Steam Engine Torque?

[rbattelle]

Does anyone happen to know what sort of torque a steam engine (as in locomotive) produces, and how that compares to a diesel of comparable horsepower?



I'm just curious. My suspicion is that the steam engine produces a lot more (and from 0 RPM, at that!).



Ryan

 

[Vaughn MacKenzie]

Ryan, there is a major difference in how power is delivered to the rail between a diesel and steam locomotive. There is also a big difference in the power curves between the two.

In the diesel electric application there is actually more start-up torque to get a train moving because the power from the prime mover is delivered to the traction motors in parallel. This supplies them with a lot of amperage, resulting in a lot of torque. Once the train picks up speed the system switches over to supply the current in series which in effect is like upshifting a gear (less torque but more HP).

But the faster a diesel electric locomotive goes the less pulling power it has. . . it falls off proportionally pretty much from the moment the train starts rolling (very much unlike a steamer).

A steam loco torque varies considerably based on cylinder bore and stroke, driver diameter and steam pressure. Certainly a Big Boy locomotive with massive steam pressure (300 psi) and cylinders has a lot of torque, whereas a Northern with 80-inch drivers doesn't - it's a speed machine.

Because steam engines essentially have one "gear" the power band will depend on speed. Steam engines with taller drivers have more difficulty getting a train rolling, but if a steam engine can get the train going there's no looking back. As a steam loco increases speed, so does horsepower, which is the opposite as what happens to a diesel. Steam locos increase HP unit it peaks somewhere around 50-60 mph, then tapers off as speed increases. However the UP #844 with its 80-inch drivers hits its max HP at 90 MPH!

One of the more interesting steamer stories of modern times was the load Challenger 3985 pulled in 1990. It hauled a double stack of 147 cars (1. 6 miles long) solo from Cheyenne to N. Platte Nebraska. It was a revenue freight and the Challenger took the place of 3 diesels and had no trouble maintaining 65 MPH.


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[WDaniels]

Hey Vaughn,

With all that information, does your head ever hurt?:-laf Or did you look that all up from a book? (Please say you looked up. No one should have that much information in their head. )

WD

 

[rbattelle]

Vaughan, great explanation. But how about some numbers!



I guess the starting torque on a steam locomotive could be easily calculated based on the steam pressure, bore, and stroke.



Check out the picture of these rods!



Here's a page discussing maximum pulling force. Couldn't find a similar page for diesels.



Ryan

 

[Headshot zod]

My suspicion is that the steam engine produces a lot more (and from 0 RPM, at that!).

I wish I could remember the numbers for steam cars, if I can find the numbers (ungodly) for Doble's steam car I'll post them. It was a much better car then the Stanley.

 

[rbattelle]

Here's another interesting article. In particular, this was interesting:

A steam engine could go approximately 100 miles without refueling or taking water, while a diesel locomotive could reach as far as 600 miles without servicing. A diesel has a much higher starting tractive effort than any steam locomotive. The diesel has a thermal efficiency greater than three times that of the best steam engine.

I haven't read the whole thing... yet.



Ryan

 

[Greenleaf]

A it was explained to me, the steam engine, be it a locomotive or a tractor has the same HP at any rpm. This is due to the fact that whatever the steam pressure is, is what it is. It doesn't change.



200 psi into the cylinders is there, be it 10 rpm or 200. A steam engine is an external combustion engine. They are nothing alike and so cannot be compared to an internal combustion engine.



I wish I could recall where I learned that and if it's 100 accurate.



BTW, I have HP facts/figures on the Roanoke built N&W RWY locomotives. They are given in # of draw bar pull.



Some of the locomotive are compound and others are mallet. (High pressure and low pressure cylinders. )

 

[Mikie12]

Wow guys; that was some great info, and articles...

Thanks!

 

[rbattelle]

A few more interesting tidbits from that large article I linked:

-The reciprocating action of steam locomotives had a tendency to tear up the track. It's not clear to me what "tear up" means.

-Ingersoll-Rand used to make diesel engines!

Ryan

 

[RustyJC]

Take a look at the discussion HERE.



Rusty

 

[Vaughn MacKenzie]

WDaniels, unfortunately I pulled all of that out of my head

rbatelle those rods are sweet How does this tickle your fancy: the side rods as an example weigh 1100 lbs per side on the Daylight 4449 (seen here in Montana in 2004) #ad

At 80 MPH (a speed this engine is sometimes operated at) the drivers turn 11 revs per second (660 RPM). You are taking 1100 pounds and shooting it back and forth 32 inches 22 times a second

Steamers tear up the track because of the counterweights on the drivers that counteract the horizontal forces of the side rods. Since there is nothing to counteract the weights on the vertical plane they literally pound down on the rail and roadbed. The Big Boys were hell on track.

Greenleaf and I have exchanged some PMs. . . there were some mighty fine steam locomotives out of the Norfolk and Western shops. They bucked the diesel trend longer than anyone, and took steam development the furthest.

The quote about diesel fuel efficiency was probably true, however does it take into account it takes more diesel units to move the same amount of freight. Fuel & water consumption and high maintenance was the demise of steam.

Back to the HP discussion. . . it seemed they never could accurately rate steam engine horsepower. One thing that is very true. . . a 5000 HP steam engine can pull a heck of a lot more train at track speed than a 5000 HP diesel. That's why the Challenger (rated around 5500 HP) could pull a train that would normally require three diesels (approx 3400 HP apiece).

 

[Greenleaf]

How does this tickle your fancy: the side rods as an example weigh 1100 lbs per side on the Daylight 4449 (seen here in Montana in 2004) #ad


At 80 MPH (a speed this engine is sometimes operated at) the drivers turn 11 revs per second (660 RPM). You are taking 1100 pounds and shooting it back and forth 32 inches 22 times a second







Don't quote me, but I have reason to believe that a number of the late models built in the N&W shops employed aluminum rods. I'll have to look again to be sure. I do know for sure they are on needle bearings. In fact they built everything on needle rollers.

 

[Vaughn MacKenzie]

Here's a good writeup Greenleaf. This does say they used light side rods. Made it able to pull 10 cars at 110 MPH with only 70" drivers:
http://en.wikipedia.org/wiki/Norfolk_and_Western_611

Now here is something I never knew before. . . it says the 611 flipped off the tracks in 1956 after the engineer took a corner too fast!

Vaughn

 

[jwgary]

A it was explained to me, the steam engine, be it a locomotive or a tractor has the same HP at any rpm. This is due to the fact that whatever the steam pressure is, is what it is. It doesn't change.



200 psi into the cylinders is there, be it 10 rpm or 200. A steam engine is an external combustion engine. They are nothing alike and so cannot be compared to an internal combustion engine.



I wish I could recall where I learned that and if it's 100 accurate.

I would think that it would have "constant" torque at any rpm. That would make HP vary linearly with rpm. You can't possibly have any HP if you aren't moving. The reason constant is in quotes, is that you would loose some pressure as your speed increased. As you expand the steam in the boiler through the pistons, you will cool the steam and lower the pressure. At greater speeds there is a point where the boiler can't possibly keep up with the steam demand. Also, as you increase the flow rate of the steam in all of the lines, you have more friction creating a head loss as well.



Another thing I was thinking about while reading this thread is how the cylinders are arranged on a locomotive. Are they staggered like the pistons in a multiple cylinder engine. Your torque is dependent on the pressure in the cylinder, the length of the crank arm and the angle of the piston rod. There should be a place where they line up and no matter how much pressure is in the cylinder you won't have any torque, only force. Are the cylinders turned so that they are off axis with the driving wheels?

 

[Greenleaf]

the 611 flipped off the tracks in 1956 after the engineer took a corner too fast!



Vaughn

HeHeHeHeHeHe



ROFLMAO



..... "Watch that first turn, It's a Duezie"!!:-laf

 

[Greenleaf]

Me... .



In J Class 611

 

[Vaughn MacKenzie]

Greenleaf, I'm gonna be in Cleveland next week, let's get together to talk steam

PM sent. . .

 

[Greenleaf]

OK, Done deal.



I'm going to write Robin and Steve to petition for a Steam Forum... ... . Oo.



Maybe a "General Steam Forum" and a "Streamliner Steam Forum" How about an "Articulated Steam Forum"



ROF Just Kidding. But seriously... ... ... ... . I am. :-laf



Scott

 

[cojhl2]

I would think that it would have "constant" torque at any rpm. That would make HP vary linearly with rpm. You can't possibly have any HP if you aren't moving. The reason constant is in quotes, is that you would loose some pressure as your speed increased. As you expand the steam in the boiler through the pistons, you will cool the steam and lower the pressure. At greater speeds there is a point where the boiler can't possibly keep up with the steam demand. Also, as you increase the flow rate of the steam in all of the lines, you have more friction creating a head loss as well.



Another thing I was thinking about while reading this thread is how the cylinders are arranged on a locomotive. Are they staggered like the pistons in a multiple cylinder engine. Your torque is dependent on the pressure in the cylinder, the length of the crank arm and the angle of the piston rod. There should be a place where they line up and no matter how much pressure is in the cylinder you won't have any torque, only force. Are the cylinders turned so that they are off axis with the driving wheels?

Ah aha!!! you guys are way ahead of me regarding all this stuff,, but I just can't hold baci here.



When I was a kid we had 4 steem engines pass every day. I wondered why the power stroke (choo choo) did not match the piston rod. What I found was the two sides are 90 out of phase. So there is always a piston that is not on dead center. (Solid axle)



Now I have a question for which I have never figured an answer. Maybe someone can help.



When a steem engine is lopeing down the track it has choo-k-tee choo-k-tee sound. Why is that? It seem like the power strokes would still be even. .

 

[rbattelle]

cojhl2 reminded me of another point. I was under the impression that all steam locomotives were double acting. Is this not accurate? If they are double acting, that would explain a lot of the unique noise.

[A "double acting" steam engine applies steam pressure to both sides of the piston in-turn, as opposed to a "single acting" engine, which only applies steam pressure to the top of the piston. ]

Oh, and another thing. Check out what I picked up at Half-Price Books yesterday:
Modern Steam Engines, By Joshua Rose. Published in 1887. An amazing book with beautiful drawings. It definetly implies that the vast majority of steam engines are double-acting.

Hey Greenleaf - I second the motion for a steam forum. Home Shop Machinist has a Live Steam forum, but I'm not smart enough to actually participate.
Can I come talk steam with you and Vaughan? Please?

Ryan