gregcit probably takes just as long for a fire to burn down by not adding coal as it does to build up when adding coal
Evidently you've never used a charcoal grill. If you put fuel on the fire it catches fire in a matter of minutes and burns for a long time.
gregcwhat do you think determines the tractive force?
As other people have stated, wheel diameter, cyclinder size, steam pressure, etc., etc.
If the question is how does a locomotive change pulling power while running? Adjusting the throttle and cut off. Very simple.
All changing the fire does is keep an adequate supply of steam based on it's usage, in economics it would be called a "trailing indicator".
You started off this discussion by articifially constraining the the controls an engineer uses to operate the engine (throttle wide open and cut off at max) and then asked how do you control the engine without using the controls.
Get a picture of a really basic locomotive and look at the controls the engineer uses that are connected to the running gear. The answer to you question is in THOSE controls and in the devices attached to those controls.
You could do exactly the same with a car. How does a driver change speed and power in a car? Look at what controls the driver has available. The gas pedal and the gear shift.
The fire and the steam pressure in the boiler may have an effect, but they are not a CONTROL. The fuel of a steam engine is steam, not coal. The boiler's job is to provide an adequate supply a fuel. It takes a relatively long time to change the pressure in the boiler and adjust the fire. That is not a CONTROL.
You appear to be trying to figure out how to run an engine by adjusting the pressure in the boiler rather that by adjusting the pressure in the cyclinders.
Dave H. Painted side goes up. My website : wnbranch.com
dehusmanThe fuel of a steam engine is steam, not coal.
that's simply not true
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greg - Philadelphia & Reading / Reading
May be helpful to remember that a steam engine is an external combustion engine (unlike an automobile motor, which is internal combustion). The coal, oil or wood burning in the firebox creates heated air that passes through the boiler tubes to the smokebox, where it is then vented out the stack. The fire isn't in the boiler.
When a steam locomotive completed it's run, the fire would be dumped in the ashpit on the way to the roundhouse. Even with no fire, there was sufficient steam to run onto the turntable and into the roundhouse stall.
Will you stop asking the same question over and over no matter how many people answer it for you, and bringing up more irrelevant details and numbers you don't understand the meaning of?
of course max speed depends on various things. but i believe the simplest answer is the speed where the train resistance equals the max tractive effort above which results in slip.
That isn't even wack enough to be wrong, as a moment's reflection on your part ought to make clear. Maximum speed is the speed at which train resistance (rising with speed) exactly balances developed drawbar tractive effort (falling with speed). It can also be thought of as the point that the locomotive no longer develops enough power to accelerate the train under the instantaneous running conditions.
There is such a thing as 'high-speed slipping', and under certain conditions it is indeed a limitation on achievable top speed. One canonical example was described by E.T.Harley (who knew his duplexes!) in his book on the Q2s -- he was on a train pulled by a T1 in bad weather and poor rail conditions, and there came a point where no further power could be transmitted through the driver contact patches on at least one of the engines (probably the forward one) and it would momentarily slip. This would of course throw the load onto the other one, the engine would slow down, and the slipping engine would 'catch its feet' -- the result being a repeated rhythmic surge, damped by the mass of the tender, not progressing to wild spinning drivers as in the general FRN conception of a T1 slip, but not permitting any further acceleration of the consist.
But notice that this isn't like a tractor pull, where the wheels start slipping when the load is too great. Even for the T1, the much more likely consequence of an overload, even at starting, would be as clearly described in the C&O road testing described by Dave Stephenson (feltonhill here) -- the engine simply stalls, refuses to accelerate, or bogs down.
And you fix that (to the extent you can) by adjusting the REVERSE, to allow more admission. To the extent you do anything with or to the boiler, you control fire and feedwater to keep the nominal boiler pressure as close to the desired pressure as careful experience and knowledge permit.
I will happily get into a discussion of how admitted steam flow translates into internal-combustion engine terms, since nobody else seems to understand that competently, either. But it doesn't apply in any real sense that would give you better understanding of the question you keep trying to ask.
At some point we might have to take up a critical difference between 'gas' engines and steam engines, which is the loss via physical phase change to liquid during the stroke duration (and then the losses involved in re-expansion to vapor when you don't want it, during release). This is not just the usual-suspects wall condensation; it involves what is called 'nucleate condensation' throughout the expanding steam mass as work is extracted via piston thrust, and nucleate condensation is THE principal reason superheating, and not steam jacketing or better external insulation, has such a tremendous effect on locomotive performance.
Actual maximum high speed depends on a number of things like admission time per stroke, shock in the intake tract or flow instabilities near valve unshrouding, and balancing effectiveness. I can assure you that the reason a British 9F can reach 90mph has nothing whatsoever to do with any Reading I-class locomotive, and comparatively little to do with Reading locomotives built using components from I-class locomotives.
Incidentally, here is a question for you: how do we 'conventionally' determine the P in the PLAN formula, and what is one of the common reasons why we do that?
OvermodWill you stop asking the same question over and over no matter how many people answer it for you, and bringing up more irrelevant details and numbers you don't understand the meaning of?
if you can provide a succinct answer?
a basic law of physics is conservation of energy, that the source of energy is the coal. a constant amount of energy is needed to overcome train resistance to maintain speed. a higher amount of energy is needed to accelerate and then maintain a higher speed because train resistance is greater. just as more gas is needed in a car (your gas mileage drop when going faster)
a common answer is that the fire is maintained to maintain boiler pressure. no one has suggested that the rate of coal consumption varies in order to maintain that pressure. Somehow adjusting throttle or cutoff increases the speed while the boiler pressure remains constant.
Overmod of course max speed depends on various things. but i believe the simplest answer is the speed where the train resistance equals the max tractive effort above which results in slip.
Yes, coal consumption varies, or ought to, with changes in boiler work. A seasoned stoker, who knew the route, would know when to start pouring the fuel to the firebox, and then when to desist. All the while, the boiler is being drawn down, sometimes harder, sometimes less, but the water injected/fed was always cooler than what was emitting from the throttle at the front end.
The HP curve of a steamer shows it rising as speed increases, but only up to a point. By the time the pistons, on a typical steamer, are reciprocating at about 3.5 - 4 times each second, the highest possible horsepower is being put to the piston. This also coincides with the shortest cutoff. Rapid, short, pulses of full-throttle steam are being puffed through the inlets and then expelled via the outlet ports, which keep the steamer at speed.
selectorYes, coal consumption varies, or ought to, with changes in boiler work.
thank you
OvermodIncidentally, here is a question for you: how do we 'conventionally' determine the P in the PLAN formula, and what is one of the common reasons why we do that?
i had never heard of PLAN and had to find a description which says the P is the mean effective pressure that results from early cutoff and expansion.
but the MEP is based of the initial pressure while the intake valve is open. it's not obvious (to me) what that pressure is
one answer is it depends on the amount of steam (lb) in the cylinder and the volume of the cylinder at cutoff which determines the density and pressure (see steam table)
i've been trying to figure out how to estimate amount of steam that enters the cylinder before cutoff.
if each cylinder were at 50% cutoff, all the steam produced by the boiler passing thru the throttle can enter one cylinder or the other because when one cylinder reaches cutoff the other cylinder is just starting its cycle
at 50% cutoff, my understanding is MEP is 87% of the initial pressure
whatever steam produced by the boiler that doesn't enter the cylinders will build up in the boiler, increasing its pressure and possibly vented thru the pop-off valve. If boiler pressure builds, the steam flow (lb/s) will increase, along with density/pressure and tractive effort. there will be some equilibrium point at some speed where all the steam produced by the boiled enters the cylinders
but at less than 50% cutoff, both intake valve will be partially closed some period of time and steam pressure is likely to build during that brief period.
I believe the result in that the same amount of steam that enters the cylinders at 50% enters when at 20% cutoff. half of what is produced by the boiler. since the volume is 40% of what it was at 50% cutoff, the density is 2.5 time higher along with pressure.
MEP for 20% cutoff is 68%. the net difference in cylinder pressure is 1.7 (2.5 * .68) which is why cutoff makes such a big difference.
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OvermodSheesh To 'go faster' you will lengthen the cutoff to increase the mass flow per stroke. This will draw additional steam from the boiler On the other hand the additional mass flow of steam means additional mass flow in the exhaust... hence more draft, hence a brighter fire. At some point, probably before balancing at 30mph, you will resume the 'firing early and often' that you should have been attending to at 20mph. A good fireman will estimate the additional fuel the engine will need at the new higher speed on the relevant part of the railroad... and fire and trim accordingly.
To 'go faster' you will lengthen the cutoff to increase the mass flow per stroke. This will draw additional steam from the boiler
On the other hand the additional mass flow of steam means additional mass flow in the exhaust... hence more draft, hence a brighter fire.
At some point, probably before balancing at 30mph, you will resume the 'firing early and often' that you should have been attending to at 20mph. A good fireman will estimate the additional fuel the engine will need at the new higher speed on the relevant part of the railroad... and fire and trim accordingly.
I apologize for not recognizing this earlier (from page 1)
i hadn't considered the increased draft on the fire and temporary increase in BTUs
but "additional fuel the engine will need at the new higher speed" implies that the fireman increases the rate of coal being added to the fire
2388
I apologize, but I can no longer post from a phone at all, thanks to Kalmbach incompetence in advertising forcing page resets and very, very, very slow typing throughput (or clever shadowbanning, perhaps).
The 'succinct' answer is that changes in steam admission are the only thing that makes the locomotive go 'faster'.
The situation is of course much more complex than that, but you'd need to study about the physics of steam, understand why Mollier charts are valuable, etc. to see just how much power can be developed (as pressure) from a comparatively small charge of initially high-pressure, high-temperature steam vs. admitting a 'whole cylinder full' and then letting it blow to exhaust, as in an engine with low or no fixed cutoff operated in full gear. You have already noted that a very small actual mass flow can have very long expansion and still produce smooth 'enough' torque above a certain (and relatively low) cyclic rpm to give effective TE at speed. For very high speed, even with large diameter drivers, the effective duration of admission is measured in milliseconds, and it becomes important to "push" an adequate mass of steam into the cylinder in that time, but there is then more time for 'long expansion' and hence both lower pressure and lower mass to be exhausted when the cylinder opens to exhaust (the thing that most people looking at higher pressure as the 'answer' to Moar Power often don't think about...)
The 'automatic action' is something that an extraordinary amount of (relatively unsung) design, proportioning, and construction goes into facilitating. Note that to go from 20 to 30mph requires more admission steam mass flow. But it is NOT proportional in lb. of steam as "33% more" than at 20mph, unless the engine is well over the peak of the torque curve or has lousy port and passage flow, etc.
It's sort of a honeytrap for armchair thermodynamicists to concentrate on front-end arrangements that provide the greatest possible road speed -- for bragging-right speed records, for example, with engines that will remain nameless. Something more important, though, is arranging the front end for best overall fuel efficiency (at least in a world where fuel was an expensive cost and water was perceived as relatively cheap and fungible) and fuel once stoked would burn 'as it wanted' without the ability to "decrease the fire" as on an oil-burning engine, or wind a chain-grate backward as on the N&W M2 Automatics or the TE-1. In the engine's normal operating range, and 20 to 30mph is certainly in that range for most locomotive designs, the 'idea' is to have the draft change by just the amount that produces the additional heat release, then heat uptake, then steam generation to sustain the higher mass flow.
Naturally, at that firing rate, you might have to stoke more frequently or using a different pattern. But that is done, as mentioned, with reference directly to boiler pressure and water level, which makes it somewhat easier for a fireman.
A 'correct' fire doesn't look at all like something in a charcoal grill, and anyone using that as an analogy has almost certainly never seen an actual locomotive fire in an engine running under load. There is usually more fuel in there than required for instantaneous power change, so that you might not need "extra" firing right away when the added draft brightens the fire still further. Fred Westing interestingly observed that some PRR engines used in commuter service, if started with a properly-built fire, would run for as much as 37 miles without any stoking (nothing was said about trimming).
Now, there's no guarantee that 'automatic action' applies to an engine in poor condition, or burning strange fuel. It is quite possible for an engine to lose the ability to 'keep up' with steam demand, and not infrequently this results in what the English call a 'blow up', where the engine has to be stopped, the blower put on, and the fire brought to effective brightness and mass flow of combustion gas to restore steam pressure for a boilerful of water.
One of the potential complications that you shouldn't let snare you when trying to understand this is that the steam needed to accelerate the train from 20 to 30mph might be easily sourced from the boiler water and existing fire, and when the reverse is adjusted to hold at steady speed the steam demand drops down to a level that existing conditions could maintain. This is less weird if you think about how a fireless cooker could accelerate a train or cut of cars, with no "fire" at all...
Can somebody like Ed find and post the graph from Wardale's Red Devil book that shows actual wheelrim torque from a 2-cylinder DA over one full driver revolution, at 15-degree increments? I think that alone would give him tremendous insight into what is happening in each of the four strokes occurring in one revolution, and why they overlap without crippling torque peaks much of the time.
The 'succinct' answer is that changes in steam admission are the only thing that makes the locomotive go 'faster'. All the fire does... ALL the fire does... is to put heat energy into the steam so it can exert more pressure over a long expansion (and incidentally give up some of the heat/pressure as work as it does). The steam does the work, and that is what dhusman meant when he called it the 'fuel' of the actual engine of the locomotive.
i don't understand why Mollar Charts are needed to understand that coal/oil provides the energy that propels a train.
as the train speed increases, the train resistance increases, requiring the (MEP) cylinder pressure to increase, requiring more steam. (assuming optimal operation)
while various controls allow more steam into the cylinder, the amount of steam can only be what the boiler produces. Any excess steam produced by the boiler is wasted thru the pop-off valves. The fire is only as strong as needed to maintain boiler pressure and not waste steam/water/fuel.
100 lb of coal can burn per hour per sq.ft of grate area. more/less depending on depth. A 100 sq.ft grate can burn 10,000 lb/hr or 166 lb/min. The density of coal is 52 lb/cu.ft. At this rate, the fireman needs to shovel 3+ cu.ft/min. (it's not like a charcoal file the lasts for hours)
~1520 BTU are needed to produce 1 lb of steam. There are ~11000 BTU per lb of coal. Burning 10,000 lb/hr of coal can produce ~72000 lb/hr steam
these are ballpark numbers
working from train resistance, tractive effort, cylinder pressure, steam density and mass (lb), a 5000T train traveling 20 mph requires ~7000 BTU/sec and 38 lb/min coal. A 30 mph train requires ~13000 BTU/sec and ~72 lb/min coal. A 50 mph train requires ~40000 BTU/sec and ~219 lb/min coal.
conservation of energy
While cutoff can be adjusted to change the admission of steam, as well as use is optimally, steam production needs to increase. I don't see how that happens without increasing the rate of coal being added to the fire.
gregc PM Railfan "..... what determines "how fast the locomtive will go"? my mistake. should be how does a steam locomotive increase speed?
PM Railfan "..... what determines "how fast the locomtive will go"?
my mistake. should be
how does a steam locomotive increase speed?
Gotcha. In that case it goes back to what ive already been saying.....
Ya turn the knob on the transformer, the light gets brighter on the loco, and the train goes faster. And like that.
I forgot we were modellers!
PMR
I don't understand what you're stuck on? The boiler was designed to produce more steam than it could use in a given time. When you admit more steam into the cylinders, the boiler is still making steam. The volume of the steam dome and super heater will have enough reserved for quite a distance. All the while the boiler is still evaporating water. The fire is still hot. The crown sheet doesn't instantly cool.
wrench567I don't understand what you're stuck on?
that you and others seem to believe the boiler is producing the maximum amount of steam at all times or only as much steam as needed.
of course you can have the boiler producing more steam than is required with the pop-off values wasting the unused steam and you can use the throttle to control speed.
The boiler pressure is not a measure of how much steam the boiler is producing. The boiler pressure will remain constant if the boiler is producing the same amount of steam (lbs) as being consumed by the cylinders.
why not build the fire only as strong as needed, some bed thickness, to maintain the boiler pressure maybe 5,10 PSI below max boiler pressure when operating at the desired speed. add more coal when it goes below that, stop adding coal when it starts to rise above it
to increase speed, the fire needs to be strengthened to accelerate. After increasing speed,
OvermodA good fireman will estimate the additional fuel the engine will need at the new higher speed
the stength of the fire, bed thickness, can vary to change the amount of steam produced by the boiler as needed.
the fireman is the "gas pedal". on an oil fired steam engine, it's a valve that can be opened more/less to control the strength of the fire and the amount of steam produced
2642
gregcthe fireman is the "gas pedal".
The fireman is the fuel pump. He make sure there is an adequate supply of steam to run the steam engine. If he supplies an inadequate amount of steam the engine will not be able to make speed. If he supplies too much steam it will be wasted.
The fireman can have the engine producing enough steam to lift the pop valves and the train can be standing still. The engine isn't going anyplace until the engineer opens the throttle.
If the throttle is fully open, all the available steam is going to the cylinders, so the engine is going as fast as it can. Theoretically, if you add more fuel to increase the boiler pressure up to the point that the safeties blow, then yes perhaps the engine will go a little bit faster.
But I think your question may point out that you're not understanding what the throttle is. The throttles regulates the amount of power - steam - that goes to the cylinders to turn the drive wheels. The more steam passed to the cylinders, the faster the engine goes. If, as in your original question, the throttle is fully open and the engine is going 20 MPH, increasing the boiler pressure by adding all the fuel you can will only increase the speed a few miles per hour. But again, that's unrealistic. A steam engine going 20 MPH is only going to have the throttle partially open, half or less.
dehusman gregc the fireman is the "gas pedal". The fireman is the fuel pump. He make sure there is an adequate supply of steam to run the steam engine. If he supplies an inadequate amount of steam the engine will not be able to make speed. If he supplies too much steam it will be wasted.
gregc the fireman is the "gas pedal".
i agree -- that's a better description
but if he builds up the fire, when the train is running at a steady speed and the boiler pressure is not maxed out, the boiler pressure will rise and more steam will increase the speed of the train.
2729
wjstixIf the throttle is fully open, all the available steam is going to the cylinders
all the available steam for that amount of fire. the fire can have different depths, producing different # of BTUs, generating different amounts of steam (lb/sec)
wjstixTheoretically, if you add more fuel to increase the boiler pressure
boiler pressure does not indicate how much steam is produce by the boiler. it indicates when more or less steam is being consumed by the cylinder than produced by the boiler. it rises when less is consumed and falls when more is consumed
adding more fuel increases steam production (lb/sec). even a slight increase in boiler pressure (~2 psi) results in more steam flow (lb/sec) into the cylinders, higher cylinder density/pressure, tractive effort, acceleration and speed.
more steam is consumed by the cylinders as speed increases, if speed doubles, there are twice as many cylinder cycles and twice as many cylinder volumes to fill.
a higher speed will consume steam at the new rate and boiler pressure will again remain constant
same boiler pressure as before, but higher steam production, consumption and speed
wjstixThe throttles regulates the amount of power - steam - that goes to the cylinders to turn the drive wheels.
it could be used that way; probably is on a switch engine in a yard running at much less than max boiler pressure. but the table below shows full throttle at 9, 20, 30 and 40 mph.
running with anything less than full throttle prevents all the steam produced by the boiler from entering the cylinders. the excess steam in the boiler builds pressure and is wasted thru the pop-off valves.
a throttle is absolutely necessary to start a locomotive, to limit the flow of steam into the cylinders when the wheels are barely turning. the throttle is just "cracked" to start the loco
In your thinking. If you dump the fire the locomotive will not move. Wrong. As long as there is steam in the boiler, you can start and move the locomotive. I read an article years ago where they put a K4s on the test plant. They tested different firing methods. One was a banked fire the other a flat bed. Lines West fireman liked running banked fires. Coal was piled up on the back of the firebox. Then raked forward as needed to cover the grates. Altoona men used level firing and liked thin beds. There was no discernable difference in steam generation. Banked firing had unburned coal when dumped while level fire consumed more coal during the testing.
While steam generation is a factor in locomotive performance. Without an ample boiler the locomotive will probably never leave the shop.
The fire is one small cog in the whole machine.
I've avoided responding to this thread for as long as I could hold out. I'll reluctantly jump in here as I see this concept of a 'thick' fire = more heat as opposed to a thin fire = less heat. Hogwash!
gregcthe fire can have different depths, producing different # of BTUs, generating different amounts of steam (lb/sec)
Probably no where in the industrial world is the marriage of 'man and machine' more pronounced than in the operation of a steam locomotive.
The variables are broad. Various coals give up their volatiles at different rates. The ash, sulpher, fixed carbon and moisture content will be a big determining factor in the ability to carry a thin fire or not. Other impurities in the coal will be another factor in weather or not the fireman will be able to perform his duties efficiently. It can be the difference between having a run that is a 'stroll in the park' or a constant battle with clinkers, grate shaking, plugges flues, plugged netting in the smokebox and finally, how much of the volitale gases can be given up in the firebox and combustion chamber before being carried out the stack.
The variety of coal will be an indication to the fireman what type of fire he will want to carry. Most will bank a fire toward the back corners and along the sides of the firebox. Some coals burn best with a level fire and yet others like a flat bed and maybe a little thin in the center.
Locomotive condition is another variable. Leaking flues and cracked staybolts were something to contend with along with the aforementioned bad coal. A regular fireman on a regular run pretty much knew what kind of coal his road provided but there were still variables.
I have never once witnessed a situation where the engineer tells the fireman to lower his boiler pressure because he wants to slow the train down. This borders on ridiculous. Likewise, I want to go faster, shovel more coal.
In the days when I was firing I kept the needle within a few pounds of 200 psig. while on the road. The engineer deserved to have the full capability of the locomotive at his disposal and it was the fireman's duty to deliver that.
I worked with about five different former B&O engineers and each one had 'his' style. One I recall had about the easiest-going demeanor and his running of the engine followed suit. Very easy going and 'low-impact' hardly working the engine at all. Another was a bit of a 'throttle jockey' and I had to work a little harder. His style was to nearly constantly work the throttle, automatic and reverser always seemingly trying to find the 'sweet spot' but never really be satisfied.
The main driver of successful firing is anticipation and cooperation. The fireman has to know the territory in order to have both the fire trimmed and the water level where he needs it (you'll carry a full glass going uphill but you'd better know when you are about ready to crest and all your water runs to the front of the boiler, leaving a pretty thin margin for keeping the crown sheet covered!) also water level can be a convenient way to bring pressure down to avoid 'popping off'.
In the steam days most roads were very concerned with heavy firing and unnecessary smoke. Charts were kept on fireman's performance and it wasn't unusual for the road foreman to give a little 'pep talk' to the under performers.
That's enough for now...
Ed
wrench567As long as there is steam in the boiler, you can start and move the locomotive.
On the engine I'm familiar with we would dump the fire on one track, move to another track for sand then head for the turntable, finally going into a stall of the roundhouse. Sometimes thirty or fourty minutes elapsing. Steam pressure would only drop about twenty pounds in this time frame.
I was more concerned with the loss of air pressure. Nosing toward the brick wall of the roundhouse isn't quite the time to find out your air is rapidly depleting!
Regards, Ed
gregcwhy not build the fire only as strong as needed, some bed thickness, to maintain the boiler pressure maybe 5,10 PSI below max boiler pressure when operating at the desired speed. add more coal when it goes below that, stop adding coal when it starts to rise above it to increase speed, the fire needs to be strengthened to accelerate.
I think you mean to say that more steam to the cylinders is needed to increase speed....not strengthening the fire?
But at some point prior to the acceleration, yes, the amount of steam produced must be in sufficient supply for the throttle to allow more steam into the cylinders for actual acceleration, so the fire must be increased some time before the need to accelerate.
The throttle puts steam (fuel combustion/mix of sorts) to the cylinders. To accelerate, its the throttle, not the fire intensity, that accelerates the locomotive, (provided that the fire already made enough steam and there is enough steam in the dome).
Just my take from following this discussion.
- Douglas
wrench567 In your thinking. If you dump the fire the locomotive will not move.
of course not. what did i say that suggests that?
there's steam in the boiler but no additional steam is being produced because there's not BTU being added to replenish what is drawn by the cylinders
boiler pressure will drop as the cylinders consume steam but will draw less and less
2900
gmpullmanI see this concept of a 'thick' fire = more heat as opposed to a thin fire = less heat. Hogwash!
so you're saying the amount of steam produced by the boiler doesn't matter on how much coal is being burned?
gmpullmanThe main driver of successful firing is anticipation and cooperation. The fireman has to know the territory in order to have both the fire trimmed
what do you mean by "trimmed"?
gmpullman I kept the needle within a few pounds of 200 psig.
what was max boiler pressure?
DoughlessI think you mean to say that more steam to the cylinders is needed to increase speed....not strengthening the fire?
yes, more steam needs to enter the cylinders. but the boiler also needs to produce more steam (see below)
DoughlessThe throttle puts steam (fuel combustion/mix of sorts) to the cylinders.
is this suggesting that the throttle increases the amount of fuel, coal to the engine ??
DoughlessTo accelerate, its the throttle, not the fire intensity, that accelerates the locomotive, (provided that the fire already made enough steam and there is enough steam in the dome).
there's probably enough steam in the boiler to accelerate the locomotive. but if the throttle is full, as that table above says it would be during normal operation at various speeds, it can't be opened further to allow more steam into the cylinders.
presumably cutoff can be increased, as Overmod described, but i'm not sure i understand how that works.
regardless of how more steam is allowed into the cylinders, additional steam needs to be generated by the boiler by increasing the BTUs added to the boiler by burning more coal.
gregcso you're saying the amount of steam produced by the boiler doesn't matter on how much coal is being burned?
How quickly the volatiles distill and 'burn off' will be a major determining factor in how much heat you derive out of each scoop of coal. Some coal varieties require a longer time on the bed to fully ignite and give off its heat through the burning of the volitale gases. Ash in the coal can vary from around 2% up to15%. A high-ash coal is going to build up much faster and this build up of ash isn't going to add anything to the heating value of the coal and will indeed impede draft through the fire.
The temperature of the fire at the time of stoking will make a difference in how quickly the coal gives off its heat, too. Obviously a fire at 950°F will take longer to ignite fresh coal than if it is at 1400°F.
How finely the coal is crushed is a factor, too. I've seen some loads of coal that are nearly dust. These fines get pulled right through the combustion chamber, some flashing off right away and others getting pulled through the tubes without combusting. I would wet the fine coal down with the squirt-hose which helped it from getting blown out the stack. Large lumps of coal will likewise take longer to ignite and give off heat. The stoker has a crusher which reduces most of the larger lumps but when hand firing you have to either spend some time with a pick and break up the lumps or risk firing heavy and the large lumps not burning very quickly.
gregcwhat do you mean by "trimmed"?
The fireman opens the firedoor occasionally and uses his scoop to direct the flow of air across the grates. Bright spots are thin and will need a few scoops directed there to avoid holes in the fire. The back inside corners always need a few scoops as the stoker has a hard time directing coal to these areas. Dark spots usually indicate a clinker forming or at least a build up of impurities in that spot.
The firebed is constantly changing, thus it needs to be 'trimmed' by hand. Constant monitoring of the stoker jets is required, too. A Simplex stoker had five steam jets that adjust the flow of the coal. A Duplex had a dividing plate plus two jets on each elevator in order to balance the distribution of the coal. An Elvin stoker has a pair of 'paddles' that slings the coal across the fire. I've never seen one of these in operation but it must have been interesting.
I never had to shake the grates while in motion, only while stopped. I imagine a road crew that spent a lot of time running would have to occasionally shake the grates 'on the run' especially with bad coal.
not many of you seems to think the a thicker coal bed is needed to increase the rate of steam produced by the boiler
despite that test data table showing the throttle full at various speeds that presumably need optimal performance, i'm trying to understand why an experienced engineers would operate the engine differently (not optimally)I'll guess the reason an engineer operates with the throttle partially closed is to be able to quickly increase the amount of steam (lb/sec) entering the cylinders. a partially closed throttle requires a greater difference in pressure between the boiler and cylinders to draw the same amount of steam (lb/sec) that a more open throttle would.
(my understanding of a throttle is that it doesn't give you some fraction of what is availble, but allows some flow (lb/hr) depending on its setting
regardless of the throttle setting, the maximum amount of steam that can pass through it is limited by how much steam is produced by the boiler. in other words, the throttle will only allow so much steam (lb/hr), it can't pass more than is available)
So while the throttle controls steam flow, it dictates the difference between boiler and cylinder pressure once equilibrium is established as speed stabilizes. If boiler pressure is maintained at some value by the fireman, then it determines the cylinder pressure.
not seeing how the throttle can restrict the flow to anything less than the steam production by the boiler without the boiler pressure rising
a locomotive running without a train (no tonnage) requires little boiler pressure and/or a slightly open throttlewhen the throttle is opened further, the steam flow (lb/s) increases into the cylinders and from the boiler resulting in the boiler pressure dropping. The boiler pressure is restored when the fireman adds coal.i'm suggesting a higher rate of coal (lb/hr) is being added by the fireman as the speed increases.
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Greg, When I quote I get the 403 Forbidden.
No. I'm looking at steam as being the fuel....ultimately being the product of water heated by coal. The steam is what pushes the cylinders, and the throttle is what determines how much steam goes to the cylinders. In a car engine, the throttle adds more fuel (mixture) directly to the cylinder, and more fuel means more combustion and faster go.
Its not exactly the same as an internal combustion engine because the "combustion" in this case happens outside of the cylinder (steam production) and is stored in the dome for use when needed. But fuel (steam...water and air mixture) to the cylinder is still what makes it go. Make sense?
This may not be the way the steam engineers think of it, but it helps me understand it.
To go faster, you need more steam.
I don't disagree with your last quotes.
More coal (more fire) and more water (I would think is needed) creates more steam (fuel, as I see it).
My question would be, can you get more steam to the cylinders when the throttle is wide open? It can only process has much as designed. Like trying to drain a bucket with a straw. Produce more steam and max out the boiler as much as you can, but if the throttle is wide open (maxed), I don't know that more steam can get to the cylinders. Dumping more water into the bucket won't produce more water into the straw, if pressure already maxed out.
In your OP, you said that throttle was wide open but boiler pressure was NEAR maximum. I would say that to accelerate, you have to increase BP to maximum and expect that the throttle is engineered to deliver that much steam to the cylinders. If not...if the throttle is maxed out (not wide open but maxed out as to volume of steam it can handle)....then increasing boiler pressure won't deliver more steam to the cylinders and it will popoff.