Elvas Tower: Diesel Electric - Engine rpm and power output - Elvas Tower

Jump to content

  • 2 Pages +
  • 1
  • 2
  • You cannot start a new topic
  • You cannot reply to this topic

Diesel Electric - Engine rpm and power output

#1 User is offline   darwins 

  • Conductor
  • Group: Status: Active Member
  • Posts: 307
  • Joined: 25-September 17
  • Gender:Male
  • Simulator:Open Rails
  • Country:

Posted 02 May 2020 - 11:40 AM

An interesting observation on setting up diesel engines on OR. I am not sure if this is intentional or some accident in the code.

First of all a little information about the locomotive I was trying to model - the diesel engine was a two-stroke with idle speed of 375 rpm and max speed of 625 rpm.

The manufacturers data shows an unusual pattern for rpm versus power as the engine is notched up:

0 = 375 rpm
1 = 360 rpm ~ 120 bhp2 = 350 rpm ~ 240 bhp3 = 385 rpm ~ 365 bhp4 = 418 rpm ~ 487 bhp

It appears to me that as load is put on the engine, the generator seems to have a braking effect, reducing the rpm, until sufficient fuel is supplied to the engine to cause it to speed up again.

I can understand why OR would not want decreasing values for rpm in a table, so I tried putting some small increases in rpm to see how this would work out.
DieselPowerTab (
0 0
375 7457
383 90230
384 181205
385 257266
386 348242
418 439217
450 530193
475 621168
525 712143
585 803119
625 894840
)


This produced the desired increase in bhp from the engine (shown in the F5 extended display). However it did not produce the desired power output at the wheels, and certainly not the force that was specified in the ORTSMaxTractiveForceCurves.

On the other hand, when the rpm figures in this DieselPowerTab are equally spaced, as well as getting the correct engine bhp, the power output at the wheels is now correct.
DieselPowerTab (
0 0
375 7457
400 90230
425 181205
450 257266
475 348242
500 439217
525 530193
550 621168
575 712143
600 803119
625 894840
)


To a certain extent if the rpm values are spread out say 10 rpm apart, the rail hp values can be adjusted by changing the tractive force curves, but it is not a linear relationship and a lot of trial and error would be needed to produce fake tractive force curves to give the desired tractive force with engine rpm values at least close to those of the real thing.








#2 User is offline   steamer_ctn 

  • Open Rails Developer
  • Group: Status: Elite Member
  • Posts: 1,267
  • Joined: 24-June 11
  • Gender:Male
  • Country:

Posted 02 May 2020 - 02:21 PM

Can you send me the ENG file that you are working on?

Thanks


#3 User is offline   steamer_ctn 

  • Open Rails Developer
  • Group: Status: Elite Member
  • Posts: 1,267
  • Joined: 24-June 11
  • Gender:Male
  • Country:

Posted 02 May 2020 - 05:54 PM

After some further investigation of the code -

View Postdarwins, on 02 May 2020 - 11:40 AM, said:

It appears to me that as load is put on the engine, the generator seems to have a braking effect, reducing the rpm, until sufficient fuel is supplied to the engine to cause it to speed up again.
I suspect that this has more to do with the field switching of the traction motors, rather then fuel supply to the prime mover.

View Postdarwins, on 02 May 2020 - 11:40 AM, said:

I can understand why OR would not want decreasing values for rpm in a table
Certainly that is the case at the moment.

View Postdarwins, on 02 May 2020 - 11:40 AM, said:

To a certain extent if the rpm values are spread out say 10 rpm apart, the rail hp values can be adjusted by changing the tractive force curves, but it is not a linear relationship and a lot of trial and error would be needed to produce fake tractive force curves to give the desired tractive force with engine rpm values at least close to those of the real thing.

The challenge is how to link the different tables to produce a reasonable outcome.

For example the tractive forces table is throttle setting vs force. If OR used the raw throttle value we would see step jumps in force as the throttle was switched up and down, So to overcome this the current power vs the maximum power is used as a de-facto throttle setting. Thus allowing the force to ramp up and down with the rpm changes in the prime mover.

Typically this assumes a linear relationship, hence the difference in powers between the linear, and non-linear approach that you have adopted.

I have a thought how this might be improved, to allow it to cope with a more non-linear table setup and will have a look at it.

#4 User is offline   steamer_ctn 

  • Open Rails Developer
  • Group: Status: Elite Member
  • Posts: 1,267
  • Joined: 24-June 11
  • Gender:Male
  • Country:

Posted 03 May 2020 - 02:11 AM

I have uploaded a patch to the unstable version that hopefully should allow better non-linear operation of the throttle vs rpm.

Can you please test and advise if there are any issues with it?

Thanks


#5 User is offline   R H Steele 

  • Vice President
  • PipPipPipPipPipPipPipPip
  • Group: ET Admin
  • Posts: 2,484
  • Joined: 14-March 13
  • Gender:Male
  • Location:known universe
  • Simulator:Open Rails
  • Country:

Posted 03 May 2020 - 06:40 AM

Question, how does the patch affect current operation of throttle vs rpm...does it affect the ORTS Diesel engine definition? Would you offer a description or explanation of how the patch works? Thanks for your continuing efforts to improve OR. Much appreciated, Gerry

#6 User is offline   darwins 

  • Conductor
  • Group: Status: Active Member
  • Posts: 307
  • Joined: 25-September 17
  • Gender:Male
  • Simulator:Open Rails
  • Country:

Posted 03 May 2020 - 09:02 AM

The patch works well.
Correct performance is now obtained with non-linear relationship between rpm and bhp, where this is in a diesel power table and providing that rpm numbers increase.
Existing locomotives are not affected and perform as previously set up.
Thanks Peter.


#7 User is offline   steamer_ctn 

  • Open Rails Developer
  • Group: Status: Elite Member
  • Posts: 1,267
  • Joined: 24-June 11
  • Gender:Male
  • Country:

Posted 03 May 2020 - 01:29 PM

View PostR H Steele, on 03 May 2020 - 06:40 AM, said:

Question, how does the patch affect current operation of throttle vs rpm...does it affect the ORTS Diesel engine definition? Would you offer a description or explanation of how the patch works? Thanks for your continuing efforts to improve OR. Much appreciated, Gerry

Instead of "assuming" a linear increase in the throttle, it allows the definition of a throttle vs rpm which is non-linear. When this is the case, it keeps the throttle setting aligned to the non-linear rpm of the prime mover.

It shouldn't impact any existing locomotive configurations. If you identify any issues, then let me know.

Thanks

#8 User is offline   R H Steele 

  • Vice President
  • PipPipPipPipPipPipPipPip
  • Group: ET Admin
  • Posts: 2,484
  • Joined: 14-March 13
  • Gender:Male
  • Location:known universe
  • Simulator:Open Rails
  • Country:

Posted 03 May 2020 - 02:11 PM

View Poststeamer_ctn, on 03 May 2020 - 01:29 PM, said:

Instead of "assuming" a linear increase in the throttle, it allows the definition of a throttle vs rpm which is non-linear. When this is the case, it keeps the throttle setting aligned to the non-linear rpm of the prime mover.

It shouldn't impact any existing locomotive configurations. If you identify any issues, then let me know.

Thanks


http://www.elvastower.com/forums/public/style_emoticons/default/hi.gifThanks, understand.

#9 User is online   ErickC 

  • Conductor
  • Group: Status: Active Member
  • Posts: 409
  • Joined: 18-July 17
  • Gender:Male
  • Simulator:ORTS
  • Country:

Posted 30 May 2020 - 10:17 PM

View Poststeamer_ctn, on 02 May 2020 - 05:54 PM, said:

If OR used the raw throttle value we would see step jumps in force as the throttle was switched up and down, So to overcome this the current power vs the maximum power is used as a de-facto throttle setting. Thus allowing the force to ramp up and down with the rpm changes in the prime mover.


Is there any way we can have the force curves use the raw throttle data, but insert an additional parameter that simply controls the rate of change of tractive force? Field excitation and engine RPM are independent anyway. For example, on the early GP units, Dick Dillworth intentionally allowed the engine to power up before the field excitation changed to create the illusion that the locomotive was loading up faster. This is why roots-blown Geeps have a characteristic sound when they power up and down - the engine powers up rapidly before the load acts on the engine, and you can hear it in the way that the engine overshoots its target RPM just before the exhaust gets deeper and the engine speed rests.

#10 User is offline   steamer_ctn 

  • Open Rails Developer
  • Group: Status: Elite Member
  • Posts: 1,267
  • Joined: 24-June 11
  • Gender:Male
  • Country:

Posted 31 May 2020 - 09:27 PM

 ErickC, on 30 May 2020 - 10:17 PM, said:

Is there any way we can have the force curves use the raw throttle data, but insert an additional parameter that simply controls the rate of change of tractive force? Field excitation and engine RPM are independent anyway. For example, on the early GP units, Dick Dillworth intentionally allowed the engine to power up before the field excitation changed to create the illusion that the locomotive was loading up faster. This is why roots-blown Geeps have a characteristic sound when they power up and down - the engine powers up rapidly before the load acts on the engine, and you can hear it in the way that the engine overshoots its target RPM just before the exhaust gets deeper and the engine speed rests.

A couple of other users have asked a similar questions as to whether it would be possible to model the load regulator operation. The relationship between the engine governor, voltage regulator, load regulator (hence field diversions) seems to be reasonably complex.

So far I haven't worked out an easy way to do this. I am loath to add parameters to control rate of change without some clear understanding of how it can be configured correctly, otherwise it just becomes another parameter to cause confusion for all.

  • 2 Pages +
  • 1
  • 2
  • You cannot start a new topic
  • You cannot reply to this topic

1 User(s) are reading this topic
0 members, 1 guests, 0 anonymous users