GWR four-cylinder arrangement?

That's a comprehensive summary of the usage of 2-cylinder compounds in England. But for the full UK picture, don't forget Bowman Malcolm's engines for the Belfast & Northern Counties. The last of the 3-ft gauge compound 2-4-2Ts was in use until 1954.

https://en.wikipedia.org/wiki/Steam...03)_&_Northern_Counties_Committee_(1903–1949)

At the height of its popularity at the end of the 19th Century, the 2-cylinder compound was being constructed in large numbers in many countries, particularly in Continental Europe but even in the USA. Although I don't know whether there were any in Denmark to inspire @Hermod!

The system lost favour after 1900, as increasing loco size and train speeds exacerbated the inherent problems of balancing and of finding space for the large low-pressure cylinder. Some railways moved onto the 4-cylinder compound (the 3-cylinder compound was rare outside UK), but the arrival of the Schmidt fire-tube superheater reduced the popularity of all forms of compounding in most countries outside of France.

There has been as lot of interesting debate on this thread, but not much has been said about 4-cylinder arrangements, on the GWR or anywhere else! Still no sign of the Mid-Hants or the Swanage looking at a new-build Drummond T14!

 

Dont forget the GNR(I) Loco's

https://www.steamtrainsireland.com/rpsi-collection/5/no85-merlin

 

Compound road engines were fairly common, but the simpler single cylinder was more common for agricultural use. Strangely the compound traction engines that looked better on paper tended to be quite shocking machines whilst the not so good on paper were often more pleasant.

 

Sorry for the late reply to this comment, thinking about it, it also depends on the characteristics of the traction motors. A shunt wound DC motor, fed from a constant DC voltage supply is essentially a constant speed machine, so the motor would only have to be running a few percent faster than the other three for the back emf to build up and reduce the armature current and the resulting torque. A locomotive is more likely to have series wound motors, because they have better starting characteristics, but if the axle slips, the reduction in armature current will also give a reduction in field current, limiting the back emf, so the motor will tend to "run away" more when slipping. It's also possible to have compound wound motors (nothing to do with compound steam engines) which have both shunt and series field windings and a characteristic in between the two extremes.

I'm also thinking of the effect of weight transfer away from the leading axle, and if I remember correctly the 1500V DC EM1s on the Woodhead line had the buffers and couplings mounted on the bogies, with the two bogies connected by a drawbar. I think the effect of this was to reduce the weight transfer between the bogies. I don't know whether the feature has been used on other locomotives.

 

Also - with apology for late reply to this interesting thread - maybe the human factor is an mportant reason for a substantial loss of fuel economy, in engines so large that their firing rates call for for a mechanical stoker?

An advantage of firing coal by a human is that the said fireman has an automatic incentive to get the firing rate just right. Put too much coal on, the engine blows off, you have wasted not only some fuel, but the extreme physical effort you've just put into firing the excess.

With a mechanical stoker, surely, there is not quite the same always-present incentive to be economical. You might only exercise sufficient care if there's an inspector on the footplate, or if actual coal consumption is being measured.

In debating overall efficiency, one has to think of the real-world applications of steam locos in everyday service, not the ideal of a heritge railway or steam charter with a carefully prepared, expertly crewed loco (and a train full of critical folk with stopwatches or magazine articles to write!).

Everyday steam crews did not always have total focus on perfect economy, they might be more concerned about private difficulties - or just getting home for a pint and watching the match.

 

One advantage of mechanical stokers were that they maximised output. This might have been the difference between double-heading and a single locomotive. in France there was a speed limit of 120kph. Over undulating routes, maximum power was necessary to keep time.