CCG/Steam Engine File Breakdown
Contents |
STEAM ENGINE FILE BREAKDOWN
Generally identical to a diesel engine file with the addition of the following:
Units:
Pressure in kPa
Volume in Litres
Mass in kg
Flow sizes (nominal figure)
Temperature degrees Kelvin
steam
firebox-volume.................. 1000.0 Physical volume of firebox in Litres.
firebox-to-boiler-heat-flow......0.055 Rate of heat flow from firebox to boiler and vice-versa.
firebox-efficiency.................0.995 Atmosphere leakage. 1.0 = No leakage.
boiler-volume......................3000.0 Physical volume of boiler in Litres.
water-injector-rate................4.0 Water injection rate into boiler in Litres/second.
westinghouse-volume...........100 Westinghouse volume in Litres.
piston-volume-min...............1.48 The volume of the space in the cylinder ahead of the piston at the end of a full stroke.
piston-volume-max...............68.7 The volume of the space in the cylinder ahead of the piston at the start of a full stroke.
piston-area.........................0.177 The cross section of one piston in m2. It is assumed there is one piston only on each side of the locomotive.
piston-angular-offsets............0.1 See the additional notes in Comments and New Tags below.
piston-to-atmosphere-flow.....0.0021 Atmospheric leakage from piston. Nominal hole size.
safety-valve-low-pressure.....956.0 When boiler pressure hits this value in kPa the safety-valve-low-flow release is initiated. (below)
safety-valve-low-flow...........0.011 Lower pressure valve release. Nominal hole size.
safety-valve-high-pressure....1010.0 When boiler pressure hits this value in kPa the safety-valve-high-flow release is initiated. (below)
safety-valve-high-flow..........0.2 Higher pressure valve release. Nominal hole size.
max-fire-coal-mass..............50.0 The maximum mass of coal the firebox can take in kilograms.
max-fire-temperature............1873.0 Maximum heat obtainable. (Kelvin scale temperature)
shovel-coal-mass.................2.0 Amount of coal in one shovel load in kilograms.
burn-rate............................0.0001 Coal consumption rate.
fuel-energy........................100.0 Relative energy in kilojoules per kilogram of coal.
boiler-to-piston-flow..............0.0017 Relative energy.
COMMENTS AND NEW TAGS
The above information is specific to the small PB 15 locomotive. A Big Boy locomotive for example, is at the other size extreme for locomotives. The following is an expanded discussion for other size locomotives, of additional tags and options, with some examples.
firebox-volume
westinghouse-volume
main-reservoir-volume
The above tags are currently not implemented.
Boiler-volume..................00000.0 maximum-volume.................00000.0 minimum-volume.................00000.0
These above three tags are used together. Because of the way fireboxes are handled in Trainz, basing these figures on the actual litre volume of the boiler results in the water being used too quickly.
All three values for real world boiler size should be multiplied by 10 to give a more realistic consumption rate.
maximum-volume - this volume should be 90% of the boiler-volume, this simulates the steam space left over the top of the water.
minimum-volume - this value should be 90% of the maximum-volume, this represents the working low water level in the boiler.
Alternatively there are three (3) sets of figures that cover all boilers, this is a relatively coarse setting and as such a broad range of vessels can be "blanket" covered:
Small locos with grate areas under 10 Sq metres
boiler-volume 37500.0
minimum-volume 28500.0
maximum-volume 32500.0
Medium locos with a grate area 10 to 25 Sq metres
boiler-volume 47500.0
minimum-volume 37750.0
maximum-volume 40500.0
Large locos with a grate area over 25 Sq metres
boiler-volume 95000.0
minimum-volume 73000.0
maximum-volume 81000.0
initial-boiler-temperature.........380
This line has been added to allow the locomotives to be at an almost ready to go state when the session starts. Then, in conjunction with the firebox-to-boiler-heat-flow-idle and burn-rate-idle values, it allows a locomotive to stay in this state with the water and fire left for as long as is required, i.e. on stand by. This is nominally 80 - 90% of working pressure.
Full pressure is not required initially, as it only takes a short time to get the fire brightened up, and the boiler to pressure from this point. Most locomotives will go to blowing off pressure with a press of the N key to turn the blower on and a single tap on the space bar for a shovel of coal, remembering that in the real world it is considered very bad practice to have the locomotive blowing the safeties, a waste of resources and energy, and shows a lack of control by the crew.
The following table may be useful as a comparison of initial-boiler-temperature and related pressures. Temperature values (e.g.369) are in degrees Kelvin, see the important Notes following the table:
369 = 869kpa / 140psi = 460.3K
380 = 1008kpa / 146psi = 466.5K
381 = 1021kpa / 148psi = 467.0K
389 = 1122kpa / 163psi = 471.5K
389.6 = 1129kpa / 165psi = 471.8K
401 = 1275kpa / 185psi = 478.2K
404 = 1297kpa / 188psi = 479.8K
409 = 1374kpa / 199psi = 482.6K
410 = 1387kpa / 201psi = 483.2K
411 = 1401kpa / 203psi = 483.7K
412 = 1410kpa / 204psi = 484.3K
413 = 1414kpa / 206psi = 484.8K
424 = 1564kpa / 227psi = 490.9K
426 = 1589kpa / 230psi = 492.4K
455 = 1956kpa / 284psi = 508.2K
Notes on the Initial Boiler Temperature Table:
Trainz does not actually use correct Kelvin temperatures for the input to the initial-boiler-temperature tag value, a correction factor is applied to these values in Trainz. The bolded values in the left column are to be entered in the tag.
The Kelvin values in the right hand column of the table are more representative of the actual Kelvin temperatures associated with the pressures shown.
If you know the initial boiler pressure, for example 1275kpa, enter 401 as the value in the tag.
If you know the initial boiler temperature, for example 467K, enter 381 as the value in the tag.
piston-angular-offsets
Determines the number of power impulses a locomotive has for each wheel revolution, thus simulating the prototype.
For a 2 cylinder locomotive use:
piston-angular-offsets 0.0174,1.5254,3.0333,4.5413
For a 3 cylinder locomotive use:
piston-angular-offsets 0.0174,1.065,2.107,3.061, 4.206,5.253
For a 4 cylinder locomotive use:
piston-angular-offsets 0.0174,0.8028,1.5254,2.3736, 3.0333,3.9444,4.5413,5.5152
These are expressed in radians (2π radians = 360 degrees, where π = 3.1416) and the values were determined so as to achieve the smoothest operation possible, they have been deliberately kept away from the sound impulse point. It is recommended not to alter these tested settings.
firebox-to-boiler-heat-flow-idle 0.003
burn-rate-idle 0.003
These two tags in conjunction with the initial-boiler-temperature tag are the "brakes" for the boiler when the locomotive is in standby mode, i.e. unattended, and they don't need any alteration, unless you desire the boiler to run out of water or fire when parked unattended.
See the separate section XXXXXX for a discussion on how a locomotive using these tags and values may be tuned to give realistic performance.
