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Imaginary Locomotives


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1 hour ago, RLBH said:

What I suspect happened was a two-pronged failure. I think they did accurately determine the power that could be sustained by steam locomotives, without fully appreciating the benefits that being able to mortgage the boiler brought in terms of temporarily exceeding what would be called a 'continuous rating' on a diesel locomotive.

 

Perhaps more significantly, I don't think they accounted for drivetrain losses. A steam engine rated at 2,000hp delivers that straight to the wheels. A diesel-electric locomotive loses about one-quarter of its' rated power between the engine and the wheels, and a diesel-hydraulic tends to lose about one-third. So, equalling an 8P rated at 2,000hp needs a 2,650hp diesel-electric, or a 3,000hp diesel-hydraulic.

Yet diesels are far more efficient than steam. The reason is simple, with a steam engine energy is lost between the boiler and the cylinder. With any form of IC engine the energy is confined to the cylinder. 

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36 minutes ago, PhilJ W said:

Yet diesels are far more efficient than steam. The reason is simple, with a steam engine energy is lost between the boiler and the cylinder. With any form of IC engine the energy is confined to the cylinder. 

Diesel engines are, locomotive transmissions are not.  Hydraulic is in theory more efficient but is still inherently mechanical in nature, so does suffer heat and noise energy losses, which is why the Westerns were actually a disappointment on the South Devon banks, showing about 40% power loss at the rail.  Electric transmission is much more efficient but probably still "only" about 80%.

Steam loco boilers are very efficient but design of the steam passages and valve gear can make or break the power extracted from a good boiler.  Duke of Gloucester is considered to be the most efficient simple expansion (as opposed to compound expansion) steam locomotive ever built.  Bullied's Merchant Navies are also exceptionally good.

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1 hour ago, PhilJ W said:

Yet diesels are far more efficient than steam. The reason is simple, with a steam engine energy is lost between the boiler and the cylinder. With any form of IC engine the energy is confined to the cylinder. 

It's a bit of a stretch, but you could probably equate the firebox to the diesel engine itself, the boiler to the generator, and the cylinders to the traction motors. Electrical machinery typically has about 90% efficiency, so that transmitting 80% of the engine's output to the wheels is fairly straighforward. Early diesel-electrics achieved a bit less, so the 65 to 70% of a well designed firebox and boiler doesn't look too bad.

 

Inconveniently, the thermodynamic cycle takes place at opposite ends of the system, but it's them that lock in the inefficiency of steam. The best steam locomotives built only used 15% to 18% of the energy in the steam - Porta's ideas about improving thermal efficiency notwithstanding. That limits them to about 12% of the energy in the fuel being turned into power at the rail.

 

By comparison, a realistic diesel engine can turn 40% to 50% of the energy in the fuel into crankshaft motion, which with realistic transmission losses gives them 30% to 35% efficiency overall. On top of which you get the advantages in availability and labour saving. Steam is really a losing proposition unless you have cheap labour and cheap coal.

 

Missing the transmission losses is one of those mistakes that seems obvious in hindsight, but was probably forgivable - those writing the specifications had likely never had to think about it, because transmission losses aren't really a concern for steam or early DC electric locomotives. In the latter case, they do exist, but are palmed off on the electricity generating company and the electrical engineering department, so the locomotive engineers don't really have to deal with them. And it's remarkable how well 'fixing' the transmission efficiency issue solves the issue of diesel Types mapping on to steam Power Classes.

 

Just looking at the Riddles classes for BR and the War Department:

  • Duke of Gloucester is right at the top of the Type 4 band; the other express Pacifics she worked with are firmly into Type 5.
  • The 9F, Britannia and Clan all equate to Type 4s - the first two are pretty close to the Peaks, the Clan is at the bottom end of the range and very comparable to a Class 40.
  • The 5MT and 4MTs all equate to Type 3s, as do the WD 2-8-0 and 2-10-0s.
  • The 3MT, 2MT and Hunslet 0-6-0 are all Type 2s.

 

That all seems broadly correct in terms of work undertaken. Steam was generally limited by tractive effort rather than by power. So it makes sense that in a classification system which is based on power, the smaller steam locomotives will be rated fairly highly. That's why almost any steam loco could put in a decent performance on a branch line freight working, but a Class 08 diesel shunter isn't much use for anything outside a goods yard.

 

The rough rule is, a steam locomotive can pull at speed anything it's capable of starting, whilst a diesel can start anything it's capable of pulling at speed. Even the smallest, least powerful diesel locomotives had tractive efforts comparable to the largest diesel locomotives - the sole exception being the LNER U1, which cheated!

 

I've tried coming back the other way to equate diesel & electric traction to steam locomotive power classes; that's easy for freight (all the main line locos are 9F!) but very difficult for passenger rating. Partly because the BR power factor formula is a bit of a fiddle to make things come out 'right', and partly because diesel locomotives have a serious lack of grate area and boiler tubes.

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Here's a random idea - steam-electric locomotives? They could use the same principles as a normal locomotive, but as opposed to burning coal, they could use electric superheaters powered by third rail (or overhead) electricity, effectively being a giant version of the Hornby Live Steam mechanism. They'd also use modern advancements, improving on the older design like they did with Tornado, or a completely new locomotive design. Opinion?

Edited by ScottishRailFanatic
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7 minutes ago, ScottishRailFanatic said:

Here's a random idea - steam-electric locomotives? They could use the same principles as a normal locomotive, but as opposed to burning coal, they could use electric superheaters powered by third rail (or overhead) electricity, effectively being a giant version of the Hornby Live Steam mechanism. Opinion?

 

Yup, the swiss went there during ww2. 

I think it's been discussed as an option on here before a few times, very long thread to go back through now though!

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1 minute ago, ScottishRailFanatic said:

*INTERNAL SCREAMING*

If they'll look like that, forget it!

I'm modifying an A4 to look like it's powered by overhead wire... I'll post some pictures when I get home.

Coal section is taken up by the pantograph with grilles on either side of the tender to give the idea that there's a backup generator powered by diesel. It's going to be running a 2nd tender due to the diesel and electrical gubbins taking up more space.

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1 minute ago, Rockalaucher101 said:

I'm modifying an A4 to look like it's powered by overhead wire... I'll post some pictures when I get home.

Coal section is taken up by the pantograph with grilles on either side of the tender to give the idea that there's a backup generator powered by diesel. It's going to be running a 2nd tender due to the diesel and electrical gubbins taking up more space.

I'm doing the same. Peculiar...

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Perhaps the electricity pickup would be more appropriately placed on the support coach. It could also have a small traction motor setup for a little bit of extra oomph starting off, and supply ETH etc  to the train without complicating the locomotive. 

 

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2 minutes ago, ScottishRailFanatic said:

I'm doing the same. Peculiar...

That is peculiar... Is yours set out as if it was modified when they were still ins service or as a fictional newbuild? Mine's the latter and I'm stumped on livery... Thinking BR Green late crest. Should look good seeing as I've utilised the tornado tender and truck frames to give it the appearance of roller bearings, which will be painted yellow with the red stripe.

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Just now, Rockalaucher101 said:

That is peculiar... Is yours set out as if it was modified when they were still ins service or as a fictional newbuild? Mine's the latter and I'm stumped on livery... Thinking BR Green late crest. Should look good seeing as I've utilised the tornado tender and truck frames to give it the appearance of roller bearings, which will be painted yellow with the red stripe.

Same over here, although my livery is going more modern... BR blue?

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3 minutes ago, JimC said:

Perhaps the electricity pickup would be more appropriately placed on the support coach. It could also have a small traction motor setup for a little bit of extra oomph starting off, and supply ETH etc  to the train without complicating the locomotive. 

 

True but in a realistic sense would that not make turning the loco a lot harder?

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3 hours ago, RLBH said:

Perhaps more significantly, I don't think they accounted for drivetrain losses. A steam engine rated at 2,000hp delivers that straight to the wheels. A diesel-electric locomotive loses about one-quarter of its' rated power between the engine and the wheels, and a diesel-hydraulic tends to lose about one-third. So, equalling an 8P rated at 2,000hp needs a 2,650hp diesel-electric, or a 3,000hp diesel-hydraulic.

2000hp? Measured where, under what conditions?

Be very careful with terminology here. Where you measure the power makes a big difference. Effectively, the boiler and firebox of a steam engine can be considered it's "engine", the cylinders, valve gear and wheels are it's "transmission".

Power at rail is not the same as drawbar power, boiler power, indicated power or brake power.

Edited by rodent279
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2 minutes ago, ScottishRailFanatic said:

Same over here, although my livery is going more modern... BR blue?

See this is what I mean, really torn on livery, but I don't think I can bring myself to put yellow ends on an A4... But wasp stripes on the rear of the tender could look cool. The reason BR green is standing out to me is because imagine the rivet counters going mad if and A4 was painted in anything other than authentic livery irl.

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1 minute ago, Rockalaucher101 said:

See this is what I mean, really torn on livery, but I don't think I can bring myself to put yellow ends on an A4... But wasp stripes on the rear of the tender could look cool. The reason BR green is standing out to me is because imagine the rivet counters going mad if and A4 was painted in anything other than authentic livery irl.

I'm just going to have yellow buffer beams and corridor connection, the rest is blue and the black smokebox is retained.

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3 minutes ago, ScottishRailFanatic said:

I'm just going to have yellow buffer beams and corridor connection, the rest is blue and the black smokebox is retained.

Think I've seen a photoshopped image of 60009 or 60007 in intercity that has a yellow buffer beam. Might see if I can find it

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33 minutes ago, ScottishRailFanatic said:

*INTERNAL SCREAMING*

If they'll look like that, forget it!

 

One designed from scratch would look even less like a traditional steam loco.  Probably like a diesel or electric, with a lot of aesthetically unpleasing equipment hidden inside a casing.

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1 hour ago, Satan's Goldfish said:

 

Yup, the swiss went there during ww2. 

I think it's been discussed as an option on here before a few times, very long thread to go back through now though!

 

Hence the derogratory term "kettle" for a steam loco...  :whistle:

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1 hour ago, rodent279 said:

Power at rail is not the same as drawbar power, boiler power, indicated power or brake power.

Indeed, and my terminology was deliberately vague because of that. When a horsepower figure is quoted for a steam locomotive, it's usually 'at rail' or drawbar power - which of course aren't quite the same thing. When it's quoted for a diesel locomotive, it's almost invariably the brake power of the prime mover, which is entirely different again and much smaller than either.

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18 minutes ago, ScottishRailFanatic said:

Right, getting the full IC livery went down the drain so I modified the BR lined blue. Not much to look at but I’m happy with it.

A1219434-F06D-4BE2-9655-0956746CEB29.jpeg

That looks cool. Quick question though, what happened to your attempt at full IC livery? Just couldn't get the lines or...

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5 hours ago, RLBH said:

What I suspect happened was a two-pronged failure. I think they did accurately determine the power that could be sustained by steam locomotives, without fully appreciating the benefits that being able to mortgage the boiler brought in terms of temporarily exceeding what would be called a 'continuous rating' on a diesel locomotive.

 

Perhaps more significantly, I don't think they accounted for drivetrain losses. A steam engine rated at 2,000hp delivers that straight to the wheels. A diesel-electric locomotive loses about one-quarter of its' rated power between the engine and the wheels, and a diesel-hydraulic tends to lose about one-third. So, equalling an 8P rated at 2,000hp needs a 2,650hp diesel-electric, or a 3,000hp diesel-hydraulic.

I knew a Carlisle driver on the WCML who had driven Coronation Pacifics, all classes of diesel and electric locomotives. He said "On a summer morning with 16 sleepers on the back a Coronation was lovely to drive as it plodded up Shap, on a frosty morning give me an 87 topping the summit at 100mph and the cab heater on full blast."

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