[steamer_ctn]

The OR steam model now is able to simulate a compound type steam locomotive. It is modeled on a balanced 4 cylinder balanced Vulcain model similar to that manufactured by Baldwin.

Definition of Steam Locomotive Type

Given the number of different steam locomotive models now supported by Open Rails, it is now necessary to definitively define which steam model is required. To allow this the following new ENG file parameters have been added:

ORTSSteamLocomotiveType (  value  ) 

Allowable values are: Simple, Compound, Geared

ORTSSteamBoilerType ( value )

Allowable values are: Saturated, Superheated

It is highly recommended that the above parameters be included in all steam ENG files regardless of the type of steam locomotive with the appropriate values above to ensure the selection of the correct model.

Compound Locomotive Parameters

Compound locomotives normally had a set of High Pressure cylinders and a set of Low Pressure cylinders. The HP Cylinder details are entered into the ENG file in the current cylinder parameters. The LP cylinders use the new parameters below.

LPNumCylinders ( 2 )

LPCylinderStroke ( 26.0in ) 

LPCylinderDiameter ( 25.0in ) 

Compound Modes of Operation

A compound locomotive could typically be operated in compound mode, or simple mode.

To operate in simple mode a steam valve was used to change the steam flow to the cylinders so that it bypassed the HP cylinders and only used the LP cylinders.

This is simulated by pressing the "P" key which toggles the valve open and closed to alter the steam flow.

To demonstrate the operation of the compound locomotive, test model can be found here.

[Kazareh]

steamer_ctn, on 05 April 2015 - 09:21 PM, said:

The OR steam model now is able to simulate a compound type steam locomotive. It is modeled on a balanced 4 cylinder balanced Vulcain model similar to that manufactured by Baldwin.

Definition of Steam Locomotive Type

Given the number of different steam locomotive models now supported by Open Rails, it is now necessary to definitively define which steam model is required. To allow this the following new ENG file parameters have been added:

ORTSSteamLocomotiveType (  value  ) 

Allowable values are: Simple, Compound, Geared

ORTSSteamBoilerType ( value )

Allowable values are: Saturated, Superheated

It is highly recommended that the above parameters be included in all steam ENG files regardless of the type of steam locomotive with the appropriate values above to ensure the selection of the correct model.

Compound Locomotive Parameters

Compound locomotives normally had a set of High Pressure cylinders and a set of Low Pressure cylinders. The HP Cylinder details are entered into the ENG file in the current cylinder parameters. The LP cylinders use the new parameters below.

LPNumCylinders ( 2 )

LPCylinderStroke ( 26.0in ) 

LPCylinderDiameter ( 25.0in ) 

Compound Modes of Operation

A compound locomotive could typically be operated in compound mode, or simple mode.

To operate in simple mode a steam valve was used to change the steam flow to the cylinders so that it bypassed the HP cylinders and only used the LP cylinders.

This is simulated by pressing the "P" key which toggles the valve open and closed to alter the steam flow.

To demonstrate the operation of the compound locomotive, test model can be found here.

That's fantastic to hear you guys have developed such an advanced steam model that this is possible!!!! Looking forward to seeing where this leads to, for sure!

[RTP]

Most Mallet compounds starts with both HP and LP cylinders, in order to maximize traction.

After, perhaps, one or two turns of wheels the valve is closed, and works in compound mode.

Regards.

[copperpen]

The problem with articulated engines is we have no sensible method of combining two eng files so compounding will not work there.

[Kazareh]

copperpen, on 20 May 2015 - 12:50 AM, said:

The problem with articulated engines is we have no sensible method of combining two eng files so compounding will not work there.

Drat, I was hoping you wouldn't say that.. Ah well, maybe sometime in the future...

[Genma Saotome]

copperpen, on 20 May 2015 - 12:50 AM, said:

The problem with articulated engines is we have no sensible method of combining two eng files so compounding will not work there.

I think it's going to require two changes: Like the second section of coupler data the eventual go-forward definition of an .eng file will probably need two "sections" to define high and low pressure cylinders etc. etc.

The second change I think will be required is being able to assemble several mesh files into one model -- call it multiple .FA definitions, or call it assembly, it doesn't matter... the problem is the same: Some game models are ill suited to be represented by a single mesh file; the solution is also the same: Allow a game model to be composed of multiple mesh files.

IMO I believe the .sd file is very well suited to host the assembly instructions in part because it describes a game shape and in part because static objects would also benefit from assembly and the .sd file is the only editable file in common with all game objects.

[Jonatan]

With OR supporting higher detail levels and afaik unlimited number of animated parts, wouldn't it be possible to build articulated locos as a single model now? Jon davis did it in MSTS, why wouldn't OR be able to do the same?

Infact, Jon Davis B&O 0-6-6-0 ccould be the first model to set up for this new compound feature.

[copperpen]

An 0-6-6-0 is fine as Jons old model proves. Come to think that is a compound IIRC. The problem comes when you start adding in front and rear trucks. I did make a very rudimentary model in MSTS a few years back about BigBoy sized to see if it were possible. Seem to recall it ran fine but the trucks needed some pivot point refining as did the first driver set.

[longiron]

Articulated steam engines for MSTS presented two challenges - one of which is solved in OpenRails. First is the model/mesh itself. The only way to get the correct pivoting of the boiler versus lead driver set was to create two models (meshes). I don't believe OpenRails solves that fundamental issue until something like Dave's suggestion is adopted.

The second issue is performance. As we all have experienced, MSTS used a much simpler physics model for non-player engines, so significant tradeoffs or hacking ENG files were necessary to get reasonably accurate performance. Since OpenRails uses the same physics model for ALL engines in the consist and offers parameters for low pressure cylinders, creating two accurate ENG files that deliver close to real world performance should be doable. The physics is something I'm only now trying to come with terms with as I really want to update my B&O EM-1 and EL articulated models for OpenRails.

chris

[copperpen]

I have at last been able to devote some time to testing the steam compound model. While the Woolfe system is a simple one to model, it was not used by most engineers who dallied with compounding. The Woolfe system operates by direct admission from the HP cylinder/s to the LP cylinder/s. Most rail applied compound systems used an LP receiver between the HP and LP, and there were also various systems used to admit small amounts of HP steam to the LP cylinder/s while starting, usually switched off after a couple of turns on the driving wheels. It would be good at some time in the future to see this type of system modelled.

Turning now to my actual testing, The model is good and does work remarkably well in most respects. I do suspect though that there is a tiny bug in there. With both models used for testing I have noticed that somewhere between 63 and 64 mph, the steam usage goes into reverse. This was observed in both the ctn_test_atlantic_compound and an LMS compound 4-4-0 I have set up. In both cases the reverser was at 40% and throttle was at 100%. As speed increases, usage continues to fall, slowly with the test atlantic, faster with my test 4-4-0. In fact with the 4-4-0, usage has dropped from 11800lb to 10100lb between 63 and 79mph and continues to fall.