GWR four-cylinder arrangement?

Call it what you like but it's not going to be much bigger than coal dust. The Pennsylvania Railroad, for one, calculated the extra coal consumption used by the stoker as 5% which includes that used by the stoker and the material going up the chimney. The 25% sounds like a finger in the air.

 

If you’ve ever emptied a smokebox you’ll know that what gets through the tubes and into there is certainly more than dust. A loco working hard will certainly end up with particles as big as 1/2”. Locos fitted with spark arrestors have fine mesh grids in the smokebox to stop large particles from being ejected up the chimney.
I can believe 25% as the small coal used in stokers will soon be burnt to a size where the exhaust will lift it and the steam jets used to place the coal help keep it off the firebed. However, I’ve no factual evidence to support it as I’m on holiday. I’m sure the stoker fitted 9F’s were tested and, if so, someone will have the report.

 

It seems to me that ......

The loco needs to be suitable to do the job required - hence the failure if the P2, sounds like a great loco BUT the rolling stock could not handle the force it could produce in the drawgear etc. Ditto the proposed Garret for the Southern would have no doubt have done an excellent job just not what was needed.

Then of course as you move into 'high performance' steam loco's you get the steam equivalent of a Deltic with manner of interesting issues living in an environment full of abrasive dirt and men with big hammers...........

 

Yes, I have emptied many a GWR smokebox, always without screens. I have never seen anything approaching 1/2". I would refer to it as char, fine, partially burnt coal particles.

 

Is this view not a little parochial? In the UK, there wasn't much requirement for anything above about 2,000hp. In France, the speed limit for express passenger at the time was 120kmh. Timetables had to be maintained and high hp was required, particularly on the undulating routes in eastern France. I don't think that anybody with any knowledge of the subject would describe the 240As, 240Ps and 242A1 as inefficient in comparison with other steam classes. Not only were they they more powerful than comparable classes but were also more economical in the use of coal and water. Maybe a little research would be advantageous? In the USA, the use of 5,000hp articulated locomotives would have been more economic than 2 x 2,500hp locomotives, which would probably have had stokers anyway. Stokers were fitted to most heavy locomotives by the mid-1920s and would later become a legal requirement, on safety grounds.

 

And the 5000 hp articulated locomotives in America were killed off by 1500 hp diesels lashed up in multiple.

 

The real issue of course is that a steam loco doesnt have a transmition.

As a result while a diesel or electric loco can produce full power across the speed range a steam loco cant hence the slogging uphill at close to walking pace

 

Erm . .. have you ever tried driving a heavily loaded diesel up a steep gradient?

 

I’ve seen the monster trains in the USA and in spite of the number and size of the locos on them, they don't go very fast up the grades.

 

Challenger 3985 slogging up the 1 in 100 of Archer Hill at “walking pace”.

 

What’s wrong with the first post? Within the limitation of adhesion, a diesel locomotive is a constant horsepower machine whereas a steam locomotive is a constant tractive effort machine within the limitations of its boiler.

 

What's wrong with it is that it suggests, even if it doesn't state, that whereas a steam engine struggles against gradients a diesel will fly up it with ease, which isn't the case. The power output of any internal combustion engine varies with the r.p.m.; there is a maximum power output at a given engine speed and the power reduces either side of that, and the engine won't necessarily reach the optimum r.p.m. at low road speed due to internal resistance within the motors and the load required by the main generator. The next problem is that, whatever the power output of the engine, the traction motors have to be able to cope with it and the wise driver, rather than pulling the controller over to the highest notch, moves it one notch at a time keeping the amps just below the red line. If you go over that the engine is going to throttle itself back and you're starting again and possibly having to reset the trips. But as speed, and therefore traction motor speed, rise the amps fall so you can apply another notch to bring the amps back up for more power to the rails. I was on a Class 85 electric leaving Preston southbound on a damp rail. Three of the ammeters were just below the red line but the leading one was much lower. This axle was slipping so not delivering power and drawing little current, but it cleaned the rails ahead of the others. Applying sand immediately brought the leading axle's amps level with the others, but it would fall again as soon as the sanders button was released.

Getting a heavy train moving with a diesel requires skill, and keeping one moving at speed also requires skill. They aren't the simply 'push-the-buttons' steam fans tend to dismiss them as. The drivers still needed skills with a heavy train, just different skills to driving steam. And they don't fly up gradients with heavy trains; they just don't need a fireman shovelling diesel fuel into the injectors.

 

Thank you for the point about traction current. In effect that limits the tractive effort at low speeds, if the adhesion limit isn't reached first. But can diesel not produce a more nearly constant power at the rail than a steam loco over a range of speeds?