Steam & Excursion > Question regarding fuel consumption

Having spent the past weekend with NKP 765 and crew, and discussing the locomotive and its operation, I have a question regarding fuel consumption and efficiency. I've heard that a steam locomotive's fuel and water consumption can actually decrease with an increase in speed. Before you jump all over me, please note that I'm in Maintenance of Way and my familiarity with steam is track gage, bridge loadings, curvature, etc. Being more familiar with internal combustion engines, it seems counter intuitive to me that increased speed can result in reduced fuel consumption. Help me Hotwater, you're my only hope. (I'm the guy on the right in the photo)

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Short answer: Most of the energy to make steam goes into "latent heat", which is the energy it takes to convert water from a liquid to a gas. Thus, once you have created the gas it takes little added energy to raise its remperature, and thus its pressure. It takes only about 1% more energy to make steam at 175 pounds than at 120 psi, yet the 175 psi steam can do far more work than 120 psi steam can.

Larry Doyle

Thank you Metra6924 for helping make last weekend so great.

Give HotWater (Jack) extra time to respond, as he is busy with the 4449 trip :)

Posted from Android



Edited 1 time(s). Last edit at 06/22/17 19:41 by mdogg.

Also as you increase speed up to the maximum allowable speed you move the reverse lever up closer toward center as it takes less steam in the cylinders to maintain the speed and thus conserve fuel and water consumption. I know from reading on the UP that we would "hook up" the reverse lever to a 33% cutoff for cruising speed. That way you still had steam being applied to all the necessary surfaces like the cylinders, lube oil heat lines and more. The 3985, my favorite loco, once hooked up to cruising 33% cut off across Nebraska on the flats would burn approximately 11 gallons of No. 5 Burner oil per mile. Of course the size of the train and weight effects the fuel consumption as well.

Bob Krieger
Cheyenne, WY



Edited 2 time(s). Last edit at 06/23/17 11:49 by Bob3985.

Most likely your car gets better gas mileage on cruise control at 60 mph than driving around at 10-15 mph.

Rich Melvin or Gary Bensman might comment on this as they have far more miles on the seatbox of the 765 than anyone else, but I have always understood from them, and the late Glenn Brendel, that the horsepower curve vs fuel economy & water consumption lines cross around 45 mph for a NKP Berkshire and only get better above that speed.

Tominde Wrote:
-------------------------------------------------------
> Most likely your car gets better gas mileage on
> cruise control at 60 mph than driving around at
> 10-15 mph.


Wont if both are not stopping or changing speed its not possible.

Loved your question.
Maybe this will help....

Fuel economy in steamers is largely based on how closely the actual trailing-load matches the designed power capacity of the boiler and the drive chassis.

The magic power that propels the steamer is wind through the firebed, and the weight behind the tender creates more wind, beneficial fire draft, with heavier trains...more wind, more fuel, more heat is released..and more steam is produced for propulsion...

For locos like the 765, they were designed for the flat-land running found in the territory that they ran in, and hauling fast trains of moderate weight.

So, they were built with small-ish diameter pistons.
Across a whole fleet of locos,
that makes a big difference in savings of coal and water.

But, how hot the fire is, gets determined by how hard the engine has to work..... The Berks were "built " to haul a medium to heavy train at better than 60-per. Lighter trains yield colder fires, and fuel and water consumption suffers, gets worse..

So, while getting up to speed, with a heavy train, the boiler and firebox must build up to a 'running heat'..... To a steady heat of about 3,000 deg F.

As they build up to speed, the steam boiled off the water is sent to the cylinders & is further heated-up by running it through steam pipes back into the path of the flames.

THAT action expands the molecular spacing of the water ( volume) of the steam on the way to the power pistons.
Remember, pure steam Is the gaseous form of water ...

Such temperature increase does not raise the steam pressure; but, a lesser amount of hottter steam molecules leaves the 'superheater', than enters it.
Superheated steam only comes as a result of a very hot, sustained fire..heating up the 'units' ----- steam does not readily'abdorb' the heat, but the very hot pipes provide an environment that further spaces the increasingly excited, vibrating
heated molecules...
This hotter gas continues its expansive pressure all the way down the stroke, and even up the stack, as so preheated steam...
In hot units, more steam exits units, than enters them--- and does more, better work, on less fie and water---Ah--botta-Boom, Ah-botta-A-Bang,,,

And, that's the engineer's job!
Thus, you're beginning to see how going faster, takes less fuel.

Mechanically, the engineer can adjust the valve gear to reduce the steam admission time, per power-stroke. As with internal combustion engines, the efficiency gets better with higher rpms...

On locos, the admission valve opens at TDC, and is closed by the end of the stroke.... The engineer regulates the cut-off point (closure), to suit the power demands ---- longer admission for starting & hills, shorter admission for speed and easy cruising..

Shorter cutoff, saves steam, fuel and water... But, a heavy train is what the Berks like best.... It's where they run the hottest.... At the shortest 'cut-off point...

So, it's a sophisticated engineering process, but a wonderful thing to observe.

In my experience, excursion trains are a very light 'load' for that boiler, and the power of the draft up the stack is low, compared to what they were built to produce.... So, on fan trips, the engines rarely get to the "heat" that they so dearly miss....

Light trains of Fan trips are big fuel consumers, but that's what, and all we've got,,,

Hope this helps....

W.

Posted from iPhone



Edited 3 time(s). Last edit at 06/23/17 17:03 by wcamp1472.

Tominde Wrote:
-------------------------------------------------------
> Most likely your car gets better gas mileage on
> cruise control at 60 mph than driving around at
> 10-15 mph.

Well comparing apples to oranges does not work. Comparing cruising (at a constant consistant speed) WILL ALWAYS mean better fuel mileage than driving around (start, stop, brake, accelerate) at any speed. That is becuase most fuel and engery used is to bring what ever vehicle it is, car, truck train, bus, airplane, from a stop upto a speed.

The simplest explanation is to say that the engine becomes more efficient at higher speeds. A couple of things lead to this increased efficiency.

SHORT CUTOFF
At lower speeds (below 45 mph) the engine has to work a fairly long cutoff in order to run smoothly at that "medium" speed. Cutoff will be in the area of 35% to 45% at this speed. (Steam is admitted to the cylinders for 35% to 45% of the piston stoke.) However, once the speed goes north of 55, the cutoff can be shortened considerably. At 70 mph, the cutoff will be down around 22%...very short. That's what makes that "machine gun" sound in the exhaust at high speed.

HIGH SUPERHEAT TEMPERATURES
The hotter the steam, the more energy it contains. To run at high speed demands high horsepower. High horsepower output requires a heavy throttle. A heavy throttle means a good draft on the fire and LOTS of heat! All that heat is imparted to the steam in the Superheaters. Thus, along with the short cutoff, the steam entering the cylinder is extremely hot...hotter than it would be at 40 mph.

The end result is that the engine runs more efficiently at higher speeds.

I have a question for those who have sat in the right hand seat on a steam locomotive and run it at mainline speeds.
I understand all about how the steam is generated in the boiler and the role the superheaters play in heating the steam so it expands, by about 30% if I recall correctly, and how that increased volume, as a result of the expansion, of steam powering the pistons was one of the big advantages of the development of the superheater in the early 1900s.
I understand how cutoff works and how at mainline speeds the idea is to run with the throttle on the roof, so the full boiler steam pressure is being worked into the cylinders, and notch the reverse lever back toward the center to control the volume of steam being admitted to the cylinders. Thus when Rich talks about cutoff at 22% once the speed is north of 55 MPH, meaning the remaining 78% of the piston travel is powered by the expansion of the steam admitted during the 22% of the stroke, I get it all. And I love that machine gun staccato of the stack exhaust; could listen to it for miles on end!
Here's my question. How's the engineer find that "sweet spot" on the reverse lever? Is it by ear, by feel, by a combination, or what? I thought I heard or read several years back Doyle McCormack talking about a back pressure gauge in the cab that I assumed read the pressure of the steam being exhausted from the cylinders and up the stack. Makes sense to me that if the back pressure was too high it would be an indication that not all of the steam being admitted to the cylinders was being used efficiently and allowed to fully expand and do its work and that would be an indication the cutoff was too long and more steam was being admitted to the cylinder than needed.
I know the New York Central Hudsons had something called a "loco valve pilot" that assisted the engineer in finding the sweet spot. Knowing the intelligence level of every engineer varies I would think there'd be something the railroad requested and the locomotive builder provided to assist them in operating the locomotive. Someone make me smart please.
And please, serious answers only to a serious question. I have never sat in the right hand seat on a steam locomotive and run it at mainline speeds so for those whose first inclination is to comment about how stupid or uninformed I might be please refrain from responding.
Thanks all,

sierrawestern,

There was a great article in a Classic Trains special issue a few years ago about the Locomotive Valve Pilot, its benefits, and the railroads that used them. There is also some discussion of the use of the back pressure gauge in selecting proper cutoff, although I thought the article was somewhat unfairly dismissive of this method. And there is discussion of the 'seat of the pants' method that gave very inconsistent results for the railroads because not all engineers were equally skilled in figuring out how best to set the cutoff for a given speed.

It just so happens that there is a copy of the 'Steam Glory 3' special issue for sale on eBay right now for a (currently) very low bid. The auction ends around 8:30pm EDT tonight if you're interested:

http://www.ebay.com/itm/2-MAGAZINES-CLASSIC-TRAINS-STEAM-GLORY-1-3-GOOD-Kalmbach-/292155538053?hash=item4405d3ba85:g:4gUAAOSwCmZZRn5T


The Valve Pilot used an internal mechanical cam to control the speed/cutoff information that was displayed to the engineer. On the New York Central, the shape of the cam was developed by over-the-road testing of the particular class of locomotive. The New York Central Historical Society has an excellent article about the testing performed on the Niagara class that mentions this:

"Pull - speed tests were run to determine the proper settings for the valve pilot. The Locomotive Valve Pilot was a combination speed recorder, back pressure gage and cutoff gage. After the optimum cutoff setting for each speed has been determined by test for a particular type of locomotive, a cam and linkage would result in the equivalent speed being shown by a needle on the dial of the speed recorder for each valve gear cutoff setting. As the speed of the locomotive changed, the engineman would adjust his reverser to keep the speed needle and cutoff needle superimposed on the dial, thereby obtaining the most efficient cutoff for each speed. To obtain the data needed to establish the proper cam contour, a series of test runs would be made. throughout each run, the valve gear would be fixed at a particular cutoff setting by a locking link. This link can be seen in the illustration of the instrumentation
on the left side of the engine. The power output and cylinder efficiency throughout the speed range would be obtained for each cutoff setting. When the curves for all the cutoff settings were superimposed onto one graph as in Figure 3, the most efficient setting for each speed could be chosen."

The NYCHS article is available for download as a pdf at:

https://nycshs.files.wordpress.com/2014/07/roadtestingniagaras.pdf


Scott Griggs
Louisville, KY

Sierrawestern...asked

"How's the engineer find that
> "sweet spot" on the reverse lever? Is it by ear,
> by feel, by a combination, or what? "


I'll add my esxperience and explorations.

Yes, it's by the combination.. of sensory inputs
The best way to explain it starts with knowing the 'landscape', track profile, speed restrictions, stops, etc.ofvthe territory you're operating over.
I can't stress that enough. Regardless of the type of motive power...
Running a steamer is all about conforming the engine's parameters, miles ahead and minutes ahead, of the present location.
Knowing the railroad, by heart , and so well, that you can navigate it at track speed, in a dense fog, on a pitch black night.

That comes from years of many hundreds of trips over the territory.
There are so many factors affecting the trailing load behind the tender.
On level,track, a fast rolling train requires almost no beneficial power input, --- on descending grades, the train pushes the engine, and on ascending grades
is the only time power is needed ( aside from accelerations from Station stops, etc). Once up to speed, the steam and power demand is minimal.

The Valve Pilot is most beneficial when ascending grades and power-matching is crucial.... But, remember railroads are built to follow the lowest grade & best geographic profile, avoiding hills as much as possible. Thus, most RR profiles are flat, with gentle grades. Half of the grades over a territory are downhill, half are uphill. So, power matching, using steam to drive the train is not needed for most of the territory that is covered.

So, now, let's take a look at handling frieght trains. There are two types: slow freights and fast freights. Slow freights are easy: you drive the engine as hard as you can to get over the road. A good example is the coal drags of the N&W, back before diesels.... their Y-class compounds were great at that..you simply drive them as hard as you can...that doesn't take much finesse.... if you fail to apply the power, you stall.

Their challenge was different hauling empty hoppers, back to the mines....that was easy work for them and they behaved docility, and sauntered along quite well..requiring a steady draft through the grates and a consistent steam supply....running the empties is all about the feel of the train under your butt.

High speed freights is different matter..... here, the mass of the train governs the condition of the fire and the steam generating capacity.
Let's look at the NKP Berkshires ...... they were proportioned and drafted for about 85 loaded freight cars, over flat to gently rolling hills...and high, consistent speeds

They were built with small-ish diameter cylinders ( 25" pistons )and huge grates ( in sq ft area)..... the power demand is best when the rolling friction of the freight keeps the cars
stretched, all the way back, like a snugged chain.... in that situation, the beneficial power to be put iinto the drawbar is about 25% of the egines's capabilities...
When run that way, there is really little adjusting to do, in powering the train: the speeding load is very light, consistent and is easily managed, mostly by feel and by "traffic conditions", meets etc...

Again it's the combination of knowing the territory, having the proper weight of Train behind the drawbar and the load matched by the type of engine for the specific service. Speedy Berkshires don't do good an heavy coal drags, and small drivered 'drag' engines don't do good at fast-freights.

"Passengers" are similar demands, smaller number of cars, higher speed. ( events come up on you very quickly) ---- you MUST be very well qualified to opertate a passenger train at timetable speeds ..... here, it's all about the feel and your extensive Road-Experience... running the train has become second nature to you and the behavior of the train tells you how to run it...you sense it very quickly when you are pounding the engine too hard, abusing the fire and the fireman and when things are going good ..... Knowledge of the track and territory is VITAL.....

Another factor, is knowing the personalities of everyone else in your section of the track where you will be running...the dispatchers, the towermen, the conductors, the other crews, who's out there , and often, which familiy members are on your territory.... etc...

Loaded trains are very easy to operate and manage,
It's tricky if the train is very light or, double-headed ( " power-balancing" , or true '2- engine need'..).trying to manage an over-powered trains is a compromise requiring experience....A Valve Pilot , optimum-power device is not compatible, with lightly loaded engines, or low power demands..

The balance between the throttle opening, the valve 'setting' ( admission-duration ) and the piston speeds, is a balancing of the factors, and, except for increasing grades, Valve Pilots are not really useful.

In my earlier discussion, I was commenting on how Doyle squeezed down the throttle, ( increasing the dwell time for steam in the units--- thus HOTTER superheat) and adjusted the valve travel ( by feel) for full-stroke positive steam pressure ....the steam flow, down stream from the throttle had the steam chest pressure at about 175 PSI, of superheated steam. Thus, a portion of the stoke is the expansive use of steam, and the power-portion ( admission valve open) is only providing modest-pressure steam... NOT the full 300 psi steam in Jack's boiler.

The Valve Pilot does NOT measure the actual pressure delivered at the piston.
Doyle's experience and coaching, was that the available power, is immense at full pressure and full valve stroke, so he has mastered the art of 'modulating' the factors that are most beneficial for all the demands that are required, for the loads-hauled and track speeds allowed, for the grades & profile.



A little more on Valve Pilots...

There is no "pressure indication " available on the Valve Pilot ..... That would be the "back pressure" gauge...
The Valve pilot device is connected to two portions of the drive-train: the 'lay-shaft' of the reverse-shaft that moves the valve timing from forward to reverse and a centered position..... and the speed sender for driver rotational speed..

The centered position of the valve gear, it does not move the piston valve; however, the valve travel, at the end of the stroke, is provided by a lever from the crosshead of the piston.
So that, when the engineer's rverrse lever is centered', the valve opens and closes, solely, by the action of the piston and the 'combination lap & lead lever' ...the engine runs along very well, with the reverse lever centered...the valves opening by the reciprocating action of the pistons

The V-P instrument operates by the 'speed needle' ( black hand) from its drive-wheel driven gear box, and the needle goes around the speed dial to match the track speed.

The " cut-off" needle (red hand), is positioned from the reverse lever "lay shaft".
At starting, when at low speed, the lay shaft drops red hand over top of the black hand, at low MPH...
(The red hand. [ valve gear operated] approaches the highest numbers on the speed dial, as the valve travel and the reverse lever, become centered...).

Thus, as the increasing speed moves the speedo's black needle, the engineer adjusts the valve gear --- to have the red needle cover the black hand.
All is good so far; but, while decreasing speeds, it's important to close down the throttle, and leave the admission valve open for most of the stroke--- lubrication purposes....

When stopping, beneficial Steam flow is required, almost to the last turn of the drivers...
So, the Valve Pilot , on deceleration, has the red needle dropping to a lower 'speed' number in the dial, than the black needle would indicate.....
The lower the red needle the longer the valve stroke ---- a GOOD thing when slowing to a stop.

The rest of the Valve Pilot's features are sales BS, -----,
Doyle, and the good engineers don't run by the Valve Pilot, ( it's too confusing and almost ambiguous) ---- it's only useful for accelerating and max power settings. But, as we stated earlier, most of the territory is flat, or descending, requiring very little of the full power that the machine is capable of....

So, running a train primarily knowing the track, the junctions, the signals, the people you rely upon ---- and your seat-of-the-pants knowledge
of the track roadbed, so well ---- that you know every bump and kink in the rails...
Running the engine is a matter of FEEL, HEARING and team work.

You can tell very quickly if she's clumsily galloping, laboring too hard, or humming along....
Stick with "humming along".

You wouldn't drive your car by the Valve Pilot, you drive it by the feel, the sound and the habits... same with a train...

W.



Edited 3 time(s). Last edit at 06/30/17 18:56 by wcamp1472.

Wes,

As far as I know, the 4449 may be the only steam locomotive operating in the excursion era that would have been equipped with a valve pilot when it was in revenue service. The Classic Trains article I mentioned above in my post indicated that the SP removed the valve pilots from their GS class engines late in their careers. I would assume that included the 4449. Do you know if the engine had had an operational valve pilot since it was restored for excursion service?

Scott Griggs
Louisville, KY

Posted from iPhone

sgriggs Wrote:
-------------------------------------------------------
> Wes,
>
> As far as I know, the 4449 may be the only steam
> locomotive operating in the excursion era that
> would have been equipped with a valve pilot when
> it was in revenue service. The Classic Trains
> article I mentioned above in my post indicated
> that the SP removed the valve pilots from their GS
> class engines late in their careers. I would
> assume that included the 4449. Do you know if the
> engine had had an operational valve pilot since it
> was restored for excursion service?
>
> Scott Griggs
> Louisville, KY

I can verify that there is NO "Valve Pilot" device on 4449. She didn't have one when removed from the park for Freedom Train service, and none was added. Besides, we don't need one of those anyway.

33% was the magic cutoff for the Jabelman power.

From the ICC 820 Runaway Report:


"Reverse lever, quadrant and latch were in good condition. Six teeth on quadrant just ahead of center had, been experimentally blanked by bronze welding to prevent overheating of rod pins and bushings as result of excessively short steam cutoff. When reverse lever is latched back of the welded portion of quadrant, valve motion is supposed to be on center, and when latched ahead of welded portion, at 33 percent cutoff. The setting of reverse gear could not be checked because of the damage to the Walschaert valve gear."


Less than 33% cutoff, the exhaust would be closed too soon such that excessive pressure would build up by the compression of the contained steam causing the grease to be wiped off the rod pins and bushings, thus overheating.




Bob3985 Wrote:
-------------------------------------------------------
> Also as you increase speed up to the maximum
> allowable speed you move the reverse lever up
> closer toward center as it takes less steam in the
> cylinders to maintain the speed and thus conserve
> fuel and water consumption.

"I know from reading on
the UP that we would "hook up" the reverse lever
to a 33% cutoff for cruising speed."

That way you
> still had steam being applied to all the necessary
> surfaces like the cylinders, lube oil heat lines
> and more.

"The 3985, my favorite loco, once hooked
up to cruising 33% cut off across Nebraska"

on the
> flats would burn approximately 11 gallons of No. 5
> Burner oil per mile. Of course the size of the
> train and weight effects the fuel consumption as
> well.