Advanced steam, operational comparisons

I'm trying to figure what advanced steam would perform like. The problem is, conventional steam was difficult to compare to diesels.

I'm talking more about the Chapelon/Porta/Wardale style of advanced steam that was actually (re)built, not high-pressure water-tube boilers and the like. My question is, these engines could develop huge horsepower, particularly for their adhesive weight. Somewhere, I read a claim that they had/would have tractive effort increases to match. How is that possible?

Example locomotive: http://www.steamlocomotive.com/texas/co.shtml
Inconsistent statements, but let's say about 92000lb TE. I recall the C&O 2-10-4 being around 6000hp.
http://www.thedieselshop.us/Data%20EMD%20SD70.HTML
4000hp, 175500 starting/137000 continuous.

This style of advanced steam might have twice the horsepower; imagine a single 12000hp locomotive. But, if it still had only 92000lb TE, it would be uselessly slippery. And how could it achieve 184000lb TE? That would require a factor of adhesion around 50%.

Honestly, with today's ability of using software controlled slip to increase adhesion (i know it sounds like an oxymoron) combined with solid-state inverters to power AC traction motors, any steam-based technology is just about impossible, especially when you consider that most trains require multiple diesels despite their monstrous tractive effort per unit.

If I was going to build a new steam engine, I'd seriously look at a dual-power system. There are three power systems that could be used:

1) A turbine-electric drive that could power traction motors on the trailing and tender trucks.
2) A diesel-style block spinning a generator to power traction motors on the trailing and tender trucks.
3) Standard piston-driven, rod-connected drivers.

I'd select #3 & either 1 or 2. if you found a way to use the steam twice, you'd be able to get a unit which burned local coal; had the high-adhesion of an AC traction diesel and the high-speed horsepower rating of a steamer.

If you ever looked at the patents on the ACE-3000, its a good start. My opinion is that they screwed up trying to use & re-use the steam over and over for all the auxiliary systems. Instead of running the pumps and the everything off the steam/water circuit, use the exhaust steam through a turbine or block to spin a generator to electrically power everything. If designed right, the power generated could be enough for a couple traction motors as well.

It's interesting that though diesels have a higher TE/HP ratio than steam, modern freights run faster than in the steam era. I've read that modern freights are generally HP-limited. I don't understand, then, why AC locomotives have achieved such success. If modern coal trains aren't like those of the Virginian in steam days (which climbed hills at 7-10mph), then why do you need those continuous TE ratings?

http://www.alkrug.vcn.com/rrfacts/hp_te.htm
This page is about diesels. Still, I can see there are at least some situations where such advanced steam would be useful. IIRC, the Missabe moved long ore trains over a ruling grade of about 0.3%. Estimating from the figures here, an advanced 2-10-4 (12000hp, TE 93000+10000 for a booster) could pull 15000 tons up that grade, and do it at over 30mph. That means an actual US 2-10-4 could move that same train at about half the speed. That does loosely fit with what I know; that C&O 2-10-4s could move very long trains.
So, on the plains, advanced steam would perform well. On anything steeper, you need to put a lot of horsepower on a train. Basically, on flat land or on hills, once you put on enough power to move a train, it can move at 25-30mph or more.

I suppose the HP/TE ratio issue is what led Porta to design a 2-10-0 for fast freight. I'm not sure how he planned to get around the instability 2-10-0s were notorious for at speed.

I know about steam-turbo-electrics. Those may be technically feasible now, but in the 1950s, they didn't work well. More advanced conventional steam, though, did work then.

http://thierry.stora.free.fr/english/achap_01.htm
An example of such steam: SNCF 242A1. It could generate 5300hp, but had a tractive effort of only 46255lb. With its axle load of 46500lb, this shows that it was still getting about the usual 25% adhesion. Being a European 4-8-4, I assume it was intended as a passenger engine.

the problem with steam is more basic than TE or drawbar HP arrangements, or rather, these discussions are moot - the problem with steam is thermal efficiency.
The steam Rankine cycle , even given modern high inlet conditions, full condensing (and closed loop), mechanical draft etc, can't achieve better than 35% thermal efficiency, which diesel electric has beat by 5points from the outset. then you get into the problems of steam engine support and maintenance fixed assets, coaling towers (and dont suggest burning oil), ash pits etc, and the operating costs of steam are simply unjustifyable.

then we get into fueling a steam boiler. the only reason to have steam power is to be able to burn coal, when there is no diesel fuel , or the supply is spotty. IF that is a strategic planning consideration then electrification offers the even broader options of buying electric power from various sources - especially high efficiency gas turbine combined cycle plants, and renewable energy.

To maximize the thermal efficiency of the rankine cycle full condensing is a must . the improvement over atmospheric pressure exhaust is at least 5 percentage points. that means exhaust steam is deep vacuum, neighborhood of 120 degrees, then returned to boiler feed pump. There is no exhaust steam energy available to drive auxileries. taking steam off the header or at a low pressure extraction point sometimes has advantages over operating everything parasitically off the generator, sometimes not. same is true for diesels - some things, like the lube oil pump and radiator fan are still shaft driven.

Not all radiator fans are shaft driven. That appears to be a choice based on mfg.

The DASH-8, DASH-9 and GEVO units from General Electric all run the air pump and the radiator fan off individual electric motors. I say "all" but I'm sure there are a few units that were specified differently, but all the units I've actually looked at are electrically driven.

As for the question re train speeds in comparison to HP/TE ratio, you have to remember that HP and TE are two separate measurements. HP measures the amount of power available to do work. TE measures how much max pull is able to be developed based on HP and adhesion.

In a diesel the combustion energy is converted to traction energy by the traction motors. In a steamer, the combustion energy is converted to traction energy in the cylinders by the pistons and drive rods.

In the diesel the combustion energy is already working, spinning the generator, which means even if the wheels are stopped dead, the engine can still apply significant power to the axles.

In the steamer, the steam must first overcome the inertia of the locomotive before beginning to generate tractive energy. This means that when they wheels are stopped dead, the engine is not producing any power in the axle.

This is why a diesel can start just about any train it is coupled to: The traction motors can produce clean even torque in the drivers even in a dead stall. A steam engine must be moving to actually generate pull, which is then affected by the uneven torque of the piston thrusts. This is why once a steam gets a train moving, it can usually keep it moving.

This is why I said the ultimate combination is a standard steam engine combined with traction motors.

Triplex--
Re: the instability that 2-10-0 were notorious for at speed.
Well, maybe heavy American 2-10-0. (I remember an alliterative phrase from Stauffer's "Pennsy Power": I1sa were "hard-riding hippos.") But a well-designed 2-10-0 could be surprisingly agile. British Rail's Class 9F 2-10-0 (from late 1940s and 1950s: last one built, I think, in 1960) were sometimes used on passenger trains, and there is an apparently well-authenticated report of one getting up to 90 mph. With 60-inch drivers!

My purpose wasn't to get into a discussion of the ideal steam locomotive or analyze its economics. I was trying to determine how fairly conservative advanced steam would run. Or, more accurately, did run, though not in North America.

I have to remind myself that, though there were 10000 ton trains in the US steam era, these appear to have been only on fairly level routes. It seems that trains in the 2000 ton range qualified as heavy freights when they were on mountain districts. The steam power necessary to move a modern coal train through Appalachia would be quite extreme.

Incidentally, D&H's high-pressure 2-8-0s and 4-8-0 supposedly had tractive effort (working simple without booster) of over 90000 lb. Doesn't that exceed the adhesion an 8-coupled locomotive has?

If memory serves, the formula for tractive effort didn't include the factor of adhesion. It only figured the weight on drivers, piston diameter & thrust, steam pressure and driver diameter.

jgallaway81 wrote:If memory serves, the formula for tractive effort didn't include the factor of adhesion. It only figured the weight on drivers, piston diameter & thrust, steam pressure and driver diameter.

don't forget the friction coefficient.... usually between .85 to 1.

My ideal of a steam locomotive would be either a 2-8-4 or a 4-8-4 with 80" drivers, 300 psi (figure about 6000 or so hp) and an additional turbine style booster under the firebox truck. i'm dissapointed that they never developed the booster design past the piston driven version. a turbine driven version with blade variability would be a great asset to a dead stop acceleration, especially with passenger trains. The heaviest 4-8-4 locomotives in service were the 2900 series on the ATSF, one of which is actually being restored. it had a driver weight of 294,000 lbs, allowing for a tractive effort of around 80,000 lbs on 80" drivers, giving a factor of adhesion of 3.67 (4.00 being nominal on a steam locomotive). adding a turbine style booster on the firebox truck not only increases tractive effort, but the overall weight on the drive wheels, including boosted wheels, giving better adhesion. a variable-vane turbine booster in theory would also be able to stay engaged at higher speeds whereas the traditional piston style boosters would need to cut out at aound 30 mph.

if you are gonna specify a booster, I think your best bet is an extended size tender with a compartment for either a variable speed turbine or a triple-expansion compound cylinder block running a generator that powered traction motors on the trailing trucks: no more movable gears, etc. The double is that with a generator you could also produce enough power to create a field in traction motors on the trailing truck (x2) plus as much as 6 additional motors on the tender axles giving the engine the option of dynamic braking, which from a train handling perspective, is the second biggest advantage diesels had over steam.

jgallaway81 wrote:if you are gonna specify a booster, I think your best bet is an extended size tender with a compartment for either a variable speed turbine or a triple-expansion compound cylinder block running a generator that powered traction motors on the trailing trucks: no more movable gears, etc. The double is that with a generator you could also produce enough power to create a field in traction motors on the trailing truck (x2) plus as much as 6 additional motors on the tender axles giving the engine the option of dynamic braking, which from a train handling perspective, is the second biggest advantage diesels had over steam.

yep... the closest a steamer has ever gotten to dynamics is C&O 614, which had an MU panel installed to operate any coupled diesels.....

I assume a tender booster would reduce in effectiveness as fuel and water were used and adhesive weight declined.

Triplex wrote:I assume a tender booster would reduce in effectiveness as fuel and water were used and adhesive weight declined.

that's evident.

getting back to your original point, as to exactly what improvements wold be achieved by applying the incremental improvements suggested by Porta, et al - all of those improvements are directed not necessarily at increasing capacity of the locomotive, but very definately at improving the economy. more pounds of steam per pound of coal from the boiler and more kwhrs (or hp-hrs) per lb of steam from the engine.
That does suggest lighter boiler, lighter engine cylinders, and smaller tender (or greater range) for a given horsepower, and less work for the fireman.
If tractive effort and adhesion are a concern due to reduced mass of machinery, then it's possible a greatly improved steam locomotive might need to be ballasted up to a required weight as indeed diesels often are, or their frames can be made more massive.

Fan Railer wrote:

jgallaway81 wrote:if you are gonna specify a booster, I think your best bet is an extended size tender with a compartment for either a variable speed turbine or a triple-expansion compound cylinder block running a generator that powered traction motors on the trailing trucks: no more movable gears, etc. The double is that with a generator you could also produce enough power to create a field in traction motors on the trailing truck (x2) plus as much as 6 additional motors on the tender axles giving the engine the option of dynamic braking, which from a train handling perspective, is the second biggest advantage diesels had over steam.

yep... the closest a steamer has ever gotten to dynamics is C&O 614, which had an MU panel installed to operate any coupled diesels.....

The 2 UP Steam Program locomotives (4-8-4 and 4-6-6-4) have M.U panels as well..

M.U. is one thing, dynamic braking another! Dynamic braking in pretty much the sense in which the term is used in talking about diesel-electric locomotives (using the "motors" backwards, as it were, to convert some of the train's kinetic energy into a form in which it can be dissipated) WAS possible on steam locomotives, and I think used on (at least some) ATSF 4-8-4. Saturated steam would be admitted to the cylinders, where the forward motion of the train would compress (& so heat: Boykle's Law) it, with the resulting superheated steam being exhausted up the stack.