Does anyone have a some test data recording the smoke box temperature of the combustion gases at the exit of the flues?
Alfred Bruce has a diagram listing 625 degrees F for the temperature at the flue exit. I would assume the range is somewhere between 600 to 800 degrees F depending on how hard the locomotive is working. Compared to power plants that use economizers and air preheaters, which bring down the combustion gases down to 350 degrees or so, the steam locomotive dumps incredible amounts of heat out of the stack.
I’ve been doing some basic combustion calculations based upon a method from Babcock & Wilcox “Steam: Its Generation and Use” in conjunction with data on the April 3, 1943 Big Boy dynamometer tests. One aspect that bothered me is that the inherent losses of combustion are charged against the locomotive, ie heating the nitrogen in air, heat in water vapor from combustion and moisture of fuel, and humidity of ambient air. The inherent losses, with no excess air, amount to 18% of the BTU content of the fuel. Adding radiation loss, unburned losses, 125% air, etc amounts to a energy loss of almost 40%.
Simple math shows that the final efficiency of the locomotive is about 5.5%. 60% of fuel is released in combustion, 80% of that heat released is absorbed by the boiler and superheater, and about 11.5% of the heat in the steam is converted to work.
See tables below for calculations and parameters used, and weather data is from historical records for Ogden, UT and Evanston, WY.
Couldn’t tell you what the temperatures of the smokebox gases were, but whatever they were they were hot enough to blister the paint off the smokeboxes through most of the steam era, hence the graphiting of smokeboxes to prevent corrosion. By the time good heat resisitant paints were available the steam era was just about over.
That’s an intriguing table , yet it would appear to allow for some marginal points :
Where did you get the , quote >> 125 % air << from ( when with a BB at work usually there was black smoke like a volcanic eruption ) ?
Where did unburnt losses go ( zero in line h ) ? Why boiler efficiency of , quote >> 80 % << ?
Quote >> about 11.5% of the heat in the steam is converted to work << ? What live steam heat content did you calculate with and what was the adiabatic and the polytrophic heat drop , at what amo
Juniatha: ( when with a BB at work usually there was black smoke like a volcanic eruption ) ?
Veto! Hard working, I guess every steamloco acts like this.
Y6b and Class A were putting an equal amount of dark smoke, in a more brownish color, dispite the better heat content of coal.
4017
-edit-
Juniatha and Burgard 540,
however, BB’s tendency for putting out a black smoke cloud from time to time maybe was caused by the grate’s reduced air intake area, if I do understand this case correctly.
Keep in mind, how much smoke a steam locomotive puts out depends on a number of factors, such as the quality of the fuel used, either coal or oil, the physical condition of the locomotive, how well the fireman’s doing his job, and how hard the engine’s working. From looking at old photos and films sometimes I think the engine crews may have been “hamming it up” to make the engine look more dramatic, i.e. “Burning of Rome” smoke effects. Remember, the last thing management wanted to see was excessive smoke, lots of smoke meant poor combustion and poor fuel economy, all things being equal, of course. Hey, when I use the fireplace at home the last thing I want to see is a lot of smoke, it means I’m doing something wrong!
each of these values would describe a certain work point of the engine , so how do you get from there to a general statement of overall locomotive efficiency of , quote >> … the final efficiency of the locomotive is about 5.5% << ?
What about their chassis/gear effeciency:?
axles,all rotating parts, cylinder, suspension, other stuff to avoid tendendies to frequency oscillatory vibrations , inherent with any rod-driven system. And then, a 200t 7axle-tender behind them??? You name more!
All I understand so far is, that cylinder hp minus drawbar hp was a loss at around ~10% (6680-6000 at ~ 40mph) . So it would increase the measured efficiency a little bit to Burgard’s data of 5.5?
(But, hey, 90 percent gear effeciency? Is that cool?)
I dont have knowledge or enough background to interpret your table data into actual figures. But all looks pretty congruent with actual test data.
A little bit of explanation might clear things up. Really only pay attention through lines 30 on the tables. After posting I noticed I left the 7.70% moisture in the Dry column on the fuel data. I gave a hydrogen content of the Rock Springs coal of 5% from data on similar coals. The only references for Rock Springs coal I have is the proximate analysis. If anyone has the ultimate analysis, please share.
Table 1 shows the inherent losses of heat in the combustion process even with perfect (stoichiometric) combustion, hence why I left the unburned, radiation and unaccounted for losses as zero. The losses are from: 1) heating the moisture in the fuel and water vapor produced from combustion of hydrogen, 2) humidity in the air, and 3) the heat lost in expelling the combustion gases at 700 degrees F, 660 degrees above the ambient air.
I wanted to see what these were before any other losses would be added in. This to me shows a huge limitation of the steam locomotive in that 18% of the heat of the fuel cannot be used at all. The inherent losses cannot be decreased expcept via drying the all coal prior to firing in the locomotive (expensive and not done) or through place some type of air preheater to try extract some heat from the expelled combustion gases (again not done on locomotives due to lack of space and complication, although in stationary plants this is done extensively cooling the gases to 350 degrees or so). I chose 700 degrees since I assumed that it would be a fair representation of conditions when the locomotive was working hard.
For Table 2, I added the unburned, radiation, and unaccounted for losses as well as increasing total air to 125% of theoretical. The 125% total air comes from Ralph Johnson’s (pg 26-27) and others, 25% more air than theoretical (what the exact amo
Veto! Hard working, I guess every steamloco acts like this. Y6b and Class A were putting an equal amount of dark smoke in a more brownish color, …<<
Nope – not every steam locomotive , only those with bad combustion , due to fuel fed at a rate draughting can’t deal with , or any other faulty handling or flawed condition of firebed . Anyways , many or few , that doesn’t make it better when it occurs . It’s still black smoke and black smoke is a visual sign of dramatically incomplete combustion .<
thank you for your enlightening answer from the point of view of an engineer, ackknowledged.
J: Nope – not every steam locomotive , only those with bad combustion
I guess, then, all or most of them is therefore the right answer . North American steam locos attempted to be standarized .In this case I noticed that German engines have a very familiar appeal to their US big brothers. Regardless imperfection. My empathy for these designs is the inside/outside tension and expressional + feelable force of the machinery.
J: Ok , you might say I wasn’t there – but from what my father said and from what it appears like on photos , heavy smoking was pretty regular with about any of the big steamers –
my case, too. There are indeed some photos of the engines you named before, with no visible smoke at all, moving fast by photographer’s comment (Otto Perry, Stan Kistler), as the opposite as well.
At least there must have been some certain agreements with the builders and the roads, how much average output should have been achieved with their designs. Some compromises were avoided, some not. - Maybe Burgard’s attempt for calculations will fail, I encourage you for helping him
It is just a black box to me, the picture is blurred., with vast imagination of inside prozesses.
Outside seeing just a given mass of doing output work. at given circumstances.
Ok, a layman’s question, how much effect would smokebox size and exh. nozzle shape have on exhaust temp? I know great thought went into these parts. It seems to me that there would be a ‘best’ speed for the exhaust to move through the flues, too fast would not give it time to transfer heat to the water, too slow would not give enough air for compleat combustion. Charles Mcshane’s ‘Classic American Locomotives’ has a large section devoted to these desgines. They range from the very simple to the very complex. Were they worth the time and cost?
Heat transfer in fire tubes is by convection. The faster a fluid flows (exhaust gasses are a form of a fluid) through a heat exchanger (the tubes) the higher the rate of heat transfer. The faster, the better. However, as you try to push or pull more gasses through the tubes, you run up against the flow capacity of the tube (determined by the diameter and length of the tube), with resultant back pressure. This is why “late steam” designed in the 1940’s generally used large diameter, shorter fire tubes than older designs from the 1930’s.
It was determined through testing that the “ideal” flue length was right around 20’ in length, with the diameter increased to 4" from the more typical 3.5" diameter found in older designs. This maximized gas flow, reduced back pressure, and maximized heat transfer. Additional flue length over 20’ added next to nothing in heating capacity, and probably caused more harm than good by allowing the corrosive exhaust gasses to condensate in the tubes.
All combustion should be complete prior to the tubes as the oxygen content is too low in the tubes for additional combustion anyway. Late steam designs generally used the additional boiler space available from the shorter tube design to increase the fire box/combustion chamber length to increase combustion efficiency of the gasses prior to entering the tubes.
Thank you, learn somthing new every day! So the faster the “spent” gases move through the tubes the better, would this be true for the flues with the superheater tubes in them?
My Father was a fireman on the B&O here in Pa, he tells me that a uncorrected slip could “pull the fire off the grates and send it up the stack”. It seems that this was “too much of a good thing”. It seems that newer locos where more pron to this than older ones. Would the bigger flues promote this? [ He might have streched this a mite]
To give you some numbers - doubling the rate of flow for the combustion gases through each tube or flue will increase the heat transfer via convection by about 90%.
Another reason for building larger fireboxes & combustion chambers is that the process of combustion ceases rather quickly after the gases enter the tubes because the temperature drops below the ignition temperature.
Ensuring proper combustion should be the dominant design characteristic since efficiency of the boiler as a whole is almost entirely dependent on the efficiency of fuel combustion. For example, an increase of 3% in combustion can increase the boiler efficiency by up to 25%.
It won’t be intuitive to some readers, so it might be worth explaining that heat transfer between two mediums, say steel tubes and surrounding water bath, works better the steeper the gradient of temperature between them. That is, heat transfers as the fourth power of the difference in heat content from the hotter medium to the cooler medium.
You might think that it would be best to slow the passage of the gases through the tubes so that all the heat could be recovered by the surrounding water bath in the boiler. You would want as little heat in the gases issuing into the smoke box at the far end of the tubes, right? Wrong! Because of this heat transfer law (a law posited by Messrs. Stefan and Boltzmann), saying that the thermodynamic heat of a radiating surface issues at the 4th power (not squared, not cubed, but fourtheth! [:o)], you are going to heat up the working medium, your water, many times more quickly and efficiently if you keep those tubes as close to red hot as you can keep them…constantly!
It is only further along when all that hot gas goes whooshing up the stack with the help of waste steam that we begin to see how the steam locomotive wastes a lot of energy.
I am not a physicist or an engineer, so I may stand some correction worth mentioning here, but I think for argument’s sake I have the basics mostly right. I’ll know soon…[:)]
So any thing to speed up the flow through the boiler would be worth the effort, within reason. Some of the efforts pictured in the book seemed to be overly complex, a maintence headache in the making. Maybe this is why U.S. builders didn’t use these items for long, as European’s did.
“Normal” people think I know everything about trains, but I am always learning more and am surprised at how much there is to learn.
Thank you, I should know that from high school science class, but its been a long time since high school. They demostraited this with 2 cups of water, 1 was warm [close to room temp] the other was hot [ close to boiling]. The question was witch cooled faster. The answer, the hot, due to the higher temperature gradient ! Witch is why you can’t keep your tea warm in the deer stand or waiting for a train!
