CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > CONVERGE

Motoring Validation

Register Blogs Community New Posts Updated Threads Search

Like Tree1Likes
  • 1 Post By Blanco

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 17, 2017, 07:33
Cool Motoring Validation
  #1
New Member
 
Avilash Jain
Join Date: Sep 2017
Posts: 7
Rep Power: 9
Avilash is on a distinguished road
Hi there,

I have been trying to do motoring validation in Converge using sector geometry for compression ratio of 15, but I am getting 5 bar higher peak pressure in simulation compared to experimental.

I have attached the image comparing simulation and experimental result.

Can you tell me any possible reason for this difference and how to rectify it?

Thank you very much.
Attached Images
File Type: png Capture.PNG (78.0 KB, 69 views)
Avilash is offline   Reply With Quote

Old   September 18, 2017, 18:30
Default
  #2
Member
 
tmburton's Avatar
 
Tristan Burton
Join Date: Sep 2017
Posts: 92
Rep Power: 9
tmburton is on a distinguished road
Avilash,

Are you confident that the experimental data was obtained at CR=15? Have you used the compression ratio calculator tool inside Studio to verify that the simulation achieves CR=15? I would also verify that trapped pressure in simulation matches the experimental data (it's a little hard to tell on the scale in your image), and that you aren't using adiabatic boundary conditions in your simulation.

Best regards,

Tristan
__________________
Tristan Burton
Senior Principal Engineer
CONVERGECFD
tmburton is offline   Reply With Quote

Old   September 19, 2017, 06:09
Question Motoring Validation
  #3
New Member
 
Avilash Jain
Join Date: Sep 2017
Posts: 7
Rep Power: 9
Avilash is on a distinguished road
Hello Tristan,

Thanks for your reply. I am confident that the experimental data was obtained at CR=15, and I have also verified compression ratio using tool for that (I have made the geometry using 'Make surface' tool for CR=15). I have initialized the trapped pressure using the pressure at IVC(closed cycle simulation) from experimental data. I am using isothermal boundary conditions(wall temperatures=300k).

I also want to mention that I have been trying different options, in one of the cases I reduced the compression ratio to 13.2 (just to see the effect) and it matched with the experimental data. I have attached a snap of the same.
Attached Images
File Type: png Capture2.PNG (88.9 KB, 44 views)

Last edited by Avilash; September 19, 2017 at 09:58.
Avilash is offline   Reply With Quote

Old   September 20, 2017, 06:26
Default
  #4
Senior Member
 
Blanco
Join Date: Mar 2009
Location: Torino, Italy
Posts: 193
Rep Power: 17
Blanco is on a distinguished road
Quote:
Originally Posted by Avilash View Post
Hello Tristan,

Thanks for your reply. I am confident that the experimental data was obtained at CR=15, and I have also verified compression ratio using tool for that (I have made the geometry using 'Make surface' tool for CR=15). I have initialized the trapped pressure using the pressure at IVC(closed cycle simulation) from experimental data. I am using isothermal boundary conditions(wall temperatures=300k).

I also want to mention that I have been trying different options, in one of the cases I reduced the compression ratio to 13.2 (just to see the effect) and it matched with the experimental data. I have attached a snap of the same.
Hi,
how did you verify that the effective CR was 15? Have you measured it on the real engine?
Moreover, even if you're considering the experimental pressure@IVC this typically need some adjustment since a reference pressure is typically needed to convert measured pressure into an absolute pressure. How did you corrected the experimental pressure? Moreover, how did you choose the in-cylinder temperature?
Blanco is offline   Reply With Quote

Old   September 20, 2017, 10:54
Default
  #5
New Member
 
Avilash Jain
Join Date: Sep 2017
Posts: 7
Rep Power: 9
Avilash is on a distinguished road
Quote:
Originally Posted by Blanco View Post
Hi,
how did you verify that the effective CR was 15? Have you measured it on the real engine?
Moreover, even if you're considering the experimental pressure@IVC this typically need some adjustment since a reference pressure is typically needed to convert measured pressure into an absolute pressure. How did you corrected the experimental pressure? Moreover, how did you choose the in-cylinder temperature?
Blanco,
I donot know the effective CR of the engine but geometric CR is 15 and it was verified by calculating volume of head and piston bowl. On other hand thanks for pointing out about reference pressure for measured pressure adjustment(I will be taking 1atm@BDC as reference pressure for NA engine). I have to correct it and see the change. By in-cylinder temperature I guess you mean wall temperatures, I have taken all wall temperatures as 300k because the motoring was done at cold-condition. Even changeing it to 330k had little effect on peak pressure.
Avilash is offline   Reply With Quote

Old   September 20, 2017, 11:33
Default
  #6
Senior Member
 
Blanco
Join Date: Mar 2009
Location: Torino, Italy
Posts: 193
Rep Power: 17
Blanco is on a distinguished road
Quote:
Originally Posted by Avilash View Post
Blanco,
I donot know the effective CR of the engine but geometric CR is 15 and it was verified by calculating volume of head and piston bowl. On other hand thanks for pointing out about reference pressure for measured pressure adjustment(I will be taking 1atm@BDC as reference pressure for NA engine). I have to correct it and see the change. By in-cylinder temperature I guess you mean wall temperatures, I have taken all wall temperatures as 300k because the motoring was done at cold-condition. Even changeing it to 330k had little effect on peak pressure.
Ok, I asked about effective CR because typically real operating engine have CR which could be quite different than nominal CR (this is caused by gasket dimension for example, in addition to tolerances, etc.). In my experience the "real" CR could be lower/higher than geometric CR by something like 0.3-0.5 max.

As far as the temperatures are concerned, I was thinking to gas temperatures because the (p,T) you're using@IVC will set the in-cylinder mass in the compression stroke. How did you choose the gas temperature? Did you set the temperature to match an intake manifold airflow measurement?

The wall temperatures could affect the heat transfer during the compression, but as you mentioned since the engine was in motoring conditions I expect something near 300 K to be quite reasonable.

I would like to add that the correction to pressure signal should be as precise as possible, as little differences in p@IVC will be amplified by the CR during the compressoin stroke.

Hope this could help!

Best
Avilash likes this.
Blanco is offline   Reply With Quote

Old   September 20, 2017, 13:23
Default
  #7
Senior Member
 
SamWijey's Avatar
 
Sameera Wijeyakulasuriya
Join Date: Jan 2016
Location: Convergent Science, Madison WI
Posts: 117
Rep Power: 10
SamWijey is on a distinguished road
Hello,

Have you considered flow in to the crevice? Does your surface file has crevice drawn? If not, you can use crevice.in to account for flow pushed in to crevice during compression. This will reduce your effective CR and will bring the pressure closer to that measured.

Thanks,
__________________
Sameera Wijeyakulasuriya
Principal Engineer, Applications
CONVERGECFD
SamWijey is offline   Reply With Quote

Old   September 22, 2017, 07:28
Default
  #8
New Member
 
Avilash Jain
Join Date: Sep 2017
Posts: 7
Rep Power: 9
Avilash is on a distinguished road
Quote:
Originally Posted by SamWijey View Post
Hello,

Have you considered flow in to the crevice? Does your surface file has crevice drawn? If not, you can use crevice.in to account for flow pushed in to crevice during compression. This will reduce your effective CR and will bring the pressure closer to that measured.

Thanks,
Hello Sameera,

Yes, I have crevice drawn on my surface, but I am not using crevice model. So, if I want to use crevice model should my surface have crevice drawn in it, or the crevice model will take care of it? I have added the crevice in bowl profile itself(please see attachment).
Attached Images
File Type: jpg crevice.JPG (41.5 KB, 36 views)
Avilash is offline   Reply With Quote

Old   September 22, 2017, 12:29
Default
  #9
Senior Member
 
SamWijey's Avatar
 
Sameera Wijeyakulasuriya
Join Date: Jan 2016
Location: Convergent Science, Madison WI
Posts: 117
Rep Power: 10
SamWijey is on a distinguished road
Drawing a crevice in the geometry can account of additional volume but cannot account for any piston blow-by. If you want to use crevice.in, you should remove the crevice from the geometry. Some questions to consider:

1. You should use real gas equation of state
2. Do you have measured intake mass flow rates? If so, you should run the full engine case with valve motion to see if you can predict the same intake mass flow rate. We recommend the error to be below 2% of the measured mass flow.
3. If there's no piston blow-by in the experimental engine, if you have matched the intake mass flow rate accurately, using real gas eos, and using the correct intake flow gas composition and your motoring pressure is still bad: Then that points to issues with your geometry.

Thanks,

Sameera
__________________
Sameera Wijeyakulasuriya
Principal Engineer, Applications
CONVERGECFD
SamWijey is offline   Reply With Quote

Reply

Tags
converge, motoring, validation


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Validation in Transient tasks MaxakCh FLUENT 0 May 17, 2013 09:59
CFX problem in ubuntu (linux) Vigneshramaero CFX 0 July 13, 2012 11:22
CFX-Pre problem, pls help!!! cth_yao CFX 0 February 17, 2012 01:52
Validation test for 2d euler equations in subsonic regime with canonical squares panou Main CFD Forum 2 August 24, 2011 16:21
Urgent: RAE 2822 validation NID Main CFD Forum 0 September 3, 2004 11:34


All times are GMT -4. The time now is 18:45.