PDA

View Full Version : Question for the steam experts among us.



x39
02-25-2004, 06:39 PM
Given two steam engines, one with a 2.00" bore x 4.5" stroke, the other with a 2.25" bore x 4.5" stroke, but otherwise identical in every respect, how would they differ in performance? Thanks.

Carl
02-25-2004, 08:31 PM
The 2" bore has 3.14 square inches of piston surface area, the 2.25" bore has 3.98 square inches of piston area. For a given brake mean effective pressure, say 100 psi, the former would have 314 pounds of pressure acting on the piston, the later would have 398. Given a 4.5 inch stroke The 2" bore engine would produce 117.75 lb.ft of torque, the 2.25 bore engine would produce 149.25 lb ft.
Sorry, I need to revise these figures, I calculated for a 4.5 inch lever arm rather than 4.5 inch stroke which is a 2.25 inch lever arm giving 58.875 lb ft for the 2" bore, and 74.625 lb ft for the 2.25" bore. Those are theoretical figures that would be reduced by factors such as friction and thermal efficiency.


[This message has been edited by Carl (edited 02-26-2004).]

wierdscience
02-25-2004, 10:34 PM
Carl is exactly right,but also another consideration of performance is operating speed,the smaller piston could operate at a higher speed at least in theory and develop similar horse power with lighter wieght like in a traction engine or automobile as compared to things like ships and locomotives where wieght is not as much of a factor.

x39
02-25-2004, 11:25 PM
Thank you both for your replies. Wow, that extra 1/4" of diameter makes a significant difference.

NAMPeters
02-25-2004, 11:35 PM
They both should operate at the same speeds as it is piston speed that is the limiting factor. The heavier piston will need more balace weighting. Wear for the bigger piston could be a limiting factor if the bearing journals are not increased in size accordingly.

------------------
Neil Peters

NAIT
02-25-2004, 11:43 PM
<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
...another consideration of performance is operating speed,the smaller piston could operate at a higher speed at least in theory and develop similar horse power with lighter wieght like in a traction engine or automobile as compared to things like ships and locomotives where weight is not as much of a factor.</font>

Interestingly, the design decision is in the opposite direction in aircraft piston engines. One would initially assume aircraft enginess should be light and horsepower should be delivered through high rpm. Actually, aircraft piston engines are slow running - 2700rpm is often max - and cylinders tend to be huge - coffee can size. This is because the determining factor is propeller tip speed, which must be kept below the speed of sound for best overall efficiency. Gears are avoided because of weight. Propellers are therefore usually driven directly, at the same slow speed as the crankshaft.


[This message has been edited by NAIT (edited 02-25-2004).]

Peter S
02-26-2004, 01:59 AM
x39,
I can't help with your question, but you may be interested in this photo posted recently on a Stationary Engine forum, it compares two steam engines, both developing 250hp.

The photo is titled "Two Engines of Equal Power".
I found the size difference quite astounding.
Apparently, the photo originally appeared in 'Power' magazine, 1903 and then as a frontispiece in a book "Modern Engines & Power Generators".

"Made by Yarrow of Poplar, the large one was built for the East London Water Works, triple expansion, 20, 32 & 53 inch cylinders with a 42 inch stroke, 16 rpm @ 150 psi, 80 ton. Small engine was for torpedo boat: triple expansion, 8, 12 & 17 inch cylinders with 9 inch stroke, 550 rpm @ 250 psi., 2 ton. Both rated at 250 hp."

http://www.photobucket.com/albums/1003/PeterS/two_engines_of_equal_power_builder_Yarrow.jpg

For your interest, I found a photo of what I believe is the same engine, in a new book I just purchased, photographed by George Watkins in 1954 at Wanstead Pumping Station.

Here is what he says - "Yarrow & Co., Poplar, 1903.
Cylinders 20in, 32in and 53in x 3ft 6in stroke, Corliss valves.
"This was completely different from any thing in Yarrow's usual practice, which was lightweight steamboats and high speed marine engines and boilers. Being so completely in contrast to stock work, the contract could have brought little profit, but was possibly given to provide work at the Thames yard which was then being transferred to the Clyde. As a pumping station, it was indifferent as the estimated water supply could not be secured, and the engine could only run part time, or unloaded."


http://www.photobucket.com/albums/1003/PeterS/Yarrow_triple_expansion_Wanstead.jpg

Rich Carlstedt
02-26-2004, 02:23 AM
Wow Peter ..nice photos !
As another point to make, unlike other engines, steam engines are not really "Horsepower" rated. The Boilers that provide the steam to them are really the limiting factor. Without a governor, the steam engine will go to destruction as long as you can provide more steam to it.
You may recall that the Stanley Steamer with a souped up boiler ( I think it was over 1000 PSI ?) set a land speed record of 125 MPH in 1904 or there abouts and I also believe the engine was "considered to be a 10 HP engine ".
This was the same time as the Wright bros were doing their stuff with a 15 HP aircraft engine

Evan
02-26-2004, 02:33 AM
Rich,

That's right. The expansion of steam is limited by the speed of sound, and that is pretty high piston speed.

Carl
02-26-2004, 03:25 AM
The C&O Allegheny type steam locomotive produced 7500 draw bar horsepower measured with a dynamometer car at approximately 40 miles per hour. http://www.zuckerfabrik24.de/pic3/co1603a.jpg

Carl
02-26-2004, 03:51 AM
Speaking of aircraft engines, one of my favorites is the Pratt & Whitney R2800 Double Wasp, 18 cylinder radial engine displacing 2800 cubic inches, two stage supercharging, 2000+ horsepower, used in several WWII planes including the F4U Corsair which had a 13 foot diameter propeller! http://www.flygplan.info/images/f4uprnt1.jpg

x39
02-26-2004, 08:52 AM
Wow! Some real interesting posts and some great images. PeterS, that's quite a contrast between those two engines. Rich Carlstedt- I have seen the engine from the Stanley that set the speed record at Daytona. It is in storage at the Smithsonian's Silver Hill, MD facility. The engine featured roller bearings throughout. If I'm not mistaken, ten replicas of that engine were recently built at a shop in Quebec. Glen Curtiss of aircraft fame ran a V-8 powered motorcycle of his own construction the same day the Stanley ran. Pretty advanced stuff for the time.

wierdscience
02-26-2004, 09:01 PM
<font face="Verdana, Arial" size="2">Originally posted by NAIT:
Interestingly, the design decision is in the opposite direction in aircraft piston engines. One would initially assume aircraft enginess should be light and horsepower should be delivered through high rpm. Actually, aircraft piston engines are slow running - 2700rpm is often max - and cylinders tend to be huge - coffee can size. This is because the determining factor is propeller tip speed, which must be kept below the speed of sound for best overall efficiency. Gears are avoided because of weight. Propellers are therefore usually driven directly, at the same slow speed as the crankshaft.

[This message has been edited by NAIT (edited 02-25-2004).]</font>

Yes,that is quite true for radial engines,but not most v-types like the Liberty 12,they ran reduction gears,as I remeber from what I have read the Liberty routinely ran up to 3900+,or at least thats what figures were given in a article on Lindberg's contribution to the flight proceedure on the P-38.



[This message has been edited by wierdscience (edited 02-26-2004).]

jim davies
02-26-2004, 11:40 PM
Sounds like we're getting the Liberty and Allison 1710 mixed up. The Liberty [V-12 version most common] was a quickee WW1 design than, due to funding constraints hung around for years, spawning all sorts of mods. It never reached anywhere near that RPM range, neither the P-38's Allison or the famous Rolls Merlin never did either. 3000RPM max. With a 6" stroke that is 3000FPM piston speed which is considered high for a continuous duty engine.

A distant derivitive of the Liberty, Hyper #2 was designed for RPM in this range, although it wasn't part of any mass produced engine in the end, being a victim of gas turbines.

For high max RPM's see Napier's Sabre, an H-24 sleeve valve. The stillborn last generation of engines were short stroke, high RPM ones such as Wright's r-2160.

While most Liberty's and other WW1 era engines were not geared, all WW2 tactical and strategic allied engines, inline or radial were geared.They swung some pretty large props and the speed of sound was reached at fairly low revs. Ballpark gear reduction was somewhere around 0.5 to 1 but it varied a lot.

Tuckerfan
02-27-2004, 12:06 AM
X39, here's a couple of steam engine related forums:

http://www.stanleysteamers.com/phorum-3.3/list.php4?f=1

http://www.steamautomobile.com/ForuM/list.php?f=1

The membership of both forums tend to overlap, but the folks there have been helpful in answering the questions I and others have had.

wierdscience
02-27-2004, 12:23 AM
OOPs!Yep I meant Allison,but the 3900 rpm thing sticks out thou,I'll have to re-read that one.

x39
02-27-2004, 12:24 AM
tuckerfan- thanks for the links.

NAIT
02-27-2004, 01:02 AM
<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
Yes,that is quite true for radial engines,but not most v-types like the Liberty 12,they ran reduction gears...</font>

Lots of things are done in wartime for military engines. I was thinking of most "modern" general aviation engines (modern being a relative term - most piston engine designs are now fifty+ years old). Engines such as the flat lycoming and Continentals, or the in-line Czech LOM M-332. Now there's an interesting engine - the LOM M-332. See www.moraviation.com (http://www.moraviation.com). (www.moraviation.com/m332C.html). I'll be choosing between the LOM M332CE and the experimental XP-360 engine for the Glastar aircraft I'm building.

[This message has been edited by NAIT (edited 02-27-2004).]

barts
02-27-2004, 02:32 AM
Steam engine power can be estimated as follows:

1/3 boiler pressure in pounds per square inch *
Length of stroke in feet *
Area of piston in square inches *
Number of power strokes per minute /
33,000.

For the smaller engine, assuming 100 psi steam, and 500 rpm, you can expect about
1.2 hp. The larger one yields almost 1.5 hp.

- Bart

wierdscience
02-27-2004, 09:44 PM
I found the article,It was in Flight Journal,it basicaly was on Lindberg's war contributions,They(ArmyAirCorp)were having trouble getting enough range out of the P-38's when they first hit the Pacific theater,the ground flight mechanics had noticed that the Allisons had the problem of burning valves if the rpm's were held any lower than 2900 for any length of time,Linberg was called in and actually went into the action in the pacific.

He developed a flight profile that would keep the rpm's up until they reached crusing altitude,then they could be throttled back to a conservative speed like 1800 for the long patrol flights and long range missions,but when called upon they could accelerate tot their combat speed of 4100 rpm.
This effectively increased the range of the plane by nearly double and became the accepted proceedure for the type.
I was impressed to find out too that he flew on actual patrols while he developed his technique and actually scored a enemy kill as a civilian.
But still the most amazing thing about Linberg is that in his lifespan we went from canvas and wood to the surface of the moon.

wierdscience
02-27-2004, 09:50 PM
Nait,nice engines,very similar to the BMW's produced during the war especially the inverted crank.
I'm assuming its a dry sump with a leading edge cooler?
I like everything about it,but the conrods,I guess there okay I just have bad memeories of al rods,nothing on a plane,but on the ground plenty.
Just what does one of those cost these days?

NAIT
02-28-2004, 03:03 AM
<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
nice engines,very similar to the BMW's produced during the war especially the inverted crank.</font>

Note the supercharger. This is why the compression ratio of the M-332 is a bit less than contemprary Lycomings or Continentals.

They don't like to talk about it now, but during WW2, LOM's predecessor was producing engines for the German Luftwaffe, and shared basic design principles with German engines of that time.


<font face="Verdana, Arial" size="2">I'm assuming its a dry sump with a leading edge cooler?</font>

It's a dry sump, but I don't recall if there is a separate oil cooler.



<font face="Verdana, Arial" size="2">Just what does one of those cost these days?</font>

Last time I asked it was about $US18,000 for a very complete kit with accessories - perhaps $5K less than an equivalent Lycoming. My impression is that the M-332 should be the engine of choice for tandem aircraft. Unfortunately, LOM does such a poor job of marketing in North America that the engine is almost unknown. For side-by-side seating, the small frontal area of the M-332CE is less of an advantage and the experimental XP-360 Lycoming clone may have an edge.

[This message has been edited by NAIT (edited 02-28-2004).]

Peter S
03-01-2004, 07:36 AM
Weird,
Somethings not right, sounds like the Allison story has got mixed up.

Those engines ran at around 3000 max, and the procedure worked out for getting maximum range in the P38s (sometimes attributed to Lindbergh)involved low rpms and maximum boost (and staying as high as possible, up to 30,000 ft).

Range increases with altitude in a turbo-supercharged P38, so firstly get up high, then fly at the recommended speed (which was 180 indicated), the carburettor mixture controls must be set to Auto Lean and the engines run at the lowest rpm available (but not lower than 1600) and whatever boost is required.

The main things were as low rpm and as high boost as possible in Auto Lean.

Lockheed quote "You see with a low rpm and a high boost (under 34 inches) you get power out of the engine without wasting fuel on engine friction and the internal supercharger. The needed power will not hurt the engine as long as the manifold pressure does not exceed 34 inches in Auto Lean (detonation limit when burning 100 octane)."

Dan Whitney (author of "Vee's For Victory The story of the Allison V-1710 Aircraft Engine") wrote about this in a couple of articles in "Torque Meter" magazine, a great magazine if you are interested in aircraft engines. He used the recommendations put out by Lockheed during WW2.

I need to read up on boost controls, mixture adjustments, throttle and propellor pitch controls and how they are used together.

One complicating factor about engines like the Allison is that it was rated to produce a certain power at a certain altitude. This makes our auto engine-based comparisons inadequate, these engines could not be run at ground level at the same settings as they used at altitude, they would blow up. Having said that, they could sustain being over-powered on take off, because it was short term, they were backed off once airborne.
I need to read up on this some more...

wierdscience
03-01-2004, 09:51 AM
Dunno if the article was correct,thats what was printed.My mothers uncle flew P-51's during the war,he said the ADS was routinely disabled in theater providing for a higher than normal boost during combat flight maybe the same was true for the P-38?Anyway I do believe that the 3000 ft per sec rule was violated on a regular basis at least in Military aircraft.

Anyway back to the original topic,Has anybody built a square cylinder steam engine?Thats one I'm interested in building myself,the Dake type,not just a square cylinder.