> The heart of what I proposed is based on a
> Chapelon 4-10-2 of around 1950's which was half built.

Nigel, don't you mean 2-10-4?

I disagree -- part of any proper modern steam system would be suppression of priming and water carryover... ;-}

There is two meanings of foam used above. One I don't want to do here and then there's the one directly relating to the boiler water treatment is important and yes a layer of foam acts like a filter on the steam. It has to be treated with antifoam to make it work correctly. High alkaline and tannin braised water treatment would be most important to a super engine. In that respect Porta's system is good. Certainly on the servicing side mentioned water treatment is a high priority and would be used on my loco.

Maybe the most important aspects of an engine are water treatment, good piston rings, good draughting and combustion along with a nice big chime whistle or two.

And yes Robert I meant the 2-10-4.

One of these:

A "doable" Jawn Henry. LOL

-Chris

I thought I'd mentioned the Steins locomotive in conjunction with Kirchhof's patent 2518024, which is almost necessary if the little truck-mounted engines are going to be kept synchronized. That is the valve gear that became Franklin type D (as fitted to USATC 2728/611).

There is an oil-fired variant of this design, with longer-wheelbase trucks and very DD2ish styling, running around out there somewhere.

Heresy: I would discard ALL reciprocating steam locomotive technology. I would build a steam electric generating plant on a rail car. Then it could supply power via a cable to any existing electric locomotive. A tank car with large radiators aboard could be used to condense used steam and supply water to the steam generator car. Little additional water would be needed.

Note that a regular steam-turbine electric already puts the important parts of that electric locomotive under the steam-generation plant, and uses the seight of the plant for adhesion. Additional connection to road slugs (or, if you want, electric locomotives) is then done if 'more motor' is needed for starting or slow-speed running. There is little reason why you could not also have a pantograph and main transformer available to run under catenary (there are good reasons for a self-powered locomotive to have a pantograph, but I will not go extensively into them here).

You are SUBSTANTIALLY underestimating the amount of radiator surface needed for effective condensing of the level of horsepower needed for a steam-electric plant of the required scale. You might need several tank cars' worth of panels, each with full pressure (and vacuum-capable) connections for the steam and condensed hot water, for just the 8800hp equivalent of two modern diesel-electrics. I have proposed the use of reclaimed 'greywater' to spray on the exterior of the heat exchangers to aid in the condensation process (for which you need separate tank cars, but you would save on the treated and deoxygenated boiler feedwater). You might also use a variant of Holcroft-Anderson 'recompression' to regain some of the latent heat of vaporization for your Rankine cycle -- you would need reasonably constant operation of your expander (steam engine driving the alternator(s)) in order for this to work reliably, but there are ways of achieving that even with the 'usual' sort of real-world train operation...

Interestingly Robert, he didn't mention the "T" word. Which begs the question of other types of expanders apart from reciprocating or turbines.......But I think we can't ignore the question of a trade off between the efficiency of the direct mechanical drive in the reciprocating engine and the inefficiency of an electrical transmission and the inefficiency of reciprocating technology and the efficiency of turbines running at steady state. Don't know what trade off consideration is required for other types of expander since he didn't spec any form.

dave

I think we can presume he meant the T word because it was a self-contained steam-electric plant, and for that particular service turbines have been preferable (think of them as compound engines with a great many stages). He might have the packaging room for the very large exhaust plena, and very large actual condenser volume and heat-exchanger surface, needed to get the requisite mass flow and low exhaust pressure appropriate for best turbine operation.

One alternative expander is the vane type, which is one of the variable-displacement motors. There are some others, like the Elliptocline or the Quasiturbine, that might have a place in locomotive propulsion but not, perhaps, in steam-electric operation. Remember that a positive-displacement piston motor with good cutoff arrangements can be more efficient at part-load than a turbine. But if you have a large plant, and just one expander, it's awfully nifty to have 'distributed drive' to the wheels, which is one thing that electric transmission does very well. (As is distributed drive to wheels not directly under the locomotive, which is something that steam does NOT do very well...)

The advantage of direct-drive reciprocating power is that there is a peak to the horsepower curve that is in the operating range, and the external combustion means that available power in the engine is not limited to the pressure work done by fuel combustion gas release directly in a cylinder. While there are many -- too many -- steps in between combustion and pressure work in an external-combustion engine compared to an IC engine, there's a combination of heat recovery via the Rankine cycle and the power 'cushion' represented by the overcritical boiler water mass that increases overall system economy... if done carefully and exhaustively (no pun intended).

I do not doubt that some of these power stations on wheels are possible but you have understand the power to weight ratio of such machines can be poor. They could be built with whole bank loads of money, no question. Fundamentally you can design any machine but its got to fit the job that's got to be done. Read the lessons of ACE.

Fundamentally an advanced stevensonian loco has still much to offer as a dream that can be realised within an affordable budget. Dreams and I like dreaming of what I could active are only as good as the money behind them.

Ok, this is my electrical engr background speaking. For a reciprocating design, I would be very interested in looking at a 3-cylinder engine, each power stroke 120 degrees apart (similar to the three phases of electric power). Three phases make for a nice smooth power curve. The Shay engine would be a good place to start. I can imagine a modern Shay engine design where each cylinder assembly is removable like a diesel powerpack, and the crankshaft is enclosed in a crankcase. All this is just me daydreaming. I have never studied the works of Chapelon, Porta, Wardale, or the N&W designs, so I am quite ignorant on second generation steam.


Pistons, Shay locomotive by roy.luck, on Flickr

The objections to a modern Shay would not center on the engine reliability, they would center on things like the off-center balance of the chassis and the downright lousy characteristics of drive to the wheels.

One thing to remember is that the power transmission of a double-acting engine is different from that of a single-acting engine like a conventional diesel; in electrical terms it is six-phase. So even torque peaking becomes less of a concern. For packaging reasons, however, it may be better to consider the V4 "Heisler" sort of arrangement, as a DA V-4 (90 degree bank angle) has exceptional balance, fits neatly under a conventional boiler, could be made with a shorter crank with just two throws, and is amenable to your sectional engine construction (in fact, even more so because there is less structure impeding removal of the 'powerpacks', and involving no more care in R&R than is already required for a V-configuration diesel engine). You also get nice Cardan-shaft drive close to the centerline, and enclosed gearing to drive the wheels is then centered, can be frame-mounted in the trucks and quill drive used to reduce the unsprung mass, etc. etc. etc.

Remember that a locomotive is a full system, not just a motor with some appurtenances attached. If you are dedicated to the three-cylinder approach, mount it transversely, either as Bulleid did in Leader, or as a vertical engine a la Sentinel (either of which you can look up online to get more details than I could use for MEGO induction on this list). The vertical approach would be easier to modularize.

I'd also mention that you must use care when building steam motors with enclosed crankcases -- if these are also used as lubricant sumps, any blowby or leakage of steam will contaminate the lubricant. You can either design explicitly for tolerating water in the lube, or design the 'powerpacks' to have a full crosshead external to the sealed part of the crankcase (as was done in some automotive steam applications).

OK, so we build a Shay with triple expansion engines on both sides of the boiler, set as much in opposition to each other as possible strokewise for minimal impulsiveness (60 rather than 120) and run a keel condenser in the wet ditch alongside the ROW.

A question I was thiniing about regarding waste heat in locomotive style boilers...... is the remaining heat in the products of combusion that come out of the tubes into the front end used for any purpose in the operation of the front end or is it just shoved out the stack having done nothing of use after leaving the tubes?

dave

Dave,

Love that condenser idea! We could even use track pans so we didn't have to worry about weeds, snakes, and snipes getting hung up in our condenser. ;-)

Any temperature difference between the gases leaving the stack and the surrounding air represents "lost" energy. The more heat you extract from those gases before they leave the boiler, the more efficient your boiler. The downside of this is that when the gases cool to a certain point (something less than 180 degrees F or so) the water (which is a product of burning fuels containing hydrogen) begins to condense out. This is good from a thermodynamic standpoint (condensing water transfers a lot of heat), but bad from a durability/maintenance one. This water combines with sulfur in the exhaust and forms sulfuric acid which tries to eat your boiler and smokebox parts. I understand this was a real problem with Franco-Crosti boilers with their supplemental preheaters. Some of them used porcelain-coated tubes to try to deal with this.

Many modern boilers used to provide heat for buildings are of "condensing" type, in which they deliberately cool the gases as far as possible to extract most of the available energy from the combustion gases. As a result of the exhaust being "cool", they can use common PVC pipe for the exhaust duct. However, many have a small supplemental system to neutralize the acid in the condensate before it's dumped to the building's sewer system.

OK, I think I caused the thread to officially 'jump the shark' by bringing up the Shay. But thanks to everyone for playing along, and thanks to Overmod for the very interesting reply. You guys really know this subject!