Which reminds me of my Palomar Mountain vs Mt Palomar rule for publications. The publications that use the former are making an effort to get the details right, where with publications that use the latter makes me wonder of what other details are wrong.
In th railfan world, the comparison might be Grand Central Terminl vs Grand Central Station.
I finally figured it out about why the late Challengers smoke so much and go through large amounts of fuel in relation to the early Challengers.
A crew on a late Challenger is under pressure to make up time, so the fireman may stoke too much coal on the fire?[:-^]
Possible, but not likely.
Remember that the fire in a locomotive is not at all what you think of. It is not flames dancing on a hearth, or burner fire as in an incinerator. It is a white sheet of vaporized lambent carbon, glowing as a blackbody, suspended by a combination of physics ideally just out of contact with relatively cold boiler and chamber inner sheet surfaces, and ideally ‘going out’ by finishing combustion to full CO2 (which, remember, is transparent for EM of many wavelengths) just as it gets to the rear tubesheet.
Now, we watch our hypothetical firing practice start falling behind, and note that the steam pressure is starting to fall, so we stoke ‘more and more’ until the bed is heavy. This decreases primary air and chills the top of the firebed; the combination reducing the gas flow through the hot carbon. Draft is likely increased as a consequence of what made the steam pressure start to fall – WOT with the reverse inching toward the corner to keep speed – but the relaxation now has an increased component of ‘various’ secondary-air sources, some of which will be increasing the ‘gas flow’ across the distributing table of the stoker… where the elevator worm is completing the crunching-up of the subbituminous and likely discharging it with a relatively high component of fines.
(I pause briefly to remind everyone that the firebox volume is purposely run as a reducing atmosphere below atmospheric pressure)
Now what you’ll see in this situation is increased fines lifting, trying to light off in the gas flow, but largely not succeeding in scrubbing gas to get adequate carburetor in the reducing atmosphere before their TOF brings them to the tubes where luminous combustion is quickly quenched (all reference I’ve seen say within 6"; some com
I’m really enjoying this discussion on how thermodynamics applies to steam locomotives.
It stands in stark contrast to the ‘training’ programs of many railroads during the steam era, where a new Fireman would write a basic rules and theory exam, make as few as three student trips, and then start working regularly.
They learned on the fly, some ‘got it’ and some didn’t. The same is true for Engineers, some guys never learned how to run a locomotive efficiently, and others delighted in making the Fireman’s life far more difficult than necessary.
“Early” and “Late” could have a double meaning, where instead of “Late” meaning the second major batch of locomotive production, it could possibly mean that the train is late, that is, behind schedule.
In honor of all of the dads out there on Fathers’ Day, I offer this as a “dad joke”, meaning a G-rated joke you can tell your young children but one that is otherwise not terribly funny.
A “dad joke” told by an airline pilot following a similar bit of comedic reasoning was just told on Rand Simberg’s Transterrestrial Musings. A Southwest Airlines pilot pointed out the Arizona Meteor crater to the passengers on one side of the airplane who could see it, reminding that that a meteor excavated that gigantic crater some 50,000 years ago, but what is even more amazing, it just missed that little house.
I hope you enjoy your stay, and I will be here all week.
…or, even more likely, that it has fallen down and died on the road… [:)]
Happy Dad’s Day!
Paul Milenkovic, everything is better with cheddar! Have a great Father’s Day behind The Cheddar Curtain!
During my Basic Officer Training when Canadian Forces Officer Candidate School (CFOCS) was in Chilliwack, we were four to a room in barracks. One of my roommates was hoping to be a helicopter pilot. He was an engineer, but in cartography. Guess…no really…guess why he failed out at CFOCS. [8-|]
OK, map reading and land navigation?
When I was at The Basic School (For Marine Officers) the word was land navigation and map reading was the ONLY thing you had to pass to get out of there!
I stopped flying sailplanes when I realized, to my horror, that I could no longer recognize the changing terrain without frequent orientation using a map.
Sailplanes require fairly frequent turns where you have to be sensitive to ridge and thermal lift and not concentrating on ‘where you are going’ – and you might be pointing ‘anywhere’ once you have come to altitude. On the other hand when you commit to land there is usually no such thing as a go-round, and it becomes much more tedious to recover the aircraft the further away from the staging point you come to rest – further both horizontally and vertically.
Helicopters require more multiple control haptics than sailplanes…
Paul,
Thank you for the references!
Just to help my own learning on the subject. I found an online articel that describes firing practices for different types of coal.
This is for stationary plants, far different than locomotives, but i’m guessing the general concepts pertain, but with even more complexity!
It seems the more volatile matter, the more air and volume is needed for efficient combustion. The more organic matter the thinner the fire needed. The article mentions Rock Springs coal specifically and states that 6-8" is ideal.
To Overmods point, with the throttle wide open and at high cutoff, I could see where it would be easy to tear holes in the fire. The articel also mentions the air needs to be very hot, ambient air will stop the combustion process. So holes in the fire would be very bad indeed.
That also I think answers a question I had about why the overfire air holes were eliminated started around 1948. Gordon McCulloh mentions it in his book A History of Union Pacific Steam but didn’t mention why. All that cold air coming in the sides of the firebox was probably hurting combustion rather than helping. Sounds like focusing on good, hot primary are was more beneficial.
Again, many you you probably already understand these things, but the article was helpful for a novice like me.
The article link is here
https://www.gutenberg.org/files/22657/22657-h/chapters/coal.html
Thanks Overmod
Happy Fathers Day to all!
Beware of studying resources for firing pulverized coal in a Benson boiler. The load characteristics, turndown, heat balance and Rankine-cycle implementation are very different from most locomotive practice.
Start by reading this carefully, including memorization of as many of the backhead controls as you can:
https://www.railarchive.net/firing/
Then peruse this for the non-US-American view (I miss Claude Bersano so badly!)
You might look into the reprinted 1947 Reading Railroad ‘Firing the Steam Locomotive’ (about $10 from Amazon but you may find a used copy from time to time from a place like Thriftbooks for less) which has some detail differences.
The overfire jets were never intended for thermodynamic performance: they are purely to avoid fines for visible smoke from the (many!) places that started imposing them. Note that there are two kinds of those guns/jets: those that use boiler steam to entrain atmosphere (doing some secondary-air preheat, but adding water to the flame and taking it away from the boiler, neither of which are good) vs. those that use main-reservoir brake air (terrible shrieking and the usual substantial chill as 140psi air exhausts to a partial vacuum, but a higher mass flow of burnable oxygen). I have always been a bit amused with the idea that the jets penetrate to the center of the gas plume, and that they don’t disturb the gasdynamics of induced draft… neither of which really happen.
On the other hand, heating the primary air can be useful, just as it is for PC firing in high-pressure utility boilers (where there is room and power to arrange adequate 650F or better primary air without difficulties). An interesti
Thanks for the references.
Looks like I have some “homework” to do!
Cinder cutting? Poor access to water side for descaling? Burn-through of the tubes?
Remember where these tubes start, and where they end. Then reflect a moment on how Nicholson syphons are supposed to work… and what their design promotes.
There should be little cinder cutting as this is just about the hottest net part of the fire, where the plume coming up under the arch reverses direction to go forward under the crown. If anything you’d get glassing there if the ash is fusible.
The designs I’ve seen all have very careful provision of washout plugs on the backhead that line up with the tubes. That might actually have exacerbated the problem… but it made scaling an easy thing to rectify.
One of the most evil things in a staybolted firebox is the development of DNB, departure from nucleate boiling. Steam is a relatively good insulator, as anyone evennpassingly familiar with the Eisenhoffer/Leidenfrost effect knows. In DNB a larger and larger area flashes to steam, while the plate behind that area begins to overheat – possibly very severely very fast.
The bright principle behind the arch tubes were to use them as longitudinal bars to hold the arch up and get a little extra free vertical circulation. But look at the situation a moment:
Water flow IN comes from a restricted volume at the throat;
The section of pipe above the arch is in a relatively high radiant heat flux, very subject to induced DNB;
The exit of the pipe butt-ends into the backhead space, virtually a flow stall for natural circulation in a pipe.
Note what happens when a relatively large mass of steam forms as a ‘plug’ in the hot upper bore – it is above saturation pressure pretty quickly and this presses down against the natural-circulation rise of heated water as well as up toward the backhead. Expect to see thermal cycling – lots and lots of thermal cycling!
that are still pricey, I cannot tell if this is in the original French or is an English-language translation.
These would be the translation since George Carpenter was the translator.
His name would not appear on the listing of an original version.
Peter
$150 plus $3.99 shipping does not strike me as excessively pricy. I stumbled across a source selling brand new ones in shrink wrap for $99 about a decade ago, and all the ‘serious correspondents’ on the old steam_tech Yahoo group were overjoyed to get one at that price.
It’s the 1938 French original that commands the astronomical price.
I’ve really been enjoying the machine side of the discussion, but I think you bring up a great point about the human side as well. There are plenty of pictures of “Jabelmann Power” shooting roiling columns of thick smoke skyward, but also many showing a “light” stack.
All the machine and fuel shortcomings aside, a good fireman definitely made a big impact. By the 1950’s many of the more senior engine crews were transitioning to diesels, which were the more desried jobs. This left the younger, less experienced crews to the Challengers and Big Boys.