[_o_OOOO_oo-Kanawha]

Oh, those mathematics.

Let me start with the easy bit first: exhaust colour.

Steam and smoke have different characteristics, i.e. volume, pressure, density and temperature. Steam is being exhausted from the cylinders through the exhaust nozzle inside the smokebox, right under the stack. It sucks the fumes and gases coming from the burning coal in the firebox through the boiler tubes, and blasts these through said stack into the atmosphere. If we disregard the gases as being colourless, we can assume the steam as being pure white and the smoke as black, or at least dark gray. The exhaust blasts sort of mix steam and smoke together. But in close up you can often still see the separate characteristics, i.e. the steam shoots out, while the smoke sort of lingers and is torn apart. So the column of exhaust often gets separated, with the smoke falling or being blown in different direction while the steam still rises before vanishing. The smoke lingers and drifts down and away when it gets cold.

I think you just have to play with the emitters of steam and smoke until you get an approximation of the prototype that pleases your eyes.

Throttle regulates the maximum allowed volume of steam to be admitted into the cylinders.
Cutoff regulates the amount of expansion that =superheated= steam is allowed to do. Superheated steam's expansive powers are considerably higher than its mass (i.e. volume * pressure) alone. A high cutoff limits the expansive power, a low cutoff allows it. The resulting expanded steam is of lower temperature and pressure, so produces softer exhaust blasts. US engines are driven very hard, full throttle and maximum cutoff, while starting. Combined with high boiler generating capacity and high boiler pressure, a starting engine still emits large volumes of relative high pressure through the exhaust. When accelerating, the engineer limits the cutoff as speed increases, allowing the steam to work its expansive properties more and more, with resulting lower exhaust pressure and temperature. So the column of steam gets lower and lower. The actual volume exhausted increases, do the greater number of power strokes as the locomotive's speed increases. As long as the boiler keeps the steam supplied, the visual spectacle of a powerful steam locomotive working hard remains. Keeping that steam supply up means admitting more and more fuel to the firebox until supply and consumption equalize and the train's acceleration eases of. So the steam gets mixed with more and more black smoke, until the desired speed is reached and the mixture remains this constant gray. Throttle, cutoff and stoking will vary during the rest of the trip due to grades, curves, speed restrictions etc.

One of the most impressive and and scariest spectacles is a large steam locomotive "popping off" when departure of a premier streamliner, fast mail express or time freight is being delayed. The fireman has prepared the best fire he could, already adding coal to the firebed for the imminent acceleraton, the boiler is filled and almost at its maximum pressure so the engineer can pull the train away and make speed as quickly as possible. When the "highball" doesn't come and the safety valves pop, its "all hands on deck" in the cab to reduce boiler pressure, quench the fire, cool the boiler, with people standing by being scared to death by the roar of the high pressure steam from the safety valves, etc. etc.

Not much help for the theoretical mathematics, sorry about that, but is is only the visual spectacle that matters in the simulator.

I'll stick with my assumption that emitted steam is a result of throttle and cutoff, while smoke is a result of firing rate, dampers/firebox door being open etc. The actual formula you suggest might just work.
When you close the throttle, the exhaust should darken immediately. When you stop firing, the smoke should diminish after a short while making for a whiter exhaust. In winter, the exhaust is often pure white.

Does OR allow synchronized exhaust beats by itself, or will you have to "fire" the emitters in your script?

[copperpen]

It is the simple animation that is the source of confusion. there is no provision for throttle or cutoff variation. You sre correct to assume that the amount of steam consumed will vary according to the control settings. The pressure of the exhausted steam will also vary because of these settings as well. I think the math as set out is good for a shot to see if it will work.

_o_OOOO_oo-Kanawha is correct in his description of the visuals but once again, these will vary according to control settings AND other engine variables like boiler pressure, along with engine size. After all, what is a big engine in the UK is a small one in the USA. Something like the Rocket would look a bit silly blasting along with a display like a BigBoy.

[_o_OOOO_oo-Kanawha]

Copperpen is right. I got carried away in my passion for big modern US steam locomotives.

The same principles apply of course to all steam locomotives worldwide.
The required parameters that allow you to "scale" the exhaust are already provided in most engine files. So a carefully chosen equation model should suffice for all engines.
There are possible snags in 3 or 4 cylinder engines, compounds, articulateds etc. Articulateds in principle are two separate engines fed from the same boiler.

It will no doubt be a process of experimentation, hits and misses before a practical working solution is found that doesn't put too much overhead on the simulation and rendering engines inside Open Rails. It all depends on the particle emitters for the visual results.
The laws of thermodynamics and particle physics are incredibly complex, so some assumptions and simplyfications will have to be made.

With excellent steam locomotives still actively being developed here at Elvas Tower, the search for the right exhaust is a worthwhile one.

I look forward to the first testing versions with great anticipation.

[rdamurphy]

One of the videos I watched last night was a D&S K-36, vs a D&S K-27. I noticed that throughout the entire video, both had their safety valves wide open. So, it would seem the D&S crews weren't balancing the steam with the load very well. Yet a video of 844 and 3985 pulling out of Cheyenne and then heading up Sherman showed absolutely no steam at the pop off valves at all.

Then, it occurred to me, the small locos were pulling at their capacity, while the big steamers weren't even working up a sweat.

Interesting...

When I worked on the diesel exhaust I found some excellent methods to bring the sim to a screeching halt. One change I tried brought frames down into the single digits.

So, yeah, that's part of the process also...

Robert

[CrisGer]

hehe, single digit eh? The Slide Show Sim we could call it ;)

thanks so much for the hard work, much appreciated!

[midneguy]

Hey all :lol2:

Great discussion and I'm thrilled more work is now going into this aspect of OR - the effort is much appreciated!

I thought I'd throw out some comments regarding smoke color that might help, as I haven't seen it described quite the way that I think about it, and with enough points of view a workable solution using the various variables and formulae may be discovered ;)

The color of the smoke is really an indication of how efficient the combustion is going on in the firebox. What really determines this is the ratio of air to the quantity of fuel at any given moment. The dark part of the smoke, the soot, is generated when the fire in the firebox is burning inefficiently - too much fuel and not enough air flow. For any given fire mass and tempreature, there is a corresponding amount of air flow through the firebox that will produce a clean stack - one with a slight haze of gray to even totally clear under perfect conditions. This is where the technique of firing with coal becomes an art, requiring the fireman to anticipate what will be happening in the future in order to keep the fire burning as efficiently as possible. An engine working under heavy load (higher fire mass, high gas volume through the firebox and up the stack) at a state with a clean stack, will likely produce a dark sooty stack if the throttle is closed or reduced. This is because the high fire mass now has reduced air flowing through it, causing a "rich" fire where soot will be generated. If the throttle is opened again, the stack will clear up as the proper volume of air is restored to the fire. If the fireman is over-firing, throwing too much coal on too quickly or getting the fire mass to be too great, dark smoky conditions will occur.

When new fuel is added it also causes an increase in soot to happen... This is because the new fuel cools the fire mass somewhat, and the new fuel doesn't ignite and burn efficiently at first. Once the new fuel gets going though after a minute or two, the temperature of the firebed will be restored and more efficient / less sooty combustion is restored - assuming the engine is working at a high enough level to draft adequate air through the firebox. Of course it is possible though to maintain a clean stack when firing, or while adding fuel, the trick being to keep everything in equilibrium.

Something else I haven't seen mentioned in the thread but needs to be considered is the difference between coal and oil burning locomotives. With oil burners you obviously avoid the problem of the lag in fire mass. When the throttle is closed or reduced, the fireman should adjust the firing valve accordingly - avoiding having to wait for excess fire mass to burn off. The adjustment of the firing valve should mean that you might have a few seconds of the fuel / air ratio being out of balance and creating soot, but should correct itself fairly quickly once the air / fuel ratio is brought back into balance. Of course the quality of the oil can influence the overall ability of the fireman to get a clean stack... correct oil for the burner would be easy to work with, though if poor quality oil is used or a type used that doesn't match the burner nozzle design it would be difficult to get a clean fire - creating those black clouds so popular with the photo run-bys lol.

Derek

[rdamurphy]

 CrisGer, on 19 September 2013 - 05:31 AM, said:

As I recall and others can correct me, colour changes when the steam is being effectively applied or not. Dark Steam or smoke comes from poor combustion of the coal (or oil) and the lighter smoke is the better or standard. So glad work is underway. I will attach my smoke ACE from MSTS here which is as far as i can tell one of the most realistic ones available for MSTS.and i added some volume to it.

Sample on LPS MSTS FX 9600 Vid card, XP SP3 System

http://imageshack.us/a/img153/6985/lpscrossingview.jpg

Are you willing to contribute your smoke ace to the project? Do you own the copyright and are will you license it under the same GNU license as OR?

Thanks, Robert

[rdamurphy]

As far as I know, there's no parameter in MSTS to be able to reference to tell what type of fuel that a steam locomotive uses. Not only are there various types of oil but different qualities and types of coal as well as different types of wood. I think some types of locomotives even burned such things as charcoal and peat.

Robert

[midneguy]

 rdamurphy, on 22 September 2013 - 05:01 PM, said:

As far as I know, there's no parameter in MSTS to be able to reference to tell what type of fuel that a steam locomotive uses. Not only are there various types of oil but different qualities and types of coal as well as different types of wood. I think some types of locomotives even burned such things as charcoal and peat.

Robert

Very true indeed... in hindsight I should have included a disclaimer in my previous post that behavior such as this for the different fuel types is something that would have to be included in a post 1.0 version of OR - allowing features beyond what standard MSTS did such as being able to specify different fuel types for steamers ;)

Something relating fire mass to exhaust gas flow seems like something that might be practical though, which in turn could approximate the diversions from ideal fuel / air mixing ratios which do directly impact the "sootiness" of the fire... This is something I've been studying somewhat since I've been reading Wardale's "The Red Devil and Other Tales from the Age of Steam" which discusses all of this quite a bit http://www.elvastower.com/forums/public/style_emoticons/default/read.gif It's definitely a very interesting read :lol2:

[jared2982]

 rdamurphy, on 22 September 2013 - 05:01 PM, said:

As far as I know, there's no parameter in MSTS to be able to reference to tell what type of fuel that a steam locomotive uses. Not only are there various types of oil but different qualities and types of coal as well as different types of wood. I think some types of locomotives even burned such things as charcoal and peat.

Robert

MSTS does contain tokens for oil burners. A list is in the .eng .wag tutorial at the Steame4Me site here http://msts.steam4me...s/EngManual.zip
It is not mentioned whether they work or not. Fuel type does eventually need to be considered in OR.