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LD Porta : Last Great Steam Loco Designer

by Helen Wed Jul 12th, 2006 at 08:47:24 AM EST

When LD died in 2003 the chapter of Great Steam Locomotive Engineers was brought to a close. It is arguable that they were never many in number: Becoming a chief engineer in any large organisation is rarely gifted to innovators. Richard Trevithick, George Stephenson, OVS Bullied and of course, the greatest of them all, Andrée Chapelon (as described by DoDo). But LD Porta was a distinguished member of the club.

His demonstration piece was his very first rebuild in 1947. Sanctioned by President Peron himself, he transformed an old 4-6-2 wheelbase locomotive into a 4-8-0 that was internally completely different from any engine that had gone before.

All of the steam circuit, the means by which high pressure steam moves through the engine from generation to exhaust, was completely re-modelled. He took Chapelon's ideas of promoting efficiency through the use of large-bore pipes and over-sized valves for low reistance to even greater heights.

However, it was his development of the coal gas circuit that was Porta's great contribution to steam engine efficiency. Previous understanding of the heat exchange from burning coal was that it burnt in the grate. So air would be intruduced through the base of the grate by means of vents to provide oxygen to feed the fire. This would, at high speed, create a white hot furnace from a hurricane force blast of air that would frequently lift the coal directly from the fireman's shovel and fire it unburnt from the chimney itself. It was not uncommon to see flames coming from the chimney of a hard-working engine as if the entire locomotive was on fire.

Porta was the first to realise that it was these gases that were being burnt as they were driven from the coal that was providing the heat and not the coal itself. If these gases were being burnt anywhere else in the engine apart from the designated combustion chamber of the firebox, then it wasn't going to happen efficiently. So he re-designed the firebox with an enlarged brick arch (burn catalyst), a reduced draught through the fire-grate and with the innovation of most of the air being introduced above the fire. This was the first use in a locomotive of the Gas Producer Combustion System common to most industrial coal burners and provided a much more effective combustion capability.

Finally he finished off with the use of a Kylchap chimney that was the most effcient way then known of dragging these exhaust gases through the engine (it is the steam being evacuated from the cylinders that "entrains" the coal gases out of the chimney).

The results were remarkable. On test the engine was found, in non-optimal track conditions, to have a thermal efficiency of 11.9%. A truly phenomenal figure considering that most British steam locomotives built in the same era was below 8%. It achieved a projected tractive effort of 52000 lb, fully 10,000 more than the most powerful British engine of similar type (Thompson A2).

And this was his first effort !!

Sadly, politics and the oil lobby were against him. Argentina largely abandoned the development of steam very soon after. He did some work breifly for the American coal producers and thereafter jobbed around the world, essentially frittering his genius away until David Waredale of South African Railways contacted him in the late 70s. Between them they re-designed one of the old 25-NC express train warhorses and created the class 26 "Red Devil".  Although SAR were belatedly following the world in energetically eliminating steam which curtailed a full examination of the engine's capabilities, preliminary studies showed that, with a reduction of fuel consumption of nearly 40%, thermal efficiency had been increased to over 15%..

With diesel fuel increasing in price, who knows whether LD Porta's work may achieve some posthumous revitalisation ? But his legacy remains as one of the great might-have-beens in railway history.

For comparison, gasoline engines (Otto cycle engines) typically operate at around 20-25% thermodynamic efficiency these days, and diesel efficiencies are above 40%. This is well above the 15% efficiency mentioned for steam engines around 1950, but it turns out that Otto cycle engines were also about 15% efficient at the time. I don't know what a steam design could accomplish with current technologies.
(References: Encarta: Internal-Combustion Engine and EFFICIENCY OF INTERNAL COMBUSTION ENGINES)

Words and ideas I offer here may be used freely and without attribution.
by technopolitical on Wed Jul 12th, 2006 at 12:52:59 PM EST
I don't know what a steam design could accomplish with current technologies.

Not much higher. The Red Devil is claimed to have reached 15.9% once, which remains the record for a normal locomotive. The machines built in the nineties by Swiss company DLM do 13%. As for future projects, check out the Advanced Technology Class 5AT 4-6-0 -- they plan for a 14.1% thermal efficiency.

Note though that various special designs (fireless, high-pressure and condenser steam locomotives) can go higher.

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Thu Jul 13th, 2006 at 03:44:39 PM EST
[ Parent ]
Unfortunately for steam engine lovers, there is more to locomotive design than thermal efficiency. One problem with steam engines is the poor balance of the driving wheels, which is hard on the track. Also, they are miserable to drive, being uncomfortable and dirty. In addition, modern diesel-electric locomotives have very sophisticated control systems that offer independent control of each axle, which improves the ability of operating at the limit of traction. The introduction of electricity into the equation allows the use of multiple un-manned helper units, and can support an integrated diesel-electric hybrid system.

Perhaps some of these difficulties might be overcome with a large development program...

by asdf on Thu Jul 13th, 2006 at 12:32:58 AM EST
The driving wheels are not unbalanced. That is the purpose of the large balance weight clearly visible in all such.

The issue is that being driving wheels, where there has to be a direct mechanical linkage between the wheel and the driving force (cylinder assembly), there is a considerable unsprung weight impacting on the track. The "hammer blow" resulting from the combination of the weight and the vertical force from the cylinders can exceed  20 tons per wheel. It is that which wears the track.

I don't dispute that it's a problem tho'.

The issue of the discomfort of working on steam engines is largely moot. Much of that was from a victorian attitude towards worker comfort and safety that was hardly restricted to railways. And anyway, even nowadays you'll find many drivers (mostly now retired) who worked on both steam and other traction who would gladly endure the discomforts of steam for the professional pride of working such beasts.

keep to the Fen Causeway

by Helen (lareinagal at yahoo dot co dot uk) on Thu Jul 13th, 2006 at 04:59:59 AM EST
[ Parent ]
poor balance of the driving wheels, which is hard on the track. Also, they are miserable to drive... independent control of each axle

Oh, no problem there, there were special solutions :-) There were of course the steam-electrics -- and the steam-motor locomotives. For example the German 19 1001, built during WWII,  ended up in the USA where it was scrapped:

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Thu Jul 13th, 2006 at 03:49:33 PM EST
[ Parent ]
Thanks for this great diary, I almost missed it! I'll controbute links and pictures.

Here is a picture of the Argentina:

If someone is interested, suggested further reading: Martyn Bane's detailed discussion of the Argentina; a more condensed article in Railway Preservation News; Trainweb article on Porta.

Also, here is an image of a SAR Class 26 "Red Devil":

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Thu Jul 13th, 2006 at 02:30:51 PM EST
I'm pleased you like it. I saw you on other threads and worried you thought it was rubbish.

I just felt that LDP should be noted along with the others in your series.

Great photo of the Red Devil

keep to the Fen Causeway

by Helen (lareinagal at yahoo dot co dot uk) on Thu Jul 13th, 2006 at 04:27:55 PM EST
[ Parent ]
Vandalism in progress... Delete parent!

Nothing is 'mere'. — Richard P. Feynman
by Migeru (migeru at eurotrib dot com) on Wed Aug 2nd, 2006 at 01:48:27 AM EST

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