined: September 08

Posted 23 October 2011 - 09:57

Those are the images from post #2, which were visible! The X are still not visible!

#26 Kelpiecross

Kelpiecross
  • Member

  • 903 posts
  • Joined: October 10

Posted 23 October 2011 - 10:31

Can see them now. Wonderful images they are too.
Back to viability - the main issue now is the absence of a market for such technology. Gas turbines have completely displaced reciprocating engines in high power propellor applications. Their efficiency is high in aero applications where exhaust thrust can be utilised. Packaging efficiency, frontal area and power to weight would all be far superior to the steam turbine.

Alternative heat sources like nuclear would also be better off using air cycle (gas) turbines in fan-jet or prop-jet configuration depending on aircraft speed.


They certainly are very interesting pictures. I have to admit that I am not too sure about the flow diagram - maybe there is some heating of the intake air by the exhaust steam?
The turbine and steam generator (presumably the "kessel") are very compact but the large cross-hatched area at the bottom (which seems to be the main condenser) appears to be awkwardly big - and its full extent is not shown.

Junkers must have been aware of the gas turbine developments when they were working on this project. Even the early gas turbines had potential power outputs similar to this steam tubine and were much more compact overall and self-contained.

Maybe the steam turbine was an attempt to get gas turbine-like power and reliability but without the need for the special alloys needed for the gas turbine's blades? I don't think the Germans ever had this metal technology (luckily for us) during WW2.

#27 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 23 October 2011 - 11:54

They certainly are very interesting pictures. I have to admit that I am not too sure about the flow diagram - maybe there is some heating of the intake air by the exhaust steam?
The turbine and steam generator (presumably the "kessel") are very compact but the large cross-hatched area at the bottom (which seems to be the main condenser) appears to be awkwardly big - and its full extent is not shown.

Junkers must have been aware of the gas turbine developments when they were working on this project. Even the early gas turbines had potential power outputs similar to this steam tubine and were much more compact overall and self-contained.

Maybe the steam turbine was an attempt to get gas turbine-like power and reliability but without the need for the special alloys needed for the gas turbine's blades? I don't think the Germans ever had this metal technology (luckily for us) during WW2.



Kessel is the boiler. The exhaust gasses from the boiler go into what is labelled "Abgasturbine" - exhaust turbine. The exhaust turbine drives a compressor (verdichter) which feeds combustion air to the boiler, and thus compensates for altitude.

The shaded area is "oberflächenkühler", which translates as surface cooler.

Junkers were aware of the gas turbine, and did have their own design in the works, though I am not sure when they started. Von Ohain certainly had tested his turbine (centrifugal compressor, radial turbine), and the He280 had flown by 1942 fitted with these engines.

There were control issues with gas turbines in WW2. I believe one of Whittle's early bench tests led to the turbine overspeeding and coming apart due to control problems. The gas turbines in WW2 also did not enjoy the reliability expected of them today. The British ones had lives measured in hundreds of hours, while the German turbines would last as little as 50 hours.

Also, gas turbines of WW2 had very poor specific fuel consumption.

German metallurgy was well up to the task of making the required materials. What they lacked was the raw materials required for such alloys. Toward the end of the war there were a lot of developments of turbine blades with less exotic steels but with air cooling using air bled from the compressor section.

#28 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 23 October 2011 - 11:57

Can see them now. Wonderful images they are too.
Back to viability - the main issue now is the absence of a market for such technology. Gas turbines have completely displaced reciprocating engines in high power propellor applications. Their efficiency is high in aero applications where exhaust thrust can be utilised. Packaging efficiency, frontal area and power to weight would all be far superior to the steam turbine.

Alternative heat sources like nuclear would also be better off using air cycle (gas) turbines in fan-jet or prop-jet configuration depending on aircraft speed.


My main interest is the viability of such a system. I doubt that one could be built to compete with the gas turbines in the marketplace.

The question is could a steam turbine be built for use in an aircraft, and if it could would the equipment required mean that the airframe would have to be excessively large for the power or have no useful payload?

#29 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 23 October 2011 - 12:09

As an aside, the steam powered land speed record was set by a British team in 2009 at 139.8mph over the mile, and 148.3mph over the measured kilometre.

http://www.steamcar....sr_history.html

This beat the previous steam LSR of 127.7mph set in 1906.

By comparison the current wheel driven lsr is held by a gas turbine car at 458.2mph. I believe that had around 3000hp.

The British steam car had only 380mph.

If they had been more ambitious, could they have beaten the wheel driven LSR, or at least matched it?

#30 Greg Locock

Greg Locock
  • Member

  • 4,536 posts
  • Joined: March 03

Posted 23 October 2011 - 22:18

The question is could a steam turbine be built for use in an aircraft, and if it could would the equipment required mean that the airframe would have to be excessively large for the power or have no useful payload?

Yes, somewhat, no, respectively. A modern gas turbine 747 carries about its own weight as payload, so you could increase the engine weight a lot before the thing couldn't fly at all.



#31 Vanishing Point

Vanishing Point
  • Member

  • 1,093 posts
  • Joined: June 09

Posted 23 October 2011 - 22:57

Yes, somewhat, no, respectively. A modern gas turbine 747 carries about its own weight as payload, so you could increase the engine weight a lot before the thing couldn't fly at all.


But a modern gas turbine jet engined 747 puts out a lot more power than a turbo prop steam turbine powered plane could which is probably why they didn't ever produce a steam powered turbo prop bomber or turbo prop airliner.The correct comparison would be fit something like a 747 with 4 steam powered turbo prop engines with all the weight of the required components and fuel and water required to generate the steam and then see if it could get off the ground,let alone fly at 500 mph + at the same max take off weight as a jet engined one.

I've already posted a comparison between the average power consumption of a 747 being more than the maximum power output of a nuclear powered Nimitz class aircraft carrier and there's probably no way that you could fit the required boilers and turbines,to match the required power outputs,into a 747,let alone get the thing off the ground if you did.


#32 Greg Locock

Greg Locock
  • Member

  • 4,536 posts
  • Joined: March 03

Posted 23 October 2011 - 23:08

But a modern gas turbine jet engined 747 puts out a lot more power than a turbo prop steam turbine powered plane could which is probably why they didn't ever produce a steam powered turbo prop bomber or turbo prop airliner.The correct comparison would be fit something like a 747 with 4 steam powered turbo prop engines with all the weight of the required components and fuel and water required to generate the steam and then see if it could get off the ground,let alone fly at 500 mph + at the same max take off weight as a jet engined one.

I've already posted a comparison between the average power consumption of a 747 being more than the maximum power output of a nuclear powered Nimitz class aircraft carrier and there's probably no way that you could fit the required boilers and turbines,to match the required power outputs,into a 747,let alone get the thing off the ground if you did.

Good points, in which case there are some fairly well known equations that allow you to estimate the performance.

If you look for Smath Studio which is a mathematical scratchpad program, in the wiki for it is a detailed worksheet I put together for estimating the performance of single screw aircraft. It would be non trivial but not hard to adapt this to estimate the performance of a steam plane. Sorry i can't give a direct link, the nanny software on this PC doesn't like smath.

Edited by Greg Locock, 24 October 2011 - 00:28.


#33 bigleagueslider

bigleagueslider
  • Member

  • 861 posts
  • Joined: March 11

Posted 24 October 2011 - 02:16

This is a very interesting topic. Steam makes a very good working fluid for turbine engines if weight is no object. That's why electrical generating plants use steam turbines. But as for using steam as the working fluid in an aircraft propulsion system, it would probably not make sense, except for some limited circumstances. If the duration of flight was short, and the required speed of the aircraft was high, a steam turbine might make sense. One would have to consider the total mass of the fuel and propulsion system for each configuration, over a given mission/flight profile, to determine which was best.

The point about the relative max propulsion horsepower between a 747 and a Nimitz carrier is quite interesting. The 4 GEnx-2B67 turbofans on the 747-8 produce about 59,000lbs MCP thrust each, while the Nimitz's steam turbines produce about 260,000shp combined. The 747 turbofan engines are definitely lighter, but I'd bet that the Nimitz steam turbines would be more efficient, even if they were converted to burn heavy fuel. It all depends upon the application.

Also, there is another type of steam turbine that has been successfully used in flight vehicles. It is the peroxide mono-propellant fueled turbopump turbine used on some liquid rocket engines. The pump turbine is driven by steam produced from the chemical reaction resulting from passing peroxide over a catalyst bed. And one might even actually consider the typical LH2/LOx rocket engine a type of "steam turbine aircraft engine", since its turbopumps are driven by the byproduct of hydrogen and oxygen combustion (ie. steam). On a power-to-weight basis (around 100 hp/lb), nothing can compare to the Space Shuttle main engine 92,000hp HP turbopumps.

slider

#34 Kelpiecross

Kelpiecross
  • Member

  • 903 posts
  • Joined: October 10

Posted 24 October 2011 - 04:00

[quote name='Wuzak' date='Oct 21 2011, 16:03' post='5352618']

On the original question of "viability" - probably a reliable and powerful steam aircraft turbine could be built but in economic, maintenance and practical senses it could not compete with a gas turbine.

Compared to a gas turbine prop-jet of similar horsepower (like those in a Hercules maybe) the steam turbine with all its associated bits would probably need at least two or three times the amount of space.
The steam generator (I don't think you can call it a "boiler") would need to be about the same size and capacity as the combustion chamber and compressor area on the Herc's engine as it would need to generate about the same amount of heat as the Herc's engine. On top of this would be the space (and weight) from the coolers, condensers, pipework etc.
On a 747-sized engine the steam generator would be of a similar size to a 747 engine's compressor, combustion chambers etc. - not Nimitz-sized boilers (but I have no idea how big a Nimitz boiler is).

I suppose the point is that you might as well leave out all the steam gubbins and just run the engine on the combustion area's compressor and turbine as this is an engine in itself.
This is a bit like a turbo piston engine where (for some applications) it is better and simpler to leave out the piston engine bit and just run on the turbo as a gas turbine.
Possibly this was Whittle's original inspiration. Speaking of Whittle - his "runaway" problems were with he very first running tests of his engine - due to fuel pooling insde the combustion chamber from leaky valves before firing the engine. Only minor damage occurred even though they all nearly shit their pants in fright (understandably). (This is according to his book "Jet").

Even though the Americans had very advanced turbo technology before WW2 it apparently never occurred to them to run the turbo alone as a gas turbine.





#35 gruntguru

gruntguru
  • Member

  • 5,367 posts
  • Joined: January 09

Posted 24 October 2011 - 04:56

The point about the relative max propulsion horsepower between a 747 and a Nimitz carrier is quite interesting. The 4 GEnx-2B67 turbofans on the 747-8 produce about 59,000lbs MCP thrust each, while the Nimitz's steam turbines produce about 260,000shp combined. The 747 turbofan engines are definitely lighter, but I'd bet that the Nimitz steam turbines would be more efficient, even if they were converted to burn heavy fuel. It all depends upon the application.

Yes horses for courses.

Thermal efficieincy would be surprisingly similar. If you took the shaft power of the 747 at something around 30% TE and added the additional work done by jet exhaust thrust, it would approach the 35-40% efficiency of the nuclear power plant. Of course the jet exhaust would be no use at all in something as slow as a ship, so the best approach would be to use the exhaust heat to run a small steam plant and see an overall efficiency approaching 60%.

#36 bigleagueslider

bigleagueslider
  • Member

  • 861 posts
  • Joined: March 11

Posted 26 October 2011 - 04:42

gruntguru,

There are significant differences between the design of aircraft gas turbine engines and land/marine turbine engines. The aircraft turbine is optimized to drive a fan and to minimize weight. While the land/marine turbine engine is designed to drive a shaft and is optimized for efficiency, with little regard for weight or space. The end result is that land/marine turbine engines typically utilize more compressor/turbine stages, and heavier blade materials/case structures which allow higher stage temperatures and tighter tip clearances.

Most modern small/medium sized naval ships use both turbine engines and recip piston diesels. The diesels are used for cruising at slow speed. The turbines are kicked-in when high dash speeds are needed.

The reason steam turbines have such good potential efficiency has to do with the pressure ratio their turbine stages can achieve without excessive steam temperatures. A conventional turbine engine could achieve higher efficiency and greater specific power output with higher cycle pressure ratios. However, even with modern materials, turbine engine pressure ratios are limited to around 50:1 at most, due to turbine inlet temperatures.

slider

#37 gruntguru

gruntguru
  • Member

  • 5,367 posts
  • Joined: January 09

Posted 26 October 2011 - 07:07

There is not much difference actually, with the best Rankine and Brayton cycle engines both at around 40%.

As you say it always comes back to temperature which is where Diesels (at 50%+) have the advantage, with intermittent combustion allowing much higher peak temperatures in the working fluid yet lower average temperatures in the same combustion space.

EDIT. Modern materials help but recent advances in pressure ratio are largely thanks to improved techniques in the areas of blade cooling and sheathing using air bled from the compressor.

Edited by gruntguru, 28 October 2011 - 03:09.


#38 Fondles

Fondles
  • Member

  • 50 posts
  • Joined: July 11

Posted 27 October 2011 - 07:08

Fascinating stuff thanks Wuzak and everyone.

#39 cheapracer

cheapracer
  • Member

  • 10,388 posts
  • Joined: May 07

Posted 27 October 2011 - 08:06

Just an old fun machine that fits in here ...

http://www.liveleak....=a15_1318636799

The keen eared will notice the governer.

It is of course not steam powered.

Edited by cheapracer, 27 October 2011 - 08:08.


Advertisement

#40 Grumbles

Grumbles
  • Member

  • 326 posts
  • Joined: September 09

Posted 27 October 2011 - 11:31

Just an old fun machine that fits in here ...

http://www.liveleak....=a15_1318636799

The keen eared will notice the governer.

It is of course not steam powered.


I bet he built that just for picking up women. A chick magnet if ever I saw one.




#41 Tony Matthews

Tony Matthews
  • Member

  • 17,499 posts
  • Joined: September 08

Posted 27 October 2011 - 11:35

http://www.liveleak....=a15_1318636799

That is so bloody funny! And of course, almost a hybrid as it has two power sources. Possibly the icing on the cake is the sympathetic mad dance from the seat!

Edited to add that the three or four little puffs of black smoke are funny too!

Edited by Tony Matthews, 27 October 2011 - 11:40.


#42 gruntguru

gruntguru
  • Member

  • 5,367 posts
  • Joined: January 09

Posted 28 October 2011 - 03:43

I bet he built that just for picking up women. A chick magnet if ever I saw one.

I don't think it would be easy to stall at the lights (he wouldn't be popular if he did).

I particularly liked the safety guards. He obviously conducted a risk assessment on frontal collision - rejected the airbags and went for the perspex screen/firewall.

Loved it Cheapy - more like this please.

Edited by gruntguru, 28 October 2011 - 03:44.


#43 bigleagueslider

bigleagueslider
  • Member

  • 861 posts
  • Joined: March 11

Posted 29 October 2011 - 01:33

There is not much difference actually, with the best Rankine and Brayton cycle engines both at around 40%.


Yup. But if weight and size are no object, nothing can touch the combined cycle turbine at 60%: http://nextbigfuture...cord-super.html




#44 cheapracer

cheapracer
  • Member

  • 10,388 posts
  • Joined: May 07

Posted 05 November 2011 - 15:08

Cute ....

http://www.wimp.com/steamengine/

#45 scolbourne

scolbourne
  • Member

  • 225 posts
  • Joined: January 09

Posted 11 November 2011 - 13:53

The use of nuclear fusion or fission power sources in aircraft could lead to the use of steam turbines if propellers or fans were to be used.

#46 24gerrard

24gerrard
  • Member

  • 2,008 posts
  • Joined: March 11

Posted 11 November 2011 - 14:40

The use of nuclear fusion or fission power sources in aircraft could lead to the use of steam turbines if propellers or fans were to be used.


http://en.wikipedia....ki/Convair_B-36

Wing Commander Ken Wallis MBE flew the B36.
One of these aircraft carried a IMW Nuclear reactor on test flights way back.

#47 bigleagueslider

bigleagueslider
  • Member

  • 861 posts
  • Joined: March 11

Posted 13 November 2011 - 02:15

The use of nuclear fusion or fission power sources in aircraft could lead to the use of steam turbines if propellers or fans were to be used.


The nuke aircraft engines were turbojets that used compressed air as a working fluid.

Posted Image


#48 Wuzak

Wuzak
  • Member

  • 3,534 posts
  • Joined: September 00

Posted 13 November 2011 - 06:33

Great pic Slider.

Another solution was to use a heat transfer fluid to transfer heat from the reactor to the compressed air.

#49 24gerrard

24gerrard
  • Member

  • 2,008 posts
  • Joined: March 11

Posted 13 November 2011 - 11:34

The nuke aircraft engines were turbojets that used compressed air as a working fluid.

Posted Image


I presume the engine/s was throttled by inserting or withdrawing the nuclear fuel rods.
Whew, I can see major problems with that.
No wonder Sculthorpe in Norfolk UK is still undeveloped.

#50 MatsNorway

MatsNorway
  • Member

  • 2,069 posts
  • Joined: December 09

Posted 13 November 2011 - 13:54

Things like that is why people loved the first Star wars movies. because the things in the movies looked like something we could have made ergo.. realistic on a unconsious level... or something.